JPH0823755B2 - Electronic silencing system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic silencing system, and in particular, it is capable of silencing unsteady noise generated in a propagation passage such as a pipeline by performing adaptive control by a computer system incorporating a digital filter. And the electronic muffling system.

[0002]

2. Description of the Related Art Passive silencers, which muffle noise in a pipe by utilizing phenomena such as interference due to the pipe structure and sound absorption by a porous material attached to the pipe, are widely used in practice. There are many demands for improvement in terms of size, pressure loss and the like. On the other hand, an active silencer that has been proposed for a long time as another method to muffle the noise in the pipe,
That is, the noise propagated from the sound source is detected by the first sensor microphone, the additional sound having the same sound pressure and opposite phase is radiated from the speaker to the detected propagated sound wave, and the sound wave interference occurs at the position of the second sensor microphone. The electronic muffling system that forcibly produces the muffling effect has been attracting attention.
With the rapid development of electronic devices and signal processing technology, research results from various viewpoints have been announced one after another.

[0003]

However, in the conventional electronic silencing system, since the sound wave emitted from the speaker is also detected by the first sensor microphone, an acoustic feedback system is provided between the speaker and the first sensor microphone. Etc. are formed, and good muffling control cannot be performed.

The present invention has been made in view of the above circumstances, and it is possible to suppress the acoustic feedback system and the like formed between the speaker and the first sensor microphone and perform good muffling control. The purpose is to provide an electronic silencing system.

[0005]

In order to achieve the above-mentioned object, the present invention detects a propagating sound wave from a noise source in a sound wave propagation path by a first sensor microphone, and detects the detected propagating sound wave. In the electronic silencing system, a sound wave having a phase opposite to that of the sound wave of the same sound pressure is generated from the speaker, and the sound is muted by the sound wave interference at the position of the second sensor microphone provided at a predetermined position in the propagation path. The first sensor microphone, the speaker, and the second sensor microphone are installed such that the distance between the first sensor microphone and the first sensor microphone is longer than the distance between the speaker and the second sensor microphone. The sound absorbing member is attached in the propagation path between the sensor microphone and the speaker.

[0006]

According to the present invention, the sound wave from the speaker is absorbed by the sound absorbing member provided at a predetermined position of the propagation path, preferably between the speaker and the first sensor microphone. Is not detected by. As a result, an acoustic feedback system or the like formed between the speaker and the first sensor microphone can be suppressed, and good muffling control can be performed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an electronic silencing system according to the present invention will be described below with reference to the accompanying drawings. Prior to the description of specific embodiments, the principle of the electronic silencing system according to the present invention will be described with reference to FIGS. 1 to 3. Fig. 1 shows a monopole sound source system (MONOP) with a single additional sound source.
OLE SYSTEM) and principle of the electronic silencer system is shown in, the sensor microphone M ₁ is in the propagation path 10 of the acoustic waves at the same figure, the sensor microphone M ₁
Microphones M ₂ for evaluating the muffling effect are respectively installed downstream of the installation positions of. Further, an additional sound source S is provided between the microphones M ₁ and M ₂ .
A controller 12 is provided between the sensor microphone M ₁ and the additional sound source S.

In the above structure, the sound wave propagated from the noise source is first detected by the microphone M ₁ , converted into an electric signal and input to the controller 12. An evaluation signal 20 for evaluating the muffling effect from the microphone 12 is input to the controller 12. At the installation position of the microphone M _2, the controller 12 adds a drive signal such that the output of the microphone M ₂ becomes zero due to the interference between the sound deadening sound wave emitted from the additional sound source S and the propagation sound wave emitted from the noise source. Output to the sound source S.

With this structure, the sound wave emitted from the noise source can be erased at the installation position of the microphone M ₂ . In order to enhance the sound deadening effect in the electronic sound deadening system having such a structure, transfer functions Gd, G'd, Gt other than the transfer functions Gd, G'd, Gt showing the sound propagation characteristics between the electroacoustic transducers shown in FIG. Microphones M ₁ , M ₂ ,
It is necessary to consider a model that also considers the conversion characteristics of each electroacoustic transducer itself such as the additional sound source S. It is also necessary that each element in the model considered in this way be clearly defined.

