JPH0883080A - Muffler - Google Patents

Abstract

PURPOSE: To provide a muffler reducing coefficient renewal operation amount in noise control operation when plural noise control points exist, concerning control. a muffler using active noise CONSTITUTION: This muffler is provided with a microphone 1a detecting noise, adaptive filters 2a-2c adaptively controlling a detected noise signal, FIR filters 3a-3c signal processing the output of the microphone la, speakers 5a-5c reproducing the output of the adaptive filters 2a-2c, microphones 1b, 1c, 1e detecting the reproducing sound and the noise from a noise source and LMS ALUs 4a-4c operating and updating the coefficients of the adaptive filters 2a-2c from the outputs of the microphones 1b, 1c, 1e and the outputs of the FIR filters 3a-3c, and a signal processing control circuit 6 allows operation start of a noise control signal 7 when the coefficients of the FIR filters 3a-3c are identified when a level difference with transmission function excepting them exist a prescribed value or above.

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.

[0002]

2. Description of the Related Art In recent years, active noise control in which a muffled sound of an engine of a car or mechanical noise in a factory is output from a speaker by using a digital signal processing technology and is muted at a plurality of points in a car room or a factory A method has been proposed.

A conventional silencer will be described below with reference to the drawings. FIG. 15 is a block diagram of a conventional silencer. In FIG. 15, 1a,
1b and 1c are microphones, 2a and 2b are adaptive filters, 3a, 3b, 3e and 3f are FIR filters,
Reference numerals 4a, 4b, 4e, and 4f are LMS calculators, 5a and 5b are speakers, and 16a and 16b are coefficient adders.

The operation of the muffler having the above structure will be described below. First, noise is detected by the microphone 1a, and the detection signals are detected by the adaptive filters 2a and 2b and the FIR filters 3a, 3b and 3a.
It is input to e and 3f. The noise signal processed by the adaptive filter 2a is output from the speaker 5a, and the noise signal processed by the adaptive filter 2b is output from the speaker 5b. In the microphones 1b and 1c, the reproduced sounds from the speakers 5a and 5b interfere with the noise from the noise source, and the adaptive filter 2
Noise is attenuated by changing the coefficients a and 2b.

Now, considering the coefficient update for the adaptive filter 2a, the detection signals of the microphones 1b, 1c arranged at the two control points are input to the LMS calculators 4a, 4e, respectively, and the detection sound and the FIR filter are inputted. Three
LMS calculation (least square method) so that the detection signals of the microphones 1b and 1c are minimized by the outputs from a and 3e.
And the obtained coefficient is added by the coefficient adder 16a to update the coefficient of the adaptive filter 2a. As a result, noise is attenuated by the control sound from the speaker 5a in the microphones 1b and 1c. Here, the transfer function C ₀₀ from the speaker 5a to the microphone 1b is approximated to the FIR filter 3a in advance, and the transfer function C ₀₁ from the speaker 5a to the microphone 1c is approximated to the FIR filter 3e as a coefficient. The adaptive filter 2b may be similarly considered. This way, Mu
ltiple Error Filtered-x LMS algorithm (see, for example, SJ Elliott, IM Stothers and P.
A. Nelson, ("A multiple error LMS algorithm and it
s application to the active control of sound and vi
bration. "IEEE Trans. Acoust. Speech Signal Proces
s. ASSP-35, pp1423-1434 (1987))). If this is generally expressed by a mathematical expression, it can be expressed as follows.

Now, for one noise, the control speaker is
If there are k microphones at the control point position,

[0007]

[Equation 1]

[0008] Applying this to (Figure 15),

[0009]

[Equation 2]

[0010] As described above, by using this algorithm, noise control at a plurality of control points becomes possible.

Next, consider the case of controlling a plurality of noises.
FIG. 16 shows a block diagram of another conventional silencer. In FIG. 16, 1a to 1d are microphones, 2a to 2d are adaptive filters, and 3a to 3h.
Is an FIR filter, 4a to 4h are LMS calculators, 5a,
5b is a speaker, 15a and 15b are control signal adders, 1
6a and 16b are coefficient adders.

As is clear from this, the microphone 1
The algorithm described in (FIG. 15) is applied to each noise detected by a and 1d, and the noise control output is added by the control signal adders 15a and 15b to obtain the same speaker 5
It is only configured to reproduce from a and 5b.

