JPH1124670A - Active muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active muffler in which silencing control can be normally functional even when the environmental state changes so that is changes acoustic propagating characteristic in system identification. SOLUTION: This device is provided with a digital filter 9 for processing the detection signal from a first microphone 3 and generating a drive signal to a speaker 5, a control device 10 for setting the control parameter of the digital filter 9 on the basis of the detection signal from a second microphone 9, and an environmental state change detecting means 11 for detecting an environmental state change in a silencing control. The control parameter setting system to the digital filter 9 is reconstructed on the basis of the detection result of the environmental change state detecting means 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active silencer for performing silence control in which a sound wave for interference cancellation of a sound wave from a noise source detected by a first microphone at a position of a second microphone is generated from a speaker.

[0002]

2. Description of the Related Art Such active silencing measures are generally
A digital filter that processes a detection signal from the first microphone to generate a drive signal to the speaker;
A control device for setting a control parameter of a digital filter based on a detection signal from the second microphone, and radiating a sound wave having the same sound pressure and an opposite phase with respect to the sound wave detected by the first microphone from a speaker. Thus, a sound deadening effect is obtained at the position of the second microphone by sound wave interference. As a conventional active silencer, for example, known from Japanese Patent Publication No. Hei 8-23755, a transfer function indicating a sound wave propagation characteristic and an electroacoustic conversion characteristic in the first and second microphones and the speaker is derived in advance. Then, control parameters for giving a predetermined transfer function to the digital filter are set based on the signals of the first and second microphones obtained in a state where the digital filter is exposed to an actual noise source. At this time, based on the signal from the second microphone, the control device considers the change of the propagation characteristics due to disturbance in the sound wave propagation route from the speaker to the second microphone and the change of the characteristics of the electroacoustic transducer itself, and the like. And a transfer function to be applied to the digital filter so that the detection signal of the second microphone for checking the noise reduction effect based on these transfer functions is determined to be zero, and this transfer function is specified. Is set in the digital filter. The work of constructing control parameter setting processing for such a digital filter, that is, system identification is usually performed at the start of noise control, and is used fixedly in subsequent noise control,
If necessary, the system identification is performed again by the judgment of the operator monitoring the noise control.

[0003]

However, when such an active silencer is applied to engine exhaust noise or the like, sound propagation from the speaker to the second microphone is caused by a sudden change in temperature and a change in flow velocity caused by a load change. Characteristics may change. For this reason, if the silencing control is performed for a long time with the control parameters based on the transfer function determined first, control may not be possible when the above-described sound propagation characteristics change. In addition, there are cases where noise suppression control is not performed correctly due to sudden noise, calculation errors, or limitations of the calculation method. In such a situation, since the active silencer outputs the sound from the speaker itself, there is a serious inconvenience that the control works not in the direction of reducing the noise but in the direction of increasing the noise. SUMMARY OF THE INVENTION An object of the present invention is to mitigate the above-described inconveniences even if a change in the environment of the environment to be silenced, which causes a change in sound propagation characteristics at the time of system identification, occurs. The object of the present invention is to provide an active type silencer that makes the device function in a normal direction.

[0004]

To achieve the above object, a digital filter for processing a detection signal from a first microphone to generate a drive signal to a speaker, and
A control device having a control parameter setting processing system for setting a control parameter of a digital filter based on a detection signal from a microphone; A change detecting means is provided, and the control parameter setting processing system for the digital filter is reconstructed based on the detection result of the environmental condition change detecting means.

[0005] In this configuration, even if a situation change of the environment subject to the silencing control occurs, which may cause a change in the sound propagation characteristic at the time of system identification, the environment situation change detecting means can detect this environment situation change. A situation change is detected, and based on the detection result, a control parameter setting processing system for the digital filter is reconstructed using a transfer function suitable for the sound propagation characteristic at that time. As a result, even if the above-described change in the environmental situation occurs, a situation in which the noise reduction control operates in a direction to increase the noise is avoided. In addition, since the control parameter setting processing system is automatically reconfigured, there is no need for the operator to constantly monitor the trend of the silencing control.

