JP7346121B2 - Noise control device, noise control method and program - Google Patents

Description

The present disclosure relates to a noise control device, a noise control method, and a program for reducing noise.

2. Description of the Related Art Conventionally, there has been known a technique for canceling noise by reproducing control sound having a phase opposite to that of the noise using a speaker. In addition, in Patent Document 1, the control sound to be reproduced by the speaker is controlled based on the engine sound so that the noise collected by the error microphone installed inside the car is minimized, and the sound is transmitted from the engine to the inside of the car. Techniques have been proposed to reduce noise.

When these conventional techniques are applied to a space such as an aircraft where many passengers are present, multi-point control is required to reduce noise at the position where each passenger is present. For example, in Patent Document 2, in order to reduce the running noise (road noise) of a car inside the car, a plurality of sensors are provided in the suspension part near the tires, and the sound is collected by each of the plurality of error microphones installed inside the car. A technique has been proposed in which control sounds to be reproduced by a plurality of speakers are controlled based on the sounds detected by the plurality of sensors so as to minimize the sound generated by the sensors.

Japanese Patent Application Publication No. 2004-20714 Japanese Patent Application Publication No. 6-59688

However, suppose, for example, noise that is not to be reduced (hereinafter referred to as non-targeted noise) occurs due to the driver significantly changing the playback sound of the car audio in response to a request from another passenger. In this case, in the conventional technique described above, the error microphone collects not only the noise to be reduced but also the noise that is not the target noise. For this reason, the control sound is controlled so as to minimize noise including non-target noise, and it is not possible to accurately reduce only the target noise.

The present disclosure solves the above conventional problems, and provides a noise control device that can accurately obtain a target noise reduction effect at a control point without being affected by non-target noise. The purpose is to provide

In order to solve the conventional problems, a noise control device according to an aspect of the present disclosure includes a noise detector that detects noise generated by a noise source, and a noise signal that indicates the noise detected by the noise detector. a control filter that performs signal processing using a control coefficient; a speaker that reproduces the output signal of the control filter as a control sound; and interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker. an error microphone installed at a control point to detect residual noise remaining at the control point due to the interference; and a transfer characteristic correction filter that processes the noise signal using a sound transfer characteristic from the speaker to the error microphone. a coefficient updater that updates the control coefficient so as to minimize the error signal using an error signal indicating residual noise detected by the error microphone and an output signal of the transfer characteristic correction filter; a correction filter that processes the output signal of the control filter using sound transfer characteristics from to the error microphone; a subtracter that subtracts the output signal of the correction filter from the error signal; , the error signal is set as a control-off signal representing the noise before the control due to the interference, and the error signal is set as the control-on signal representing the noise after the control due to the interference, based on the difference between the control-off signal and the control-on signal. and an effect measurement unit that measures the noise reduction effect at the control point.

According to the above aspect, the effect of reducing target noise can be obtained with high accuracy at the control point without being affected by non-target noise.

1 is a configuration diagram of a noise control device according to Embodiment 1. FIG. It is a figure showing an example of composition of an effect measurement part. FIG. 3 is a diagram showing an example of a noise reduction effect measured by an effect measurement section. It is a figure which shows another example of the noise reduction effect measured by the effect measurement part. It is a figure which shows another example of the noise reduction effect measured by the effect measurement part. It is a figure showing an example of other composition of an effect measurement part. FIG. 2 is a configuration diagram of a noise control device according to a second embodiment. 3 is a flowchart showing the flow of adaptive operation. It is a block diagram of an adaptable state determination part. It is a figure which shows an example of the determination condition used by an adaptable state determination part. FIG. 3 is a diagram showing the distance from a sensor to an error microphone and the distance from a speaker to an error microphone in the noise control device. It is a figure which shows another example of the noise reduction effect measured by the effect measurement part. FIG. 3 is an operation flow diagram showing a flow of a control coefficient design operation based on a result of determining a noise reduction effect in an effect measurement unit. FIG. 3 is an operation flow diagram showing the flow of design operations for control coefficients in the entire noise control device. FIG. 3 is an operation flow diagram showing the flow of design operations for control coefficients in the entire noise control device. FIG. 1 is a configuration diagram of a conventional noise control device for reducing engine noise of an automobile. FIG. 2 is a plan view showing a configuration inside an automobile in which a conventional noise control device for reducing road noise is arranged. FIG. 2 is a side view showing a configuration inside an automobile in which a conventional noise control device for reducing road noise is arranged. FIG. 2 is a configuration diagram of a noise control device for reducing road noise according to a conventional example. It is a figure which shows the noise control effect of the road noise by the noise control apparatus based on a conventional example. FIG. 3 is a configuration diagram showing a modification of the noise control device according to the first embodiment.

(Findings that formed the basis of this disclosure)
2. Description of the Related Art Conventionally, there has been known a technique for canceling noise by reproducing control sound having a phase opposite to that of the noise from a speaker. This technology has already been put to practical use in headphones and innerphones (hereinafter referred to as earphones). Such headphones or earphones are generally known as noise canceling headphones. Headphones and earphones are devices that are worn directly on the ears. Therefore, when applying the conventional technology to headphones or earphones, it is only necessary to control the noise propagated to an extremely small space inside the ear that is sealed by the headphones or earphones.

On the other hand, assume that the above-mentioned conventional technology is applied to a space where several or more passengers are present, such as in a car or an airplane. In this case, it is necessary to perform multi-point control to reduce noise at the position where each passenger is present, which makes the control complex and difficult to put into practical use. In particular, it has been difficult to apply the above-mentioned conventional technology to a large space such as an aircraft where many passengers are present.

However, in recent years, simple noise control specifically designed for automobile engine noise has been put into practical use. FIG. 14 is a configuration diagram of a noise control device 1000a for reducing engine noise of an automobile 100 according to a conventional example. For example, as shown in FIG. 14, in the noise control device 1000a, when the engine 101 of the automobile 100 is started, the tacho pulse generator 110 outputs a pulse signal synchronized with the engine rotation speed. This pulse signal is converted by a low-pass filter (hereinafter referred to as LPF) 111 into a cosine wave having a frequency equal to a predetermined frequency that becomes a problem as noise inside the vehicle. The cosine wave output from the LPF 111 is input to a first phase shifter 112 and a second phase shifter 113.

The first phase shifter 112 is set so that the phase characteristic leads the second phase shifter 113 by π/2 (rad). Therefore, the output signal of the first phase shifter 112 becomes a cosine wave signal (hereinafter referred to as a reference cosine wave signal) having a frequency equal to the frequency of the noise. On the other hand, the output signal of the second phase shifter 113 becomes a sine wave signal (hereinafter referred to as a reference sine wave signal) having a frequency equal to the frequency of the noise. The reference cosine wave signal and the reference sine wave signal are input to the microcomputer 200 after being converted into digital signals.

The reference cosine wave signal input to the microcomputer 200 is multiplied by the filter coefficient W0 in the coefficient multiplier 211 of the adaptive notch filter 210. The reference sine wave signal input to the microcomputer 200 is multiplied by the filter coefficient W1 in the coefficient multiplier 212 of the adaptive notch filter 210. Then, in the adder 213, the output signal of the coefficient multiplier 211 and the output signal of the coefficient multiplier 212 are added, and then the resultant signal is reproduced by the speaker 160 as a control sound.

The control sound reproduced from the speaker 160 interferes with the noise propagated from the engine at the control point where the error microphone 150 is installed. This reduces noise at the control point. At this time, the noise remaining at the control point that has not been completely reduced (hereinafter referred to as residual noise) is detected by the error microphone 150 as an error signal. The error signal detected by the error microphone 150 is input to two LMS calculators 207 and 208.

In the transfer element 201, the reference cosine wave signal output from the first phase shifter 112 is convolved with a coefficient that simulates the sound transfer characteristic C0 from the speaker 160 to the error microphone 150. In the transfer element 202, the reference sine wave signal output from the second phase shifter 113 is convolved with a coefficient that simulates the sound transfer characteristic C1 from the speaker 160 to the error microphone 150. In the transfer element 203, the reference sine wave signal output from the second phase shifter 113 is convolved with a coefficient that simulates the sound transfer characteristic C0 from the speaker 160 to the error microphone 150. In the transfer element 204, the reference cosine wave signal output by the first phase shifter 112 is convolved with a coefficient simulating a transfer characteristic −C1 that is opposite to the sound transfer characteristic C1 from the speaker 160 to the error microphone 150.

Then, the output signal of the transfer element 201 and the output signal of the transfer element 202 are added by the adder 205 and then input to the LMS arithmetic unit 207 . Further, the output signal of the transfer element 203 and the output signal of the transfer element 204 are added by an adder 206 and then input to the LMS calculator 208 .

The LMS calculator 207 updates the filter coefficients used by the coefficient multiplier 211 using a known coefficient updating algorithm such as the LMS (Least Mean Square) algorithm (least square method) so that the error signal input from the error microphone 150 is minimized. Calculate W0. Similarly, the LMS calculator 208 calculates the filter coefficient W1 used by the coefficient multiplier 212 so that the error signal input from the error microphone 150 is minimized.

In this way, the filter coefficients W0 and W1 used by the coefficient multipliers 211 and 212 of the adaptive notch filter 210 are recursively updated so that the error signal input from the error microphone 150 is minimized, and converge to the optimal value. I will do it. That is, the filter coefficients W0 and W1 are recursively updated so that the noise propagated from the engine is minimized at the installation location of the error microphone 150, and converge to the optimum values.

Therefore, the conventional noise control device 1000a shown in FIG. 14 uses an inexpensive microcomputer 200 without using an expensive DSP to reduce the noise propagated from the engine at the control point where the error microphone 150 is installed. can do.

However, since the noise control device 1000a uses a cosine wave signal and a sine wave signal based on the noise generated by the engine as the signals referenced by the adaptive notch filter 210, the noise propagated from noise sources other than the engine is Cannot be reduced.

Therefore, when reducing vehicle running noise (hereinafter referred to as road noise) including engine noise, a plurality of sensors are used.

FIG. 15A is a plan view showing a configuration inside an automobile 100 in which a conventional noise control device 1000b for reducing road noise is arranged. FIG. 15B is a side view showing a configuration inside the automobile 100 in which a conventional noise control device 1000b for reducing road noise is arranged. FIG. 16 is a configuration diagram of a conventional noise control device 1000b for reducing road noise.

As shown in FIGS. 15A and 15B, the suspension section near the tires of the automobile 100 includes four sensors (noise detectors) 1a that detect road noise (noise) generated in the suspension section (noise source); 1b, 1c, and 1d are installed. Specifically, each of the sensors 1a, 1b, 1c, and 1d detects vibrations of the suspension section when the automobile 100 is traveling as road noise.

As shown in FIG. 16, vibration signals detected by sensors 1a, 1b, 1c, and 1d are input to control filters 20aa, 20ab, 20ba, and 20bb, respectively. For convenience of explanation, FIG. 16 shows two sensors 1a, 1b, two speakers 3a, 3b, two error microphones 2a, 2b, which are provided in the front half of the automobile 100. only is illustrated.

However, in reality, the noise control device 1000b includes two sensors 1c and 1d, two speakers 3c and 3d, and two error microphones 2b and 2c in the rear half of the automobile 100. Prepare more. The noise control device 1000b similarly performs control to reduce road noise in the front half of the vehicle 100 and the rear half of the vehicle 100. Therefore, in the following, only the control by which the noise control device 1000b shown in FIG. 16 reduces road noise in the front half of the automobile 100 will be described in detail.

As shown in FIG. 16, when performing control to reduce road noise in the front half of the automobile 100, the noise control device 1000b includes four control filters 20aa, 20ab, 20ba, and 20bb, two sensors 1a, 1b, two adders 30a, 30b, two speakers 3a, 3b, two (one or more) error microphones 2a, 2b, and eight LMS calculators (coefficient updaters) 61aaa, 61aab. , 61aba, 61abb, 61baa, 61bab, 61bba, 61bbb, and eight transfer characteristic correction filters 62aaa, 62aab, 62aba, 62abb, 62baa, 62bab, 62bba, 62bbb are used.

Note that the noise control device 1000b includes a microcomputer (not shown) including a CPU, memory such as RAM, ROM, and the like. Control filters 20aa, 20ab, 20ba, 20bb, adders 30a, 30b, LMS calculation units 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, 61bbb, and transfer characteristic correction filters 62aaa, 62aab, 62aba, 62abb, 62baa, 62 bab , 62bba, and 62bbb are constructed by executing a program stored in the ROM in advance by the CPU.

The two control filters 20aa and 20ab perform convolution processing (signal processing, first signal processing) on a vibration signal (noise signal) indicating vibration detected by the sensor 1a using a predetermined control coefficient. The two control filters 20ba and 20bb perform convolution processing on the vibration signal indicating the vibration detected by the sensor 1b using predetermined control coefficients.

The adder 30a adds the output signal of the control filter 20aa and the output signal of the control filter 20ba, and outputs the added signal to the speaker 3a. Adder 30b adds the output signal of control filter 20ab and the output signal of control filter 20bb, and outputs the added signal to speaker 3b.

The speaker 3a reproduces a signal obtained by adding the output signal of the control filter 20aa and the output signal of the control filter 20ba by the adder 30a as a control sound. The speaker 3b reproduces a signal obtained by adding the output signal of the control filter 20ab and the output signal of the control filter 20bb by the adder 30b as a control sound.

The two error microphones 2a and 2b are installed in an area where interference occurs between road noise propagated into the vehicle from the suspension section and control sound reproduced by the speakers 3a and 3b. The two error microphones 2a and 2b detect residual noise that remains at the control point where they are installed due to the interference.

