JPH0350998A - Noise reduction device - Google Patents

Abstract

PURPOSE:To reduce noise in an excellent way by using plural BPFs with different bands so as to separate a noise wave in an automobile, and applying delay, amplification and addition to the separated waves as a silencing wave. CONSTITUTION:A noise wave is processed by plural BPFs 1 and separated into noise waves whose frequency band differs, the phase is deviated by a delay means 2 for each noise wave, amplified by an amplifier 4 and added by an adder 3. The changing frequency of the noise waves is specified to form a silencing wave whose phase is inverted to reduce noise in an excellent way.

Description

Detailed Description of the Invention [Summary of the Invention] The present invention is characterized by a bandpass filter means or engine speed means having a plurality of mutually different passbands and an 8000 bandpass filter or 8000 engine speed means. The present invention is a noise reduction device having a delay means for delaying the phase of a noise wave having a frequency, and is capable of reducing noise by following changes in the noise frequency.

(Industrial Application Field) The present invention relates to a noise reduction device in an automobile. Generally, a noise reduction device in an automobile includes a muffler for suppressing noise, a noise insulating material, a sound absorbing material, etc.

[Conventional technology]

FIG. 11 is a diagram illustrating a conventional noise reduction device. The configuration of this figure is shown below. It should be noted that similar components will be represented by the same reference numbers or symbols throughout.

The noise reduction device shown in the figure includes a microphone 14, a delay means 2 connected to the microphone 14, a power amplifier 18 connected to the delay means 2, and a speaker 15 connected to the power amplifier 18.

Next, the operation of the noise reduction device will be explained. When a noise wave a is generated at a noise source point Pa in FIG. 11, the microphone 14 converts the noise wave a into an electrical signal. The electrical signal is delayed by delay means 2. The power of the delayed signal is amplified by the power amplifier 18 and converted into sound by the speaker 15. In this way, the speaker 15 can generate sound that is out of phase with the noise wave a. On the other hand, when the noise wave a generated at the noise source point Pa reaches the listening point Pb, the delay amount of the delay means 2 is adjusted to create a sound damper whose phase is inverted with respect to the noise wave a that reaches the listening point Pb. By radiating the waves from the speakers and overlapping them, the damping wave can eliminate the noise waves a and reduce the noise.

[Problem to be solved by the invention]

As a means of reducing noise entering the car,
Measures have been taken to increase the rigidity of the car body and to improve the muffler's muffler, which is the source of exhaust noise, but this increases the weight of the car, resulting in decreased performance and a significant increase in cost. Therefore, an economical noise reduction means is desired. Although the noise reduction device shown in FIG. 11 is economically superior, it has the following problems in reducing noise inside an automobile.

Low-frequency noise is generated inside a car, with exhaust noise as the noise source. This noise is caused by exhaust noise, that is, pressure fluctuations caused by the exhaust gas periodically pushed out by engine explosions, and its frequency changes as the engine speed changes. This generation frequency is several tens to several hundreds of Hz.

Therefore, with the noise reduction device shown in Fig. 11, there is no problem if the frequency of the noise wave a is constant, but when the frequency of the noise wave a changes with the engine speed, such as in the case of noise in a car, the phase of the noise wave a is changed. The problem is that it becomes difficult to form an inverted sound damper.

Therefore, in view of the above-mentioned problems, an object of the present invention is to provide a noise reduction device that reduces noise in an automobile whose frequency changes.

[Means to solve the problem]

FIG. 1 is a diagram showing the first principle configuration of the present invention. In the present invention, the bandpass filter means 1 has a plurality of mutually different normal bands, and separates the electric signal Sin obtained by converting the noise wave into a plurality of frequency bands. The delay means 2 is connected to each of the plurality of band-pass filter means 1, and delays the signals separated by the band-pass filter means.

Amplifying means 4' is connected to each of the plurality of delay means 2, and amplifies each delayed signal, respectively. Adding means 3 adds each of the amplified signals and produces a silencing signal 5out.
Output.

