JPH09319381A - Active muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active muffler capable of generating a muffling sound wave for a long term. SOLUTION: A detecting microphone 10, four speakers 20a-20d, an evaluating microphone 30 from the upper stream side are arranged on a pipe path 1 that a noise source 2 exists on the upper stream side. A first sound wave propagated from the noise source 2 is detected by a detecting microphone 10, and a sound with a phase opposite to and the same volume as the first sound wave is generated from one among the speakers 20a-20d, and further, a controller 40 feedback controls the generated sound from the speakers 20a-20d so that the sound detected by the evaluating microphone 30 becomes minimum. The transfer functions of the sounds different according to respective speakers 20a-20d are corrected by correction digital filters 50a-50d according to the speakers 20a-20d, and a proper second sound wave is generated from the speakers 20a-20d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an active silencer that reduces noise in a pipeline by generating a secondary acoustic wave having a phase opposite to that of a primary acoustic wave propagating in the pipeline.

[0002]

2. Description of the Related Art For example, Japanese Examined Patent Publication (Kokoku) No. 5-74835 discloses an active silencer for reducing noise due to sound wave interference by generating sounds having the same volume and opposite phase with respect to noise in a pipe. . In this silencer, a detection microphone, a secondary sound source (speaker), and an evaluation microphone are arranged in this order from upstream to downstream, and noise from the secondary sound source is detected based on the noise detected by the detection microphone. The opposite phase sound is generated and the resulting noise level is detected by the evaluation microphone. The detection microphone, the secondary sound source, and the evaluation microphone are connected to a control device.The control device controls the sound to be generated by the secondary sound source based on the sound detected by the detection microphone, and at the same time, the evaluation microphone. The sound of the secondary sound source is feedback-controlled based on the detected sound.

[0003]

In the above active muffling apparatus, there is only one speaker for the secondary sound source, and when this speaker fails due to a disconnection or the like, the noise is naturally not muted and the replacement is required. Will be required. If the installation location is an environment such as a clean room where clean and airtightness is required, it is not desirable to replace the speaker. In addition, since the load on the speaker increases when the speaker is operated all day long, the frequency of failure increases and the life of the device is shortened.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an active muffling device in which generation of sound waves for muffling is ensured for a long period of time.

[0005]

In order to achieve the above object, the present invention is an active silencer for reducing noise in a pipeline by generating a sound wave in the pipeline, which propagates in the pipeline. Primary sound wave detecting means for detecting the incoming primary sound wave, and a plurality of means for generating in the conduit a secondary sound wave having substantially the same volume and opposite phase as the primary sound wave based on the detection of the primary sound wave detecting means. The secondary sound wave generating means and the control means for generating the secondary sound wave from one of the secondary sound wave generating means. Under this configuration, the secondary sound wave is generated in the duct from the secondary sound wave generation means selected by the control means, and the noise is reduced. When the secondary sound wave generating means fails for some reason, the generation of the secondary sound wave is switched to another secondary sound wave generating means. As a result, it is not necessary to immediately replace the defective secondary sound wave generating means with a new one, and it is possible to secure the generation of the secondary sound wave for a long period of time. Also, one secondary sound wave generating means for generating the secondary sound wave is periodically switched to another secondary sound wave generating means. Then 1
The load on each secondary sound wave generating means is reduced, and the life of the device is extended.

Further, the control means detects the generation state of the secondary sound wave from the secondary sound wave generation means, and when the generation of the secondary sound wave from the secondary sound wave generation means is stopped, the generation of the secondary sound wave is stopped. It is preferable to perform control to switch to another secondary sound wave generating means. According to this, the switching of the secondary sound wave generating means is smoothly performed without interruption, and the temporary generation of noise due to the failure of the secondary sound wave generating means is prevented.

Further, it is preferable that the control means performs control to periodically switch one secondary sound wave generating means for generating a secondary sound wave to another secondary sound wave generating means. In this case, the switching of the secondary sound wave generating means is automatically performed, and
The labor for reducing the load on each secondary sound wave generating means is eliminated.

Further, in the above structure, an evaluation sound wave detecting means for detecting the sound volume of the sound wave which is the result of applying the secondary sound wave to the primary sound wave is provided downstream of the plurality of secondary sound wave generating means,
It is preferable that the control means feedback-controls the secondary sound wave generation means in response to the detection result of the evaluation sound wave detection means.
According to this, it is possible to further improve the sound deadening effect of the secondary sound wave generation means based on the offsetting result of the secondary sound wave and the primary sound wave generated from the secondary sound wave generation means in the evaluation sound wave detection means.