The error microphone 2a outputs an error signal indicating the detected residual noise to the four LMS computing units 61aaa, 61aba, 61baa, and 61bba. The error microphone 2b outputs an error signal indicating the detected residual noise to the four LMS computing units 61aab, 61abb, 61bab, and 61bbb. On the other hand, the sensor 1a outputs a vibration signal indicating the detected vibration to four transfer characteristic correction filters 62aaa, 62aab, 62aba, and 62abb.

Here, the transfer characteristic correction filter 62aaa performs convolution processing (signal processing, second signal processing) on the vibration signal output by the sensor 1a using coefficients that approximate the sound transfer characteristic C11 from the speaker 3a to the error microphone 2a. The signal after the convolution processing is output to the LMS arithmetic unit 61aaa. The transfer characteristic correction filter 62aab performs convolution processing on the vibration signal output from the sensor 1a using coefficients that approximate the sound transfer characteristic C12 from the speaker 3a to the error microphone 2b, and performs LMS calculation on the signal after the convolution processing. output to the device 61aab. Similarly, the transfer characteristic correction filters 62aba and 62abb perform convolution processing on the vibration signal output from the sensor 1a using coefficients that approximate the transfer characteristics C21 and C22 of the sound from the speaker 3a to the error microphones 2a and 2b, respectively. The signal after the convolution processing is output to the LMS calculation units 61aba and 61abb.

The LMS calculator 61aaa calculates the error signal input from the error microphone 2a by executing the LMS algorithm using the signal input from the transfer characteristic correction filter 62aaa and the error signal input from the error microphone 2a. The control coefficient of the control filter 20aa is updated so as to minimize it. The LMS calculator 61aab calculates the error signal input from the error microphone 2b by executing the LMS algorithm using the signal input from the transfer characteristic correction filter 62aab and the error signal input from the error microphone 2b. The control coefficient of the control filter 20aa is updated so as to minimize it.

Similarly, the LMS calculation units 61aba and 61abb execute the LMS algorithm using the signals input from the transfer characteristic correction filters 62aba and 62abb and the error signals input from the error microphones 2a and 2b. Thereby, the LMS calculators 61aba and 61abb update the control coefficients of the control filter 20ab so as to minimize the error signals input from the error microphones 2a and 2b.

Similarly, the sensor 1b outputs a vibration signal indicating the detected vibration to four transfer characteristic correction filters 62baa, 62bab, 62bba, and 62bbb. The transfer characteristic correction filters 62baa and 62bab perform convolution processing on the vibration signal output from the sensor 1b using coefficients that approximate the sound transfer characteristics C11 and C12 from the speaker 3a to the error microphones 2a and 2b, and perform the convolution processing. The latter signal is output to the LMS calculation units 61baa and 61bab. The transfer characteristic correction filters 62bba and 62bbb perform convolution processing on the vibration signal output from the sensor 1b using coefficients that approximate the sound transfer characteristics C21 and C22 from the speaker 3b to the error microphones 2a and 2b, and perform the convolution processing. The latter signals are output to the LMS computing units 61bba and 61bbb.

The LMS calculation units 61baa and 61bab execute the LMS algorithm using the signals input from the transfer characteristic correction filters 62baa and 62bab and the error signals input from the error microphones 2a and 2b. Thereby, the LMS calculators 61baa and 61bab update the control coefficients of the control filter 20ba so as to minimize the error signals input from the error microphones 2a and 2b. Similarly, the LMS calculation units 61bba and 61bbb execute the LMS algorithm using the signals input from the transfer characteristic correction filters 62bba and 62bbb and the error signals input from the error microphones 2a and 2b. Thereby, the LMS calculators 61bba and 61bbb update the control coefficients of the control filter 20bb so as to minimize the error signals input from the error microphones 2a and 2b.

From the above, the road noise caused by the vibration signals indicating the vibrations detected by the sensors 1a, 1b, 1c, and 1d will eventually reach the speakers at the control points where the error microphones 2a, 2b, 2c, and 2d are installed. 3a, 3b, 3c, and 3d are reduced by interfering with the reproduced control sound.

By the way, when driving a car, a driver usually adjusts the driving speed of the car and the rotational speed of the engine according to the situation by changing the opening degree of the accelerator depending on the driving state of the car. Therefore, while the car is running, the frequency and level of the engine sound fluctuate frequently. Therefore, in the control for reducing engine noise, it is necessary to always adapt the control sound played by the speaker to the driving condition. In other words, even if the frequency of the engine sound (engine speed) once converges, it is necessary to continue the operation of updating the control coefficient (hereinafter referred to as the adaptive operation). In this way, the control for reducing the engine sound can be achieved simply and inexpensively because it is sufficient to continue the adaptive operation for only the engine sound.

On the other hand, road noise is highly random noise generated from multiple noise sources and has a wide frequency band. Therefore, in the control for reducing road noise, the tap length of the control coefficient may be set to be long, and a plurality of sensors may be provided to detect noise generated from the plurality of noise sources. Further, in order to appropriately reduce road noise at multiple locations in the vehicle, multiple speakers and multiple error microphones may be provided, and the adaptive operation may be continued. In this case, by continuing to update each control coefficient so as to minimize the residual noise collected by each error microphone, it is possible to reduce road noise at the control point where each error microphone is installed. .

Note that, as described above, road noise generally has a wide frequency band with strong randomness. For this reason, for example, the control coefficients of the control filters 20aa and 20ab shown in FIG. 16 converge according to the sound transmission characteristics when road noise generated in the suspension section near the sensor 1a is transmitted to the error microphones 2a and 2b. do. That is, when reducing road noise, once the control coefficient is converged to the one that corresponds to the transfer characteristic, a constant noise reduction effect can be maintained without continuing the adaptive operation.

Specifically, it is assumed that the control coefficient converges to a control coefficient that reduces road noise in a band of 100 to 500 Hz by 10 dB in a certain driving state (for example, when traveling at 60 km/h). In this case, by using the control coefficient, it is possible to reduce road noise in the band of 100 to 500 Hz by 10 dB even in other driving conditions (for example, when driving at 100 km/h).

In this way, control to reduce road noise differs from control to reduce engine noise in that it does not depend on changes in vehicle speed (or engine speed), and even if the control coefficient is fixed, the noise level remains constant. A reduction effect can be obtained. Therefore, when applying the noise control device 1000b to an automobile to reduce road noise, it is conceivable to determine an initial value of the control coefficient and fix the control coefficient to the initial value. A specific example of a method for determining the initial value of such a control coefficient will be described below.

Car manufacturers must understand in advance the driving conditions of the car, such as where the user will drive the car, how many people besides the driver will be on board, and whether the car will be driven while playing music etc. on the car audio. is impossible. For example, even if the driving position of a car can be determined based on information stored in a navigation system, it is not possible to accurately grasp or predict the condition of the road surface on which the car is driving. For example, it is difficult to accurately understand or predict whether the road surface on which a car is driving is not a constant asphalt road surface, such as whether the road surface has many irregularities or a road surface with a manhole. It is.

In addition, it is difficult to accurately understand or predict that the road surface on which a car is driving is a road surface that has changed suddenly from a bumpy road to a new asphalt flat road surface before and after the completion of road construction. be. Furthermore, it is difficult to accurately grasp or predict whether the road surface on which the vehicle is running is wet due to rain or snowfall, or whether it is not dry. Furthermore, when the road surface conditions of the main line and the passing lane are not the same, it can be accurately determined whether the car is traveling on the main line or the passing lane, or whether the car is changing lanes. It is difficult to understand or predict.

Therefore, car manufacturers usually run their cars on test courses where road surface conditions are controlled to be constant. Then, the car manufacturer determines the control coefficients while keeping the car running at a constant state, such as driving at 60 km/h without playing anything on the car audio. Then, the car manufacturer fixes the control coefficient to the determined control coefficient and measures the road noise for a certain period of time (for example, 10 seconds) when the car is running in a predetermined effect measurement section (for example, a straight section of a test course). Measure by averaging each time.

FIG. 17 is a diagram showing the effect of noise control on road noise by the conventional noise control device 1000b. Then, the car manufacturer derives a control-off characteristic indicating the relationship between the measured road noise frequency and the measured road noise level (sound pressure), for example, as shown by the solid line in FIG. 17. Specifically, if the noise control device 1000b is not caused to perform the adaptive operation, and the road noise is averaged and measured every fixed period (for example, 10 seconds) while the car is traveling in the effect measurement section. good. Next, while causing the noise control device 1000b to perform the adaptive operation, the car manufacturer averages and measures the road noise at regular intervals (for example, 10 seconds) while the vehicle is traveling in the effect measurement section. Then, the car manufacturer derives a control-on characteristic indicating the relationship between the measured road noise frequency and the measured road noise level, for example, as shown by the broken line in FIG. 17.

Next, the car manufacturer calculates the difference in the level of each frequency in the derived control-off characteristic and control-on characteristic, and confirms whether the road noise reduction effect indicated by the difference has achieved a predetermined target value. . Thereby, the car manufacturer confirms whether the control coefficients have converged. If the road noise reduction effect indicated by the difference does not reach a predetermined target value, the car manufacturer determines that the control coefficient has not converged. In this case, the car manufacturer again causes the noise control device 1000b to perform the adaptive operation while causing the automobile to travel through the effect measurement section, and derives the control-on characteristic again in the same manner as above. Then, the car manufacturer repeats this process until the reduction effect reaches a predetermined target value.

Thereafter, when the reduction effect reaches a predetermined target value, the car manufacturer determines that the control coefficient has converged, and determines that the control coefficient can be fixed from now on. Then, the car manufacturer stores the control coefficient at the time of convergence in the ROM in advance as an initial value of the control coefficient.

However, with this method, car manufacturers have to design control coefficients for each car, which requires a huge amount of effort in order to sell cars in large quantities. Assume that the initial value of the control coefficient determined using one vehicle is set as a representative value, and the representative value is set as the initial value of the control coefficient in other vehicles. However, in this case, not all vehicles have the same road noise transmission characteristics, so there is no guarantee that the desired reduction effect will be obtained.

In particular, products of speakers are generally controlled by allowing for variations in output characteristics of about 10 to 20%. Furthermore, it is considered that the output characteristics of speakers installed in automobiles will further vary. In addition to this, it is thought that variations occur in the characteristics of microphones, microphone amplifiers, power amplifiers, and other circuits. Therefore, even if the initial value of the control coefficient determined using one vehicle is set as the representative value and the initial value of the control coefficient for other vehicles, the road noise reduction effect will not be as desired for all vehicles. There is no guarantee that the target value will be achieved. In some cases, the noise control device 1000b may oscillate.

Therefore, it is conceivable to have the user who purchased the car set the initial value of the control coefficient. However, it is difficult for the user to derive the difference between the control-off characteristic and the control-on characteristic under stable driving conditions such as the above-mentioned car manufacturer's test course. For this reason, it can be said that it is difficult for the user to determine appropriate initial values of the control coefficients.

Based on the above, the inventor of the present invention considered that it would be difficult to continue reducing road noise while keeping the control coefficient fixed. Therefore, when a situation arises in which the desired reduction effect cannot be obtained when the fixed operation of fixing the control coefficient is performed, the inventor performs the adaptive operation, and then the desired reduction effect is obtained. If the situation arises, we considered fixing the control coefficients to the current control coefficients and performing the fixed operation again.

However, suppose, for example, noise that is not to be reduced (hereinafter referred to as non-targeted noise) occurs due to the driver significantly changing the playback sound of the car audio in response to a request from another passenger. In this case, in the conventional technique described above, the error microphone collects not only the noise to be reduced but also the noise that is not the target noise.

For this reason, the control sound is controlled so as to minimize noise including non-target noise, and it is not possible to accurately reduce only the target noise. In other words, with the above-mentioned conventional technology, it was not possible to accurately grasp the effect of reducing the noise to be reduced. Therefore, the inventor of the present invention conducted extensive studies to accurately understand the effect of reducing the noise to be reduced, and as a result, came up with the present disclosure.

In an embodiment according to the present disclosure, a noise detector that detects noise generated by a noise source; a control filter that performs signal processing using a predetermined control coefficient on a noise signal indicating the noise detected by the noise detector; A speaker that reproduces the output signal of the control filter as a control sound, and a speaker that is installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker, and that remains at the control point due to the interference. an error microphone that detects residual noise detected by the error microphone; a transfer characteristic correction filter that processes the noise signal using a sound transfer characteristic from the speaker to the error microphone; and an error signal that indicates the residual noise detected by the error microphone. and an output signal of the transfer characteristic correction filter to update the control coefficient so as to minimize the error signal; a correction filter that processes an output signal of the control filter; a subtracter that subtracts the output signal of the correction filter from the error signal; and an output signal of the subtracter that is used as a control off signal representing noise before control due to the interference. , an effect measurement unit that uses the error signal as a control-on signal representing the noise after the control due to the interference and measures the noise reduction effect at the control point based on the difference between the control-off signal and the control-on signal; Provided is a noise control device comprising:

Further, in an embodiment according to the present disclosure, the computer of the noise control device detects noise generated by a noise source using a sensor, and uses a predetermined control coefficient to adjust the noise signal indicating the noise detected by the sensor. The control point is installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker. Using an error microphone, detect the residual noise remaining at the control point due to the interference, perform second signal processing on the noise signal using the sound transfer characteristics from the speaker to the error microphone, and The control coefficient is updated to minimize the error signal using the error signal indicating the residual noise detected by the controller and the signal after the second signal processing, and the sound is transmitted from the speaker to the error microphone. Perform third signal processing on the signal after the first signal processing using the characteristic, subtract the signal after the third signal processing from the error signal, and use the signal after the subtraction to remove the noise before the control due to the interference. and the error signal is a control-on signal representing noise after control due to the interference, and the noise reduction effect at the control point is measured based on the difference between the control-off signal and the control-on signal. A noise control method is provided.