FIG. 2 is a diagram showing the second principle configuration of the present invention. In the present invention, the first. The second bandpass filter means 1, 1' has a plurality of mutually different passbands and separates the electric signal Sin obtained by converting the noise wave into a plurality of frequency bands. Delay child/
The stages 2 are connected to each of the plurality of bandpass filter means 1 and respectively delay the signals separated by the bandpass filter means. Amplifying means 4 adjusts the gain of each delayed signal. Adding means 3 adds the mixed signals and outputs a silencing signal 5out.

The averaging means 6 includes each second bandpass filter means 1'.
Average the output of . A gain control means 7 controls the gain of the amplification means 4 according to the output level of the averaging means 6. Incidentally, the first and second bandpass filter means 1.1' may be the same. That is, the first bandpass filter means 1 (BPF 1 , BPF 2 , BP
F n ) may be input to each of the averaging means 6 (averaging means 1, averaging means 2, . . . averaging means n).

FIG. 3 is a diagram showing the third principle configuration of the present invention. In the present invention, the delay means 2 converts the noise wave into an electrical signal Sin.
is variably delayed. The amplifying means 4 variably amplifies the delayed signal and outputs a silencing signal 5out. The bandpass filter means 1' has a plurality of mutually different passbands and separates the electrical signal Sin into a plurality of frequency bands. Averaging means 6 averages the outputs of each bandpass filter 1'. The maximum level band detecting means 8 detects and outputs the frequency band in which the output level of the averaging means 6 is maximum. The parameter memory means 9 is read out in response to the output from the maximum level band detection means 8,
and a delay constant and a gain constant set in the amplifying means 4, respectively.

FIG. 4 is a diagram showing the fourth principle configuration of the present invention. In the present invention, the delay means 2 converts the noise wave into an electrical signal Sin.
is variably delayed. The amplifying means 4 variably amplifies the delayed signal and outputs a silencing signal 5out. The engine speed detection means 1o detects and outputs the engine speed using, for example, a crank angle sensor used to detect ignition timing. The parameter memory means 9 stores delay constants and gain constants which are read out in accordance with the engine speed output from the engine speed detecting means 10 and set in the delay means 2 and the amplification means 4, respectively. .

FIG. 5 is a diagram showing the fifth principle configuration of the present invention. In this figure, engine speed detection means 10 detects and outputs the engine speed using, for example, a crank angle sensor used to detect ignition timing.

The signal generating means 11 generates a sine wave signal of a frequency corresponding to the detected engine speed which is the output of the engine speed detecting means 10. The phase control means 12 is the signal generating section]
The phase of the output signal from l is controlled in accordance with the detected rotational speed. The amplitude control means 13 controls the amplitude of the output signal from the phase control means 12 in accordance with the rotation speed. The parameter means 9 stores a phase constant and an amplitude constant which are read out in accordance with the detected engine speed output from the engine speed detecting means 10 and set in the phase control means 12 and the amplitude control means 13.

In the invention of FIGS. 1 to 4, the microphone 14
is a device that converts noise waves into electrical signals and is placed in the trunk of a car. The speaker 15 converts the processed electrical signal into sound and generates a damping sound wave, and is placed in the cabin.

[For production]

In FIG. 1, an input electrical signal Sin representing a noise wave whose frequency changes with time passes through a bandpass filter means 1 in one of the frequency bands, is delayed by a delay means 2 having a predetermined amount of delay, and is delayed by a delay means 2 having a predetermined amount of delay. Since the signal is amplified by the amplification means 4' having an amplification amount, even if the frequency changes, appropriate delay and amplification corresponding to the frequency can be performed. The delayed amplified signal is added to a delayed amplified signal of another frequency band by an adding means to form a sound wave cancellation signal 5out.

By adjusting the amount of delay, the phase of the damping sound wave is inverted with respect to the noise sound wave at the listening point.

