JPH05106418A - Noise control device - Google Patents

Abstract

PURPOSE:To improve accuracy of noise eliminating sound by reducing a process focusing time for generating noise eliminating sound against noise. CONSTITUTION:A noise control device forms higher harmonics of noise generated from noise source 1 of an engine in a vehicle or the like and is provided with an adaptive type filter 73 which equalizes the high harmonics given as input signals so as to form characteristic which is opposite to characteristic of noise, and furthermore, updates a coefficient so as to minimize the error signal thereof so as to carry out feed back control. A pre-positioned process filter is provided on the input step of the adaptive type filter 73 which is provided in order to requlate the level of each higher harmonics according to the damping frequency characteristic or the like of the noise transferring/ passage 4 of a muffler or the like, and to previously equalize the damping frequency characteristic of the noise transfer passage 4 so as to input the higher harmonics of noise. And a coefficient for equalizing damping frequency characteristic of the muffler 4 or the like is initially set to the filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise control device for erasing noise by using a speaker, and particularly to the present invention to shorten the processing convergence time for forming the erasing sound for noise and improve the accuracy of the erasing sound. And

[0002]

2. Description of the Related Art Conventionally, a passive muffler such as a muffler has been used to reduce noise generated from an internal combustion engine, etc., but improvement has been desired from the viewpoint of size, muffling characteristics and the like. On the other hand, conventionally, there has been proposed an active noise control device which 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. However, the frequency characteristics, stability, etc. of the active noise control device itself are 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. 63-3).
11396 publication). This is a feedforward system that detects noise with a noise source supplement microphone installed upstream of the duct and outputs a signal of opposite phase and equal sound pressure to the noise with a signal processing circuit from a speaker installed downstream of the duct, and muffling. This is a so-called two-microphone / one-speaker type active noise control device that combines a feedback system that detects the generated result with a microphone for a muffling point and minimizes the muffling result. In this device, an adaptive filter that forms a compensating sound of opposite phase and equal sound pressure is a DSP (Digit).
al SignalProssor).

[0003]

However, when the conventional noise control device is installed in an automobile, an air conditioning system, etc., the frequency characteristic of noise changes in response to changes in operating conditions such as changes in speed of the automobile or air conditioning system. The coefficient of the adaptive filter that performs digital signal processing is updated in order to cope with the above.However, this signal processing requires a certain convergence time, so when the change in the operating condition such as the speed of the automobile suddenly changes. Due to this convergence time, a time delay occurs and accuracy deteriorates, which causes a problem that noise cancellation is deteriorated.

Therefore, in view of the above problems, it is an object of the present invention to improve the coefficient convergence of the adaptive filter and improve the noise elimination characteristics.

[0005]

In order to solve the above problems, the present invention forms a harmonic of noise generated from a noise source, and uses this as an input signal to form a characteristic opposite to the characteristic of noise. In a noise control device having an adaptive filter that performs feedback control by equalizing the error signal to minimize its error signal, the level of each harmonic is adjusted according to the attenuation frequency characteristic of the noise transmission path. Then, the attenuation frequency characteristic of the noise transmission path is equalized in advance. Further, a pre-processing filter may be provided at the input stage of the adaptive filter for inputting the harmonics of noise, and a coefficient for equalizing the attenuation frequency characteristic of the noise transmission path may be initialized in advance. Of the frequencies of the noise of the noise source, the frequencies of harmonics that give discomfort may be emphasized and removed.

[0006]

According to the noise control device of the present invention, the level of each harmonic is adjusted according to the attenuation frequency characteristic of the noise transmission path to equalize the attenuation frequency characteristic of the noise transmission path in advance. Further, a preprocessing filter is provided at the input stage of the adaptive filter for inputting the harmonics of noise, and a coefficient for roughly equalizing the attenuation frequency characteristic of the noise transmission path is initialized in advance to the adaptive filter. Type filter does not require equalization processing for the frequency characteristics of the noise transmission path, so the convergence time is shortened by the equalization processing and the response is improved when the noise generation state of the noise source changes drastically. Therefore, it becomes possible to enhance the effect of noise control.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a noise control device according to a first embodiment of the present invention, which is an example of a case where an automobile engine is used as a noise source. The overall configuration of the present invention will be described with reference to this figure. The device is an engine 1 of an automobile or the like,
The exhaust pipe 2 for releasing the exhaust gas of the engine 1 to the atmosphere, and the exhaust gas 2 is gradually decompressed in the middle of the exhaust pipe 2 until it is released to the atmosphere to suppress noise generation. Sub-muffler 3-1 and 3-2 that muffle the generated noise by interference due to reflection on the wall, and a main muffler provided at the subsequent stage of the sub-muffler 3-1 and 3-2 for the same purpose as above. 4 and a tail pipe 5 which is connected to the main muffler 4 and discharges exhaust gas to the atmosphere,
Revolution signal (Sr), pressure signal (Sp) of the engine 1
An engine control section 6 for controlling the engine based on the above, a compensation signal forming section 7 for forming a compensation signal for noise based on an engine speed signal from the engine 1 which is a signal indicating a noise generation state of the engine, A digital / analog converter 8 for converting the digital output signal from the compensation signal forming unit 7 into an analog signal, a low-pass filter 9 connected to the digital / analog converter 8 for removing harmonics, the low-pass filter A power amplifier 10 connected to the pass filter 9, a speaker 11 driven by a signal from the power amplifier 10 to emit a sound wave to cancel noise from the tail pipe 5, and a noise from the tail pipe 5 to the speaker. A microphone 12 for supplementing the result offset by 11 and converting it into an electric signal, and an amplifier 13 connected to the microphone 12. A low-pass filter 14 connected to the amplifier 13, an analog / digital converter 15 connected to the low-pass filter 14 for converting an analog signal into a digital signal, the compensation signal forming section 7, the digital / digital converter 15. A sampling frequency changing unit 16 is provided which supplies a sampling signal to the analog converter 8 and the analog / digital converter 15 and changes the sampling frequency depending on the change in the rotation speed by the rotation speed signal of the engine 1.