From this point of view, as a result of detailed examination of the flow of the electric signal and the propagation of the sound wave in FIG. 1, the output of the microphone M ₁ , the input of the additional sound source S and the output of the microphone M ₂ are obtained. It was clarified that a model which is a basis for designing the control system of the electronic silencing system can be constructed by providing the terminals with electrically measurable evaluation points V _A , V _B and V _C. The specific model will be described with reference to FIG.

In the figure, thick arrows indicate the propagation direction of sound waves, and solid arrows indicate the flow of electrical signals. Further, P ₁ and P ₂ are sound pressures V _{A at} the installation positions of the microphones M ₁ and M ₂ of a sound wave propagating from a noise source propagating downstream in the propagation path 10.
As described above, V _B and V _C are voltages at the measurement points provided in the microphone M ₁ , the speaker S as the additional sound source, and the microphone M ₂ , respectively. Further, H _M1 is a transfer function showing a sound pressure-voltage conversion characteristic with respect to a sound wave propagating in the downstream direction of the microphone M ₁ , and H _M2 is a sound pressure with respect to a sound wave propagating in the downstream direction in the propagation path 10 of the microphone M _2. A transfer function indicating a voltage conversion characteristic, H _M1 ′, is a microphone M ₁ for a sound wave propagating from the direction of the additional sound source S.
Is a transfer function indicating the sound pressure-voltage conversion characteristic, H _M2 ′ is a transfer function indicating the sound pressure-voltage conversion characteristic for the sound wave propagating from the direction of the additional sound source S of the microphone M ₂ , and H _S is the microphone M of the additional sound source S. _The transfer function indicating the voltage-sound pressure conversion characteristic in the direction of ₂ , H _S ′ is the microphone M _{1 of the} additional sound source S
It is a transfer function showing a voltage-sound pressure conversion characteristic in a direction. The H _e is the transfer function showing the control characteristics of the controller 12.

In the model shown in FIG. 2, the transfer function indicating the propagation characteristic of the sound wave transmitted from the additional sound source S to the microphone M ₁ by considering the conversion characteristics of the additional sound source S and the microphone M ₁ is Hr, and the additional sound source S is also shown. To microphone M
Letting Ht be a transfer function indicating a propagation characteristic in which the conversion characteristics of the additional sound source S and the microphone M ₂ are added to the sound wave propagating in the direction of ₂ , the transfer function is expressed by the following equation. Hr = H _M1 ′ · G′d · Hs ′ (1) Ht = H _S · Gt · H _M2 ′ (2) As described above, the model shown in FIG.
The model is further simplified as shown in FIG.

Next, based on FIG. 3, a transfer function H _e showing the control characteristic of the controller 12 for generating a sound wave for canceling the sound wave propagated from the noise source radiated from the additional sound source S is derived. Here in the installation position of the microphone M ₂ sound pressure P _2, in the voltage V _A at each measurement point, V _B, V _C, respectively represented by the following formula.

P ₂ = P ₁ · Gd ··· (3) V _A = P ₁ · H _{M 1} + V _B · H _r ··· (4) V _B = _VA · He ··· (5) V _C = P _{2 · H M2 + V B · Ht} ...... (6) the (4), V _A from (5) can be expressed by the following equation.

[0015]

[0016] As can be seen from equation (10), to determine the transfer function He It is important to note that the measurement points are V _A , V _B , V
It became clear that it could be identified as _C.

As described above, based on the analysis result based on the model showing the basic principle of the electronic silencing system of the present embodiment, the transfer function He showing the control characteristic of the controller 12 is the additional sound source S and the sensor microphone M ₁ 1-He · Hr = which is a characteristic equation of an acoustic feedback system including
Stable when all roots of 0 are within the unit circle. The stability determination of this feedback system is based on Shur-Coh
It can be easily confirmed by the determination method of n.