That is, in order to deal with a plurality of noise sources, the algorithm shown in (Equation 1) may be applied to each of the noise sources.

[0014]

However, as shown in FIG.
5), Mu which controls a plurality of control points (microphones 1b, 1c) by a plurality of speakers 5a, 5b as shown in FIG.
The ltiple Error Filtered-x LMS algorithm has a problem that a large amount of calculation is required to update the coefficient and a problem that there is a large memory capacity for buffering the coefficient and the input signal. This means that when actually constructing a silencer, a large number of arithmetic units such as DSPs (digital signal processors) for executing arithmetics are required, or high-speed and expensive DSPs with large memory capacity must be used. It does not occur, or the operating speed of the entire device cannot be increased.

The present invention solves the above problems. A first object of the present invention is to reduce the coefficient update calculation amount and the coefficient update calculation amount under the conditions determined by the signal processing control circuit even when noise is attenuated at a plurality of control points. An object of the present invention is to provide a silencer capable of reducing the amount of memory required. A second object of the present invention is to provide a muffling apparatus that can bring the noise control effect of the error detector close to the auditory effect in addition to the first object.
A third object is to provide a muffling device that improves the low frequency reproduction capability of the speaker in addition to the second object, and a fourth object is to add both ears to the noise control area in addition to the third object. It is to provide a muffling device that can be guided so that it is always positioned.

[0016]

In order to achieve the first object, a silencer of the first invention comprises a noise detector for detecting noise from a noise source, m adaptive filters, and m
Digital filters, m coefficient calculators, m speakers, m error detectors installed at noise control points, and a signal processing control circuit that controls the start and stop of noise control signal processing. It consists of

In order to achieve the second object, a silencer of the second invention is a noise detector for detecting noise from a noise source, an Lch, Rch adaptive filter, an Lch,
Rch digital filter, Lch and Rch coefficient calculator, Lch and Rch speakers installed near the head, and Lc installed near the right and left ears near each speaker
The h and Rch error detectors and the signal processing control circuit that controls the start and stop of the noise control signal processing.

In order to achieve the third object, the silencer of the third invention is an Lch / Rch speaker and an Lch / R speaker.
It has a headrest on which a ch error detector is installed.

Further, in order to achieve the fourth object, the silencer of the fourth invention has a headrest provided with a recess for fixing the head to the noise control area.

[0020]

According to the configuration of the first invention, when noise is controlled at m error detector positions by using m speakers for a certain noise, a normal Multiple Error Filtered-x LM is used.
The S algorithm requires (m × m) adaptive filters, (m × m) digital filters, and (m × m) coefficient calculators, but as in the configuration of the first invention, i Noise control operation when the reproduced sound from the i-th speaker in the i-th error detector is louder than the reproduced sound from speakers other than the i-th speaker and the level difference is greater than the noise attenuation amount in the i-th error detector By providing the signal processing control circuit for controlling the device so as to start, it is only necessary to use m adaptive filters, m digital filters and m coefficient calculators, and the calculation amount in coefficient update and Set the required memory capacity to (1 /
m) It can be reduced twice.

Similarly, in the configuration of the second aspect of the present invention, the amount of calculation in coefficient updating and the memory capacity required therefor can be reduced to (1/2) times, and the speaker and the error detector are installed near the head. The noise control effect of the error detector can be approximated to the actual auditory effect.

Further, in the configuration of the third aspect of the invention, the speaker and the error detector are integrated with the headrest so as to control the noise around the ears, so that the noise control effect of the error detector can approach the actual auditory effect. In addition, since the baffle effect of the headrest improves the low-frequency reproduction capability of the speaker, the low-frequency noise control band is expanded. In addition, the headrest can be applied to the seats of automobiles, trains, airplanes, etc. to reduce the noise inside the vehicle, and by applying it to the pillow, you can sleep without worrying about external noise and snoring of others at bedtime. .

With the structure of the fourth aspect of the invention, since both ears can be guided so as to be always located in the noise control area, the optimum noise control effect can always be heard.

