JP2962602B2 - Noise control device - Google Patents

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 canceling noise using a speaker, and more particularly to an object of the present invention is to shorten a processing convergence time for forming a cancel sound for noise and improve the accuracy of the cancel sound. And

[0002]

2. Description of the Related Art Conventionally, a passive silencer such as a muffler has been used to reduce noise generated from an internal combustion engine or the like. However, improvement has been desired from the viewpoints of size, silencing characteristics, and the like. On the other hand, conventionally, an active noise control device has been proposed in which a compensating sound having the opposite phase and the same sound pressure as the noise generated from the sound field is output from a speaker to cancel the noise. However, the frequency characteristics or stability of the active noise control device itself were not sufficient, and its practical use was delayed. In recent years, signal processing techniques using digital circuits have been developed and the frequency range that can be handled has been expanded.
No. 11396). This is a feed-forward system that detects noise with a microphone for supplementing the noise source installed upstream of the duct and outputs a signal of opposite phase and equal sound pressure from the speaker installed downstream of the duct by a signal processing circuit, and a silencer This is a so-called 2-microphone / 1-speaker type active noise control device that combines a feedback system that detects the obtained result with a microphone for a silencing point and minimizes the silencing result. In this apparatus, an adaptive filter for forming a compensation sound of opposite phase and equal sound pressure is provided by a DSP (Digit).
al SignalProcessor).

[0003]

However, when the conventional noise control device is mounted on an automobile or an air conditioning system, the frequency characteristics of the noise change in response to a change in the operating state such as a change in the speed of the automobile or the air conditioning system. The coefficient of the adaptive filter that performs digital signal processing is updated in order to cope with this.However, this signal processing requires a certain convergence time. Due to this convergence time, a time delay occurs, and accuracy is deteriorated, thereby causing a problem that noise cancellation is deteriorated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the convergence of the coefficients of an adaptive filter to improve the noise canceling characteristics in view of the above problems.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention forms harmonics of noise generated from a noise source, and uses the harmonic as an input signal to form a characteristic opposite to the characteristic of the noise. In a noise control device having an adaptive filter that performs feedback control by updating a coefficient so as to minimize the error signal by adjusting the level of each harmonic 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 harmonics of noise, and a coefficient for equalizing the attenuation frequency characteristic of the noise transmission path may be initialized in advance. Of the noise frequencies of the noise source, harmonic frequencies that give discomfort may be emphasized and removed.

[0006]

According to the noise control apparatus of the present invention, the level of each of the harmonics 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 pre-processing filter is provided at an input stage of the adaptive filter for inputting harmonics of noise, and a coefficient for substantially equalizing an attenuation frequency characteristic of the noise transmission path is initially set in advance in the pre-processing filter. Since the type filter does not need to perform equalization processing on the frequency characteristics of the noise transmission path, the convergence time is shortened by the equalization processing, and the responsiveness is improved when the noise generation state of the noise source changes drastically. As a result, the effect of noise control can be enhanced.

[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, and is an example in which an automobile engine is used as a noise source. The overall configuration of the present invention will be described with reference to FIG. The device comprises an engine 1 of an automobile or the like;
An exhaust pipe 2 for discharging the exhaust gas of the engine 1 to the atmosphere, and gradually reducing the exhaust gas in the middle of the exhaust pipe 2 until the exhaust gas is released to the atmosphere in order to suppress noise generation. Sub-mufflers 3-1 and 3-2 for suppressing noise by interference of generated noise due to reflections on the wall, and a main muffler provided at a stage subsequent to the sub-mufflers 3-1 and 3-2 for the same purpose as described above. 4 and a tail pipe 5 connected to the main muffler 4 and discharging exhaust gas to the atmosphere.
The engine speed signal (Sr) and pressure signal (Sp) of the engine 1
An engine control unit 6 for controlling the engine based on the above, a compensation signal forming unit 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 a 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; A power amplifier 10 connected to the pass filter 9; a speaker 11 driven by a signal from the power amplifier 10 to emit sound waves to cancel noise from the tail pipe 5; A microphone 12 for supplementing the result canceled by 11 and converting it to an electric signal, and an amplifier 13 connected to the microphone 12 A low-pass filter 14 connected to the amplifier 13, an analog-to-digital converter 15 connected to the low-pass filter 14 for converting an analog signal to a digital signal, the compensation signal forming unit 7, It includes a sampling frequency varying unit 16 that supplies a sampling signal to the analog converter 8 and the analog / digital converter 15 and varies a sampling frequency depending on a change in the number of revolutions according to the number of revolutions of the engine 1.

The compensation signal forming section 7 uses a rotational 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 controller 72 for controlling the level of each harmonic from the harmonic generator 71, and an adaptive filter 73 for forming a compensation signal using a signal formed by the level controller 72 as a controlled signal. , The analog / digital converter 1
And a minimizing unit 74 for determining coefficients so as to minimize the control signal from 5 and supplying the coefficients to the adaptive filter 73. This is a set of first-order, second-order, third-order,..., N-order harmonic components in which the noise source of the engine 1 depends on the rotation speed, and increases as the rotation speed 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 for delaying the input signal from the level control unit 72 by one sampling period, and to the input signal and the output signal of each of the delay units 731. And a plurality of adders 733 connected to each of the variable multipliers 732. The coefficients a0, a1, a2,... An of each of the variable multipliers 732 are variable by the supply from the minimizing section 74.

Here, if the sampling frequency is fs, the sampling period T is T = 1 / fs, and if 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 represented by 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, and a predetermined time is required until the coefficient ak (n) converges 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, the convergence time is expected to be short.