In FIG. 2, the human electric signal Sin
The signal passes through the bandpass filter means 1' and is further averaged by the averaging means 6. The gain control means 7 increases the gain of the amplification means 4 in stages according to the output of each of the averaging means 6,
For example, for the maximum value among the average values, the gain of the corresponding amplification means 4 is set to a predetermined value, and the other values are controlled to be O. As a result, only the signal in the frequency band having the maximum amplitude of the input electrical signal Sin passes through the first band-pass filter means 1, is delayed and amplified, and becomes a sound wave-suppression via the addition means 3. In this way, the gain of the amplification means 4 is adjusted to eliminate the influence of the interference of the first bandpass filter means 1 in the adjacent frequency band.

In FIG. 3, an input electrical signal Sin is delayed by a variable delay means 2 and further amplified by a variable gain amplification means 4 to form a damping sound signal 5out. On the other hand,
The input electrical signal Sin passes through the bandpass filter means 1', is averaged by the averaging means 6, and the maximum level of the average value is selected by the maximum level band detection means 8, thereby determining the frequency band of the input electrical signal. be identified. The specific frequency from the maximum level band detection means 8 is output to the parameter memory means 9, and the delay amount and gain amount corresponding to the specific frequency band are read out from the parameter memory means 9 and sent to the delay means 9 and the amplification means 4. Set.

In FIG. 4, the rotation speed detected by the engine rotation speed detection means 10 is output to the parameter memory means 9, and the delay amount and gain amount corresponding to the engine rotation speed are read out from the parameter memory means 9, and the delay amount and the gain amount corresponding to the engine rotation speed are read out from the parameter memory means 9. It is set in the amplification means 4. It takes advantage of the fact that engine speed is closely related to the frequency of noise waves. Input electrical signal Sin
is delayed by a delay amount and a gain amount corresponding to the frequency, and is amplified to become a damped sound signal 5out.

In FIG. 5, a signal with a frequency corresponding to the rotational speed detected by the engine rotational speed detection means 10 is generated by the signal generating means 11, and a phase constant and an amplification constant of the frequency corresponding to the rotational speed are stored in the parameter memory means 9. The generated signal is phase-controlled and amplitude-controlled by the phase control means 12 and amplitude control means 13, which are read out and set, and become a sound wave damping signal 5out.

In the invention of FIGS. 1 to 4, the microphone 14
Howling can be prevented by separating the speaker 15 from the speaker 15.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 6 is a diagram illustrating a noise reduction device according to a first embodiment of the present invention. In this figure, components different from those in FIG. 11 are A/D connected to the microphone 14.
converter 16, a plurality of band pass filter means 1 (BPFI, B) connected to the A/D converter 16;
rF3, BrF3, -, BPFn), a plurality of delay means 2 connected to each said bandpass filter means 1, a plurality of amplification means 4' connected to each said delay means 2,
Adding means 3 connected to each amplifying means 4'; D/A connected to the adding means 3 and connected to the power amplifier 18;
There are 17 converters.

The components within the square frame in this figure, for example, the bandpass filter means 1, the delay means 2, the amplification means 4', and the addition means 3 in other embodiments are DSP (Digital
The noise reduction device is configured with a signal processor (Signal Processor), which enables high-speed processing and miniaturization of the noise reduction device.

Next, the operation of the noise reduction device according to the first embodiment will be explained. The electrical analog signal of the microphone 14 that has received the noise wave a is converted into a digital signal Sin by the A/D converter 16, and is subjected to processing by the DSP. The digital signal Sin is separated into signals in a plurality of frequency bands by a plurality of bandpass filter means 1. Each of the separated signals is separately delayed by each delay means 2, each delayed signal is separately amplified by each amplification means 4', and the amplified signals are added together by an adder 3.

Next, the added signal 5out is sent to the D/A converter 17.
The signal is converted into an analog signal by the power amplifier 18, and the power is amplified by the power amplifier 18, and the sound is damped to be emitted from the speaker 15.

The damping sound wave overlaps and cancels the noise sound wave a at the listening point Pb.

The delay amount of each delay means 2 is also +.

jZ+L3, ..., t7, the gain G1゜G,, G, ... tufi of each amplification means uses a simulated noise wave at the noise source point Pa, and eliminates this simulated noise wave by a damping sound wave at the listening point. It is determined as follows. Therefore, even if the frequency of the noise wave a changes, the noise wave a
A sufficiently appropriate delay amount ti and gain FJ to eliminate
A sound absorber having A i can be formed.