[0024]

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, 1c, 1e are microphones which are error detectors, 2a-2c are adaptive filters, 3a-3c
Is a FIR filter, which is a digital filter,
4a to 4c are LMS calculators, which are coefficient calculators,
Reference numerals 5a to 5c are speakers, 6 is a signal processing control circuit, and 7 is a noise control signal processing block.

The operation of the muffler having the above structure will be described below. First, the signal processing control circuit 6 determines whether or not to perform noise control, and thereby controls the operation start / stop of the noise control signal processing block 7. Here, regarding the operation of the signal processing control circuit 6,
This will be described with reference to FIG.

In FIG. 2, 1b is a microphone which is an error detector, 3l to 3n are FIR filters which are digital filters, 4l to 4n are LMS calculators which are coefficient calculators, 5a to 5n. 5c is a speaker, 6 is a signal processing control circuit, 8 is an M series noise generator, 9a to 9c are subtractors, 10 is a level difference calculator, 11
Is a silence volume input circuit, 12 is a comparator, 13 is an operation determination circuit, and 17 is a switch. In FIG. 2, transfer functions C _{0 0} and C ₀ between the microphone 1b and the speakers 5a to 5c are shown.
_{Although 10} and C ₂₀ are taken as an example, first consider the case where the switch 17 is connected to the terminal α and brought into conduction.

The measurement noise from the M-sequence noise generator 8 is the speaker 5a, the FIR filter 3l, and the LMS calculator 4
input to l. Then, noise is reproduced from the speaker 5a, detected by the microphone 1b, and input to the subtractor 9a. On the other hand, the output from the FIR filter 3l is also input to the subtractor 9a, and the subtractor 9a subtracts the output of the FIR filter 3l from the output of the microphone 1b and outputs the result to L.
Input to the MS calculator 41. The LMS calculator 4l uses the noise from the M-sequence noise generator 8 as a reference signal,
The LMS operation is performed using the output of the subtractor 9a as an error signal. Then, the calculation result is updated as the coefficient of the FIR filter 3l. The above calculation is shown in (Equation 3).

[0029]

(Equation 3)

By this calculation, the coefficient w (n) of the FIR filter 3l is approximated to the transfer function C ₀₀ from the speaker 5a to the microphone 1b.

Next, the switch 17 is conducted to the terminal β,
Similarly, the coefficient of the FIR filter 3m is obtained, and then the switch 17 is connected to the terminal γ to obtain the coefficient of the FIR filter 3n. As a result, the coefficient of the FIR filter 3m is approximated to the transfer function C ₁₀ from the speaker 5b to the microphone 1b, and similarly, the coefficient of the FIR filter 3n is the speaker 5c.
It is approximated to a transfer function C ₂₀ to the microphone 1b from.

As described above, each FIR filter 3l to 3n
If the coefficient of is calculated, the level difference calculator 10 calculates the minimum level difference for each frequency between the coefficient of the FIR filter 3l and the coefficient of the FIR filters 3m and 3n. The comparator 12 compares the level difference and the volume of silence input in advance in the volume of silence input circuit 11 for each frequency. As a result, at all frequencies, if the level difference calculated by the level difference calculator 10 is larger than the mute level of the mute volume input circuit 11, the noise determination operation is permitted by the operation determination circuit 13.

Explaining this concretely, first, in the muffling volume input circuit 11, the muffling level (which is the difference between the original noise level shown by the dotted line in FIG. 3 and the noise level at the time of noise control shown by the solid line ( For example, in the case of FIG. 3, D1 is input when the frequency is f1, and D2) is input when the frequency is f2. Then, in the level difference calculator 10, the level difference between the coefficient C ₀₀ of the FIR filter 3l shown by the dotted line in FIG. 4 and the coefficient C ₁₀ of the FIR filter 3m shown by the solid line (for example, in the case of FIG. P1 when f2 and P2 when f2), the coefficient C _{00 of the} FIR filter 3l shown by the dotted line in FIG. 5 and the FI shown by the solid line.
The level difference with the coefficient of the R filter 3n (for example, in the case of FIG. 5, Q1 at the frequency f1 and Q2 at the frequency f2) is calculated to obtain the minimum level difference for each frequency. In the case of this example, if Q1 <P1, Q2> P2, the minimum level difference at the frequency f1 is Q1, and the minimum level difference at the frequency f2 is P.
It becomes 2. The comparator 12 compares D1 with Q1 and D2 with P2. Now, assuming that D1> Q1 and D2 <P2, since the mute level of the mute volume input circuit 11 is higher at the frequency f1, the operation determination circuit 13 prohibits the noise control operation. However, the control band f3
If the level difference calculated by the level difference calculator 10 is larger than the mute level of the mute volume input circuit 11 (ie, D1 <Q1, D2 <P2) at all the frequencies below, the operation control circuit 13 controls the noise control. Allow the action.