Next, FIG. 4 shows a specific configuration of the electronic silencing system according to the present invention constructed based on the above model. In the figure, a microphone M ₁ for extracting information of a propagating sound wave is provided on the noise source side of the propagation path 10 such as a duct, and a sound deadening effect by sound wave interference is provided on the downstream side of the microphone M _{1 in} the propagation path 10. Microphone M for evaluation
₂ , and a speaker S as an additional sound source is installed on the tube wall between the microphone M ₁ and the microphone M _{2 in the} propagation path 10. Here, the microphone M ₁ is unidirectional and the microphone M ₂ is omnidirectional. This is to suppress acoustic feedback from the speaker S to the microphone M ₁ . In order to suppress this acoustic feedback, the electroacoustic transducers M ₁ , M ₂ and S are installed so that the distance between the speaker S and the microphone M ₁ is longer than the distance between the speaker S and the microphone M ₂ . It

A sound absorbing material 14 such as glass wool is provided between the speaker S and the microphone M _{1 in the} propagation path 10.
Is pasted inside. The sound absorbing material 14 absorbs a sound wave propagating to the microphone M ₁ side among the sound waves emitted from the speaker S. An input / output interface 22 is composed of A / D converters 24 and 28 and a D / A converter 26. Further, 30 is a digital filter, and the digital filter 30 is based on the transfer function given by the control unit 50, and the input / output interface 22
The electric signal indicating the sound wave propagating from the noise source from the microphone M ₁ taken in through the A / D conversion unit 24 in FIG. 2 is taken in, and predetermined amplitude characteristics and phase characteristics based on the transfer function from the electric signal. A drive signal for driving the speaker S having

The control unit 50, in a state where no sound wave is generated from the noise source in the propagation path 10, preliminarily detects the propagation sound wave between the electroacoustic transducers of the microphone M ₁ , the speaker S, and the microphone M ₂ . When a test signal for deriving a transfer function indicating a transfer characteristic or a transfer characteristic of each electroacoustic transducer itself is output to each part of the circuit, or a sound wave from a noise source is actually propagating in the propagation path 10. Input / output interface 22 from the microphones M ₁ and M ₂
Via the input signal, and the control parameter for giving a predetermined transfer function to the digital filter 30 is set in the digital filter 30 based on these input signals. Further, the control unit 50 performs adaptive control so as to correct the control parameters according to changes in the propagation characteristics due to disturbances such as fluctuations in the air flow in the propagation passage 10 and changes in the characteristics of the control system.

In the above-mentioned structure, first, the control parameter is set in the digital filter 30 by the control unit 50 to give a transfer function corresponding to the transfer function He shown in FIG. It When propagating waves emitted from the noise source at the propagation passage 10 at this state is detected by the microphone M _1, the output signal from the microphone M ₁ O interface 22
Is input to the digital filter 30 and the control unit 50 via the A / D conversion unit 24 in FIG.

The propagation wave from the other noise source is detected by the microphone M _2, the detection output of the microphone M ₂ is taken into the control unit 50 via the in A / D converter 28 to the input-output interface 22. The control unit 50 obtains transfer functions showing these characteristics in consideration of changes in the propagation characteristics due to disturbances in the propagation path 10 and changes in the characteristics of each electroacoustic transducer itself, and the muffling is performed based on these transfer functions. Microphone M ₂ for detecting the effect, that is, the state of interference between the sound wave propagated from the noise source and the sound wave emitted from the speaker S
The transfer function to be applied to the digital filter 30 is determined so that the output signal of 1 becomes zero, and the control parameter for specifying the transfer function is set in the digital filter 30. As described above, the control unit 50 modifies the control parameters as needed according to the change in the propagation characteristic of the propagation path 10 and the change in the characteristic of the control system. As a result, the microphone M
_The sound wave propagating from the noise source detected by ₁ is converted into an electric signal, and the A / D in the input / output interface 22 is converted.
The signal is input to the digital filter 30 via the converter 24, and the input signal is converted by the digital filter 30 into a digital signal having predetermined amplitude characteristics and phase characteristics based on the transfer function given by the controller 50.
The digital signal is D / A converted by the D / A converter 26 in the input / output interface 22, and the speaker S
Is applied to the drive coil of the speaker S as a drive signal of
From the speaker S, a sound wave for canceling the propagating sound wave emitted from the noise source is emitted to the microphone M ₂ .