FIG. 7 is a diagram illustrating a noise reduction device according to a second embodiment. In this figure, the components different from those in FIG. 6 are a mixing amplification means 4'' provided between the amplification means 4' and the addition means 3, and a mixing amplification means 4'' for separating the digital signal Sin into a plurality of frequency bands. Multiple bandpass filter means
(KBIF'F 1, KBPF2, KBPF3
. A mix control means 7 is connected to adjust the gain.

Incidentally, a plurality of band pass filter means 1' (KBPF
1.

KBPF 2, KBPF 3, ..., KB
PF n ) is a plurality of bandpass filter means 1 (B
PFI, BrF3, BrF3, -, BP
Fn) have the same center frequency and different Q (sharpness), and the bandpass filter means 1 has a low Q,
The Q of the bandpass filter means B is set high.

Next, the operation of the noise reduction device according to the second embodiment will be explained. The digital signal Sin is clearly separated into signals in a plurality of frequency bands by a plurality of high-Q bandpass filter means 1'. Each of the separated signals is converted into an average audio level by converting the positive and negative audio signals into absolute values by the averaging means 6, and is outputted to the mix control means 7. The mix control means 7 selects, for example, a frequency band with the maximum sound level from the audio levels of each frequency band, and corresponds to this frequency band.
The gain of the amplifying means 4' is set to C;'imax=1, and the gain of the other amplifying means 4' is set to G'i(i'f-imax
)=.

, to control the mix of audio signals in each frequency band. In order to simplify the control, in this embodiment, the variable amplifying means 4 is composed of a fixed amplifying means 4' and an amplifying means 4# whose coefficient is switched stepwise between 1 and O. The variable amplifying means 4 whose coefficients are switched stepwise between 0 and 0 may be configured as a single variable amplifying means 4. In this embodiment, the mix control technique for the audio signals in each frequency band is adopted because the signals passing through the cut-off region of the bandpass filter means 1 in adjacent frequency bands are superimposed on each other in the adding means 3 to form the original signal. This is to prevent deformation. Therefore, the signal of the bandpass filter means 1 in the maximum level frequency band is passed through, and the signals in other frequency bands are blocked, thereby eliminating the influence of passing through the cutoff band. Note that the output of the band-pass filter 1 may be connected to the averaging means 6 instead of the band-pass filter 1', that is, the band-pass filter 1 and the band-pass filter 1' may be the same, but preferably this embodiment It is better to separate them and make Q different as in the example.

FIG. 8 is a diagram illustrating a noise reduction device according to a third embodiment of the present invention. In this figure, the components that are different from those in FIG.
one delay means 2 in place of the delay means 2, an amplification means 4 connected to the delay means 2 and further connected to the D/A converter 17, a maximum level band detection means 8 connected to the averaging means 6, and a maximum level band detection means 8 connected to the averaging means 6; Parameter memory means 9 stores constants read out by the output from band detection means 8 and further set in delay means 2 and amplification means 4.

Next, the operation of the noise reduction device according to the third embodiment will be explained. The digital signal Sin is separated into each frequency band by a bandpass filter means 1', and further averaged by an averaging means 6. Among the plurality of averaged signals, the maximum level band detecting means 8 detects the averaged signal having the maximum level, and outputs the frequency band for this signal. Each bandpass filter means 1 is stored in the parameter memory means 9.
Since a set of delay constants and gain constants (Li, Gi; i=1, ++, n) corresponding to the frequency band ' is stored, the maximum level band detection means 8
A constant set corresponding to the output is read out and set in the delay means 2 and the amplification means 4, respectively. The delay means 2 and the amplification means 4, whose constants are set in this way, delay the digital signal in accordance with the frequency even if the frequency of the digital signal Sin changes,
Can be amplified. Therefore, when compared with the second embodiment, this embodiment can achieve similar effects by reducing the number of components such as bandpass filter means by providing the parameter memory means 9.