In the configuration of FIG. 1, the same processing is performed for the microphones 1c and 1e, and in all cases of the microphones 1b, 1c and 1e, the level difference calculated by the level difference calculator 10 is more muted. If it is higher than the muffling level of the quantity input circuit 11, the noise control operation is permitted by the operation determination circuit 13.

In this way, if the noise control operation is permitted by the signal processing control circuit 6, the operation of the noise control signal processing block 7 (FIG. 1) is started. Here, that the noise control operation is permitted means that the speakers 5a to 5c are
It can be considered that the transmission paths from the microphones to the microphones 1b, 1c, and 1e are only C ₀₀ , C ₁₁ , and C ₂₂ shown in (FIG. 1).

Now, the noise is detected by the microphone 1a,
The detection signal is transmitted to the adaptive filters 2a to 2c and the FI.
It is input to the R filters 3a to 3c. The noise signal processed by the adaptive filter 2a is output from the speaker 5a, the noise signal processed by the adaptive filter 2b is output from the speaker 5b, and the noise signal processed by the adaptive filter 2c is output from the speaker 5a.
It is output from c. In the microphones 1b, 1c, and 1e, the reproduced sounds from the speakers 5a to 5c interfere with the noise from the noise source, and the interference sound is generated by the microphones 1b, 1c, and
Detect with 1e. Then, the LMS calculators 4a to 4c perform the LMS calculation so that the detection signals of the microphones 1b, 1c, and 1e are minimized by the detected sounds and the outputs from the FIR filters 3a to 3c, respectively, and the adaptive filters 2a to 2c perform the LMS calculation. The coefficient is changed so that the noise is attenuated at the control points in the microphones 1b, 1c, 1e.

Here, the transfer function C ₀₀ from the speaker 5a to the microphone 1b is transferred to the FIR filter 3a by the FI
The R filter 3b includes a speaker 5b to a microphone 1c.
The transfer function C ₁₁ until the, the FIR filter 3c is identified as a factor obtained when the transfer function C ₂₂ from the speaker 5c to the microphone 1e, respectively, the signal processing control circuit 6 to determine whether to noise control ing. The coefficient updating formula is shown below.

[0038]

[Equation 4]

As a result, the adaptive filter 2a
2c operate | move so that noise may be attenuated in the microphones 1b, 1c, and 1e.

Comparing (Equation 4) with (Equation 2), it can be seen that the amount of calculation for obtaining the coefficient of one adaptive filter is obviously smaller in (Equation 4). Therefore, according to the configuration of the present embodiment, the coefficient update calculation amount and the memory capacity required for it can be reduced. That is, it is possible to reduce the size of the silencer, reduce the cost, or operate at high speed.

The first embodiment of the second invention will be described below with reference to the drawings. (FIG. 6) is a block diagram of a silencer according to a first embodiment of the second to fourth inventions. In FIG. 6, 1a is a microphone that is a noise detector, 1b and 1c are microphones that are Lch and Rch error detectors, and 2
a, 2b are Lch and Rch adaptive filters, 3a, 3b are FIR filters which are Lch and Rch digital filters, and 4a, 4b are Lch.
And an LMS calculator which is an Rch coefficient calculator,
Reference numerals 5a and 5b are Lch and Rch speakers, 6 is a signal processing control circuit, and 7 is a noise control signal processing block.
Here, the Lch speaker 5a and the Rch speaker 5b, and the Lch microphone 1b and the Rch microphone 1c.
Are attached to the chair 14 as shown in (FIG. 7).