Further, the control means corrects the transfer function of sound accompanying the distance between each secondary sound wave generating means and the evaluation sound wave detecting means, and outputs each secondary sound wave based on the corrected transfer function. It is preferable to perform control to generate the secondary sound wave. The provision of a plurality of secondary sound wave generating means means that the distance between the secondary sound wave generating means and the evaluation sound wave detecting means is naturally different depending on each secondary sound wave generating means, so that between the two, The transfer function of sound with a time delay, which represents the transmission characteristic, differs for each secondary sound wave generating means. The control means corrects the transfer function in accordance with each secondary sound wave generating means, so that an appropriate sound wave, that is, a silencing sound wave is generated from each secondary sound wave generating means.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a silencer according to the present invention will be described below with reference to the drawings. (1) First Embodiment A. Configuration of First Embodiment FIG. 1 is a sectional view of a pipeline provided with an active silencer according to a first embodiment. In the figure, reference numeral 1 is a pipeline of the air conditioning duct. A noise source 2 such as a ventilation suction fan exists on the left side of the pipe 1 in the drawing. In addition, the present invention can be applied to pipelines used in various facilities such as refrigerators, automobiles, and heat pumps. The noise generated from the noise source 2 propagates in the duct 1 from left to right in the figure. Here, the left side of the pipeline 1 is defined as "upstream side" and the right side is defined as "downstream side" with reference to the noise propagation direction.

The active silencer of this embodiment is provided in the middle of the pipeline 1 on the downstream side of the noise source 2. This active silencer includes a detection microphone (primary sound wave detection means) 10 for detecting the noise of the noise source 2 propagating from the upstream side into the conduit 1 as a primary sound wave, and a secondary sound wave for reducing the primary sound wave. Four (1st to 1st) generated in the pipeline 1
Fourth) speaker (secondary sound wave detecting means) 20a, 20
b, 20c, 20d and these speakers 20a to 20d
And an evaluation microphone (evaluation sound wave detection means) 30 for detecting the sound waves that have passed through. These are arranged in the order of the detection microphone 10, the speakers 20 a to 20 d, and the evaluation microphone 30 from the upstream side to the downstream side of the conduit 1 at appropriate intervals. In this case, the speakers are arranged such that the first and second speakers 20a and 20b are substantially opposed to each other, and the third and fourth speakers 20 are provided on the downstream side.
Similarly, c and 20d are arranged substantially opposite to each other. The distance between each of the speakers 20a to 20d and the evaluation microphone 30 is different for each speaker.

Detection microphone 10, speakers 20a-2
0d and the evaluation microphone 30 are connected to a single controller (control means) 40. As the detection microphone 10, a unidirectional microphone is used because only the noise from the upstream side is detected without being affected by the sounds generated from the speakers 20a to 20d. It is preferable to use a non-directional one in order to detect the sound wave of.

The controller 40 includes a control unit 4
1, FIR digital filter 42, detection microphone 10
Corresponding to the A / D conversion unit 15 and the speakers 20a to 20
It has a D / A converter 25 corresponding to d and an A / D converter 35 corresponding to the evaluation microphone 30. The control unit 41 includes a control circuit unit 43 that determines a transfer function for control (a transfer function of sound accompanying a distance between the speakers 20a to 20d and the evaluation microphone 30) and each speaker 20a.
.About.20d, the first to fourth correction digital filters 50a, 5 for giving the filter coefficients to the control circuit unit 43.
0b, 50c, 50d. The control circuit unit 43 uses a control algorithm such as LMS (Least Mean Square). Correction digital filter 50a
˜50d add the correction coefficient of the transfer function parameter corresponding to each speaker 20a˜20d to the transfer function parameter of the control circuit unit 43. Each correction digital filter 50
A to 50d are switched by the filter changeover switch 45.

Under such a configuration, the output signal of the detection microphone 10 is converted into a digital signal by the A / D conversion section 15, and the correction digital filter 50 of the control section 41 is converted.
a to 50d and the FIR digital filter 42. On the other hand, the output signal of the evaluation microphone 30 is converted into a digital signal by the A / D conversion section 35 and supplied to the control circuit section 43 of the control section 41.

The control circuit section 43 receives the detection signal from the evaluation microphone 30 and the correction digital filters 50a.about.
The transfer function parameter for control is determined based on the filter coefficient given in 50d, and this transfer function parameter is supplied to the FIR digital filter 42. FIR
The digital filter 42 creates a drive signal based on the supplied transfer function parameter and the detection signal of the detection microphone 10 supplied from the A / D conversion unit 15. This drive signal is the D / selected by the speaker changeover switch 60.
It is supplied to the A conversion unit 25. Then, the D / A converter 25
Converts the drive signal into an analog signal, and the corresponding speaker 20a
To 20d. Speakers 20a-20
Any one of d transmits the secondary sound wave to the conduit 1 based on the drive signal.
Occurs within.