The reconstructing operation of the control parameter setting processing system for the digital filter based on the detection of the change of the environmental condition, that is, the system identification, may be performed by temporarily suspending the silencing control. It can be carried out. When the system identification is performed by temporarily suspending the silencing control, only the test noise is output from the speaker. When the system identification is performed while the silencing control is continued, the test noise is added to the speaker drive signal for noise control, and only the test noise is extracted from the detection signal of the second microphone to perform the system identification. The experimental results show that a system identification with sufficient stability can be obtained even when approximately one-fourth of the test noise level used for system identification at the start of control is added to the speaker drive signal for noise control. It has been confirmed that it is possible.

Depending on the application of the active silencer, when a change in the environmental condition is detected, it is better to temporarily stop the silencer rather than reconstruct the control parameter setting processing system for the digital filter. There are cases. The active silencer according to the present invention, which is suitable for such use, is provided with environmental situation change detecting means for detecting environmental situation change in silencing control, and based on the detection result of the environmental situation change detecting means. The mute control is stopped.

In one preferred embodiment of the present invention, the environmental condition change detecting means detects that the level of a detection signal of the second microphone exceeds a preset threshold value for a predetermined time. Some are configured to detect as a change. From experiments and experiences, the level of the detection signal of the second microphone, which is regarded as an error in the silencing control, is within a predetermined value unless a change in environmental conditions that causes a change in sound propagation characteristics occurs in the operating silencing control. It can be determined that a significant change in environmental conditions has occurred if an error exceeding this predetermined value continues for a predetermined time. For this reason, the environmental condition change is detected using the predetermined value as a threshold value.

In another preferred embodiment according to the present invention, the environmental condition change detecting means is configured such that a ratio of a detection signal of the first microphone to a detection signal of the second microphone exceeds a predetermined threshold value for a predetermined time. Some are configured to detect the fact as a change in the environmental situation. The purpose of this configuration is the same as the above-described configuration, and when the ratio of the detection signal of the second microphone to the detection signal of the first microphone falls below a threshold value, for example, 1 for a predetermined time,
It is determined that the silencing control is not functioning properly, and that some significant environmental change has occurred.

In another preferred embodiment according to the present invention, the environmental condition change detecting means detects the execution of the silencing control for a predetermined time as an environmental condition change.
Depending on the application target of the active silencer, there may be a case where an environmental situation change that almost inevitably causes a change in the sound propagation characteristic occurs after a lapse of a predetermined time. Progress can be linked to changes in environmental conditions. That is, the environmental condition change detecting means may be configured as a timer.

In a preferred embodiment in which the noise reduction control is applied to engine noise, there is a configuration in which the environmental condition change detecting means detects a change in engine load as the environmental condition change. . This configuration takes into account the fact that the acoustic characteristics of the noise emitted from the engine change due to changes in the engine load, and each time the engine load exceeds the predetermined engine load range obtained from experiments and experiences. In order to prompt system identification, a signal is sent to the effect that a change in the environmental condition has been detected.

In a preferred embodiment in which the noise reduction control is applied to noise propagating in the duct, the environmental condition change detecting means detects a change in the temperature and humidity in the duct based on the change in the environmental condition. Some are configured to detect as. This configuration also takes into account the fact that the acoustic characteristics of noise propagating in the duct will change due to fluctuations in the temperature and humidity in the duct.The temperature and humidity in the duct can be obtained from experiments and experiences. Every time a predetermined range is exceeded, a signal indicating that a change in the environmental condition has been detected is issued in order to prompt system identification. As a preferred technique for reconstructing the control parameter setting processing system, the present invention proposes to reset a model of an acoustic transfer function from the speaker to the second microphone. The detailed contents regarding this will be clarified by the description using the principle diagram described later. Other features and advantages according to the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An active silencer according to the present invention 1
FIG. 1 is a functional block diagram showing a configuration according to one embodiment.
Is shown in A duct 2 connected to the engine 1 as a noise source is a noise propagation path, and the first microphone 3 is located on the engine 1 side of the duct 2, that is, on the upstream side in the noise propagation direction, and on the downstream side in the noise propagation direction. Is provided with a second microphone 4. The first microphone 3
This is for detecting the characteristics of sound waves transmitted as noise, and functions as an input device for silencing control by this active silencer. The second microphone 4 is for checking the effect of sound wave interference by the active silencer, and functions as an error detection device for silencing control by the active silencer. A concave portion is formed on a wall surface of the duct 2 between the first microphone 3 and the second microphone 4, and a speaker 5 as a sound source for sound wave interference is provided in the concave portion.

