JPH04314100A - Active muffling device - Google Patents

Abstract

PURPOSE:To obtain an active muffling device capable of properly executing processing relating to noise elimination even at the time of detecting noise from the external. CONSTITUTION:The active muffling device is provided with a sensor 25 capable of detecting noise from a sound source 15, a filter 27 whose transmission coefficient G can be changeably set up, a speaker 33 for generating a control sound for eliminating noise generated from the sound source 25, error signal output means 39, 45 for outputting error signals relating to the deviation G of the transmission coefficient G, and a control means for changing the coefficient G when an error signal is converged to a fixed level or above or stopping the change of the coefficient G when the error signal is not converted to the fixed level or above.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise reduction device that employs an active control method to muffle noise.

0003

[Prior Art] In recent years, various active noise muffling devices have been developed that emit a control sound with the same amplitude and opposite phase to the noise from the sound source, and muffle the noise by causing the two sounds to interfere. There is.

FIG. 4 is a system configuration diagram of a conventional active type muffler.

Duct 1 having an opening with one end open
There is a noise source 103 such as a compressor inside 01. A silencing system section 105 is arranged closer to the opening than the noise source 103. The microphone 107 placed at the position Ps detects noise from the noise source 103 and sends the detection signal to the control unit 109.
Send to. The control unit 109 has a filter, and uses this filter to generate a control signal for obtaining a signal having an opposite phase and the same amplitude with respect to the detection signal, and transmits the control signal to the speaker 11.
Send to 1. The speaker 111 placed at position Pa generates a control sound in response to the control signal. The control sound generated from the speaker 111 and the noise from the noise source 103 interfere with each other at the position Po and are muted. The microphone 113 placed at the position Po detects the residual sound after the sound is muted.

By the way, in order to generate a control signal in the control section 109, the acoustic characteristics of the duct 101, the characteristics of the microphones 107, 113, and the speaker 111 are measured in advance, and the above-mentioned filter is adjusted in consideration of these measurement results. It is necessary to set the coefficient.

For this purpose, first, random noise is generated from the speaker 111, and the transfer coefficient Gao between the positions Pa and Po is measured. Next, while generating random noise from the speaker 111, position Ps and position P
Measure the transfer coefficient Gso between the Let Gsa be the transmission coefficient until the control sound is generated at position Pa after signal processing is applied to the detection signal detected at position Ps.
Gso=Gsa・Gao
...(1)
The relationship of equation (1) above holds true. Therefore, the control unit 109
The transmission coefficient G in is expressed by the following equation (2).

G=-Gsa=-Gso/Gao
...(2)
Here, in order to always maintain a high silencing effect, processing related to silencing is automatically controlled in consideration of changes in the microphones 107, 113 and speakers 111 over time, and changes in sound transmission characteristics due to changes in temperature. That was what was hoped for.

[0009] Therefore, an adaptive active control device is disclosed in Japanese Patent Laid-Open Publication No. 61-296392. According to this device, a microphone is provided at the silencing position and the residual sound after silencing is constantly monitored, and a high silencing effect can be maintained by applying feedback to the control unit so that this monitor signal is minimized.

FIG. 5 is a block diagram of a control section used in a conventional adaptive active control device. Note that the configurations of the duct, silencing system section, etc. other than this control section are the same as those shown in FIG. 4.

As described above, the transmission coefficient Gao from the speaker arrangement point to the silencing point is measured in advance, and the transmission coefficient Gao is set by the coefficient setting section 115. here,
Assuming that the sound signal from the sound source is Sx and the sound signal at the opening of the duct is Sy, the relationship between these sound signals Sx and Sy is shown as follows.

[0012] Sy=Gso・Sx

(3) In order to muffle the sound signal Sy at the opening of the duct, a sound signal -Sy having the opposite phase and the same amplitude as the sound signal Sy may be superimposed at the opening of the duct. Therefore, if the control sound output from the speaker is Sa, then
The sound signal -Sy is shown as follows.