Further, in an embodiment according to the present disclosure, a program for causing a computer to execute the noise control method is provided.

Further, in an embodiment according to the present disclosure, there is provided a noise detector that detects noise generated by a noise source, and a control filter that performs signal processing using a predetermined control coefficient on a noise signal indicating the noise detected by the noise detector. and a speaker that reproduces the output signal of the control filter as a control sound, installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker, and the control point is an error microphone that detects residual noise remaining in the error microphone; a correction filter that processes the output signal of the control filter using sound transfer characteristics from the speaker to the error microphone; and an output of the correction filter from the error signal. a subtracter for subtracting a signal; the output signal of the subtracter is a control off signal representing the noise before the control due to the interference; and the error signal is a control on signal representing the noise after the control due to the interference; A noise control device is provided, comprising: an effect measurement unit that measures a noise reduction effect at the control point based on a difference between an off signal and the control on signal.

According to the above aspect, a signal obtained by subtracting the output signal of the correction filter from an error signal indicating the residual noise detected by the error microphone is used as the control-off signal, and the error signal is used as the control-on signal, and the control-off signal and the control-on signal are combined. Based on the difference, the noise reduction effect at the control point is measured. That is, the noise reduction effect at the control point is measured based on the output signal of the correction filter, which is the difference between the error signal and a signal obtained by subtracting the output signal of the correction filter from the error signal.

Therefore, sounds unrelated to the noise generated by the target noise source propagate to the control point, and the error signal indicating the residual noise detected by the error microphone includes sounds unrelated to the noise generated by the noise source. Even so, the effect of reducing the noise propagated from the noise source at the control point can be measured with high accuracy based only on the output signal of the correction filter that is unrelated to the unrelated sound.

The above aspect may further include an adaptable state determination unit that determines whether or not to cause the coefficient updater to update the control coefficients.

According to this aspect, it can be determined whether or not to cause the coefficient updater to update the control coefficients. Therefore, if having the coefficient updater update the control coefficients will worsen the noise at the control point, the coefficient updater will not update the control coefficients and the coefficient updater will update the control coefficients. The coefficient updater can be caused to update the control coefficients only when the noise at the control point is reduced by performing the above.

In the above aspect, the coefficient updater updates the control coefficient using a predetermined convergence constant, and the effect measurement unit measures the difference between the control off signal and the control on signal as the reduction effect, A determination process is performed to determine whether the reduction effect has achieved a predetermined target value, and if it is determined in the determination process that the reduction effect has achieved the target value, the control coefficient is optimal. If the update of the control coefficient by the coefficient updater is stopped and the control coefficient is fixed at the optimum value, and it is determined that the reduction effect has not achieved the target value, then Assuming that the control coefficient has not converged to the optimal value, a new convergence constant is set by adding a predetermined value to the convergence constant that was used by the coefficient updater at the time of measuring the reduction effect, and The updating of the control coefficient using the new convergence constant may be restarted.

According to this aspect, if the difference between the control off signal and the control on signal has achieved a predetermined target value and the control coefficient is considered to have converged to the optimal value, the control coefficient is It is possible to avoid unnecessary updating of the control coefficient by fixing it to the optimum value. On the other hand, if the difference has not achieved the predetermined target value and it is considered that the control coefficient has not converged to the optimal value, a new convergence constant that is larger than the one at the time of measuring the reduction effect is used. Control coefficients can be updated. In this manner, according to this aspect, the control coefficients can be efficiently converged to the optimum value.

In the above aspect, the effect measurement unit performs signal processing on each of the control-off signal and the control-on signal using an A-characteristic coefficient indicating A-characteristic that simulates human auditory characteristics, and A difference between the control-off signal and the control-on signal after the signal processing may be measured as the reduction effect.

According to this aspect, the reduction effect can be measured by taking human hearing characteristics into account. Therefore, even if a person at a control point can hear a sound that is unrelated to the noise generated by the target noise source, it will propagate from the noise source at the control point without being affected by the unrelated sound. The noise reduction effect can be measured with high accuracy.

In the above aspect, the effect measurement unit includes a frequency analysis unit that calculates frequency characteristics of the control-off signal and the control-on signal, and a difference between the control-off signal and the control-on signal for each frequency in the frequency characteristics. and a frequency difference effect calculation unit that calculates a first difference as an index of the reduction effect.

According to this aspect, the first difference, which is the difference between the control-off signal and the control-on signal at each frequency in the frequency characteristics of the control-off signal and the control-on signal, can be calculated as an index of the reduction effect. Therefore, it is possible to determine whether or not the reduction effect has achieved a predetermined target value, depending on the number of first differences that have achieved a predetermined value corresponding to the target value.

In the above aspect, the effect measurement unit includes a frequency analysis unit that calculates frequency characteristics of the control-off signal and the control-on signal, and a frequency analysis unit that calculates frequency characteristics of the control-off signal and the control-on signal, using the frequency characteristics. an overall calculation unit that calculates an overall value in all frequency bands; and an overall value difference that calculates a second difference, which is a difference between the overall value of the control off signal and the overall value of the control on signal, as an index of the reduction effect. The computer may also include an effect calculation section.

According to this aspect, the second difference, which is the difference between the overall value of the control-off signal and the overall value of the control-on signal, calculated using the frequency characteristics of the control-off signal and the control-on signal, is used as an index of the reduction effect. can be calculated. Therefore, it is possible to determine whether the reduction effect has achieved a predetermined target value by determining whether the second difference has achieved a predetermined value corresponding to the target value. can.

In the above aspect, the effect measurement unit includes a frequency analysis unit that calculates frequency characteristics of the control-off signal and the control-on signal, and a difference between the control-off signal and the control-on signal for each frequency in the frequency characteristics. a frequency difference effect calculation unit that calculates a first difference as an index of the reduction effect; and a frequency difference effect calculation unit that calculates an overall value of each of the control off signal and the control on signal in all frequency bands using the frequency characteristic. and an overall value difference effect calculation unit that calculates a second difference, which is the difference between the overall value of the control off signal and the overall value of the control on signal, as an index of the reduction effect. Good too.

According to this aspect, the first difference, which is the difference between the control-off signal and the control-on signal at each frequency in the frequency characteristics of the control-off signal and the control-on signal, can be calculated as an index of the reduction effect. Therefore, it is possible to determine whether or not the reduction effect has achieved a predetermined target value, depending on the number of first differences that have achieved a predetermined value corresponding to the target value.

Further, a second difference, which is the difference between the overall value of the control-off signal and the overall value of the control-on signal, calculated using the frequency characteristics of the control-off signal and the control-on signal, may be calculated as an index of the reduction effect. can. Therefore, it is possible to determine whether the reduction effect has achieved a predetermined target value by determining whether the second difference has achieved a predetermined value corresponding to the target value. I can do it.

In the above aspect, the effect measuring section includes a band limiting section that uses the frequency characteristic to extract signals of frequencies within a predetermined evaluation target frequency band included in each of the control off signal and the control on signal. Furthermore, the overall calculation unit calculates overall values in all frequency bands of the signals extracted by the band limiting unit from the control-off signal and the control-on signal, and the overall value difference effect calculation unit: The second difference may be a difference between an overall value of the signal extracted by the band limiter from the control-off signal and an overall value of the signal extracted by the band-limiter from the control-on signal.

According to this aspect, the difference between the overall value of the signal in the evaluation target frequency band included in the control off signal and the overall value of the signal in the evaluation target frequency band included in the control on signal is calculated as the second difference. Therefore, even if a signal outside the evaluation target frequency band is included in the control-off signal and the control-off signal due to non-target noise occurring, etc., the second difference will be adjusted to the predetermined value according to the target value. To accurately determine whether the reduction effect has achieved a predetermined target value by excluding the influence of signals outside the evaluation target frequency band by determining whether or not the reduction effect has achieved a predetermined target value. I can do it.

In the above aspect, the coefficient updater updates the control coefficient using a predetermined convergence constant, and the effect measurement unit performs a determination process to determine whether the reduction effect has achieved a predetermined target value. and in the determination process, the first difference of the majority of frequencies among the frequencies included in the predetermined frequency band to be evaluated, calculated by the frequency difference effect calculation unit, is determined to be a predetermined difference corresponding to the target value. If one target value has been achieved, it is determined that the reduction effect has achieved the target value, and the update of the control coefficient by the coefficient updater is stopped, assuming that the control coefficient has converged to the optimal value. and fix the control coefficient to the optimum value, and the first difference of the majority of the frequencies included in the evaluation target frequency band calculated by the frequency difference effect calculation unit is equal to the first target value. If the target value has not been achieved, it is determined that the reduction effect has not achieved the target value, and the coefficient updater is used at the time of calculating the first difference, assuming that the control coefficient has not converged to the optimal value. A new convergence constant may be obtained by adding a predetermined value to the previously used convergence constant, and the coefficient updater may restart updating of the control coefficient using the new convergence constant.

According to this aspect, whether or not the reduction effect has achieved the target value is determined by achieving a predetermined first target value corresponding to the target value among frequencies included in a predetermined evaluation target frequency band. The determination can be made with high accuracy based on the ratio of frequencies corresponding to the first difference.

Then, if the reduction effect has achieved a predetermined target value and the control coefficient is considered to have converged to the optimal value, the control coefficient is fixed at the optimal value and the control coefficient is updated unnecessarily. This can be avoided. On the other hand, if the reduction effect has not achieved the predetermined target value and it is considered that the control coefficient has not converged to the optimal value, a new convergence constant larger than that at the time of calculating the first difference is used. control coefficients can be updated. In this manner, according to this aspect, the control coefficients can be efficiently converged to the optimum value.

In the above aspect, the coefficient updater updates the control coefficient using a predetermined convergence constant, and the effect measurement unit performs a determination process to determine whether the reduction effect has achieved a predetermined target value. and in the determination process, if the second difference has achieved a predetermined second target value corresponding to the target value, it is determined that the reduction effect has achieved the target value, and the control Assuming that the coefficient has converged to the optimum value, the update of the control coefficient by the coefficient updater is stopped and the control coefficient is fixed to the optimum value, and the second difference does not reach the second target value. In this case, it is determined that the reduction effect has not achieved the target value, and the control coefficient has not converged to the optimal value, and the convergence that was used by the coefficient updater at the time of calculating the second difference A new convergence constant may be obtained by adding a predetermined value to the constant, and the coefficient updater may restart updating of the control coefficient using the new convergence constant.

According to this aspect, whether or not the reduction effect has achieved the target value is determined depending on whether or not the second difference has achieved a predetermined second target value corresponding to the target value. It can be determined with high accuracy.

Then, if the reduction effect has achieved a predetermined target value and the control coefficient is considered to have converged to the optimal value, the control coefficient is fixed at the optimal value and the control coefficient is updated unnecessarily. This can be avoided. On the other hand, if the reduction effect has not achieved the predetermined target value and it is considered that the control coefficient has not converged to the optimal value, a new convergence constant larger than that at the time of calculating the second difference is used. control coefficients can be updated. In this manner, according to this aspect, the control coefficients can be efficiently converged to the optimum value.

In the above aspect, the coefficient updater updates the control coefficient using a predetermined convergence constant, and the effect measurement unit performs a determination process to determine whether the reduction effect has achieved a predetermined target value. and in the determination process, the first difference of the majority of frequencies among the frequencies included in the predetermined evaluation target frequency band calculated by the frequency difference effect calculation unit is set to a predetermined first difference corresponding to the target value. When the target value is achieved and the second difference achieves a predetermined second target value according to the target value, it is determined that the reduction effect has achieved the target value, and the control Assuming that the coefficient has converged to the optimum value, the update of the control coefficient by the coefficient updater is stopped and the control coefficient is fixed to the optimum value, and the frequency band to be evaluated calculated by the frequency difference effect calculation unit is If the first difference of a majority of the frequencies included in the frequency range does not achieve the first target value, it is determined that the reduction effect has not achieved the target value, and the control coefficient is set to the optimum value. Assuming that the convergence constant has not converged to If the updating of the control coefficient using a constant is restarted and the second difference has not achieved the second target value, it is determined that the reduction effect has not achieved the target value, and the control coefficient is Assuming that the optimum value has not been converged, a new convergence constant is determined by adding a predetermined value to the convergence constant that was used by the coefficient updater at the time of calculating the second difference, and the new convergence constant by the coefficient updater The updating of the control coefficients using a convergence constant may be restarted.

According to this aspect, whether or not the reduction effect has achieved the target value is determined by achieving a predetermined first target value corresponding to the target value among frequencies included in a predetermined evaluation target frequency band. The determination can be made with high accuracy based on the ratio of frequencies corresponding to the first difference. Further, whether or not the reduction effect achieves the target value is accurately determined depending on whether or not the second difference achieves a predetermined second target value corresponding to the target value. be able to.

Then, if the reduction effect has achieved a predetermined target value and the control coefficient is considered to have converged to the optimal value, the control coefficient is fixed at the optimal value and the control coefficient is updated unnecessarily. This can be avoided. On the other hand, if the reduction effect has not achieved the predetermined target value and it is considered that the control coefficient has not converged to the optimal value, a new value larger than that at the time of calculation of the first difference or the second difference The convergence constant can be used to update the control coefficients. In this manner, according to this aspect, the control coefficients can be efficiently converged to the optimum value.

