JPH0540483A - Noise controller - Google Patents

Abstract

PURPOSE:To eliminate a higher harmonic noise by a constitution of one microphone and one loudspeaker, with regard to the noise controller for erasing a noise by outputting a signal being out-of-phase and having equal acoustic pressure to a noise detected by a microphone, from a loudspeaker. CONSTITUTION:In the noise controller provided with an electric signal/acoustic wave converter for erasing a noise from a noise generation source 1, an acoustic wave/electric signal converter 3 for converting a residual sound of a joise erased by an acoustic wave from the electric signal/acoustic wave converter 2 to an electric signal, and an adaptive type filtering means 4 for forming a compensating signal for erasing a noise to the electric signal/acoustic wave converter 2, based on a signal of the acoustic wave/electric signal converter 3, a higher harmonic generating part 5 for generating a higher harmonic signal of a fundamental wave related to a timing signal, and supplying the higher harmonic signal to the adaptive type filtering means 4 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise control apparatus for eliminating noise by outputting a signal of noise and anti-phase equal sound pressure detected by a microphone from a speaker. The purpose is to remove harmonic noise.

[0002]

2. Description of the Related Art Conventionally, a passive muffling device such as a muffler has been used to reduce noise generated from an internal combustion engine, etc., but improvements have been made from the viewpoint of size and muffling characteristics. On the other hand, conventionally, there has been proposed an active noise control device that cancels noise by outputting from a speaker a compensating sound having an opposite phase and equal sound pressure to the noise generated from a sound source.

By the way, the frequency characteristic or stability of the active noise control device itself is not sufficient, and its practical application has been delayed. As a result of the recent development of signal processing technology using digital circuits and expansion of the frequency range that can be handled, many practical noise control devices have been proposed (for example, Japanese Patent Laid-Open No. 63-311396).

This is the result of noise being detected by a noise source microphone installed upstream of the duct, and a signal processing circuit outputting a signal of opposite phase and equal sound pressure to the noise from a speaker installed downstream of the duct, and the result being silenced. This is a so-called two-microphone / one-speaker type active noise control device in which a feedforward system and a feedback system for detecting and feeding back the noise by a microphone for a sound deadening point are combined.

[0005]

However, in the conventional noise control device, when the noise control device is mounted on an automobile and a feedforward system is adopted for muffler noise control, etc. The sensor detects the pipe sound closer to the engine side than the muffler's tail hype that is the transmission path, and it is used, but in such a method, the sensor is exposed to high temperature and high pressure,
There is a problem that a water-cooled piezoelectric sensor or the like having environment resistance is required.

Therefore, in view of the above problems, an object of the present invention is to provide a noise control device which can be realized by a simple system without using a sensor having environment resistance.

[0007]

FIG. 1 is a diagram showing the principle configuration of the present invention. In order to solve the above problems, the present invention provides an electric signal for eliminating noise from the noise source 1.
The sound wave converter 2, the sound wave / electric signal converter 3 for converting the residual sound of the noise erased by the sound wave from the electric signal / sound wave converter 2 into an electric signal, and the sound wave / electric signal converter 3 The harmonic generator 5 is provided in a noise control device having an adaptive filtering means 4 for controlling a filter coefficient on the basis of a signal to form a compensation signal for canceling noise in the electric signal / sound wave converter 2.

The harmonic generator 5 generates a harmonic signal based on the fundamental wave associated with the timing signal and supplies the harmonic signal to the adaptive filtering means 4.

[0009]

According to the noise control device shown in FIG. 1, the harmonic generator 5 generates the harmonic of the period based on the timing signal of the noise signal and supplies the harmonic signal to the adaptive filtering means 4. Therefore, based on this harmonic signal, the level and phase shift are controlled for each frequency by the adaptive filtering means, even if the sensor is not directly attached to the vehicle muffler or the like to detect the harmonic as in the conventional case. It is possible to form harmonics similar to the conventional one from the timing signal which can be easily detected and use them as the harmonics of noise.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing a noise control device according to the first embodiment of the present invention. The configuration of this figure will be described. The noise control device of this figure includes a speaker 2 for canceling noise from a noise source 1 such as an automobile engine near a muffling point, and an amplifier 2-1 for amplifying the output to the speaker 2.
And a D / A (Digital To Analog Converter) converter 2-2 for converting a digital signal to the amplifier 2-1 into an analog signal, and noise from the noise source 1 is erased by a sound wave from the speaker 2. A microphone 3 for converting the residual sound of the generated noise into an electric signal, and the microphone 3
Amplifier 3-1 for amplifying the electric signal of A, and A / A for converting the analog signal of the amplifier 3-1 into a digital signal
A D (Analog To Digital Converter) converter 3-2, and an adaptive filtering means 4 for forming a compensation signal for canceling noise to the speaker 2 based on a signal from the A / D converter 3-2. Receiving a rotation timing signal or an ignition timing signal obtained from an engine speed detector of an automobile engine which is the noise source 1 or an ignition timing control device, and forming a harmonic signal of a fundamental wave related to the timing signal. And a harmonic generator 5 for supplying the harmonic signal to the adaptive filtering means 4. Here, the adaptive filtering means 4 and the higher harmonic wave generating section are constituted by a DSP (Digital Signal Processor).