A speaker changeover switch 60 for supplying the drive signal from the FIR digital filter 42 to one of the speakers 20a to 20d, and a correction digital filter 50a.
The filter changeover switch 45 for selecting .about.50d is interlocked with each other. In each of the changeover switches 45 and 60, one of the two changeover switches may be manually operated, or both of them may be manually operated.
When (60) is activated, the other changeover switch 60 (4
The configuration corresponding to 5) is desirable.

B. Operation / Effects of First Embodiment Next, the operation of the active silencer will be described. First, one speaker for generating the secondary sound source is selected by the speaker changeover switch 60. If the first speaker 20a is selected here, the first correction digital filter 50a is accordingly switched to the filter changeover switch 4a.
5, automatically selected. The detection microphone 10 detects the sound wave of the noise source 2 propagating in the conduit 1, that is, the primary sound wave, and the detection signal is detected by the A / D converter 15.
Is converted into a digital signal by and is supplied to the FIR digital filter 42 and the control unit 41. The detection signal is supplied to the control unit 41 via the first correction digital filter 50a and reaches the control circuit unit 43. The control circuit unit 43 determines the transfer function parameter based on the detection signal of the detection microphone 10 and supplies the transfer function parameter to the FIR digital filter 42. The FIR digital filter 42 creates a drive signal based on the transfer function parameter and the detection signal of the detection microphone 10 supplied from the A / D conversion unit 15.

Now, assuming that the first speaker 20a is selected by the speaker changeover switch 60, the drive signal output from the D / A converter 25 corresponding to this is transmitted to the first speaker 20a. As a result, the first speaker 20a generates a secondary sound wave having the same amplitude and frequency as the primary sound wave but opposite phase, in the conduit 1. As a result of the secondary sound wave generated by the first speaker 20a and the primary sound wave generated by the noise source 2 being canceled out, noise is significantly reduced on the downstream side of the first speaker 20a in the conduit 1.

The evaluation microphone 30 detects a sound wave based on the reduced noise, and the detection signal is A /
The signal is converted into a digital signal by the D conversion unit 35 and then supplied to the control circuit unit 43. This detection signal and the speaker 20 supplied from the first correction digital filter 50a
The transfer function parameter supplied to the FIR digital filter 42 is changed in order to correct the amplitude or frequency of the secondary sound wave from the first speaker 20a based on the transfer parameter correction coefficient corresponding to a. That is, the control circuit unit 43 performs control so that the detection signal of the evaluation microphone 30 is always less than the allowable value. By performing the control in this way, the secondary sound wave that minimizes the propagating noise is emitted from the first speaker 20a, and the noise is extremely reduced on the downstream side of the conduit 1.

Here, when the first speaker 20a which is generating the secondary sound wave fails for some reason such as disconnection (which can be recognized by the noise generation), the speaker changeover switch 60 is used.
Generates secondary sound waves by the other speakers 20b to 20d.
Switch to one of these. That is, normally, the secondary sound wave is generated from the first speaker 20a, and the other three (first
-Third) speakers 20b to 20d are reserved. In addition, in the case of performing all-day operation for a long period of time, an operation method may be adopted in which the speaker that generates the secondary sound wave is periodically switched to another speaker by the speaker changeover switch 60. For example, every 12 hours, the first speaker 20a, the second speaker 20b, the third speaker 20c, the fourth speaker 20d, and the first speaker 20.
Periodically operate as a, ....

When the speakers 20a to 20d are switched,
The distance from the evaluation microphone 30 differs from that of the speaker that has generated the secondary sound wave, and the transfer function parameter changes. However, the correction coefficients corresponding to the speakers 20a to 20d are set to the selected correction digital filter 5
Since 0a to 50d are applied, appropriate secondary sound waves are generated also from the switched speakers 20a to 20d.

According to the muffler of the first embodiment,
When one of the speakers 20a to 20d that is generating the secondary sound wave fails due to some cause such as disconnection, the generation of the secondary sound wave is switched to the other speakers 20a to 20d, thereby causing the failed speaker 20a. There is no need to replace ~ 20d with a new one immediately. Therefore, the generation of secondary sound waves can be ensured for a long period of time. One of the failed speakers 20a to 20d may be replaced using the time when the operation of the noise source 2 is stopped. In addition, speakers 20a to 20d that generate secondary sound waves
By adopting the operation method in which the switch is periodically switched, the load on the speakers 20a to 20d is reduced and the life of the device is prolonged. For these reasons, for example, it is suitable for use in an environment where clean and airtightness is required in a clean room or the like and replacement work of the speaker is not desirable.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. A. Configuration / Operation of Second Embodiment FIG. 2 shows an active silencer of the second embodiment. This active silencer has the same basic configuration as that of the first embodiment shown in FIG. 1, and a switch controller 65 is newly added. The switch control unit 65
Speaker switch 60 and filter switch 45
Are switched in tandem. In addition, the switch control unit 65
Includes each speaker 20a to 20d and each D / A converter 25.
A detection signal for detecting the energization state between the two is supplied. The switch control unit 65 controls the speaker 2
The generation of secondary sound waves from 0a to 20d is detected depending on whether or not the power is on. Here, it is assumed that the secondary sound wave is generated from the first speaker 20a, and when the current between the first speaker 20a and the D / A conversion unit 25 is not energized, the first speaker 20a has failed. Then, the speaker changeover switch 60 is operated to generate a secondary sound source from one of the other speakers 20b to 20d.