In the above aspect, the effect measurement unit may detect a predetermined number or more of frequencies within a predetermined noise increase band included in the evaluation target frequency band, which are calculated by the frequency difference effect calculation unit in the determination process. If the first difference exceeds a predetermined tolerance value corresponding to the target value, it may be assumed that an abnormality has occurred in the control coefficient, and the update of the control coefficient by the coefficient updater may be stopped.

According to this aspect, the occurrence of an abnormality in the control coefficient is determined by indicating that the control coefficient exceeds a predetermined tolerance value corresponding to the target value among frequencies within a predetermined noise increase band included in a predetermined evaluation target frequency band. The determination can be made with high accuracy based on the ratio of frequencies corresponding to the first difference. Then, when it is determined that an abnormality has occurred in the control coefficient, updating of the control coefficient by the coefficient updater can be appropriately stopped.

In the above aspect, the predetermined number may be one.

According to this aspect, among the frequencies within the predetermined noise increase band included in the predetermined evaluation target frequency band, one frequency corresponds to the first difference that exceeds the predetermined tolerance value according to the target value. However, if the control coefficient exists, it is assumed that an abnormality has occurred in the control coefficient, and the update of the control coefficient by the coefficient updater can be stopped.

In the above aspect, a plurality of the error microphones are provided, and the effect measuring section sets the installation location of each error microphone as the control point, and individually measures the error microphone for each of the plurality of error microphones in advance. The determination process may be performed using an individual target value set as the target value.

According to this aspect, it is possible to individually determine whether the noise reduction effect at the installation location of each error microphone has achieved the individual target value set individually in advance for each error microphone.

In the above aspect, the individual target value is associated with a priority order, and the effect measurement unit is configured to perform the determination process in which the individual target value associated with the highest priority order is used as the target value. When it is determined that the reduction effect has achieved the target value, it may be determined that the reduction effect has achieved the target value in the determination processing for all the control points.

According to this aspect, without determining whether the noise reduction effect at each of one or more control points has achieved the individual target value, the noise reduction effect is determined by the highest priority. By determining that the assigned individual target value has been achieved, it can be easily determined that the noise reduction effect at all control points has achieved the individual target value.

In the above aspect, the adaptable state determining unit causes the coefficient updater to update the control coefficient when a value obtained by averaging instantaneous value levels of the error signal over a predetermined period is within a predetermined threshold range. It may be determined that the

According to this aspect, even if the instantaneous value level of the error signal instantaneously exceeds the threshold range, the value obtained by averaging the instantaneous value level of the error signal over a predetermined period is within the predetermined threshold range. If so, the coefficient updater can be caused to update the control coefficients.

The embodiments described below are examples of preferred specific examples of the present disclosure. The components, arrangement positions and connection forms of the components, order of operations, etc. shown in the following embodiments are merely examples, and do not limit the present disclosure. The disclosure is limited only by the claims.

Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims representing the topmost concept of the present disclosure are not necessarily necessary to achieve the object of the present disclosure, but may be more effective. It is described as constituting a preferred form.

(Embodiment 1)
The configuration of the noise control device according to Embodiment 1 will be explained. FIG. 1 is a configuration diagram of a noise control device 1000 according to the first embodiment.

The noise control device 1000, like the conventional noise control device 1000b shown in FIG. The road noise caused by the vibration signals shown is reduced at the control points where the error microphones 2a, 2b, 2c, and 2d are installed.

For convenience of explanation, FIG. 1 only shows the components used by the noise control device 1000 to control road noise reduction in the front half of the automobile 100, similar to the conventional noise control device 1000b shown in FIG. . However, in reality, the noise control device 1000 further includes components similar to those shown in FIG. 1 in the rear half of the automobile 100. Similar to the noise control device 1000b, the noise control device 1000 similarly performs control to reduce road noise in the front half of the vehicle 100 and the rear half of the vehicle 100. Therefore, only the control by which the noise control device 1000 shown in FIG. 1 reduces road noise in the front half of the automobile 100 will be described in detail below.

Two sensors 1a, 1b, four control filters 20aa, 20ab, 20ba, 20bb, eight transfer characteristic correction filters 62aaa, 62aab, 62aba, 62abb, 62baa, 62bab, 62bba, 62bbb, eight shown in FIG. FIG. This is the same configuration as shown in . In other words, like the conventional noise control device 1000b, the noise control device 1000 performs an adaptive operation of updating the control coefficients of the control filters 20aa, 20ab, 20ba, and 20bb to generate noise caused by vibration signals indicating vibrations detected by the sensors 1a and 1b. The road noise caused by the error microphones 2a and 2b is reduced at the control point where the error microphones 2a and 2b are installed.

Further, once the control coefficient converges to the optimum value, the noise control device 1000 performs a fixing operation to fix the control coefficient to the optimum value. Below, a method for the noise control device 1000 to determine whether the control coefficient has converged to the optimal value will be described.

First, in the error microphone 2a, as a result of interference between road noise in the vehicle interior caused by vibration signals indicating vibrations detected by the sensors 1a and 1b and control sounds reproduced by the speakers 3a and 3b, the error microphone 2a is installed at the location where the error microphone 2a is installed. An error signal is output indicating the residual noise remaining at a certain control point. Here, if the signal indicating road noise at the installation location of the error microphone 2a is the signal N1, the signal reproduced by the speaker 3a is the signal y1, and the signal reproduced by the speaker 3b is the signal y2, then the error signal e1 output by the error microphone 2a is can be expressed by Equation 1.
e1=N1+C11*y1+C21*y2...(Formula 1)
Here, C11 indicates the sound transfer characteristic from the speaker 3a to the error microphone 2a.
C21 indicates the sound transfer characteristic from the speaker 3b to the error microphone 2a.
* indicates a convolution operation.

On the other hand, the signal y1 is input to the subtracter 41a via the transfer characteristic correction filter 40aa. The transfer characteristic correction filter (correction filter) 40aa performs convolution processing (signal processing, 3 signal processing) and outputs the signal after the convolution processing to the subtracter 41a. Similarly, the signal y2 is input to the subtracter 41a via the transfer characteristic correction filter 40ba.

The subtracter 41a subtracts the output signals of the transfer characteristic correction filter 40aa and the transfer characteristic correction filter 40ba from the error signal output by the error microphone 2a. Specifically, the subtracter 41a performs the calculation of Equation 2.
off1=e1-C11*y1-C21*y2...(Formula 2)
Here, C11 indicates the sound transfer characteristic from the speaker 3a to the error microphone 2a.
C21 indicates the sound transfer characteristic from the speaker 3b to the error microphone 2a.
off1 indicates the output signal of the subtracter 41a.

When Expression 1 is substituted into Expression 2, the output signal off1 of the subtracter 41a can be expressed by Expression 3.
off1=N1...(Formula 3)

In this way, the output signal off1 of the subtractor 41a is the same signal as the signal indicating the road noise at the location where the error microphone 2a is set, and is the same signal as the road noise at the location where the error microphone 2a is set and the outputs of the two speakers 3a and 3b. This signal represents the noise before control due to interference with the signal. On the other hand, the error signal e1 in Equation 1 is a signal on1 representing the noise after control due to the interference.

In other words, in the noise control device 1000, a signal off1 representing the noise before the control due to the interference between the road noise at the setting location of the error microphone 2a and the output signals of the two speakers 3a and 3b, and a signal off1 representing the noise after the control due to the interference. The signal on1 representing the above is calculated simultaneously. The calculated signal off1 representing the noise before control and the signal on1 representing the noise after control are input to the effect measuring section 50a.

Similarly, in the noise control device 1000, a signal off2 representing the noise before the control due to the interference between the road noise at the setting location of the error microphone 2b and the output signals of the two speakers 3a and 3b, and a signal off2 representing the noise after the control due to the interference. A signal on2 representing noise is calculated at the same time. The calculated signal off2 representing the noise before control and the signal on2 representing the noise after control are input to the effect measuring section 50b.

The effect measurement unit 50a generates a signal (control off signal) off1 representing the noise before control due to interference between the road noise at the setting location of the error microphone 2a and the output signals of the two speakers 3a and 3b, and a signal after control due to the interference. Based on the signal representing noise (control-on signal) on1, the road noise reduction effect at the setting location of the error microphone 2a is measured. The effect measurement unit 50b generates a signal (control off signal) off2 representing the noise before the control due to interference between the road noise at the setting location of the error microphone 2b and the output signals of the two speakers 3a and 3b, and a signal after the control due to the interference. Based on the signal representing noise (control-on signal) on2, the road noise reduction effect at the setting location of the error microphone 2b is measured.

FIG. 2 is a diagram showing an example of the configuration of the effect measuring section 50a. The effect measuring section 50b has the same configuration as the effect measuring section 50a. Therefore, below, only the configuration of the effect measuring section 50a will be described as a representative. As shown in FIG. 2, the effect measurement section 50a includes two A-characteristic filter sections 51a and 51b, two frequency analysis sections 52a and 52b, two overall calculation sections 53a and 53b, and a frequency difference effect. It includes a calculation section 54a and an overall value difference effect calculation section 54b.

A signal representing noise before control (hereinafter referred to as a signal before noise control) due to interference between the road noise input to the effect measurement unit 50a and the output signals of the two speakers 3a and 3b, and road noise and the two speakers. Signals on1 representing noise after control due to interference with the output signals of 3a and 3b (hereinafter referred to as post-noise control signals) are input to A-characteristic filter sections 51a and 51b, respectively.

The A-characteristic filter unit 51a performs convolution processing (signal processing) on the input pre-noise control signal off1 using coefficients (A-characteristic coefficients) indicating A-characteristics that simulate human auditory characteristics. Similarly, the A-characteristic filter section 51b performs convolution processing on the input noise-controlled signal on1 using coefficients representing A-characteristics that simulate human auditory characteristics (hereinafter referred to as A-characteristic coefficients).

The frequency analysis unit 52a calculates the frequency characteristics of the pre-noise control signal off1 after the convolution process by the A-characteristic filter unit 51a by performing a predetermined frequency analysis process such as FFT. The frequency analysis section 52b calculates the frequency characteristics of the noise-controlled signal on1 after the convolution processing by the A-characteristic filter section 51b by performing predetermined frequency analysis processing such as FFT.

The frequency difference effect calculation unit 54a calculates the pre-noise control signal off1 after the convolution process by the A-characteristic filter unit 51a and the signal by the A-characteristic filter unit 51b for each frequency in the frequency characteristics calculated by the frequency analysis unit 52a and the frequency analysis unit 52b. The difference from the noise-controlled signal on1 after the convolution process (hereinafter referred to as the first difference) is calculated as an index of the road noise reduction effect at the setting location of the error microphone 2a.

The overall calculation unit 53a uses the frequency characteristics of the pre-noise control signal off1 after the convolution process by the A-characteristic filter unit 51a, calculated by the frequency analysis unit 52a, to calculate the overall value of the pre-noise control signal off1 in all frequency bands. Calculate. Hereinafter, the overall value calculated by the overall calculation unit 53a will be referred to as a first overall value. The overall calculation unit 53b uses the frequency characteristics of the noise-controlled signal on1 after the convolution process by the A-characteristic filter unit 51b, calculated by the frequency analysis unit 52b, to calculate the overall value of the noise-controlled signal on1 in all frequency bands. Calculate. Hereinafter, the overall value calculated by the overall calculation unit 53b will be referred to as a second overall value.

The overall value difference effect calculation unit 54b calculates the difference between the first overall value calculated by the overall calculation unit 53a and the second overall value calculated by the overall calculation unit 53b (hereinafter referred to as second difference) of the error microphone 2a. Calculated as an index of the road noise reduction effect at the setting location.

FIG. 3 is a diagram showing an example of the noise reduction effect measured by the effect measurement section 50a. In section (a) of FIG. 3, the frequency characteristic of the pre-noise control signal off1 calculated by the frequency analyzer 52a is shown as a solid line, and the frequency characteristic of the post-noise control signal on1 calculated by the frequency analyzer 52b is shown as a broken line. has been done. Section (b) of FIG. 3 shows the first frequency difference calculated by the frequency difference effect calculation unit 54a, which corresponds to the difference between the frequency characteristics shown by the solid line and the frequency characteristics shown by the broken line in section (a) of FIG. Differences are shown.

For example, in the example shown in sections (a) and (b) of FIG. 3, at the setting location of the error microphone 2a, the road noise at frequencies above f1 and below f2 corresponding to the first difference below 0 dB is reduced. be able to understand that. Further, since there is no frequency corresponding to the first difference above 0 dB, it can be understood that the road noise of all frequency components has not increased.

Furthermore, on the right side of the frequency characteristics in section (a) of FIG. For example, 80 dBA). Further, on the right side of the frequency characteristic in section (a) of FIG. 3, a second difference (for example, - 5dBA) is shown. In the example shown in section (a) of FIG. 3, the second difference is -5 dBA, so it can be seen that the road noise at the location where the error microphone 2a is set has been reduced by 5 dBA.

Note that if it is desired to evaluate the road noise reduction effect without considering human auditory characteristics, the effect measuring section 50a does not need to include the A-characteristic filter sections 51a and 51b. In accordance with this, the frequency analysis section 52a calculates the frequency characteristics of the pre-noise control signal (control off signal) off1 inputted to the effect measurement section 50a, and the frequency analysis section 52b calculates the frequency characteristics of the signal before noise control (control off signal) off1 inputted to the effect measurement section 50a. The frequency characteristics of the noise-controlled signal (control-on signal) on1 may be calculated.

The effect measurement unit 50a further uses the first difference for each frequency calculated by the frequency difference effect calculation unit 54a and the second difference calculated by the overall value difference effect calculation unit 54b to measure the error microphone 2a. A determination process is performed to determine whether the road noise reduction effect at the set location has achieved the target value.