Next, the adaptive filtering means 4 will be briefly described, but it is a known technique per se. The noise S _N of the noise source 1, the transfer characteristic up to the microphone 3 is H _NOISE , the compensation signal of the adaptive filtering means 4 is S _C, and the output of the adaptive filtering 4 is
The transmission characteristic up to the microphone 3 via the D / A converter 2-2, the amplifier 2-1, and the speaker 2 is set to H _sp , and the microphone 3 through the amplifier 3-1 and the A / D converter 3-2 are used. When the transfer characteristic up to the differential input of the adaptive filtering means 4 is H _mic , the residual sound signal S _M output from the microphone 3 is S _M = S _N · H _NOISE + S _C · H
_sp and the differential input S of the adaptive filtering means 4 are
S _E = S _M · H _mic . Based on this output signal S _E , the adaptive filtering means 4 determines the coefficient of the adaptive filter by the method of least squares, and the residual sound signal S _E = 0.
So that the input signal S of the adaptive filtering means 4 becomes
_The compensation signal S _C is formed by controlling the level and phase of _i . Since S _M = 0 when S _E = 0, noise reduction at the sound deadening point is realized.

Next, the harmonic generator 5 will be described. The high frequency generator 5 inputs a signal related to the noise generation period as a timing signal and generates a harmonic signal of the fundamental wave related to the timing signal. In the muffler noise control device for an automobile, the noise generation period is Since it is synchronized with the explosion cycle of the internal combustion engine, it is effective to generate a high frequency signal whose fundamental wave is this explosion cycle. Therefore, when using the ignition timing signal as the timing signal,
It suffices to generate higher harmonics using the ignition timing signal as the fundamental wave, but when using the engine rotation timing signal, it is effective to generate higher harmonics using the signal that is divided according to the explosion cycle as the fundamental wave. ..

FIG. 3 is a diagram showing a waveform generated by the harmonic generating section. As shown in this figure, the harmonic generator 5 is a noise source 1
When a timing signal having a period T as shown in FIG. 3A is input, a triangular wave signal of the following formula as shown in FIG. 3B is generated.

[0014]

[Equation 1]

When the triangular wave signal (harmonic signal) shown in FIG. 3 (b) is input to the adaptive filtering means 4 from the harmonic generating portion 5, the adaptive filtering means 4 performs the adaptive processing described above, For example, the signal having the waveform shown in FIG. 3C is output. The harmonic generation unit is not limited to the one that generates a triangular wave signal as a harmonic, but the first, second, ..., Nth harmonics of the timing signal are individually created and a signal obtained by adding these is generated. It may be one.

Next, a series of operations of this embodiment will be described. When the timing signal of the cycle T is input from the noise generation source 1 to the harmonic generation unit 5, a harmonic signal for the cycle T is generated, and the signal of the engine ignition cycle (or rotation cycle) and its harmonic signal S _i are adaptive type. It is input to the filtering means 4. The compensation signal from the adaptive filtering means 4 is D /
It becomes a sound wave from the speaker 2 through the A converter 2-2 and the amplifier 2-1 to eliminate the noise. The microphone 3 at the erasing point converts the residual sound of the noise that cannot be erased by the speaker 2 into an electric signal, and the converted signal is an amplifier 3-
1. The coefficient of the adaptive filter of the adaptive filtering means 4 is changed via the A / D converter 3-2. Thus, even if the noise including the harmonic is not directly detected from the noise generating source 1 as in the conventional case, the harmonic generating section 5 generates the waveform of the harmonic based on the timing signal, and using this signal, Since the adaptive filtering means 4 controls the level and the phase shift (delay amount) for each frequency, an ideal cancel sound can be generated.