FIG. 9 is a diagram illustrating a noise reduction device according to a fourth embodiment of the present invention. Components in this figure that are different from those in FIG. 8 are a bandpass filter means 1' averaging means 6 and an engine rotational speed detecting means 10 in place of the maximum level band detecting means 8. A constant corresponding to the engine rotation speed is read from the parameter means 9 based on the detected rotation speed which is the output of the engine rotation speed detection means 10, and is set in the delay means 2 and the amplification means 4. For example, a crank angle sensor for detecting ignition timing is used as the engine rotation speed detection means 10. The explanation of the operation of the noise reduction device according to the fourth embodiment, that is, the operation of generating sound damping gas, will be omitted since it is the same as that described above. In comparison with the third embodiment, this embodiment is equipped with an engine rotation speed detection means that takes advantage of the close relationship between the engine rotation speed and the frequency of the noise sound a, so that the bandpass filter means 1 A similar effect can be obtained by eliminating the number of parts such as .

FIG. 10 is a diagram illustrating a noise reduction device according to a fifth embodiment of the present invention. In this figure, the components that are different from those in FIG. 9 are a microphone 14 and an A/D converter 1.
6, a signal generating section 11; a phase control section 12 connected to the signal generating section 11; and an amplitude control section 13 connected to the phase control section 12 and further connected to a D/A converter 17. Parameter memory means 9 stores constants of phase control section 12 and amplitude control section 13 corresponding to the engine rotation speed.

Next, the operation of the noise reduction device according to the fifth embodiment will be explained. This embodiment utilizes the fact that there is a closer relationship between the engine speed and the frequency of the noise sound a than in the fourth embodiment. In the signal generation section 1, engine rotation speed detection means 1
For example, a sine wave of a frequency corresponding to the detected rotational speed, which is an output of 0, is generated. This sinusoidal time reference is obtained, for example, from the ignition timing detection of a crank angle sensor. A phase constant and an amplitude constant are outputted from the parameter memory means 9 to the phase control section 12 and the amplitude control section 13 in accordance with the detected rotation speed which is the output of the engine rotation speed detection means 10.

Therefore, the phase control section 12 delays the sine wave generated by the signal generation section in accordance with the engine rotation speed, and then the amplitude control section 13 outputs an output signal 5out whose amplitude is changed in accordance with the engine rotation speed. is generated. The operation of generating the sound damping gas is the same as described above. Compared to the fourth embodiment, this embodiment generates a signal that mutes noise waves a according to the rotation speed detected by the engine rotation speed detection means 10, so parts such as a microphone can be reduced. This has the effect that there is no need to consider the influence of howling due to the microphone.

Next, a noise reduction device according to a sixth embodiment will be explained. The microphone 14 in the first to fourth embodiments is placed in the trunk of a car, and the microphone 1
A speaker 15 for processing the noise wave a added to the noise wave 4 and emitting a damping sound wave is disposed in the passenger room. When the microphone 14 and the speaker 15 are installed in the same room, sound tends to circulate and cause howling. For this reason, the microphone 14 is placed in the trunk room and placed further away from the speaker 15. This arrangement of the microphone 14 is preferable because it is located near the muffler that generates the exhaust noise, which is the noise source a.

(Effects of the Invention) As described above in detail, according to the present invention, the frequency at which the noise wave changes is specified by the bandpass means or the engine rotation speed detection means having a plurality of mutually different passbands, and the frequency at which the noise wave changes is further delayed. By means of the means, it is possible to form a damping sound wave that inverts the phase of the noise sound wave of the specific frequency, and it is possible to reduce the noise by following the change in the noise frequency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the first principle of the present invention; FIG. 2 is a diagram showing the second principle of the present invention; FIG. 3 is a diagram showing the third principle of the present invention; FIG. FIG. 5 is a diagram illustrating the fifth principle configuration of the present invention. FIG. 6 is a diagram explaining the noise reduction device according to the first embodiment of the present invention. 8 is a diagram illustrating a noise reduction device which is a third embodiment of the present invention, and FIG. 9 is a diagram illustrating a noise reduction device which is a fourth embodiment of the present invention. FIG. 10 is a diagram illustrating a noise reduction device according to a fifth embodiment of the present invention. FIG. 11 is a diagram illustrating a conventional noise reduction device. In the figure, 1.1'...Band pass filter means, 2...Delay means, 3...Addition means, 4.4'...Amplification means, 6...Averaging means, 7...Gain Control means, 8 Maximum level band detection means, 9 Parameter memory means, 10 Engine rotation speed detection means, 11 Signal generation section, 13 Amplitude control means. 12...phase control means,