The operation of the muffling device having the above structure will be described below. Now, speaker 5
a, 5b and microphone 1b, since 1c is attached to the chair 14 as shown (FIG. 7), the transmission path of C _00, C ₁₁ when not sitting person in the chair 14 as shown in (Fig. 8) Although the effects of C ₀₁ and C ₁₀ other than the above can not be ignored, when a person sits on the chair 14 as shown in (Fig. 9), the head of the person is transferred to the transmission paths C ₀₁ and C _10.
Since it is cut off, its effect is reduced. Therefore, if the level difference between C ₀₀ and C ₁₀ is larger than the volume reduction in the microphone 1b and the level difference between C ₁₁ and C ₀₁ is larger than the volume reduction in the microphone 1c, the signal processing control circuit 6 Permits the operation of the noise control signal processing block 7 to start. Note that, in (FIG. 7), the mounting position of the microphone 1a, which is the noise detector, is not particularly limited, and is not shown.

By the way, comparing (FIG. 6) with (FIG. 1), since the signal processing of (FIG. 6) is deleted for one channel of (FIG. 1), the basic operation is the same as that described above. . Therefore, the coefficient update calculation amount and its memory capacity can be reduced as in the case of the present embodiment (FIG. 1). That is, it is possible to reduce the size of the silencer, reduce the cost, or operate at high speed. Further, the speakers 5a and 5b and the microphone 1
By arranging b and 1c with the chair 14 so as to control the noise around the ears, the noise control effect of the microphones 1b and 1c can be approximated to the actual audible effect, and the baffle effect of the chair 14 enables the speaker Since the low frequency reproduction capability of 5a and 5b is improved, the noise control effect in that band is also improved. Further, it can be applied to seats of automobiles, trains, airplanes, etc. to reduce noise in the passenger compartment.

In the chair 14 of this embodiment, as shown in FIG. 7, the backrest portion and the headrest portion are integrally formed, but in the case where the headrest portion is removable like a car seat. However, the same effect can be obtained by installing the speakers 5a and 5b and the microphones 1b and 1c in the headrest portion and operating the headrest portion and the backrest portion connected (normal use state). In addition, as shown in FIG.
4 is provided with a recess for fixing in the center of the speaker 5a, 5b
When the microphones 1b and 1c are installed as shown in FIG. 11 and FIG. 12, both ears can be guided near the microphones 1b and 1c, so that the optimum noise control effect can always be heard. In addition, in FIG. 10, the mounting position of the microphone 1a, which is a noise detector, is not particularly limited, and is not shown.

A second embodiment of the second to fourth inventions will be described below with reference to the drawings.

FIG. 13 shows L in the configuration of FIG.
ch speaker 5a, Rch speaker 5b, and Lch
An embodiment in which the microphone 1b and the Rch microphone 1c are attached to the pillow 17 is shown. Since the operation is the same as that in the case of (FIG. 6), the explanation is omitted. The person puts his or her head on the pillow 17, and at this time, the microphone 1a.
It becomes possible to sleep in a quiet environment by (not shown) detecting external noise or snoring of a person sleeping next to the noise and performing noise control by the above-mentioned algorithm.

Finally, a third embodiment of the second to fourth inventions will be described with reference to the drawings.

FIG. 14 is a block diagram of a silencer according to the third embodiment of the second invention. (Fig. 1
In 4), 1a and 1d are microphones which are noise detectors, 1b and 1c are microphones which are Lch and Rch error detectors, 2a and 2c are Lch.
Adaptive filters 2b and 2d are Rch adaptive filters, 3a and 3c are Lch digital filters, and FIR filters 3b and 3d are Rch.
FIR filter, which is a digital filter, 4
a, 4c are LMS coefficient calculators that are Lch coefficient calculators, and 4b, 4d are LMs that are Rch coefficient calculators.
S arithmetic units, 5a and 5b are Lch and Rch speakers, 6 is a signal processing control circuit, 7 is a noise control signal processing block, and 15a and 15b are Lch and Rch control signal adders. Here, the Lch speaker 5a and the Rch speaker 5b, and the Lch microphone 1b and the Rch microphone 1c are attached to the chair 14 as shown in (FIG. 7) as in the case of (FIG. 6).