First microphone 3 and second microphone 4
And the speaker 5 are analog input / output devices of an active silencer configured as a digital signal processing device.
The microphone 3 and the second microphone 4 each have A
The / D converters 6 and 8 are connected to the speaker 5, and the speaker driver 7 is connected to the speaker 5.

The digital filter 9 processes a detection signal from the first microphone 3 so as to emit a sound having the same sound pressure in the opposite phase to the noise propagating through the duct 2 from the speaker 5 and a speaker driving signal. Generate The control device 10 sets control parameters for giving a predetermined transfer function to the digital filter 9 based on the detection signals from the first microphone 3 and the second microphone 4. This digital filter 9 is LM
The control device 1 is configured as an adaptive filter using an S algorithm (least-mean-squqre algorithm).
0 has the function of processing the LMS algorithm.

The principle of an active silencer using an adaptive filter will be described with reference to the block diagram of FIG. In FIG. 2, T is an acoustic transfer function from the first microphone 3 to the second microphone 4, W is adaptive filter processing, C is an acoustic transfer function from the speaker 5 to the second microphone 4, and C ＾.
Indicates a model of C, and LMS indicates an LMS algorithm. That is, the digital signal processing unit of the active silencer includes W, C と, and LMS.

When the reference signal x (t) detected by the first microphone 3 is input, a speaker output y (t) is generated. That is, the convolution of the N W values and x (t) becomes the output y (t), so that in the expression, y (t) = Sum [w (i) x (ti), i, 0, N-1]. Here, Sum [f, i, min, max] is a parameter: i
Add from i to min to max of a function (variable) f with
This is a mathematical notation indicating so-called Σ. When the active silencer outputs -y (t), an error: E is obtained by the second microphone 4, which is the evaluation point, based on the acoustic transfer function. E (z) = T (z) X (z) -C (z) Y (z) In order to maintain a causal relationship between the reference signal: x (t) and the error signal: e (t), x (t) is represented by C Filtered reference as an ideal value by filtering with ＾: d (t)
Ask for. d (t) = Sum [c ＾ (i) x (ti), i, 0, N−1] Here, C ＾ is determined by system identification, and is fixed and used until the system is identified again. Error signal: e (t) and filtered reference:
From d (t), as shown in the following equation, the filter coefficient w (i) is updated using the LMS algorithm. w [t + 1] (i) = w [t] (i) + Ke (t) d (t-1) where 0 <= i <= N-1.

As can be understood from the principle of the silencing control described above, if it is not necessary to reset C ＾, that is, unless the acoustic transfer function from the speaker 5 to the second microphone 4 changes, the system is identified first. Only this silencing control works properly. However, if it is determined that the sound transfer function from the speaker 5 to the second microphone 4 changes due to a change in the environmental conditions surrounding the silencing control, the system identification is performed again, and C ＾ is reset,
That is, the control parameter setting processing system for the digital filter 9 is reconstructed. That is, in this embodiment, the control parameter setting processing system for setting the control parameters of the digital filter based on the detection signal from the second microphone is composed of W, C ＾, and LMS, and the reconstruction is performed by C ＾. It is realized by resetting.

For this purpose, the control device 10 is provided with an environmental condition change detecting means 11, and the system identification is performed by using the environmental condition change detecting means 11 detecting the environmental condition change as a trigger. ＾ is reset. Such additional system identification can be performed as parallel processing while performing silencing control. In that case, a test noise of about one-fourth of the test noise level normally used for system identification is added to the speaker drive signal for noise control and sent to the speaker 5, and the control device 10 transmits the signal from the second microphone 4. Then, only the test noise component is extracted from the detected signal and used for system identification. Of course, the additional system identification may be performed in a state where the silencing control is temporarily stopped.