FIG. 3 is a diagram showing the harmonic forming unit and the level control unit in FIG. As shown in FIG.
Reference numeral 1 denotes a fundamental wave generator 711 for converting the engine speed into a predetermined fundamental frequency, and a plurality of multipliers 712 for multiplying the fundamental frequency of the fundamental wave generator 711 by 1, 2,.
And The level control unit 72 includes a plurality of variable multipliers 721 for varying the signal level from each of the multipliers 712, a plurality of adders 722 for adding the output signals of the respective variable multipliers 721, and each of the variable multipliers. And a coefficient supply unit 723 that stores the multiplication coefficient of the variable multiplier 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 unit in FIG. FIG. 6A is a diagram showing a change in the frequency of a harmonic of noise using the engine speed as a parameter. The harmonic forming section 71 forms the harmonic corresponding to the engine speed. The upper part of FIG. 3B shows the sound attenuation characteristics of the sub-mufflers 3-1 and 3-2 and the main muffler 4. As shown in FIG. 2B, the sound attenuation characteristic is not flat but has an inherent resonance.
The first-order, second-order, third-order,..., And n-th harmonic components depending on the rotation speed show the above-mentioned resonance portion with higher order as the rotation speed increases.
.. The frequencies passing through the third, second, and primary were switched and changed. For this reason, the adaptive filter 73 has conventionally had to converge the compensation signal in consideration of the characteristics of the muffler, and it has taken time to converge. Therefore, the characteristics of the muffler are measured in advance with respect to the noise frequency as shown in the lower diagram of this figure (b), and based on this, the gain of each harmonic of the noise shown in this figure (a) is adjusted. It can be understood that the convergence time described above can be reduced. This figure (c) shows the noise frequency f based on the frequency characteristics of the muffler.
The variable multiplier 72 is designated as 0, f1, f2,.
The multiplication coefficients g0, g1, g2,... Gn of 1 are stored in the coefficient supply unit 723 in the form of a map.

According to this embodiment, the adaptive filter 73
Therefore, the load on the processing of the adaptive filter 73 is reduced and the convergence time can be reduced as compared with the case where 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 increasing the multiplication coefficient of the multiplier 721 for the second-order component of the multiplier 712 to be larger than the other coefficients, the second-order component is forcibly emphasized, and noise 2 which is likely to cause discomfort. It is also possible to remove the next component. FIG. 5 is a diagram illustrating 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 at the input stage of the adaptive filter 73 and has substantially the same configuration as that of the first embodiment. A filter 75 and the recursive filter 75
Memory 76 for supplying coefficients to the memory, and an initial setting circuit 77 for externally setting initial coefficients in the coefficient memory 76.
And FIG. 6 is a diagram illustrating an example of measuring the initial setting coefficient. As shown in the figure, a speaker is set on an actual muffler, and a reference signal is given by a reference signal generator 100. Since the attenuation characteristic of the muffler is fixed as shown in FIG. 4 by the measuring system according to this example, the coefficient is set via the initial setting circuit 77 and the coefficient memory unit 76 so that the recursive filter 75 equalizes it in advance. Is set in the recursive filter 75.

Thus, the latter adaptive filter 73 can reduce the load on the equalizing filter, speed up 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 in accordance with the attenuation frequency characteristic of the noise transmission path to equalize the attenuation frequency characteristic of the noise transmission path in advance. A pre-filter is provided at an input stage of the adaptive filter for inputting harmonics of noise, and a coefficient for substantially equalizing a fixed portion such as a damping frequency characteristic of the noise transmission path is initially set in advance in the pre-filter, and the noise transmission path is initialized. , The load on the adaptive filter is reduced, and the effect of noise control in which the convergence time is shortened even for a drastic change in the generation state of the noise source can be enhanced.

[Brief description of the 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 illustrating a configuration of an adaptive filter of FIG. 1;

FIG. 3 is a diagram illustrating a harmonic forming unit and a level control unit in FIG. 1;

FIG. 4 is a diagram illustrating coefficients stored in a coefficient storage unit in FIG. 3;

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

FIG. 6 is a diagram illustrating an example of measuring an initial setting coefficient.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Exhaust pipe 3 ... Sub muffler 4 ... Main muffler 5 ... Tail pipe 7 ... Compensation signal formation part 11 ... Speaker 12 ... Microphone 71 ...・ Harmonic generator 72 ・ ・ ・ Level controller 73 ・ ・ ・ Adaptive filter 74 ・ ・ ・ Minimizer 75 ・ ・ ・ Cyclic filter 76 ・ ・ ・ Coefficient memory 77 ・ Initial setting circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-48910 (JP, A) JP-A-63-311396 (JP, A) JP-A-5-11778 (JP, A) JP-A-5-118 108081 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 1/00 G10K 11/178

Claims (3)

(57) [Claims] 1. A coefficient for forming harmonics of noise generated from a noise source (1) and using the same as an input signal so as to form a characteristic opposite to the characteristic of the noise, and minimizing the error signal. A noise control device having an adaptive filter (73) for performing feedback control by updating the noise transmission path (73) by adjusting the level of each harmonic in accordance with 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 noise generated from the noise source (1) and using the same as an input signal so as to form a characteristic opposite to the characteristic of the noise, and minimizing the error signal. A noise control device having an adaptive filter (73) for performing feedback control by updating the above-mentioned filter, wherein a pre-processing filter (75) is provided at an input stage of the adaptive filter (73) for inputting harmonics of noise. A noise control apparatus, wherein a coefficient for equalizing the attenuation frequency characteristic of the noise transmission path (4) is initially set in advance. 3. The noise apparatus according to claim 1, wherein, of the noise frequencies of the noise source, the frequency of a harmonic that gives discomfort is emphasized and removed.