The operation of the muffling device having the above structure will be described below. (FIG. 14) shows a case where one more noise source is added to the configuration of (FIG. 6). That is, the control signal adders 15a and 15b (FIG. 6) are combined into two (FIG. 1).
It becomes the configuration of 4). Therefore, the noises detected by the microphones 1a and 1d are processed in the same manner as in the case of (FIG. 6). Therefore, even when there are two noise sources, the noise can be attenuated while the coefficient update calculation amount and the memory capacity thereof are reduced.

[0050]

As described above, the muffler of the present invention is
The reproduced sound from the i-th speaker in the th-error detector is louder than the reproduced sound from the speakers other than the i-th speaker,
Further, by providing the signal processing control circuit for controlling the device so as to start the noise control operation when the level difference is larger than the noise attenuation amount in the i-th error detector, m
The number of adaptive filters, the number of digital filters and the number of coefficient calculators need only be used, and the amount of calculation in coefficient update and the memory capacity required for the calculation can be reduced by (1 / m) times compared to the conventional case.

Furthermore, by installing the speaker and the error detector near the head and arranging for noise control at the ears,
The noise control effect of the error detector can be approximated to the actual auditory effect.

Further, by integrating the speaker and the error detector with the headrest, the baffle effect of the headrest improves the low-frequency reproduction capability of the speaker, and the noise control effect in that band is also improved. By providing a recess for fixing the, it is possible to guide both ears to the optimum noise control area at all times, and this headrest can be applied to the seats of cars, trains, airplanes, etc. to reduce the noise in the vehicle interior, Furthermore, when it is applied to a pillow, it has an excellent effect such that it can sleep without worrying about external noise and snoring of others.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an operation of a signal processing control circuit 6 shown in FIG.

FIG. 3 is a frequency characteristic diagram showing a noise control effect in the microphone 1b of FIG. 1;

FIG. 4 is a frequency characteristic diagram showing a level difference between transfer functions C ₀₀ and C ₁₀ in (FIG. 2).

FIG. 5 is a frequency characteristic diagram showing a level difference between transfer functions C ₀₀ and C ₂₀ in (FIG. 2).

FIG. 6 is a block diagram of a first embodiment of the second to fourth inventions.

FIG. 7 is a view showing a chair 14 in which speakers 5a and 5b and microphones 1b and 1c are installed in the first embodiment of the second to fourth inventions.

FIG. 8 is a speaker 5a, 5b when the person in the first embodiment of the second to fourth inventions is not sitting on the chair 14;
Showing the transmission path from the microphone to the microphones 1b and 1c

FIG. 9 is a diagram showing transmission paths from the speakers 5a, 5b to the microphones 1b, 1c when a person is sitting on the chair 14 in the first embodiment of the second to fourth inventions.

FIG. 10 is a view showing the chair 14 in the first embodiment of the second to fourth aspects of the invention provided with a recess.

FIG. 11 is a view showing the chair 14 in the first embodiment of the second to fourth aspects of the invention provided with a recess.

FIG. 12 is a view showing a chair 14 provided with a recess in the first embodiment of the second to fourth inventions.

FIG. 13 is a diagram showing a pillow 17 in which speakers 5a and 5b and microphones 1b and 1c are installed in a second embodiment of the second to fourth inventions.

FIG. 14 is a block diagram of a third embodiment of the second to fourth inventions.

FIG. 15 is a block diagram showing a conventional silencer.

FIG. 16 is a block diagram showing a conventional silencer.

[Explanation of symbols]

1a, 1b, 1c, 1d, 1e Microphones 2a, 2b, 2c, 2d Adaptive filters 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3h
1, 3m, 3n FIR filters 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4
1, 4m, 4n LMS calculator 5a, 5b, 5c speaker 6 signal processing control circuit 7 noise control signal processing block 8 M series noise generator 9a, 9b, 9c subtractor 10 level difference calculator 11 silence volume input circuit 12 comparison Device 13 motion determination circuit 14 chair 15a, 15b control signal adder 16a, 16b, 16c, 16d coefficient adder 17 pillow

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

Claims (8)