FIG. 4 is a diagram showing a noise control device according to a second embodiment of the present invention. In the configuration of this figure, the difference from the first embodiment is the transfer characteristic (H _sp · H _mic = H) of the system from the adaptive filtering means 4 to the difference signal calculating means 8 to be described later via the speaker 2 and the microphone 3. _d1 )
Of the transmission characteristic simulating means 7 for simulating the noise, a difference signal calculating means 8 for calculating a difference signal between the output of the microphone 2 and the output of the transmission characteristic simulating means 7, It is the waveform shaping unit 6 that forms the timing signal corresponding to the generation cycle.

FIG. 5 is a diagram for explaining a method of detecting the cycle of the timing signal in the waveform shaping section of FIG. The positive side input signal of the difference signal calculation means 8 is S _E , and the output signal is S _{E
Let R} be S _E = S _N · H _NOISE · H _mic + S _c · H _sp
· H _mic, S than _{H d1 = H sp · H mic} R = S E -S c ·
H _d1 = S _N · H _NOISE · H _mic + S _c · H _sp · H _mic −
S _c · H _sp · H _mic = S _N · H _NOISE · H _mic .
Therefore, the output signal S _R of the difference signal calculation means 8 is a signal representing the noise generation period, and this output signal S _R is used as a timing signal. Using this output signal S _R , a rectangular wave is generated when the noise signal level exceeds a certain level in this signal processing as shown in FIG. 7A, and the period T is obtained by the interval of the rectangular wave.

This figure (b) is a BP for obtaining the noise period T after digitizing the noise signal input to the microphone.
The F (Band Pass Filter) peak detection method is shown. This method includes a plurality of band pass filters 1, 2, ..., N, an absolute value conversion unit (ABS) connected to each band pass filter 1, 2, ..., N, and an absolute value conversion unit. Averaging unit (LPF)
And a maximum band detection unit that detects the maximum value of each averaging unit, detects the maximum frequency band of the noise level, and sets the cycle of the maximum frequency band as the cycle of the noise signal.

FIG. 3C shows a cycle detection method using an adaptive filter, which is a delay device for inputting the difference signal S _R of the difference signal calculating means 8 and an output of the delay device. An adaptive filter (ADF), an adder that takes the difference signal between the output of the adaptive filter and the through input signal, and the least squares method of the difference signal of the adder to determine the coefficient of the adaptive filter. It consists of a square method processing unit (LMS) and calculates the period of the noise signal from the coefficient of the adaptive filter.

This embodiment is useful when the timing signal cannot be obtained from the noise source 1. As an example of extracting the timing signal, in addition to the first and second embodiments described above, for example, from a noise transmission path (for example, a muffler) from the noise generation source 1 to the sound wave / electric converter 3, You may make it extract by a vibrometer.

[0022]

As described above, according to the present invention,
Instead of directly using the sensor output, the harmonic signal is generated based on the timing signal of the noise signal from the noise source, and this harmonic signal is supplied to the adaptive filtering means, so that a simple system can be realized. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram showing a noise control device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a waveform generated by a harmonic generation unit.

FIG. 4 is a diagram showing a noise control device according to a second embodiment of the present invention.

5 is a diagram illustrating a method of detecting a cycle of a timing signal in the waveform shaping section of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Noise generating source 2 ... Electric signal / sound wave converter 3 ... Sound wave / electric signal converter 4 ... Adaptive filtering 5 ... Harmonic generation part 6 ... Waveform shaping part 7 ... Transfer characteristic simulating means 8 ... Difference signal calculating means

Claims (4)

[Claims] 1. An electric signal / sound wave converter (2) for eliminating noise from a noise generating source (1), and residual sound of noise eliminated by sound waves from the electric signal / sound wave transducer (2). Wave / electric signal converter (3) for converting sound into electric signals
And an adaptive filtering means (4) for controlling a filter coefficient based on the signal of the sound wave / electrical signal converter (3) to form a compensation signal for canceling noise to the electric signal / sound wave converter (2). And a noise generation device (5) for generating a harmonic signal of a fundamental wave related to a timing signal and supplying the harmonic signal to the adaptive filtering means (4). A noise control device comprising: 2. The noise control according to claim 1, wherein the noise generating source (1) is an internal combustion engine, and a cycle of a fundamental wave related to the timing signal is equal to an explosion cycle of the internal combustion engine. apparatus. 3. The noise generating source (1) is an internal combustion engine, and the timing signal is a rotation timing signal representing the number of revolutions of the internal combustion engine, and the high frequency generator (5).
Is a noise control device, wherein a harmonic signal is generated using a signal obtained by dividing the rotation timing signal as a fundamental wave. 4. The timing signal is formed from the difference signal between the output of the acoustic / electrical signal converter (3) and the output of the adaptive filtering means (4). Noise control device.