Specifically, in the determination process, the effect measurement unit 50a determines whether the road noise reduction effect at the setting location of the error microphone 2a has achieved the target value, as shown in 1) to 2) below. Determine whether
1) The first difference between the majority of frequencies included in a predetermined evaluation target frequency band (for example, frequencies f1 to f2 in sections (a) and (b) of FIG. 3) is set in advance. If the first target value has been achieved, it is determined that the reduction effect has achieved the target value. Note that the effect measurement unit 50a may make the determination under more severe conditions. For example, when the effect measurement unit 50a determines that the first difference of a predetermined number (for example, 70%) or more of the frequencies included in the evaluation target frequency band has achieved the first target value. Furthermore, it may be determined that the reduction effect has achieved the target value.
2) If the second difference has achieved a preset second target value different from the first target value, it is determined that the reduction effect has achieved the target value.

Note that the effect measuring section 50b performs a determination process to determine whether the road noise reduction effect at the setting location of the error microphone 2b has achieved the target value in the same manner as the effect measuring section 50a.

As a result of the determination processing performed by the effect measurement unit 50a and the effect measurement unit 50b, it is determined that the road noise reduction effect at the setting locations of all the error microphones 2a and 2b installed in the vehicle has achieved the target value. do. In this case, the effect measuring section 50a or the effect measuring section 50b determines that the control coefficients of all the control filters 20aa, 20ab, 20ba, and 20bb have converged to the optimal values, and stops the adaptive operation.

Specifically, the effect measurement unit 50a or the effect measurement unit 50b includes four control filters 20aa by eight LMS calculation units (coefficient updaters) 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, and 61bbb. , 20ab, 20ba, and 20bb are stopped from updating. Then, the effect measuring section 50a or the effect measuring section 50b fixes the control coefficients of each control filter 20aa, 20ab, 20ba, and 20bb to the respective control coefficients when it is determined that the control coefficients have converged to the optimum value.

According to the above configuration, the pre-noise control signal off1 represents the road noise before control due to the interference between the road noise at the control point where each error microphone 2a, 2b is installed and the control sound reproduced by each speaker 3a, 3b. , off2, and post-noise control signals on1 and on2 representing road noise before control due to the interference at the control point can be obtained at the same time.

Furthermore, a pre-noise control signal off1 is obtained by subtracting the output signals of the transfer characteristic correction filters 40aa and 40ba from an error signal indicating the residual noise detected by the error microphone 2a, and an error signal indicating the residual noise detected by the error microphone 2a. The noise reduction effect at the installation location of the error microphone 2a is measured based on the output signals of the transfer characteristic correction filters 40aa and 40ba, which are the difference between the noise control signal on1 and the output signal of the transfer characteristic correction filters 40aa and 40ba.

Therefore, sounds unrelated to the noise generated by the target noise source propagate to the control point, and the error signal indicating the residual noise detected by the error microphone 2a includes sounds unrelated to the noise generated by the noise source. Even if the error microphone 2a is installed, the noise reduction effect at the location where the error microphone 2a is installed can be accurately measured based only on the output signals of the transfer characteristic correction filters 40aa and 40ba that are unrelated to the unrelated sound.

Therefore, for example, the car manufacturer does not have to drive each automobile 100 it sells on a test course to determine the control coefficients of the control filters 20aa, 20ab, 20ba, and 20bb, as described above. A general user can appropriately set the control coefficients of each control filter 20aa, 20ab, 20ba, and 20bb while driving the automobile 100.

In addition, in the case of broadband noise such as road noise, once the control coefficient is determined, a certain effect can be maintained without changing the control coefficient frequently. By operating 20ab, 20ba, and 20bb, the noise reduction effect at the location where the error microphone 2a is installed can be measured.

FIG. 18 is a configuration diagram showing a modification of the noise control device 1000 according to the first embodiment. In such a case, the LMS calculators 61aaa to 61bbb and the transfer characteristic correction filters 62aaa to 62bbb may be removed from the noise control device 1000 (FIG. 1). Thereby, a noise control device 1002 with a simplified configuration as shown in FIG. 18 may be configured.

In other words, when the noise control device 1002 performs control to reduce road noise in the front half of the automobile 100, the two sensors 1a and 1b and the vibration signals output by the two sensors 1a and 1b have predetermined Four control filters 20aa, 20ab, 20ba, 20bb that perform convolution processing using control coefficients, two adders 30a, 30b, two speakers 3a, 3b, and two error microphones 2a, 2b. , four transfer characteristic correction filters (correction filters) 40aa, 40ab, 40ba, 40bb, two subtractors 41a, 41b, and two effect measurement units 50a, 50b. .

FIG. 4 is a diagram showing another example of the noise reduction effect measured by the effect measurement section 50a. In section (a) of FIG. 4, as in section (a) of FIG. The frequency characteristic of the rear signal on1 is shown by a broken line. Similar to section (b) in FIG. 3, section (b) in FIG. The first difference calculated by the section 54a for each frequency is shown.

Section (a) of FIG. 4 also shows the frequency characteristics of the pre-noise control signal off1 and noise control when the noise propagating to the error microphone 2a changes while the effect measurement unit 50a is measuring the road noise reduction effect. The frequency characteristic of the rear signal on1 is shown by a dotted line. For example, the noise propagating to the error microphone 2a changes when the traveling speed of the automobile 100 changes, or when road conditions such as the road surface on which the automobile runs changes. In addition, the noise propagated to the error microphone 2a is generated when passengers talk, when music is played on the car audio, when voice guidance is provided on the navigation system, or when large vehicles such as trucks pass each other. It also changes depending on the situation.

According to the above configuration, as shown by the dotted line in section (a) of FIG. 4, even if the noise propagating to the error microphone 2a changes, the frequency characteristics of the signal off1 before noise control and the Similar changes appear in the frequency characteristics of signal on1. Therefore, as shown in section (b) of FIG. 4, the first difference between each frequency has the same characteristics as section (b) of FIG.

This can also be understood from the above equations 1, 2, and 3. The reason is that in Equation 1, if signal N1 indicating road noise at the installation location of error microphone 2a changes to signal N1', then by substituting Equation 1 in which signal N1' is substituted into Equation 2, Equation This is because off1=N1', which is a formula similar to 3, can be obtained. That is, both the noise control signal on1, which is the error signal e1 outputted by the error microphone 2a, and the pre-noise control signal off1, shown in Equation 1, include the same signal N1' indicating the changed noise. Therefore, by calculating the difference between the post-noise control signal on1 and the pre-noise control signal off1, the signal N1' is canceled out.

By the way, as shown in Fig. 4, when a sound with a frequency within the evaluation target frequency band (frequency f1 to f2) occurs as a sound unrelated to the target noise, a particularly big problem occurs with the configuration described so far. does not occur. FIG. 5 is a diagram showing another example of the noise reduction effect measured by the effect measuring section 50a. However, as shown in the dotted line in section (a) of Figure 5, a sound with a frequency outside the evaluation target frequency band is generated as a sound unrelated to the target noise, and the level of the unrelated sound is It is assumed that the level is not sufficiently low compared to the sound level of the frequency within the frequency band. In this case, as shown in section (b) of FIG. 5, the first difference is similar to the first difference shown in section (b) of FIGS. 3 and 4. However, the level of the unrelated sound affects the first overall value and the second overall value, and the second difference, which is the difference between them, is different from the second difference without the unrelated sound. There is.

For example, in the example shown in section (a) of FIG. 5, the first overall value, which is the overall value of the pre-noise control signal off1, is 87 dBA, which is 2 dBA higher than the example shown in section (a) of FIG. Further, the second overall value, which is the overall value of the noise-controlled signal on1, is 85 dBA, which is 5 dBA higher than the example shown in section (a) of FIG. As a result, the second difference, which is the difference between the first overall value and the second overall value, is -2 dBA, and the noise reduction effect is degraded by 3 dBA compared to the example shown in section (a) of FIG. become.

In this way, even if no problem occurs with the first difference shown in section (b) of FIG. 5, if a problem occurs with the second difference, setting a second target value that is the target of the second difference; This will hinder the determination of whether the goal has been achieved.

Therefore, as shown in FIG. 6, the configuration of the effect measuring section 50a may be changed. FIG. 6 is a diagram showing an example of another configuration of the effect measuring section 50a. That is, the effect measuring section 50a may further include band limiting sections 55a and 55b. Then, the band limiter 55a uses the frequency characteristics of the pre-noise control signal off1 calculated by the frequency analyzer 52a to calculate frequencies within the evaluation target frequency band (frequencies f1 to f2) included in the pre-noise control signal off1. It is also possible to extract only the signal of , and output the extracted signal to the overall calculation section 53a. Similarly, the band limiter 55b uses the frequency characteristics of the noise-controlled signal on1 calculated by the frequency analyzer 52b to evaluate the evaluation target frequency band (frequencies f1 to f2) included in the noise-controlled signal on1. It is also possible to extract only signals with frequencies within the range and output the extracted signals to the overall calculation section 53b.

Then, the overall value difference effect calculation unit 54b calculates a second difference, which is the difference between the first overall value calculated by the overall calculation unit 53a and the second overall value calculated by the overall calculation unit 53b. You may also do so. The second difference may be used as an index of the road noise reduction effect at the location where the error microphone 2a is set.

In the first embodiment, an example in which the noise control device 1000 is applied to the automobile 100 has been described, but the present invention is not limited to this, and the noise control device 1000 may be applied to an airplane, a train, or the like.

(Embodiment 2)
The configuration of a noise control device according to Embodiment 2 will be explained.

In the first embodiment, it has been explained that the adaptive operation of updating the control coefficient and the measurement of the road noise reduction effect can be performed simultaneously. However, if noise louder than the road noise generated by the user driving the car 100 propagates, for example, if the driver plays audio at a high volume or if a truck larger than the car 100 runs alongside, the control This may adversely affect the adaptive operation that updates the coefficients.

In preparation for such a case, the noise control device 1001 according to the second embodiment, unlike the noise control device 1000 according to the first embodiment, performs adaptation only when a predetermined condition that does not adversely affect the adaptive operation is satisfied. perform an action. Note that if the adaptive operation is stopped and the control coefficient is fixed, the control coefficient will not change even if noise louder than road noise propagates, so there is no need to make the configuration in this case different from the first embodiment. .

The flow of the adaptive operation performed in the noise control device 1001 according to the second embodiment will be described below. In the following description, eight LMS computing units 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, 61bbb and eight transfer characteristic correction filters 62aaa, 62aab, 62aba, 62abb, 62baa, 62bab, 62bba are used. , 62bbb are collectively referred to as a coefficient updater 60. In addition, when the two effect measurement units 50a and 50b are collectively referred to as an effect measurement unit 50.

FIG. 7 is a configuration diagram of a noise control device 1001 according to the second embodiment. As shown in FIG. 7, the noise control device 1001 includes an adaptable state determination unit 70 in addition to the configuration of the noise control device 1000 (FIG. 1) according to the first embodiment. The adaptable state determining unit 70 is configured by executing a program stored in the ROM in advance by the CPU. The adaptable state determining unit 70 determines whether or not the coefficient updater 60 is to update the control coefficients by determining whether the environment inside the vehicle satisfies a predetermined adaptation condition for performing an adaptive operation. judge.

FIG. 8 is a flowchart showing the flow of the adaptive operation. As shown in FIG. 8, when the adaptive operation is started at a predetermined timing such as when the power is turned on to the noise control device 1001, the adaptable state determination unit 70 determines that the environment inside the vehicle is such that the adaptive operation is not possible. It is determined whether the adaptation conditions for implementation are satisfied (step S1). If it is determined in step S1 that the adaptation condition is satisfied (YES in step S1), the effect measurement unit 50 causes the coefficient updater 60 to perform the adaptation operation (step S2). Note that details of step S1 will be described later.

Thereafter, the adaptable state determining unit 70 performs the same determination as in step S1 in parallel even while the adaptive operation is being performed (step S3). If it is determined in step S3 that the adaptation condition is not satisfied (NO in step S3), the effect measurement unit 50 causes the coefficient updater 60 to suspend execution of the adaptation operation (step S4). After that, the processing from step S1 onwards is performed again. Note that details of step S3 will be described later.

On the other hand, if it is determined in step S3 that the adaptation condition is satisfied (YES in step S3), the effect measurement unit 50 starts the adaptation operation in step S2 while causing the coefficient updater 60 to continue implementing the adaptation operation. Then, it is determined whether a preset predetermined time (for example, 30 seconds) has elapsed (step S5). If the effect measurement unit 50 determines in step S5 that the predetermined time has elapsed (YES in step S5), the effect measurement unit 50 ends the adaptive operation by the coefficient updater 60 and fixes the control coefficient to the control coefficient at the end point. A fixed coefficient operation is performed (step S6).

Then, as described in the first embodiment, the effect measurement unit 50 performs a determination process to determine whether the road noise reduction effect at the control point where each error microphone is set has achieved the target value. (Step S7). When the effect measurement unit 50 determines in step S7 that the road noise reduction effect has not achieved the target value (NO in step S7), the process returns to step S1. On the other hand, if the effect measurement unit 50 determines in step S7 that the road noise reduction effect has achieved the target value (YES in step S7), it continues the fixed coefficient operation (step S8). Further, if the effect measurement unit 50 determines that an abnormality has occurred in the control coefficient during the execution of step S7, it stops designing the control coefficient (step S9).

Next, details of step S1 and step S3 will be explained in detail. As shown in FIG. 7, information is input to the adaptable state determining unit 70 from a navigation system 81, an audio system 82, a tachometer (rotation speed) 83, and a speed meter 84. Further, the output signals of the error microphones 2a and 2b are also input to the adaptable state determination section 70.