[Claims] 1. A noise detector for detecting noise from a noise source, m adaptive filters, m digital filters, m coefficient calculators, and m speakers.
In a muffling device including m error detectors installed at a noise control point and a signal processing control circuit that controls start and stop of noise control signal processing, i (i = 1, 2, ..., The m) th digital filter identifies the transfer function from the i-th speaker to the i-th error detector as a coefficient in advance, and convolves the coefficient and the noise signal detected by the noise detector, Output to the coefficient calculator of, the i-th coefficient calculator calculates and updates the coefficient of the i-th adaptive filter by the signal from the i-th digital filter and the signal from the i-th error detector, The adaptive filter of (1) performs noise control by creating a noise control signal from the coefficient from the i-th coefficient calculator and the noise signal from the noise detector and outputting it to the i-th speaker. In the control circuit, the reproduced sound from the i-th speaker in the i-th error detector is larger than the reproduced sound from the speakers other than the i-th speaker, and the level difference is larger than the noise attenuation amount in the i-th error detector. When the noise control operation is started, a silencer. 2. The signal processing control circuit comprises a transfer function from the i-th speaker to the i-th error detector and (m-1) transfer functions from a speaker other than the i-th speaker to the i-th error detector. , A level difference calculator for calculating the minimum level difference at each frequency, and a mute volume input circuit to which the target muffling level at each frequency is input, and a level difference obtained by the level difference calculator and the mute volume input. A comparator that compares the target muffling level of the circuit for each frequency, and that the level difference obtained by the level difference calculator at all frequencies within the noise control band is greater than the target muffling level of the mute volume input circuit. 2. The silencer according to claim 1, further comprising: an operation determination circuit that controls to start a noise control operation when the comparator detects. 3. A noise suppressor for reducing noise at the Lch and Rch error detectors installed near the right and left ears near each speaker by the Lch and Rch speakers installed near the head. Detector for detecting noise from the Lch digital filter for identifying the transfer function from the Lch speaker to the Lch error detector as a coefficient in advance and convolving the coefficient and the noise signal detected by the noise detector A signal from the Lch digital filter and the Lch
An Lch coefficient calculator that calculates and updates the coefficient of the Lch adaptive filter by the signal from the error detector, and an Lch noise control signal is created by the coefficient from the Lch coefficient calculator and the noise signal from the noise detector. L
A ch adaptive filter, an Lch speaker for performing noise control in the Lch error detector by reproducing the noise control signal, and a transfer function from the Rch speaker to the Rch error detector is identified in advance as coefficients. Rch digital filter for convolving the coefficient and the noise signal detected by the noise detector, the signal from the Rch digital filter and the Rch
An Rch coefficient control unit that calculates and updates the coefficient of the Rch adaptive filter by a signal from the error detector, and an Rch noise control signal is created by the coefficient from the Rch coefficient calculator and the noise signal from the noise detector. R
a ch adaptive filter, an Rch speaker that performs noise control in the Rch error detector by reproducing the noise control signal, and a reproduced sound from the Lch speaker in the Lch error detector is larger than a reproduced sound from the Rch speaker, Further, the level difference is larger than the noise attenuation amount in the Lch error detector, and the Rch in the Rch error detector is further increased.
And a signal processing control circuit for controlling to start the noise control operation when the reproduced sound from the speaker is larger than the reproduced sound from the Lch speaker and the level difference is larger than the noise attenuation amount in the Rch error detector. A silencer characterized by being performed. 4. A signal processing control circuit, wherein the level difference between the transfer function from the Lch speaker to the Lch error detector and the transfer function from the Rch speaker to the Lch error detector at each frequency, and the Rch speaker to the Rch error detector. Level difference calculator that calculates the level difference at each frequency between the transfer function up to and the transfer function from the Lch speaker to the Rch error detector, and the silence volume input at which the target silence level at each of the Lch and Rch frequencies is input. A circuit, a comparator for comparing the level difference obtained by the level difference calculator with the target muffling level of the mute volume input circuit for each frequency, and the level difference calculator for all frequencies within the noise control band When the comparator detects that the level difference is larger than the target mute level of the mute volume input circuit, the noise control operation is started. Silencer according to claim 3, characterized in that they are composed of the operation determination circuit for controlling to. 5. Lch and Rch speakers and Lch and R
4. The silencer according to claim 3, wherein the ch error detector is installed on the headrest. 6. The silencer according to claim 5, wherein the headrest has a recess that necessarily fixes the head. 7. The muffler according to claim 5, wherein the headrest is provided on a chair. 8. The muffler according to claim 5, wherein the headrest is a pillow.