-Sy=Gao・Sa

(4) Furthermore, if the characteristic of the noise reduction filter 117 shown in FIG. 5, that is, the transmission coefficient, is G, then the control sound Sa is expressed as follows.

[0014] Sa=G・Sx=−Gso/Gao・Sx
...(5) Substituting equation (5) into equation (4), Sy=(-G)・Gao・Sx
...(6
) Therefore, as is clear from equation (6), from Gao·Sx obtained by filtering the sound signal Sx from the sound source using the transfer coefficient Gao of the coefficient setting unit 115 and the sound signal Sy at the duct opening, The transfer coefficient -G can be identified and obtained using an adaptive filter (not shown), and the characteristics of the noise reduction filter 117 can be obtained by inverting the sign of the transfer coefficient -G. When the processing described above is performed using a digital filter, the characteristics of the silencing filter are obtained as filter coefficients, and the sign inversion of the coefficients can be obtained by subtracting each tap coefficient value from zero.

[0015] Furthermore, due to the shift of the transfer coefficient Gso to Gsoa, the optimum value Gnew of the characteristics of the silencing filter
If G deviates from the current value Gold by ΔG, that is, Gnew=Gold−ΔG
……
In the case of (7), the sound signal Sya of the residual sound at the opening of the duct after muffling is shown as follows.

[0016] Sya=Sx・G・Gao+Sx・Gsoa
...(8) Therefore, the relationship at the time of optimum noise reduction is shown as follows.

[0017] Sx・(G−ΔG)・Gao+Sx・Gsoa
=0...(9) Above (8), (9
) When Gsoa is eliminated from the equation, it is shown as follows.

[0018] Sya=Sx・G・Gao−Sx(G−ΔG)
・Gao = (Sx・Gao)ΔG

... (10) Therefore, similarly to the above equation (6), Gao Sx obtained by filtering the sound signal Sx from the sound source using the transfer coefficient Gao of the coefficient setting unit 115 and the residual sound after muffling at the duct opening. ΔG, which is a deviation component of the transfer coefficient G, can be identified and determined from the sound signal Sya using an adaptive filter (not shown). This deviation component ΔG is sent from the filter 119 to the silencing filter 117, and from the above equation (7), the optimum value G of the characteristics of the silencing filter 117 is
You can find new.

Comparing equation (6) with equations (7) and (10), the characteristic G of the silencing filter 117 initially determined is equation (7), and Gnew=0.

It can be seen that this corresponds to the case (11). The initial value of the characteristics of the noise filter 117 is set to 0, and (10)
By repeating the adaptation process expressed by equation (7) and the coefficient update process expressed by equation (7), it is possible to shift the process related to muffling to an optimal state.

The calculation formula for the actual coefficient updating process is calculated by multiplying ΔG in equation (7) by the feedback gain parameter μ.
The convergence speed and stability are improved by using the following equation (12).

Gnew=Gold-μ・ΔG
...(12)
That is, when the feedback gain parameter μ is a value smaller than 1, the rate at which feedback is applied is small, and the system is not affected by disturbance. Conversely, when the feedback gain parameter μ is a value larger than 1, the rate at which feedback is applied increases, accelerating the update of the coefficients. Therefore, the feedback gain parameter μ
The convergence speed and stability can be adjusted according to the value of .

[0022]

[Problem to be Solved by the Invention] However, when a microphone for detecting residual sound after muting detects not only the residual sound after muting, but also a higher level external sound, that is, external noise. The sound signal of the residual sound at the duct opening is canceled by the external noise,
Since an accurate value of the deviation ΔG cannot be obtained, there is a problem in that the characteristics of the silencing filter deviate from the optimum state.

The present invention has been made in view of the above-mentioned problems, and it is possible to appropriately perform processing related to sound muffling even when a microphone for detecting residual sound after sound muffling detects sound from the outside. The purpose of this invention is to provide an active silencing device that can.