The compensating signal forming unit 7 uses the revolution speed signal of the engine 1 as a basic signal to form a harmonic signal of the engine 1 in order to simulate noise harmonics.
A level control section 72 that controls the level of each harmonic from the harmonic forming section 71; and an adaptive filter 73 that forms a compensation signal by using the signal formed by the level control section 72 as a controlled signal. , The analog / digital converter 1
And a minimization unit 74 for supplying the coefficient to the adaptive filter 73. This is a collection of first-order, second-order, third-order, ..., N-th order harmonic components in which the noise source of the engine 1 depends on the number of revolutions, and rises as the number of revolutions increases.

FIG. 2 is a diagram showing the configuration of the adaptive filter of FIG. As shown in the figure, the adaptive filter 73 is connected to a plurality of delay units 731 that delay the input signal from the level control unit 72 by one sampling cycle, and the input signals and the output signals of the respective delay units 731. And a plurality of adders 733 connected to the respective variable multipliers 732. The coefficients a0, a1, a2, ... An of each of the variable multipliers 732 are variable by the supply from the minimization unit 74.

Here, when the sampling frequency is fs, the sampling period T is T = 1 / fs, and when the input signal is x (t) = exp (jωt), the output signal y
(T) can be expressed as follows. y (t) = a0 · exp (jωt) + a1 · expjω (t−T) + a2 · expjω (t−2T) + ... + am · expjω (t−mT) = exp (jωt) · (a0 + a1 · exp) (−jωT) + a2 · exp (−j2ωT) + ... + am · exp (−jmωT)) Next, the minimizing unit 74 that updates the coefficient will be described. When the input signal is expressed as x (n) = exp (jnωt) and the coefficient ak (n) in the above equation, each coefficient ak (n) is obtained by converging by the following equation.

[0011]

[Equation 1]

In this equation, e (n) is an output signal of the analog / digital converter 15 and represents an error signal. Α is a convergence constant. It takes a predetermined time for the coefficient ak (n) to converge to a constant value. When the input signal of the adaptive filter 73 is far from the desired signal, the convergence time becomes particularly long. Therefore, if the input signal of the adaptive filter 73 is close to the desired signal, it is expected that the convergence time will be shortened.

FIG. 3 is a diagram showing the harmonic wave forming unit and the level control unit of FIG. As shown in this figure, the harmonic wave forming section 7
Reference numeral 1 denotes a fundamental wave generator 711 that converts the engine speed into a predetermined fundamental frequency, and a plurality of multipliers 712 that multiply the fundamental frequency of the fundamental wave generator 711 by 1, 2, ..., N times.
Including and The level control unit 72 includes a plurality of variable multipliers 721 that vary the signal level from each of the multipliers 712, a plurality of adders 722 that adds the output signals of each of the variable multipliers 721, and each of the variable multipliers. And a coefficient supply unit 723 that stores the multiplication coefficient of 721 and supplies the multiplication coefficient to each of the variable multipliers 721 based on the noise frequency signal of the multiplier 712.

FIG. 4 is a diagram for explaining the coefficients stored in the coefficient storage section in FIG. This figure (a) is a figure which shows the change of the harmonic frequency of noise with an engine speed as a parameter, and this harmonic formation part 71 forms this harmonic according to an engine speed. The upper part of this figure (b) shows the sound attenuation characteristics of the sub-muffler 3-1 and 3-2 and the main muffler 4. As shown in this figure (b), this acoustic attenuation characteristic is not flat but has an inherent resonance.
The first-order, second-order, third-order, ..., N-order harmonic components depending on the number of revolutions are higher than the resonance part as the number of revolutions increases.
..The frequencies passed through the 3rd, 2nd, and 1st order were changed and changed. Therefore, in the adaptive filter 73, the compensation signal must be converged in consideration of the characteristic of the muffler, and it takes a long time to converge. Therefore, if the characteristic of the muffler is measured in advance with respect to the noise frequency as shown in the lower part of this figure (b) and the gain of each harmonic of the noise shown in this figure (a) is adjusted based on this. It can be understood that the convergence time described above can be shortened. This figure (c) shows the noise frequency f based on the muffler frequency characteristics.
0, f1, f2, ..., Fn as the variable multiplier 72
The multiplication coefficients g0, g1, g2, ..., Gn of 1 are stored in the coefficient supply unit 723 in a map form.

