JPH06332477A - Muffler - Google Patents

Abstract

PURPOSE:To provide a muffler which employs an active noise control and expands the noise control range without increasing the number of adaptive filters by approximating the transfer functions of a first control point and a second control point using the filter circuit connected to the adaptive filter which especially controls the first control point. CONSTITUTION:The muffler consists of a microphone 1a which detects noise from a noise source, an adaptive filter 2 which adaptively controls detected noise signals, a speaker 6a which reproduces the output of the filter 2, a microphone 1b which detects the reproduced sound and noise, a filtered-x FIR filter 3 which processes the output signals of the microphone 1a, an LMS computing element 4 which computes and updates the coefficients of the filter 2 from the output of the filter 3 and the output of the microphone 1b, an FIR filter 5 which processes the output signals of the filter 2 and a speaker 6b which reproduces the output of the filter 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler using active noise control in a noisy environment.

[0002]

2. Description of the Related Art In recent years, an active noise control method has been proposed in which a control sound is output from a speaker by using a digital signal processing technique to mute environmental noise at a listening position.

A conventional silencer will be described below with reference to the drawings. FIG. 3 is a block diagram of a conventional silencer. In FIG. 3, 1a and 1b are microphones, 2 is an adaptive filter, and 3 is Filtered-xFIR.
A filter, 4 is an LMS calculator, and 6 is a speaker.

The operation of the muffler having the above structure will be described below. Microphone 1a
The noise signal detected by the
It is input to the ltered-x FIR filter 3. The signal adaptively controlled by the adaptive filter 2 is reproduced by the speaker 6. Then, the reproduced sound and the noise from the noise source interfere with each other, and the interference sound is detected by the microphone 1b.
The detected signal is input to the LMS calculator 4, while the Filtere
The output of the d-xFIR filter 3 is also input to the LMS calculator 4.
Here, in the Filtered-x FIR filter 3, the transfer function C from the speaker 6 to the microphone 1b is identified in advance. Therefore, the LMS calculator 4 updates the coefficient of the adaptive filter 2 according to W (n + 1) = W (n) + αr ^T (n) e (n). However, the coefficient of the adaptive filter 2 is W, Filtered-xFI
The output of the R filter 3 is r, and the output of the microphone 1b is e.
And As a result, the noise at the position of the microphone 1b cancels out the reproduced sound and the noise is reduced.

This control algorithm is a Filtered-x LMS
(B.Widrow, SDStearns, "AdaptiveSignal Processin
It is called g ").

[0006]

However, the problem to be solved by the invention (FIG. 3)
With such a configuration, even if the noise is attenuated in the microphone 1b, there is a problem that the amount of attenuation is small or does not attenuate as compared with the microphone 1b in a place distant from the microphone 1b such as point A or point B. Was. That is, if the actual position of the ear and the position of the microphone 1b are far from each other, it becomes difficult to obtain the audible effect.

Further, when it is desired to attenuate the points A and B in order to obtain the audible effect, the conventional method also has a problem that the number of adaptive filters and the like must be increased in order to control at each point.

The present invention solves the above-mentioned problems, and a place where a microphone can be installed is used as a control point of an adaptive filter by using a filter circuit, and an actual attenuation effect is obtained at a position other than the control point (for example, the ear). The present invention provides a muffling device that can be used.

[0009]

To achieve this object, a silencer of the first invention comprises a noise detector for detecting noise from a noise source and an adaptive filter for adaptively controlling the detected noise signal. A first speaker that reproduces the output of the adaptive filter, an error detector that detects the output sound and noise of the first speaker, and a filter circuit that processes the output signal from the adaptive filter. There is.

Further, the silencer of the second invention comprises a noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal, and a speaker for reproducing the output of the adaptive filter. An error detector for detecting the output sound and noise of the speaker and a filter circuit for signal processing the output from the error detector.

[0011]

According to the first aspect of the invention, the transfer function from the error detector, which is the control point of the adaptive filter, to the point controlled by the second speaker is corrected by the filter circuit, and the transfer function is transmitted to the output of the adaptive filter by this filter circuit. By convolving the function, noise can be attenuated at points other than the position of the error detector, the number of adaptive filters can be reduced, and the hardware can be downsized.

According to the second aspect of the invention, the transfer function from the error detector, which is the control point of the adaptive filter, to the point controlled by the speaker is corrected by the filter circuit, and the output of the error detector is convolved with the transfer function by the filter circuit. By using the result as coefficient update information of the adaptive filter, noise can be attenuated at points other than the error detector position.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the first invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a silencer according to an embodiment of the first invention. In FIG. 1, 1a is a microphone, which is a noise detector,
1b is a microphone which is an error detector, 2 is an adaptive filter, 3 is a Filtered-x FIR filter, 4
Is an LMS calculator, 5 is an FIR filter, 6a and 6b are speakers, and 7a and 7b are chairs.