The propagation waves from the results propagating sound wave from the noise source by interference of sound waves at the installation position of the microphone M ₂ is deleted, the noise source on the downstream side of the installation position of at microphone M ₂ in the propagation path Is never propagated. Further, the sound wave for silencing emitted from the speaker S is slightly detected by the microphone M ₁ , and the speaker S
Although it is undeniable that an acoustic feedback system is formed between the microphone M ₁ and the microphone M ₁ , the microphone M ₁ having the unidirectional characteristic is used as described above, the speaker S and the microphone M 1. _The respective electroacoustic transducers are installed so that the distance to ₁ is longer than the distance between the speaker S and the microphone M ₂ , and the sound absorbing material 14 such as glass wool having a sound absorbing effect particularly in a high range is provided. Propagation path 10 between the speaker S and the microphone M _1.
The acoustic feedback system formed between the speaker S and the microphone M ₁ is significantly suppressed because the acoustic feedback system is arranged on the inner wall surface of the.

As a result, the electronic silencing system of this embodiment can perform good silencing control. Although only one electronic muffling system is shown in the above embodiment, the propagation passage 1
When 0 is a large-diameter pipe or when the propagation path 10 is required to have a super-high-performance silencing effect, it is possible to deal with them by connecting an electronic silencing system in parallel or in series.

Further, although glass wool is used as the sound absorbing material 14 in this embodiment, the sound absorbing material 14 is not limited to this.

[0026]

As described above, according to the electronic sound deadening system of the present invention, the sound wave from the speaker is absorbed by the sound absorbing member provided at the predetermined position of the propagation path and is not detected by the first sensor microphone. Therefore, the acoustic feedback system and the like formed between the speaker and the first sensor microphone can be suppressed. As a result, good muffling control can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a basic model of an electronic silencing system according to the present invention.

FIG. 2 is an explanatory diagram showing a model in consideration of the propagation characteristics of the propagation path of the electronic silencing system according to the present invention and the conversion characteristics of each electroacoustic transducer itself.

FIG. 3 is an explanatory diagram showing a model obtained by simplifying the model shown in FIG.

FIG. 4 is a block diagram showing a specific configuration of an electronic silencing system according to the present invention.

[Explanation of symbols]

10 ... Propagation path, 12 ... Controller, 14 ... Sound absorbing material, 24, 28 ... A / D conversion part, 26 ... D / A conversion part, 22 ... Input / output interface, 30 ... Digital filter, 50 ... Control part, M ₁ , M ₂ ... microphone, S ... speaker.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tanetoshi Miura 1-11-20 Minamimachi, Kokubunji, Tokyo (72) Inventor Minoru Takahashi 1-1-14 Uchikanda, Chiyoda-ku, Tokyo Hiritsu Plant Construction Co., Ltd. (72) Inventor Taku Kuribayashi 1-1-14, Uchikanda, Chiyoda-ku, Tokyo Hito Plant Construction Co., Ltd. (72) Kinichiro Asami 1-1-14, Uchikanda, Chiyoda-ku, Tokyo Hitochi Plant Construction Co., Ltd. Incorporated (72) Inventor Keigo Oguri 1-1-14, Uchikanda, Chiyoda-ku, Tokyo Inside Hirtitsu Plant Construction Co., Ltd. (56) Reference JP-A-57-97989 (JP, A) JP-A-52 -84701 (JP, A)

Claims (1)

[Claims] 1. A sound wave propagating from a noise source in a sound wave propagation path is detected by a first sensor microphone, and a sound wave having a phase opposite to that of the detected sound wave and having the same sound pressure is generated from a speaker. In the electronic muffling system that muffles sound by the sound wave interference at the position of the second sensor microphone provided at a predetermined position in the propagation path, the distance between the speaker and the first sensor microphone.
Is the distance between the speaker and the second sensor microphone.
The first sensor microphone, switch so that it is longer than
Install a peaker and a second sensor microphone, and
In the propagation path between the sensor microphone and the speaker
An electronic sound deadening system, which is equipped with a sound absorbing member .