According to this embodiment, the adaptive filter 73
Since the harmonics are adjusted in advance, the processing load of the adaptive filter 73 is reduced and the convergence time can be shortened as compared with the case where the harmonics are always input at the same level.
Since the multiplication coefficient stored in the coefficient supply unit 723 may change under the negative pressure condition of the engine 1, the negative pressure may be stored as a parameter.

Further, in FIG. 3, by making the multiplication coefficient of the multiplier 721 of the secondary component of the multiplier 712 larger than the other coefficients, the secondary component is forcibly emphasized and the noise 2 It is also possible to remove the next component. FIG. 5 is a diagram showing a noise control device according to a second embodiment of the present invention. The configuration shown in this figure, which is different from that of the first embodiment, is provided in the input stage of the adaptive filter 73 and has substantially the same configuration as that of the adaptive filter 73. Filter 75 and the recursive filter 75
And a coefficient memory unit 76 for supplying coefficients to the coefficient memory unit 76, and an initialization circuit 77 for externally setting initial coefficients in the coefficient memory unit 76.
And. FIG. 6 is a diagram showing an example of measuring the initial setting coefficient. As shown in the figure, a speaker is set in an actual muffler, and the reference signal generator 100 gives a reference signal. Since the muffler attenuation characteristic is fixed as shown in FIG. 4 by the measurement system according to this example, the coefficient is set in advance through the initialization circuit 77 and the coefficient memory unit 76 so that the cyclic filter 75 equalizes it. Are set in the recursive filter 75.

Thus, the adaptive filter 73 in the subsequent stage can reduce the load of the equalizing filter and accelerate the convergence, improve the responsiveness, and increase the cost of noise control even when the frequency changes drastically.

[0018]

As described above, according to the present invention, the level of each harmonic is adjusted according to the attenuation frequency characteristic of the noise transmission path to equalize the attenuation frequency characteristic of the noise transmission path in advance. A prefilter is provided at the input stage of the adaptive filter for inputting noise harmonics, and a coefficient for roughly equalizing a fixed portion such as the attenuation frequency characteristic of the noise transmission path is initially set in advance in the noise transmission path. Since the attenuation frequency characteristics of are equalized, the load of the adaptive filter is reduced, and the effect of noise control in which the convergence time is shortened even with a drastic change in the generation state of the noise source can be enhanced.

[Brief description of drawings]

FIG. 1 is a diagram showing a noise control device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an adaptive filter of FIG.

FIG. 3 is a diagram showing a harmonic wave forming unit and a level control unit of FIG.

4 is a diagram illustrating coefficients stored in a coefficient storage unit in FIG.

FIG. 5 is a diagram showing a noise control device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of measuring an initialization coefficient.

[Explanation of symbols]

 1 ... Engine 2 ... Exhaust pipe 3 ... Sub muffler 4 ... Main muffler 5 ... Tail pipe 7 ... Compensation signal forming unit 11 ... Speaker 12 ... Microphone 71 ... Harmonic wave forming unit 72 ... Level control unit 73 ... Adaptive filter 74 ... Minimization unit 75 ... Recursive filter 76 ... Coefficient memory unit 77 ... Initial setting circuit

Claims (3)

[Claims] 1. A coefficient for forming a harmonic of noise generated from a noise source (1), equalizing it with the input signal as an input signal to form a characteristic opposite to the characteristic of the noise, and minimizing the error signal thereof. In a noise control device having an adaptive filter (73) for performing feedback control by updating the noise transmission path (4) by adjusting the level of each harmonic according to the attenuation frequency characteristic of the noise transmission path (4). A noise control device characterized in that the attenuation frequency characteristic of 4) is equalized in advance. 2. A coefficient for forming a harmonic of the noise generated from the noise source (1) and equalizing it so as to form a characteristic opposite to the characteristic of the noise using this as an input signal to minimize the error signal. In a noise control device having an adaptive filter (73) for performing feedback control by updating the pre-processing filter (75) at the input stage of the adaptive filter (73) for inputting harmonics of noise. A noise control device, wherein a coefficient for equalizing the attenuation frequency characteristic of the noise transmission path (4) is initialized in advance. 3. The noise device according to claim 1, wherein among the frequencies of the noise of the noise source (1), the frequencies of the harmonics that give discomfort are emphasized and removed.