The operation of the muffler having the above structure will be described below. First, the noise detected by the microphone 1a is transmitted to the adaptive filter 2 and
Input to the Filtered-x FIR filter 3. The output signal-processed by the adaptive filter 2 is reproduced by the speaker 6a embedded in the chair 7a. Then, the noise from the noise source and the control sound from the speaker 6a are detected by the microphone 1b and input to the LMS calculator 4. On the other hand, Filtered-
The signal from the microphone 1a input to the xFIR filter 3 is convolved with the transfer function C (the transfer function from the speaker 6a to the microphone 1b) previously identified here, and is input to the LMS calculator 4. Therefore, the LMS calculator 4 is Filt
The output from the ered-x FIR filter 3 is used as a reference signal, and the output from the microphone 1b is used as an error signal LM
The S filter (least squares method) is performed and the adaptive filter 2
Obtain and update the coefficient of. Since the coefficient is updated so that the detection signal of the microphone 1b, which is an error signal, is minimized, the output of the adaptive filter 2 changes so as to attenuate the noise in the microphone 1b.

Next, the output of the adaptive filter 2 that attenuates noise in the microphone 1b is also input to the FIR filter 5. In the FIR filter 5, the transfer function G from the microphone 1b to the point A which is the control point is previously obtained as a coefficient. Here, it is assumed that the transfer function from the speaker 6b to the point A is similar to the transfer function C from the speaker 6a to the microphone 1b. Since the noise reaches the point A through the microphone 1b, if it is muted by the microphone 1b, it is also muted at the point A.

As described above, according to this embodiment, the output of the adaptive filter 2 for controlling the microphone 1b by approximating the transfer function G from the microphone 1b to the point A using the FIR filter 5 is used. By processing the signal with, the noise can be attenuated only by the FIR filter 5 without using the adaptive filter for controlling the point A, the Filtered-xFIR filter, the LMS calculator, the microphone, and the miniaturization can be realized. .

Next, an embodiment of the second invention will be described. (FIG. 2) is a block diagram of a silencer according to an embodiment of the second invention. In (Fig. 2), 1
a is a microphone that is a noise detector, 1b is a microphone that is an error detector, 2 is an adaptive filter, 3 is a Filtered-x FIR filter, 4 is an LMS calculator, 5 is a FIR filter, 6 is a speaker, 7 Is a chair.

The operation of the muffler having the above structure will be described below. First, the noise detected by the microphone 1a is transmitted to the adaptive filter 2 and
Input to the Filtered-x FIR filter 3. The output signal-processed by the adaptive filter 2 is reproduced by the speaker 6 embedded in the chair 7. And microphone 1b
Then, the noise from the noise source and the control sound from the speaker 6 are detected and input to the FIR filter 5. FIR filter 5 here
Includes a transfer function C1 from the speaker 6 to the microphone 1b.
The coefficient C2 / C1 for correcting the transfer function C2 to the ear is calculated in advance. Therefore, the output from the microphone 1b is corrected by the FIR filter 5 and input to the LMS calculator 4. On the other hand, the signal from the microphone 1a input to the Filtered-x FIR filter 3 is convolved with the transfer function C2 (= C1 × C2 / C1) previously identified here, and LM
Input to the S calculator 4. Therefore, the LMS calculator 4 is Filtered
-The output from the xFIR filter 3 is used as a reference signal,
The output from the microphone 1b is used as an error signal to perform LMS calculation (least squares method) to obtain and update the coefficient of the adaptive filter 2. The coefficient is the error signal FIR
Since the output signal of the filter 5 is updated so as to be the minimum, the output of the adaptive filter 2 changes so that the noise is actually attenuated at the ear position while the microphone 1b is the control point.

As described above, according to this embodiment, the transfer function from the speaker 6 to the ear is corrected by using the FIR filter 5, and this output is used as the error signal of the LMS calculator 4 to make the microphone 1b Although it is a control point, the noise can be actually attenuated at the position near the ear, and the auditory effect is not impaired.

[0021]

As is apparent from the above description, the first aspect of the present invention uses a filter circuit to approximate the transfer function from the error detector, which is the control point of the adaptive filter, to the point controlled by the filter circuit. As a result, it is possible to realize an excellent silencer capable of expanding the noise attenuation range without increasing the number of adaptive filters.

According to a second aspect of the invention, the transfer function from the speaker to the ear is corrected using a filter circuit, and this is used as coefficient update information of the adaptive filter.
The adaptive filter can realize an excellent silencer that does not impair the audible effect by attenuating the noise near the ears even if the position of the error detector is far from the ears.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the first invention.

FIG. 2 is a block diagram of an embodiment of the second invention.

FIG. 3 is a block diagram showing a conventional silencer.

[Explanation of Codes] 1a, 1b Microphone 2 Adaptive filter 3 Filtered-xFIR filter 4 LMS calculator 5 FIR filter 6, 6a, 6b Speaker 7, 7a, 7b Chair

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tadashi Tamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masao Kiba, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A noise detector that detects noise from a noise source, an adaptive filter that adaptively controls the detected noise signal, a first speaker that reproduces the output of the adaptive filter, and the first speaker. The error detector includes an error detector that detects the output sound and noise of the speaker, a filter circuit that processes the output signal from the adaptive filter, and a second speaker that reproduces the output of the filter circuit. A silencer, wherein an output from the control unit is used as a control signal of the adaptive filter. 2. A noise detector that detects noise from a noise source, an adaptive filter that adaptively controls the detected noise signal, a speaker that reproduces the output of the adaptive filter, and an output sound and noise of this speaker. And a filter circuit for signal-processing the output from the error detector, and an output of the filter circuit as a control signal of the adaptive filter. 3. The silencer according to claim 1 or 2, wherein the speaker is attached to a chair.