Various concrete configurations of the environmental condition change detecting means 11 are proposed. For example, when the level of the detection signal of the second microphone 4 exceeds a preset threshold value for a predetermined time. May be used to output a trigger signal for system identification, or when the ratio between the detection signal of the first microphone 3 and the detection signal of the second microphone 4 exceeds a preset threshold for a predetermined period of time. May be output. In any case, it is simple because it can be constituted by a threshold value setting circuit and a comparison circuit. A timer may be employed as the environmental condition change detecting means having a simpler configuration, and a trigger signal for system identification may be output when a predetermined period of the silencing control is performed.

Further, depending on the field to which the active silencer is applied, a unique configuration of the environmental situation change detecting means 11 is proposed. For example, when the noise reduction control is applied to engine noise, the acoustic characteristics of the noise emitted from the engine change due to the change in the engine load, so that the system identification trigger signal is output according to the change in the engine load. You may comprise. When applied to noise propagating in a duct, consider that the acoustic characteristics of noise propagating in the duct may change due to changes in the temperature and humidity in the duct. The system may be configured to output a trigger signal for system identification in response to a change in humidity.

In any case, it is desirable that the environmental condition change detecting means 11 be selected as appropriate depending on the case, and all or some of the environmental condition change detecting means described above as an active silencer. Eleven configurations may be provided so that they can be selectively used.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of an active silencer according to the present invention.

FIG. 2 is a block diagram showing the principle of silencing control in the active silencer according to the present invention.

[Explanation of symbols]

 Reference Signs List 3 1st microphone 4 2nd microphone 5 Speaker 9 Digital filter 10 Control device 11 Environmental state change detecting means

Claims (10)

[Claims] The present invention processes a detection signal from a first microphone in order to perform a noise reduction control for generating, from a speaker, a sound wave that interferes and cancels a propagation sound wave from a noise source detected by a first microphone at a position of a second microphone. And a control device having a control parameter setting processing system for setting a control parameter of the digital filter based on a detection signal from the second microphone. In the apparatus, it is provided that environmental condition change detecting means for detecting a environmental condition change in the silencing control is provided, and a control parameter setting processing system for the digital filter is reconstructed based on a detection result of the environmental condition change detecting means. Active silencer. 2. The active silencer according to claim 1, wherein the silence control is interrupted when the control parameter setting processing system is reconfigured. 3. The active silencer according to claim 1, wherein reconstruction of the control parameter setting processing system is performed simultaneously with the silencing control. 4. A process for processing a detection signal from the first microphone in order to perform a noise reduction control in which a sound wave for interference cancellation of a propagation sound wave from a noise source detected by the first microphone at a position of the second microphone is generated from a speaker. And a control device having a control parameter setting processing system for setting a control parameter of the digital filter based on a detection signal from the second microphone. An active silencer, comprising: an environment situation change detecting means for detecting an environmental situation change in the silencing control; and stopping the silencing control based on a detection result of the environmental situation change detecting means. 5. The method according to claim 5, wherein the environmental condition change detecting means is configured to detect the second condition.
4. The system according to claim 1, wherein the detection of a change in the environmental condition is performed when a level of a detection signal of a microphone exceeds a preset threshold value for a predetermined time.
The active silencer according to any one of claims 4 to 10. 6. The method according to claim 1, wherein the environmental condition change detecting means includes:
2. The apparatus according to claim 1, wherein a change in the environmental condition is detected when a ratio between a detection signal of the microphone and a detection signal of the second microphone exceeds a preset threshold value for a predetermined time. The active silencer according to any one of claims 1 to 4. 7. The active silencer according to claim 1, wherein the environmental situation change detection means detects the execution of the silencing control for a predetermined time as the environmental situation change. apparatus. 8. The system according to claim 1, wherein said muffling control is applied to engine noise, and said environmental condition change detecting means is configured to detect a change in engine load as said environmental condition change. The active silencer according to any one of claims 1 to 4. 9. The noise reduction control is applied to noise propagating in a duct, and the environmental condition change detecting means is configured to detect a change in temperature and humidity in the duct as the change in the environmental condition. The active silencer according to any one of claims 1 to 4, wherein: 10. The method according to claim 1, wherein a model of an acoustic transfer function from the speaker to the second microphone is reset when the control parameter setting processing system is reconfigured. An active silencer as described.