[Configuration of the invention]

[0025]

[Means for Solving the Problems] To achieve the above object, the present invention provides a sound detection means for detecting sound propagated in or near a sound propagation path from a sound source; a coefficient setting means for setting a coefficient for generating a signal having an opposite phase and the same amplitude as the detection signal related to the sound detected by the sound detection means; control sound generating means for generating a control sound for muffling the sound from the control sound; error signal output means for evaluating the silencing effect of the control sound generating means and outputting an error signal based on the evaluation; and this error signal output. When changing the coefficients of the coefficient setting means sequentially based on the error signal of the means, when the error signal is in the convergence direction, the coefficient set by the coefficient setting means continues to be changed, and when the error signal is not in the convergence direction, the coefficients set by the coefficient setting means are changed continuously. The gist of the present invention is to have a control means for stopping the continuation of the coefficient change.

[0026]

[Operation] When the sound detection means detects a sound source and a sound from outside the sound source, a coefficient is set to generate a signal having an opposite phase and the same amplitude as the detection signal from the sound detection means. It is set by the coefficient setting means. The control sound generating means generates a control sound for muffling the sound from the sound source according to the set coefficient, and muffles the sound by superimposing this control sound with the sound in or near the propagation path. . Further, it has an error signal output means for evaluating the silencing effect of the control sound generation means and outputting an error signal based on the evaluation, and the error signal from the error signal output means is
When the sound is gradually muted and in the convergence direction, the values of the coefficients set by the coefficient setting means are sequentially changed. Conversely, when the error signal is not in the convergence direction due to input of sound from outside the sound source, etc., the continuation of the coefficient change is stopped.

[0027]Therefore, even when external sound is detected, processing related to muting can be performed appropriately.

[0028]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a case where the active silencing device according to the present invention is applied to the refrigerator 1. First, to explain the structure, the refrigerator 1 is composed of a freezer compartment 3, a refrigerator compartment 5, and a vegetable compartment 7. An evaporator 9 and a fan 11 are arranged in the freezer compartment 3. Further, a machine room 13 is formed at the rear of the lower part of the vegetable compartment 7, and a compressor 15, which is a noise source, and an evaporating dish 17 are arranged. This evaporating dish 17 is for evaporating water generated when defrosting the frost adhering to the evaporator 9. Further, a machine compartment cover 19 is provided on the back side of the refrigerator 1.

Next, an active silencing device according to the present invention and its peripheral parts will be explained with reference to FIG.

An opening 23 is formed in the machine room cover 19, and the machine room 13 is formed in a structure similar to a so-called one-dimensional duct. Therefore, noise from compressor 15 can only propagate to the outside through opening 23. A vibration pickup sensor (hereinafter simply referred to as a sensor) 25 is fixed to the compressor 15 and detects vibrations of the compressor 15. The vibration detected by this sensor 25 has a high correlation with the noise generated by the compressor 15, so the sensor 25
5 is used as a sound detection means for detecting sound from a sound source. The sensor 25 includes a noise reduction filter 27 and a filter 29.
The detection signal of the sensor 25 is connected to the filters 27 and 2.
It is sent to 9. The filter 27 is a coefficient setting means in which coefficients for generating a signal having an opposite phase and the same amplitude as the signal detected by the sensor 25, which is a sound detection means, are set to be changeable. The filter 27 is connected to a fixed contact 31a of the switch 31, and a movable contact 31c of the switch 31.
is connected to a speaker 33 for silencing. speaker 3
Reference numeral 3 denotes a control sound generating means for generating a control sound for muffling the sound from the sound source according to the coefficient set by the filter 27, which is the coefficient setting means. In addition, an evaluation microphone (hereinafter simply referred to as a microphone) 35 is provided in the machine room section 13.
is arranged to detect the residual sound after the sound is muted. microphone 35
includes an A-FIR filter (hereinafter simply referred to as filter) 37, a subtracter 39, and an evaluation microphone level evaluation section (hereinafter referred to as
It is connected to a level evaluation section (simply referred to as a level evaluation section) 41. The subtracter 39 is connected to an adaptive filter error level evaluation section (hereinafter simply referred to as a level evaluation section) 43, and
A-FIR filter (hereinafter simply referred to as filter)
It is connected to 45. The subtracter 39 and the filter 45 form an error signal output means that outputs an error signal, and outputs an error signal of the deviation ΔG of the transfer coefficient G from the optimum value to the level evaluation section 43, and also outputs this error signal to the filter. 45
Give feedback to. The level evaluation unit 43 determines whether the input error signal has converged to a certain level or higher. Furthermore, the level evaluation sections 41 and 43 are connected to a coefficient calculation device 47. The level evaluation section 43 and the coefficient calculation device 47 constitute a control means, and when it is determined that the error signal from the error signal output means has converged to a certain level or higher, the deviation ΔG input from the filter 45
The value of is output to the filter 27. As a result, the value of the transfer coefficient G set by the filter 27 is changed. Conversely, if it is determined that the error signal has not converged to a certain level or higher, the change in the value of the transfer coefficient G set by the filter 27 is stopped. Further, the white noise generator 49 is connected to the fixed contact 31b of the switch 31, and is also connected to the subtracter 51. This subtractor 51
The output signal from the filter 37 is fed back to the filter 37.