The information input from the audio system 82 to the adaptable state determination unit 70 includes, for example, switch information and audio signals indicating whether the audio system 82 is activated. If the switch information input from the audio system 82 indicates that the audio system 82 is activated, the adaptable state determining unit 70 determines that the adaptive condition is not satisfied. Further, the adaptable state determining unit 70 determines that the adaptive condition is not satisfied when the signal level of the audio signal input from the audio system 82 is equal to or higher than a predetermined threshold.

The information input from the navigation system 81 to the adaptable state determination unit 70 includes, for example, an audio guidance signal. If the signal level of the audio guidance signal input from the navigation system 81 is equal to or higher than a predetermined threshold, the adaptable state determining unit 70 determines that the adaptable condition is not satisfied.

The engine speed related to road noise is input to the adaptable state determination unit 70 from the tachometer 83 . The adaptable state determination unit 70 determines that the adaptive condition is not satisfied when the input engine rotation speed is less than or equal to a predetermined first rotation speed (for example, 1000 rpm) or is greater than or equal to a predetermined second rotation speed (for example, 4000 rpm). It is determined that there is no. Furthermore, the travel speed related to road noise is inputted to the adaptable state determination unit 70 from the speed meter 84 . The adaptable state determination unit 70 determines that the adaptive condition is not satisfied if the input traveling speed is less than or equal to a predetermined first speed (for example, 40 km/h) or greater than or equal to a predetermined second speed (for example, 130 km/h). It is determined that there is no.

The reason why the adaptable state determining unit 70 makes the determination is that when the traveling speed is slow or the engine speed is low, the level of road noise is presumed to be lower than when driving normally. This is because it is thought that this has not yet been achieved. Furthermore, if the traveling speed is considerably high or the engine rotational speed is considerably high, the level of road noise is presumed to be higher than during normal driving, and it is considered that the adaptive conditions are exceeded.

The signals input from the error microphones 2a and 2b to the adaptable state determination unit 70 are the sounds of the interior of the vehicle, including road noise during driving, conversational voices of passengers, sounds played by the audio system 82, and the navigation system. 81 guidance voice, noise propagated from outside the vehicle (for example, noise from other vehicles traveling alongside or passing each other), etc. Therefore, the adaptable state determining unit 70 determines that the adaptive condition is not satisfied when the level of the signal input from the error microphones 2a and 2b is equal to or higher than a predetermined first threshold or equal to or lower than a predetermined second threshold.

Next, a method for the adaptable state determination unit 70 to measure the level of the input signal will be described. FIG. 9A is a configuration diagram of the adaptable state determination unit 70. FIG. 9B is a diagram illustrating an example of determination conditions used by the adaptable state determination unit 70. As shown in FIG. 9A, the adaptable state determination section 70 includes an instantaneous value level calculation section 71, an averaging section 72, and a threshold determination section 73.

The instantaneous value level calculating section 71 calculates the level (for example, -26 dB) at the moment when the output signal of the error microphone 2a is input.

The averaging section 72 averages the instantaneous value levels calculated by the instantaneous value level calculating section 71 over a predetermined period. The predetermined period may be determined by time, such as 1/10 second, or may be determined by the number of input instantaneous value levels, such as a period in which 1000 instantaneous value levels are input. It's okay to be hit.

The threshold determination unit 73 determines whether the signal level (value) averaged by the averaging unit 72 is within a predetermined threshold range. FIG. 9B shows a graph showing a time-series change in the signal level averaged by the averaging unit 72, and the lower limit value THL1 and upper limit value THL2 of the threshold range. The threshold determination unit 73 determines that the adaptive condition is satisfied when the averaged signal level is greater than or equal to the lower limit value THL1 and less than or equal to the upper limit value THL2.

Therefore, as shown in the graph of FIG. 9B, when the signal level (value) averaged by the averaging section 72 is input to the threshold determining section 73, the averaged signal level remains unchanged until time t1. Since it is within the threshold value range, the threshold value determination unit 73 determines that the adaptive condition is satisfied. Since the averaged signal level exceeds the upper limit value THL2 during the period from time t1 to time t2, the threshold determination unit 73 determines that the adaptive condition is not satisfied. Since the averaged signal level is within the threshold range during the period from time t2 to time t3, the threshold determination unit 73 determines that the adaptive condition is satisfied again. Since the averaged signal level is less than the lower limit value THL1 during the period from time t3 to time t4, it is determined that the adaptive condition is not satisfied.

9A and 9B, an example has been described in which the adaptable state determining unit 70 determines whether or not the adaptable condition is satisfied when the output signal of the error microphone 2a is input. A similar determination is made when the output signal of the error microphone 2b is input to the section 70. Further, as described above, the information used by the adaptable state determining unit 70 to determine whether or not the adaptable condition is satisfied includes not only the output signals of the error microphones 2a and 2b but also the input signals from the audio system 82 and the speed meter 84. This also includes the information that will be sent. The adaptable state determination unit 70 uses all of the input information to determine whether or not the adaptive conditions are satisfied, and only when it is determined that the adaptive conditions are satisfied in all of the determinations, the in-vehicle environment is determined. It is determined that the adaptive conditions for performing the adaptive operation are satisfied.

According to the above configuration, the update of the control coefficient by the coefficient updater 60 is performed only when the adaptable state determining unit 70 determines that the environment inside the vehicle satisfies the adaptive condition for performing the adaptive operation. Therefore, the optimum control coefficient can be set more stably.

However, when the adaptive operation is actually performed, as shown in FIGS. 3 and 4, there is almost no increase in road noise and only a reduction effect is obtained. This is because, as shown in FIG. 15A, FIG. 15B, and FIG. This is because there are practical limitations. Hereinafter, when sensors 1a, 1b, 1c, and 1d are collectively referred to as sensor 1, they will be referred to as sensor 1. When the error microphones 2a, 2b, 2c, and 2d are collectively referred to as error microphone 2, they are referred to as error microphone 2. When the speakers 3a, 3b, 3c, and 3d are collectively referred to as speaker 3.

FIG. 10 is a diagram showing the distance D1 from the sensor 1 to the error microphone 2 and the distance D2 from the speaker 3 to the error microphone 2 in the noise control device 1001. For example, as shown in FIG. 10, the difference D1-D2 between the distance D1 from the sensor 1 that detects noise to the error microphone 2 and the distance D2 from the speaker 3 to the error microphone 2 is determined by the signal processing in the noise control device 1001. It is assumed that it is not possible to secure a sufficient distance in terms of time. In this case, the causality condition in the noise control device 1001 is not satisfied.

When the signal processing time in the noise control device 1001 is T, Equation 4 must be satisfied at all frequencies in order to satisfy the causality condition.
T≦(D1-D2)/v (Formula 4)
Here, v indicates the speed of sound.

However, as described above, if the distance D1-D2 is not long enough, the causality condition (Equation 4) will not be satisfied, especially when processing a high frequency signal with a short wavelength. On the other hand, when considering the noise reduction effect, there is a tendency that the closer the sensor 1 that detects noise is to the control point where the error microphone 2 is installed, the better the reduction effect is. Therefore, if an attempt is made to install the sensor 1, the error microphone 2, and the speaker 3 in consideration of the noise reduction effect, the distance D1-D2 will be shortened, resulting in a dilemma in which it will be difficult to satisfy the causality condition.

Furthermore, the characteristics of the speaker 3 also affect the causality conditions. In particular, the speaker 3 has a large phase rotation at a low resonance frequency, and a delay (group delay) of a signal near the low resonance frequency becomes large. Therefore, when processing a signal near the low resonance frequency, it becomes difficult to satisfy the causality condition. In other words, in the noise control device 1001, the distance D1-D2 needs to be sufficiently long in order to correct the group delay of signals below the low resonance frequency.

If the causality condition is not fully satisfied, the noise reduction effect of the noise control device 1001 will be as shown in FIG. 11, for example. FIG. 11 is a diagram showing another example of the noise reduction effect measured by the effect measurement unit 50. In the example shown in sections (a) and (b) of FIG. 11, the road noise at frequencies f1 to f3 increases, but this is caused by the group delay near the low resonant frequency of speaker 3. There are often Note that the reason why the road noise at frequencies below f1 has not increased is because the performance of the speaker 3 does not allow it to reproduce sounds at frequencies below f1.

Furthermore, the road noise at frequencies f4 to f2 is also increasing, but this is because phase shifts are more likely to occur due to the high frequency. Note that the reason why the road noise at frequency f2 or above has not increased is because the signal level of the road noise itself is low, and also because the signal level is further increased as a result of convolving the control coefficients by the control filters 20aa, 20ab, 20ba, and 20bb. This is because it decreases.

In this way, the general control effect in most noise control cases is that the frequency band in which the expected noise reduction effect is obtained and the frequency band in which the unexpected noise increase occurs coexist. It is. Therefore, when actually designing control coefficients, it becomes a challenge to strike a balance between achieving a desired noise reduction effect and suppressing an increase in noise.

Below, determination of the noise reduction effect, which is a key point in designing the control coefficients, will be explained using FIG. 12. FIG. 12 is an operation flowchart showing the flow of the control coefficient design operation based on the result of determining the noise reduction effect in the effect measurement unit 50. Note that the flow shown in FIG. 12 corresponds to step S7 in FIG. 8.

In other words, assume that the effect measurement unit 50 has started the determination process in step S7 to determine whether the road noise reduction effect at the control point where the error microphone 2 is set has achieved the target value. In this case, as shown in FIG. 12, the A-characteristic filter sections 51a and 51b (FIG. 2) use the A-characteristic coefficients for the pre-noise control signal off1 and the post-noise control signal on1 input to the effect measurement section 50. Convolution processing is performed (step P1). Next, the frequency analysis units 52a and 52b (FIG. 2) calculate the frequency characteristics of the pre-noise control signal off1 and the post-noise control signal on1 after the convolution process in step P1 by performing frequency analysis processing (step P2). ).

When step P2 is performed, the frequency difference effect calculation unit 54a (FIG. 2) calculates the noise pre-control signal off1 after the convolution process by the A-characteristic filter unit 51a and the A-characteristic signal for each frequency in the frequency characteristic calculated in step P2. A first difference from the noise-controlled signal on1 after convolution processing by the filter unit 51b is calculated (step P4).

On the other hand, when step P2 is performed, the overall calculation units 53a and 53b (FIG. 2) calculate a first overall value and a second overall value, respectively (step P3). It is assumed that the effect measuring section 50a has a configuration including band limiting sections 55a and 55b, as shown in FIG. In this case, in step P3, the overall calculation unit 53a may calculate the overall value in all frequency bands of the signal extracted by the band limiting unit 55a as the first overall value. Similarly, the overall calculating section 53b may calculate the overall value in all frequency bands of the signal extracted by the band limiting section 55b as the second overall value. Next, the overall value difference effect calculation unit 54b calculates a second difference, which is the difference between the first overall value and the second overall value calculated in step P3 (step P5).

The effect measuring unit 50 determines whether the second difference calculated in step P5 has achieved the second target value set in advance (step P6). For example, assume that the second target value is set to -3 dBA. In this case, the effect measurement unit 50 determines that the second difference has achieved the second target value when the second difference is less than the second target value.

On the other hand, the effect measurement unit 50 uses the first difference between each frequency calculated in step P4 to calculate the majority of the frequencies included in the predetermined effect expected band (FIG. 11) within the predetermined evaluation target band. It is determined whether the first difference has achieved the preset first target value (step P7). For example, assume that the first target value is set to 5 dB. In this case, the effect measurement unit 50 determines that when the first difference between the majority of frequencies included in the expected effect band (FIG. 11) is larger than the first target value, the first difference between the majority of frequencies is larger than the first target value. It is determined that the first target value has been achieved.

Note that, in step P7, the effect measuring section 50 may perform the determination under stricter conditions. For example, the effect measuring unit 50 determines whether a first difference of a predetermined number (e.g., 80%) of frequencies included in the expected effect band has achieved the first target value. It may be determined whether the

In addition, the effect measurement unit 50 uses the first difference between the frequencies calculated in step P4 to determine the frequency of the majority of the frequencies included in the predetermined noise increase band (FIG. 11) within the predetermined evaluation target band. It is determined whether the first difference exceeds a preset tolerance value (step P8). For example, assume that the tolerance value is set to 2 dB. In this case, when the first difference between the majority of frequencies included in the noise increase band (FIG. 11) is larger than the tolerance value, the effect measurement unit 50 determines that the first difference between the majority of frequencies is the tolerance value. It is judged that it exceeds.

Note that, in step P8, the effect measuring section 50 may perform the determination under stricter conditions. For example, the effect measuring unit 50 determines whether a first difference of a predetermined number (for example, 30%) or more of frequencies that are less than a majority of the frequencies included in the noise increase band exceeds the allowable value. You can do it like this. Further, the effect measurement unit 50 determines whether the first difference between one or more of the frequencies included in the noise increase band exceeds the tolerance value, and performs the determination under even stricter conditions. You may also do so. Alternatively, in step P8, the effect measurement unit 50 may perform the determination under more gentle conditions. For example, the effect measurement unit 50 determines whether a first difference of a predetermined number (for example, 70%) or more of frequencies included in the noise increase band exceeds the tolerance value. You can do it like this.

Then, the effect measurement unit 50 determines in step P6 that the second difference has not achieved the second target value (NO in step P6), or (OR), and in step P7, the first difference of the majority frequency Suppose that it is determined that the first target value has not been achieved (NO in step P7). In this case, it is assumed that the effect measurement unit 50 further determines (AND2) that the first difference between the majority of frequencies does not exceed the allowable value in step P8 (NO in step P8). In this case, the effect measurement unit 50 determines that the road noise reduction effect at the control point has not achieved the target value (corresponding to NO in step S7). In this case, the effect measuring unit 50 assumes that the control coefficients have not converged to the optimal value and continues the adaptive operation in order to continue designing the control coefficients (step P9 (corresponding to NO in step S7 in FIG. 8). ).