Claims (1)

[Claims] 1. In a noise reduction device that cancels noise by superimposing a noise wave with a phase-shifted noise wave on a noise wave, the electric signal (Sin) of the noise wave is separated into a plurality of frequency bands. bandpass filter means (1) having a plurality of mutually different passbands; a plurality of delay means (2) for respectively delaying each of the separated signals; and amplification means for amplifying each of the delayed signals. (4
') and an adding means (3) for adding the amplified signals and outputting a silencing signal (Sout). 2. In a noise reduction device that cancels a noise sound wave by overlapping a noise wave with a phase shift of the noise sound wave, a plurality of mutually different electric signals (Sin) of the noise sound wave are separated into a plurality of frequency bands. A first bandpass filter means (1) having a passband, a plurality of delay means (2) for delaying each of the separated signals, and an amplification means (4) for adjusting the gain of each of the delayed signals. and an adding means (3) for adding each of the mixed signals and outputting a silencing signal (Sout), and a plurality of mutually different passbands for separating the electrical signal (Sin) into a plurality of frequency bands. and averaging means (6) for averaging the outputs of each of the second bandpass filter means (1'), depending on the output level of the averaging means (6). and said amplifying means (
4) A noise reduction device comprising: gain control means (7) for controlling the gain of step 4). 3. In a noise reduction device that cancels a noise sound wave by superimposing a damping sound wave that is out of phase with the noise sound wave, a delay means (2) that variably delays the electric signal (Sin) of the noise sound wave; The generated signal is variably amplified to produce a silencing signal (So
an amplifying means (4) for outputting the electrical signal (S ut);
bandpass filter means (1'
), averaging means (6) for averaging the outputs of each of the bandpass filters (1'), and maximum level band detection for detecting and outputting a frequency band in which the output level of the averaging means (6) is maximum. storing a delay constant and a gain constant, respectively, which are read out in response to the output from the means (8) and the maximum level band detection means (8) and are further set in the delay means (2) and the amplification means (4). A noise reduction device characterized in that it is provided with parameter memory means (9). 4. In a noise reduction device that cancels a noise sound wave by superimposing a damping sound wave that is out of phase with the noise sound wave, a delay means (2) that variably delays the electric signal (Sin) of the noise sound wave; The generated signal is variably amplified to produce a silencing signal (So
an amplification means (4) for outputting a signal (ut); an engine rotation speed detection means (10); and an output of the engine rotation speed detection means (10) which is read out in response to the detected engine rotation speed; (2) and parameter memory means (9) for storing delay constants and gain constants respectively set in the amplification means (4'). 5. In a noise reduction device that cancels noise by superimposing a noise wave with a phase-shifted noise wave, the engine speed detecting means (10) and the engine which is the output of the engine speed detecting means (10) a signal generating means (11) for generating a signal with a frequency corresponding to the detected rotational speed; and a phase control means (12) for controlling the phase of the output signal from the signal generating means (11) in accordance with the detected rotational speed. ), amplitude control means (13) for controlling the amplitude of the output signal from the phase control means (12) in accordance with the rotation speed, and a detected rotation speed that is the output of the engine rotation speed detection means (10). is read out corresponding to the phase control means (1).
2) and parameter memory means (9) for storing the phase constant and amplitude constant set in the amplitude control means (13).
) A noise reduction device characterized by comprising: 6. At least a microphone (14) that converts noise waves from the car into electrical signals, and a speaker (15) that delays the electrical signals and generates damping waves with the phase of the noise waves shifted.
) The noise reduction device according to any one of claims 1, 2, 3, or 4, wherein the microphone (14) is placed in a trunk of a car, and the speaker (15) is placed in a passenger compartment of the car. Device.