Next, the operation will be explained with reference to FIGS. 1 to 3.

First, it is necessary to obtain the transfer characteristic Gao from the speaker 33 to the microphone 35 in advance. With the operation of the compressor 15, which is the noise source, stopped, the movable contact 31c of the switch 31 is switched to the fixed contact 31b side to output white noise from the white noise generator 49 to the speaker 33 and the subtracter 51. When the microphone 35 detects the sound generated from the speaker 33 at this time, a detection signal is sent to the filter 37. The filter 37 identifies the transfer characteristic Gao from the speaker 33 to the microphone 35 based on the detection signal from the microphone 35 and the white noise from the white noise generator 49. This identified transfer characteristic Gao is set to the filter 29.

Next, the operation related to silencing will be explained. At the start of the silencing operation, the movable contact 31c of the switch 31 is switched to the fixed contact 31a side. Furthermore, at the start of the silencing operation, the transmission coefficient G set by the filter 27 is
The initial value of G is set to 0, and the value of the transfer coefficient G is updated every time the operation related to silencing is repeated. When the compressor 15, which is a noise source, is operating, it generates vibrations in response to noise generation, and the sensor 25 detects these vibrations. A detection signal from sensor 25 is sent to filters 27 and 29. When the filter 27 receives the detection signal from the sensor 25, it processes the signal so that it has the opposite phase and the same amplitude as the input detection signal, and outputs it to the speaker 33 via the switch 31. The speaker 33 generates control sound in response to the signal from the filter 27. As a result,
The control sound generated from the speaker 33 and the compressor 15
The noise from the opening 23 interferes and is muffled, and the sound becomes small in the vicinity of the opening 23. At this time, water vapor and heat from the evaporating dish 17 can be freely released to the outside of the refrigerator through the opening 23. Similarly, the transmission coefficient G is set by the filter 27 so that the sound near the opening 23 is minimized.
is sequentially updated to the optimal value.

Next, the operation related to updating the transfer coefficient G set by the filter 27 will be explained. The microphone 35 detects the residual sound after the sound is muted, and outputs a detection signal to the subtracter 39 and the level evaluation section 41. Further, a detection signal from the sensor 25 is sent to a filter 29. When the filter 29 receives the detection signal from the sensor 25, it processes the input detection signal using the transfer characteristic Gao and sends it to the filter 4.
Output to 5. When the filter 45 receives the signal from the filter 29, it identifies and determines ΔG, which is a deviation component of the transfer coefficient G. That is, when the detection signal from the microphone 35 is input to the subtracter 39, the error signal from the subtracter 39 is fed back to the filter 45. Based on this error signal and the signal from the filter 29, the filter 45 determines ΔG, which is a deviation component of the transfer coefficient G from the optimum value. Further, when the level evaluation section 43 receives the error signal a from the subtracter 39, it determines the amount of convergence of the error signal a every predetermined time T, for example, every 1 to 5 seconds, as shown in FIG. For example, at time t3, the difference from the level Ha at time t1 to the level Hb at time t3 is calculated as the convergence amount Hx. Further, when the level evaluation unit 43 determines that the convergence amount Hx is greater than or equal to a predetermined value, it outputs a signal indicating that the convergence amount Hx is greater than or equal to the predetermined value to the coefficient calculation device 47. When the coefficient calculation device 47 receives a signal indicating that the convergence amount Hx is greater than or equal to a predetermined value, it outputs the value of the deviation ΔG input from the filter 45 to the filter 27. As a result, the transfer coefficient G set by the filter 27
The value of is changed by ΔG. When the value of the transmission coefficient G is updated in this way, the silencing amount b increases as shown in FIG. 3, and the sound near the opening 23 becomes smaller.