Further, the effect measurement unit 50 determines that the second difference has achieved the second target value in step P6 (YES in step P6), and (AND1), in step P7, the first difference of the majority frequency Suppose that it is determined that the first target value has been achieved (YES in step P7). In this case, it is assumed that the effect measurement unit 50 further (AND1) determines in step P8 that the first difference between the frequencies of the majority does not exceed the allowable value (NO in step P8). In this case, the effect measurement unit 50 determines that the road noise reduction effect at the control point has reached the target value (corresponding to YES in step S7). In this case, the effect measurement unit 50 assumes that the control coefficient has converged to the optimal value, successfully completes the design of the control coefficient, and fixes the control coefficient to the optimal value (step P10 (corresponding to step S8 in FIG. 8). )).

Further, assume that the effect measuring unit 50 determines in step P8 that the first difference between the majority of frequencies exceeds the allowable value (YES in step P8). In this case, it is assumed that the increase in noise has reached a level that cannot be ignored. Therefore, the effect measuring unit 50 determines that an abnormality has occurred in the control coefficient during the execution of step S7, and forcibly cancels the coefficient design (step P11 (corresponding to step S9 in FIG. 8)).

According to the above configuration, even when an increase in noise occurs as shown in FIG. 11, it is possible to realize a realistic and practical design of control coefficients. Furthermore, among the frequencies included in the expected effect band, the proportion of frequencies for which the first difference has reached the first target value, and among the frequencies included in the noise increase band, the proportion of frequencies for which the first difference has reached the allowable value. By understanding these, it is possible to achieve a desired noise reduction effect while suppressing an increase in undesirable noise. Thereby, the design of the control coefficients can be appropriately balanced. As a result, in any case, the user can be provided with the optimal control effect at that time.

Note that, for example, when the noise control device 1001 is applied to an automobile, the characteristics of road noise are often different between the front seats (driver's seat and passenger seat) and the rear seats of the vehicle. For this reason, a determination process (step S7) for determining whether the road noise reduction effect at each control point has achieved the target value for each control point that is the setting location of each error microphone 2 installed in the automobile. The same target value may be used when performing the following. However, instead of this, individual target values individually set in advance may be used for each error microphone 2. Then, values corresponding to each individual target value may be individually set as the first target value, the second target value, and the allowable value.

In this case, the noise reduction effect is optimized for each seat. In particular, the noise control device 1001 is applied to a space such as an airplane, which has a large number of seats and various types of seats such as window seats and aisle seats. In such a case, set individual target values for each seat where error microphone 2 is set, and also set the first target value, second target value, and tolerance value according to the individual target value. , may be set individually.

For example, in FIG. 7, the noise reduction effect of the error microphone 2a installed near the head of the driver's seat is measured by the effect measurement unit 50a, and the noise reduction effect of the error microphone 2b installed near the head of the passenger seat is measured by the effect measurement unit 50a. is measured by the effect measuring section 50b. In this case, the target values used by the effect measurement unit 50a and the effect measurement unit 50b in the determination process of step S7 may be set as the individual target value Ka and the individual target value Kb, respectively. In response to this, the effect measurement unit 50a sets the first target value, second target value, and tolerance value used in step P7, step P6, and step P8 to the first individual target value K1a and the second individual target value K1a according to the individual target value Ka. Two individual target values K2a and an individual allowable value K3a may be set. Similarly, the effect measuring unit 50b adds a first individual target value K1b corresponding to the individual target value Kb, a second individual target value K1b and a second individual A target value K2b and an individual allowable value K3b may be set. Note that the expected effect band and the noise increase band shown in FIG. 11 are not limited to these, and may be set individually so as to be associated with each error microphone 2.

As shown in FIG. 7, the noise control device 1001 as a whole simultaneously controls the noise at the installation locations of the error microphones 2a and 2b. Therefore, not only the control filters 20aa and 20ba control the noise at the installation location of the error microphone 2a, but similarly, only the control filters 20ab and 20bb control the noise at the installation location of the error microphone 2b. Do not mean.

In other words, the control as a whole operates so that the noise at the installation locations of the error microphones 2a and 2b is optimized all at once. Therefore, as mentioned above, when setting the target value etc. individually for each error microphone 2, if the target value etc. is set to a value that significantly deviates from other target values etc., the noise at the installation location of the error microphones 2a, 2b will increase. is not optimized, and there is a possibility that the design of the control coefficients will not be completed forever.

For example, assume that the second individual target value K2a corresponding to the error microphone 2a is set to 3 dBA, and the second individual target value K2b corresponding to the error microphone 2b is set to 4 dBA. In this case, when the second target value is not set individually for each error microphone 2, assuming that the noise reduction effect of the error microphones 2a and 2b both settles within the range of 3.0 to 3.5 dBA, the second target value If the individual target value K2b is set to 4 dBA, there is a possibility that this will become a hindrance and the design of the control coefficients will not be completed.

Therefore, in order to avoid this situation, in the case of a control configuration that controls multiple control points collectively, prioritize the control points within that control configuration unit, and The design of the control coefficients may be completed when the target value is achieved. For example, if the second individual target value K2a is set to 3 dBA and the priority is set to the highest, even if the second individual target value K2b is set to 4 dBA, regardless of the noise reduction effect at the installation location of the error microphone 2b, The design of the control coefficient can be completed when the noise reduction effect at the installation location of the error microphone 2a reaches 3 dBA or more. Note that when the design of the control coefficients is completed, the control coefficients at the time of completion may be used as the final control coefficients.

On the other hand, if an increase in noise occurs, it is considered undesirable for any control point to exceed the allowable value, so the reduction effect will exceed the allowable value at one of all control points. If it exceeds this value, the coefficient design may be stopped. Note that when the adaptive operation is canceled, the most effective control coefficient up to the time of the cancellation may be used as the final control coefficient.

For example, in the case of the automobile 100, all of the seats in the front of the vehicle body (driver's seat and passenger seat) and the rear seats can be assumed to be "within the control component unit," but when controlling noise in a large space such as an aircraft, There is no need to collectively treat seats that are separated by a predetermined distance or more from each other as "within a control unit" to control noise within the control unit. For example, a control building block may be constructed such that adjacent seats are "within the control building block."

Based on the above explanation, we have measured the noise reduction effect, and based on the results, we have determined whether the design of the control coefficient has been completed, whether it is necessary to continue designing the control coefficient, and whether the level of noise at a specific frequency has been adjusted. We were able to show the overall flow of control coefficient design operations, including whether to stop the control coefficient design depending on the situation.

On the other hand, for example, when applying the noise control device 1001 to an aircraft, the seats in front of the engine (first class or business class), the seats next to the engine (part of business class or economy class), and the seats behind the engine (economy class) class) and the noise level and frequency characteristics of the noise are significantly different. Furthermore, since there are 100 to 200 or more seats in an aircraft, the optimal noise reduction effect usually differs for each seat. Therefore, as described above, it is conceivable to install the error microphone 2 for each seat and to individually set the first target value, second target value, and tolerance value corresponding to each error microphone 2. However, in addition to this, it is preferable that the operating conditions for the adaptive operation for updating the control coefficients are also set individually for each error microphone 2.

Specifically, the operating condition is the convergence constant μ of the LMS computing units 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, and 61bbb. Hereinafter, when the LMS computing units 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, and 61bbb are collectively referred to, they will be referred to as the LMS computing unit 61. As described in Patent Document 1 and the like, in the LMS calculator 61, the control coefficient is updated according to Equation 5 below.
W(n+1)=W(n)-μ・e・r...Formula (5)
Here, W(n) indicates the control coefficient of the control filter before updating (for example, control filter 20aa in FIG. 7), and W(n+1) indicates the control coefficient of the control filter after updating.
e indicates an error signal (for example, the output signal of the error microphone 2a in FIG. 7).
r indicates a reference signal (for example, the output signal of the transfer characteristic correction filter 62aaa in FIG. 7).
μ indicates a convergence constant (step size parameter).
・ indicates multiplication.

In other words, the convergence constant μ is a value that adjusts the convergence speed and degree of convergence. As the convergence constant μ increases, the speed at which the control coefficients converge to the optimal value (hereinafter referred to as convergence speed) increases, but the risk that the control coefficient update operation diverges increases. On the other hand, when the convergence constant μ becomes small, the control coefficients are updated stably, but the convergence speed becomes slow and it takes time to obtain a sufficient noise reduction effect. .

Therefore, it is important to set an appropriate convergence constant μ. However, when many seats have different noise characteristics and noise levels, such as in an airplane, the optimal convergence constant μ for each seat is also considered to be different. Since it takes a huge amount of time and effort to confirm the optimal value of the convergence constant μ in advance, it is desirable that the noise control device 1001 automatically derives the optimal value of the convergence constant μ. Therefore, below, a method for deriving the optimal value of the convergence constant μ will be explained.

13A and 13B are operation flowcharts showing the flow of the control coefficient design operation in the entire noise control device 1001. The operational flow shown in FIGS. 13A and 13B includes the same steps as shown in FIGS. 8 and 12. In the following, a detailed explanation of the same step will be omitted, and the method for deriving the optimal value of the convergence constant μ will be mainly explained.

As shown in FIG. 13A, before executing step S1, the effect measurement unit 50 sets a predetermined initial value to the convergence constant μ used by the LMS calculator 61 (step S0). The convergence constant μ is a decimal number between 0 and 1. For example, the initial value of the convergence constant μ is determined to be close to 0 in consideration of the stability of the adaptive operation. However, the initial value of the convergence constant μ is not limited to this, and may be 0. In step S0, when the initial value is set for the convergence constant μ, the processes from step S1 onwards are performed.

Thereafter, as shown in FIG. 13B, the effect measuring unit 50 determines that the second difference has not achieved the second target value in step P6 (NO in step P6), or (OR), and in step P7, the effect measurement unit 50 determines that the second difference has not achieved the second target value. Assume that it is determined that the first difference of the majority of frequencies has not achieved the first target value (NO in step P7). In this case, it is assumed that the effect measurement unit 50 further determines (AND2) that the first difference between the majority of frequencies does not exceed the allowable value in step P8 (NO in step P8). As a result, it is assumed that the effect measurement unit 50 determines that the road noise reduction effect at the control point has not achieved the target value (corresponding to NO in step S7).

In this case, the effect measurement unit 50 assumes that the control coefficient has not converged to the optimal value, and sets the convergence constant μ in advance when calculating the first difference in step P4 or when calculating the second difference in step P5. The predetermined value Δ is added to the new convergence constant μ+Δ. Then, the effect measuring unit 50 causes the coefficient updater 60 to resume updating the control coefficient using the new convergence constant μ+Δ. Thereby, the effect measuring unit 50 continues the adaptive operation (step S79). After that, the processing from step S1 onwards is performed.

Therefore, after performing steps S1 to S6, each time the control coefficient design process from step P1 to step S79 is repeated, the convergence constant μ increases by a predetermined value Δ. During this time, since the noise reduction effect is also measured, the convergence constant μ is adjusted to a convergence constant μ that provides the optimum noise reduction effect.

Further, the effect measurement unit 50 determines that the second difference has achieved the second target value in step P6 (YES in step P6), and (AND1), in step P7, the first difference of the majority frequency Suppose that it is determined that the first target value has been achieved (YES in step P7). In this case, it is assumed that the effect measurement unit 50 further (AND1) determines in step P8 that the first difference between the frequencies of the majority does not exceed the allowable value (NO in step P8). As a result, it is assumed that the effect measurement unit 50 determines that the road noise reduction effect at the control point has reached the target value (corresponding to YES in step S7). In this case, the effect measuring unit 50 assumes that the control coefficient has converged to the optimal value, completes the design of the control coefficient normally, and fixes the control coefficient to the control coefficient at the time of completion (the last control coefficient) (step S81 (corresponding to step S8 in FIG. 8)).

Further, if the effect measurement unit 50 determines in step P8 that the first difference between the frequencies of the majority exceeds the allowable value (YES in step P8), the effect measurement unit 50 determines that the increase in noise has reached a level that cannot be ignored. Therefore, it is determined that an abnormality has occurred in the control coefficient during the execution of step S7. In this case, the control coefficient design operation is forcibly stopped, and the control coefficient is fixed at the optimal value that was determined to have converged to the optimal value in step S81 before determining that the abnormality has occurred (step P91 (corresponding to step S9 in FIG. 8)).

As described above, the noise control device 1001 performs adaptive operation when the convergence constant μ is the initial value, fixes the control coefficient and measures the road noise reduction effect, updates the convergence constant μ to a new convergence constant μ+Δ, and The adaptive operation using a convergence constant μ+Δ is repeated. Thereby, even if the noise control device 1001 is applied to a large space including many seats, such as an aircraft, the convergence constant μ can be automatically adjusted to the optimal convergence constant μ. As a result, the optimal noise reduction effect can be quickly achieved at each seat.

In the above embodiment, an example is shown in which the noise control device 1001 is applied to the automobile 100 or an aircraft, but the application of the noise control device 1001 is not limited to this.

(Modified embodiment)
Although the embodiments of the present disclosure have been described above, the embodiments of the present disclosure are not limited to the above embodiments, and may be, for example, modified embodiments shown below.

In the noise control device 1001 of the second embodiment, step P8 and step P11 may be omitted. In this case, the effect measurement unit 50 determines that the second difference has not achieved the second target value in step P6 (NO in step P6), or (OR), and in step P7, the effect measurement unit 50 determines that the second difference has not achieved the second target value. Assume that it is determined that the first difference has not achieved the first target value (NO in step P7). In this case, the effect measurement unit 50 may determine that the road noise reduction effect at the control point has not achieved the target value (corresponding to NO in step S7). Further, the effect measurement unit 50 determines that the second difference has achieved the second target value in step P6 (YES in step P6), and (AND1), in step P7, the first difference of the majority frequency Suppose that it is determined that the first target value has been achieved (YES in step P7). In this case, the effect measurement unit 50 may determine that the road noise reduction effect at the control point has reached the target value (corresponding to YES in step S7).

Furthermore, in the noise control device 1001 of the second embodiment, step P7 may be omitted. In this case, if the effect measurement unit 50 determines in step P6 that the second difference has not achieved the second target value (NO in step P6), the effect measurement unit 50 determines that the road noise reduction effect at the control point has achieved the target value. Alternatively, it may be determined that it has not been performed (corresponding to NO in step S7). In addition, when the effect measurement unit 50 determines that the second difference has achieved the second target value in step P6 (YES in step P6), the effect measurement unit 50 determines that the road noise reduction effect at the control point has achieved the target value. (corresponding to YES in step S7).

Alternatively, in the noise control device 1001 of the second embodiment, step P6 may be omitted. In this case, if the effect measurement unit 50 determines in step P7 that the first difference of the majority of frequencies has not achieved the first target value (NO in step P7), the effect measurement unit 50 determines the road noise reduction effect at the control point. It may be determined that the target value has not been achieved (corresponding to NO in step S7). Further, if the effect measurement unit 50 determines in step P7 that the first difference of the majority of frequencies has achieved the first target value (YES in step P7), the effect of reducing road noise at the control point is It may be determined that the target value has been achieved (corresponding to YES in step S7).

Moreover, the above-mentioned sensors 1, 1a, 1b, 1c, and 1d may be microphones that detect noise generated at the installation location and output a noise signal indicating the detected noise.

1, 1a, 1b, 1c, 1d Sensor (noise detector)
2, 2a, 2b Error microphone 3, 3a, 3b, 3c, 3d Speaker 20aa, 20ab, 20ba, 20bb Control filter 40aa, 40ba Transfer characteristic correction filter (correction filter)
41a, 41b subtractor 50, 50a, 50b effect measurement section 52a, 52b frequency analysis section 53a, 53b overall calculation section 54a frequency difference effect calculation section 54b overall value difference effect calculation section 60 coefficient updater 61, 61aaa, 61aab, 61aba, 61abb, 61baa, 61bab, 61bba, 61bbb LMS calculator (coefficient updater)
62aaa, 62aab, 62aba, 62abb, 62baa, 62bab, 62bba, 62bbb Transfer characteristic correction filter (coefficient updater)
70 Adaptable state determination unit 1000, 1001 Noise control device C11, C12, C21, C22 Transfer characteristics Ka, Kb Individual target value e1 Error signal off1, off2 Signal before noise control (control off signal)
on1, on2 Signal after noise control (control on signal)
μ convergence constant

Claims (19)

a noise detector that detects noise generated by the noise source;
a control filter that performs signal processing on a noise signal indicating noise detected by the noise detector using a predetermined control coefficient;
a speaker that reproduces the output signal of the control filter as a control sound;
an error microphone installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker, and detecting residual noise remaining at the control point due to the interference;
a transfer characteristic correction filter that processes the noise signal using a sound transfer characteristic from the speaker to the error microphone;
a coefficient updater that updates the control coefficient so as to minimize the error signal using an error signal indicating residual noise detected by the error microphone and an output signal of the transfer characteristic correction filter;
a correction filter that processes the output signal of the control filter using sound transfer characteristics from the speaker to the error microphone;
a subtracter that subtracts the output signal of the correction filter from the error signal;
The output signal of the subtracter is a control-off signal representing the noise before the control due to the interference, and the error signal is a control-on signal representing the noise after the control due to the interference. an effect measurement unit that measures the noise reduction effect at the control point based on the difference between the
A noise control device equipped with. further comprising an adaptable state determination unit that determines whether to cause the coefficient updater to update the control coefficients;
The noise control device according to claim 1. The coefficient updater updates the control coefficients using a predetermined convergence constant,
The effect measuring section includes:
Measuring the difference between the control off signal and the control on signal as the reduction effect,
Performing a determination process to determine whether the reduction effect has achieved a predetermined target value,
In the determination process,
If it is determined that the reduction effect has achieved the target value, it is assumed that the control coefficient has converged to the optimum value, and the update of the control coefficient by the coefficient updater is stopped, and the control coefficient is changed to the optimum value. fixed to,
If it is determined that the reduction effect has not achieved the target value, it is assumed that the control coefficient has not converged to the optimal value, and the control coefficient is changed to the convergence constant that was used by the coefficient updater at the time of measuring the reduction effect. adding a predetermined value to a new convergence constant, and restarting the coefficient updater to update the control coefficient using the new convergence constant;
The noise control device according to claim 1 or 2. The effect measuring section includes:
Signal processing is performed on each of the control-off signal and the control-on signal using an A-characteristic coefficient indicating A-characteristic that simulates human auditory characteristics, and the control-off signal after the signal processing and the signal processing after the signal processing are processed. measuring a difference from the control on signal as the reduction effect;
The noise control device according to claim 3. The effect measuring section includes:
a frequency analysis unit that calculates frequency characteristics of the control off signal and the control on signal;
a frequency difference effect calculation unit that calculates a first difference, which is the difference between the control off signal and the control on signal, as an index of the reduction effect for each frequency in the frequency characteristic;
The noise control device according to claim 1 or 2, comprising: The effect measuring section includes:
a frequency analysis unit that calculates frequency characteristics of the control off signal and the control on signal;
an overall calculation unit that calculates an overall value in each of the respective frequency bands of the control off signal and the control on signal using the frequency characteristic;
an overall value difference effect calculation unit that calculates a second difference, which is the difference between the overall value of the control off signal and the overall value of the control on signal, as an index of the reduction effect;
The noise control device according to claim 1 or 2, comprising: The effect measuring section includes:
a frequency analysis unit that calculates frequency characteristics of the control off signal and the control on signal;
a frequency difference effect calculation unit that calculates a first difference, which is the difference between the control off signal and the control on signal, as an index of the reduction effect for each frequency in the frequency characteristic;
an overall calculation unit that calculates an overall value in each of the respective frequency bands of the control off signal and the control on signal using the frequency characteristic;
an overall value difference effect calculation unit that calculates a second difference, which is the difference between the overall value of the control off signal and the overall value of the control on signal, as an index of the reduction effect;
The noise control device according to claim 1 or 2, comprising: The effect measuring section includes:
further comprising a band limiting unit that uses the frequency characteristic to extract signals of frequencies within a predetermined evaluation target frequency band included in each of the control off signal and the control on signal,
The overall calculation unit calculates an overall value in each entire frequency band of the signals extracted by the band limiting unit from the control off signal and the control on signal,
The overall value difference effect calculating section calculates the difference between the overall value of the signal extracted by the band limiting section from the control off signal and the overall value of the signal extracted from the control on signal by the band limiting section. Two differences,
The noise control device according to claim 6 or 7. The coefficient updater updates the control coefficients using a predetermined convergence constant,
The effect measuring section includes:
Performing a determination process to determine whether the reduction effect has achieved a predetermined target value,
In the determination process,
The first difference of a majority of the frequencies included in the predetermined evaluation target frequency band, which is calculated by the frequency difference effect calculation unit, achieves a predetermined first target value according to the target value. In this case, it is determined that the reduction effect has achieved the target value, and the control coefficient is assumed to have converged to the optimum value, and the update of the control coefficient by the coefficient updater is stopped, and the control coefficient is changed to the optimum value. fixed to a value,
If the first difference of a majority of the frequencies included in the evaluation target frequency band calculated by the frequency difference effect calculation unit does not achieve the first target value, the reduction effect does not reach the target value. It is determined that the control coefficient has not been achieved and the control coefficient has not converged to the optimal value, and the convergence constant used by the coefficient updater at the time of calculating the first difference is added to the predetermined value. a new convergence constant, and restarting the update of the control coefficient by the coefficient updater using the new convergence constant;
The noise control device according to claim 5. The coefficient updater updates the control coefficients using a predetermined convergence constant,
The effect measuring section includes:
Performing a determination process to determine whether the reduction effect has achieved a predetermined target value,
In the determination process,
If the second difference has achieved a predetermined second target value according to the target value, it is determined that the reduction effect has achieved the target value, and the control coefficient has converged to the optimal value. stopping the update of the control coefficient by the coefficient updater and fixing the control coefficient to the optimum value;
If the second difference has not achieved the second target value, it is determined that the reduction effect has not achieved the target value, and it is assumed that the control coefficient has not converged to the optimal value. Adding a predetermined value to the convergence constant used by the coefficient updater at the time of calculating the difference is set as a new convergence constant, and the coefficient updater restarts updating of the control coefficient using the new convergence constant. let,
The noise control device according to claim 6 or 8. The coefficient updater updates the control coefficients using a predetermined convergence constant,
The effect measuring section includes:
comprising a frequency difference effect calculation unit that calculates a first difference, which is a difference between the control off signal and the control on signal, as an index of the reduction effect for each frequency in the frequency characteristic;
Performing a determination process to determine whether the reduction effect has achieved a predetermined target value,
In the determination process,
the first difference of a majority of frequencies among the frequencies included in the predetermined evaluation target frequency band calculated by the frequency difference effect calculation unit achieves a predetermined first target value corresponding to the target value, and If the second difference has achieved a predetermined second target value according to the target value, it is determined that the reduction effect has achieved the target value, and the control coefficient has converged to the optimal value. stopping the update of the control coefficient by the coefficient updater and fixing the control coefficient to the optimum value;
If the first difference of a majority of the frequencies included in the evaluation target frequency band calculated by the frequency difference effect calculation unit does not achieve the first target value, the reduction effect does not reach the target value. It is determined that the control coefficient has not been achieved and the control coefficient has not converged to the optimum value, and the convergence constant used by the coefficient updater at the time of calculating the first difference is added to the predetermined value. a new convergence constant, and restarting the update of the control coefficient by the coefficient updater using the new convergence constant;
If the second difference has not achieved the second target value, it is determined that the reduction effect has not achieved the target value, and it is assumed that the control coefficient has not converged to the optimal value. Adding a predetermined value to the convergence constant used by the coefficient updater at the time of calculating the difference is set as a new convergence constant, and the coefficient updater restarts updating of the control coefficient using the new convergence constant. let,
The noise control device according to claim 7 or 8. The effect measuring section includes:
In the determination process, the first difference of a predetermined number or more of frequencies within a predetermined noise increase band included in the evaluation target frequency band calculated by the frequency difference effect calculation unit is equal to the target value. If the corresponding predetermined tolerance value is exceeded, it is assumed that an abnormality has occurred in the control coefficient, and the update of the control coefficient by the coefficient updater is stopped;
The noise control device according to claim 9 or 11. The noise control device according to claim 12, wherein the predetermined number is one. Equipped with a plurality of the error microphones,
The effect measuring section includes:
For each of the plurality of error microphones, the determination process is performed using the installation location of each error microphone as the control point and an individual target value that is individually set in advance for each error microphone as the target value. ,
The noise control device according to claim 3, 4, 9, 10, 12 or 13. The individual target values are associated with priorities,
The effect measuring section includes:
In the determination process using the individual target value associated with the highest priority as the target value, if it is determined that the reduction effect has achieved the target value, the In the determination process, determining that the reduction effect has achieved the target value;
The noise control device according to claim 14. The adaptable state determining unit includes:
determining that the coefficient updater is to be caused to update the control coefficient when a value obtained by averaging the instantaneous value level of the error signal over a predetermined period is within a predetermined threshold range;
The noise control device according to claim 2. The noise control device computer
Detect the noise generated by the noise source using a sensor,
performing first signal processing on a noise signal indicating noise detected by the sensor using a predetermined control coefficient;
causing a speaker to reproduce the signal after the first signal processing as a control sound;
Using an error microphone installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker, detecting residual noise remaining at the control point due to the interference,
performing second signal processing on the noise signal using sound transfer characteristics from the speaker to the error microphone;
updating the control coefficient so as to minimize the error signal using an error signal indicating residual noise detected by the error microphone and the signal after the second signal processing;
performing third signal processing on the signal after the first signal processing using sound transmission characteristics from the speaker to the error microphone;
subtracting the signal after the third signal processing from the error signal;
The signal after the subtraction is used as a control-off signal representing the noise before the control due to the interference, and the error signal is used as the control-on signal representing the noise after the control due to the interference, and the control-off signal and the control-on signal are combined. measuring the noise reduction effect at the control point based on the difference between the
Noise control methods. A program for causing a computer to execute the noise control method according to claim 17. a noise detector that detects noise generated by the noise source;
a control filter that performs signal processing on a noise signal indicating noise detected by the noise detector using a predetermined control coefficient;
a speaker that reproduces the output signal of the control filter as a control sound;
an error microphone installed at a control point where interference occurs between the noise propagated from the noise source and the control sound reproduced by the speaker, and detecting residual noise remaining at the control point due to the interference;
a correction filter that processes the output signal of the control filter using sound transfer characteristics from the speaker to the error microphone;
a subtracter that subtracts the output signal of the correction filter from an error signal indicating residual noise detected by the error microphone ;
The output signal of the subtracter is a control-off signal representing the noise before the control due to the interference, and the error signal is a control-on signal representing the noise after the control due to the interference. an effect measurement unit that measures the noise reduction effect at the control point based on the difference between the
A noise control device equipped with.

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