Next, an explanation will be given of the effect when sound from the outside enters the refrigerator 1.

When the microphone 35 detects external sound, the error signal a increases as shown at time t5 in FIG. Therefore, when it is determined at time t7 in FIG. 3 that the convergence amount Hx is less than or equal to the predetermined value, updating of the transfer coefficient G in the filter 27 is stopped. As a result, even if sound intrudes from the outside, it is possible to prevent the sound from increasing in the vicinity of the opening 23.

As described above, when the amount of convergence of error signal a is greater than a predetermined value, the value of the transfer coefficient G is updated, and conversely, when the amount of convergence of error signal a is less than the predetermined value, the value of the transfer coefficient G is updated. By stopping the update of the value of G and setting the value of the transmission coefficient G to an optimal value, the operation related to noise reduction can be appropriately controlled so that the sound in the vicinity of the opening 23 is reduced.

[0039]If it is determined that the amount of silencing has decreased after updating the value of the transfer coefficient G, the value of the transfer coefficient G is returned to the value before the update, so that the control related to silencing can be further improved. It can be done stably. At this time, when determining the decrease in the muted volume, the level of the detection signal from the microphone 35 is calculated as an average value over a predetermined time, and it is determined whether this average value is lower than the previous value by a predetermined level or more. This is done by making a judgment. Alternatively, by updating the value of the transfer coefficient G multiple times and then determining whether the amount of silencing has decreased, the influence of external noise can be reduced and the control related to silencing can be stabilized. You can do it by doing this.

Further, in the above embodiment, the case where the present invention is applied to a refrigerator has been described, but the present invention is not limited to this and can be applied to any appropriate device.

[0041]

As explained above, according to the present invention, when the error signal is in the convergence direction, the coefficients set by the coefficient setting means continue to be changed, and conversely, when the error signal is not in the convergence direction, Since the configuration is configured such that the continuation of the coefficient change is sometimes stopped, even when a sound that interferes with the muffling control is input from the outside, the process related to muffling can be appropriately performed.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment according to the present invention.

FIG. 2 is a longitudinal sectional view of a refrigerator to which the embodiment shown in FIG. 1 is applied.

FIG. 3 is an explanatory diagram showing an error signal a and a muting amount b.

FIG. 4 is a configuration diagram of a conventional example.

FIG. 5 is a configuration diagram of a control section of another conventional example.

[Explanation of symbols]

15 Compressor 25 Vibration pickup sensor 27 Filter 33 Speaker 35 Evaluation microphone 39 Subtractor 43 Adaptive filter error level evaluation unit 45 Filter 47 Coefficient calculation device

Claims (1)

[Claims] Claim 1: A sound detection means for detecting sound propagated through the sound propagation path within or in the vicinity of the sound propagation path from the sound source, and a detection signal related to the sound detected by the sound detection means and an inverse detection signal. a coefficient setting means for setting a coefficient for generating a signal with the same phase and the same amplitude; and a control sound for generating a control sound for muffling the sound from the sound source according to the coefficient set by the coefficient setting means. generating means; error signal output means for evaluating the silencing effect of the control sound generating means and outputting an error signal based on the evaluation; and sequentially changing the coefficients of the coefficient setting means based on the error signal of the error signal output means. When the error signal is in the convergence direction, the coefficient set by the coefficient setting means continues to be changed;
An active muffling device comprising: control means for stopping the continuation of the coefficient change when the error signal is not in the convergence direction.