B. Effects of the Second Embodiment According to the second embodiment, even if the speakers 20a to 20d that generate the secondary sound wave fail, the other speakers 2 are not used.
Switching to 0a to 20d is smoothly performed by the switch control unit 65 without interruption, and generation of temporary noise due to a failure of the speakers 20a to 20d can be prevented.

A timer is provided in the switch control section 65 of the second embodiment, and the above-mentioned speakers 20a to 20a are provided.
The switch control unit 65 may be configured to perform the periodical switching operation of d based on a timer. As a result, the speakers 20a to 20d are automatically switched,
The labor for reducing the burden on each of the speakers 20a to 20d is saved.

(3) Modified Examples of the Present Invention The above-described embodiments are embodiments based on the present invention, and the present invention is not limited to these. For example, the following modifications are possible. When the speakers 20a to 20d are switched in place of the correction digital filters 50a to 50d, a transfer function based on the distance between the newly used speakers 20a to 20d and the evaluation microphone 30 is calculated and used as correction data. You may use it. In addition, the control unit 41 includes the speakers 20a to 20a.
A memory in which the correction parameter corresponding to d is stored may be provided, and the transfer function may be determined from this memory. A sound absorbing material such as glass wool is put on the inner surface of the pipe line 1 to enhance the sound deadening effect.

[0027]

As described above, according to the present invention,
In the active silencer that applies the secondary sound wave to the primary sound wave of the noise source and reduces the noise by the canceling action of the sound wave, since the secondary sound wave is generated from one of the plurality of secondary sound wave generating means, Even if the secondary sound wave generating means that is generating the secondary sound wave fails, it is not necessary to replace it immediately, and the load on the secondary sound wave generating means is reduced and the life of the device is extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a pipeline 1 equipped with an active silencer according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a pipe line 1 equipped with an active silencer according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Pipe line, 10 ... Microphone for detection (primary sound wave detection means),
20a, 20b, 20c, 20d ... Speaker (secondary sound wave generation means), 30 ... Evaluation microphone (evaluation sound wave detection means), 40 ... Controller (control means).

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H03H 21/00 G10K 11/16 B (72) Inventor Ning Shimizu 10-1 Nakazawa-machi, Hamamatsu-shi, Shizuoka Yamaha shares In-company (72) Inventor, home Yawa 10-1 Nakazawa-machi, Hamamatsu-shi, Shizuoka Yamaha stock company (72) Inventor Shinji Kishinaga 10-1-1, Nakazawa-machi, Hamamatsu-shi, Shizuoka Yamaha stock company

Claims (5)

[Claims] 1. An active silencer for reducing noise in the pipeline by generating sound waves in the pipeline, comprising primary sound wave detection means for detecting a primary sound wave propagating in the pipeline. A plurality of secondary sound wave generating means for generating a secondary sound wave having substantially the same volume and opposite phase as the primary sound wave in the conduit based on the detection by the primary sound wave detecting means, and these secondary sound waves. An active muffling device, comprising: a control unit that generates the secondary sound wave from one of the generation units. 2. The control means detects the generation state of the secondary sound wave from the secondary sound wave generation means, and when the generation of the secondary sound wave from the secondary sound wave generation means is stopped, the secondary sound wave is generated. The active silencer according to claim 1, wherein the generation is switched to another secondary sound wave generating means. 3. The control means switches the one secondary sound wave generating means for generating the secondary sound wave to another secondary sound wave generating means on a regular basis. Active silencer described. 4. Downstream of the plurality of secondary sound wave generating means,
Evaluating sound wave detection means for detecting the sound volume of the sound wave which is the result of applying the secondary sound wave to the primary sound wave is provided, and the control means receives the detection result of the evaluation sound wave detecting means and generates the secondary sound wave. The active silencer according to claim 1, wherein the means is feedback-controlled. 5. The control means corrects a transfer function of sound accompanying a distance between each of the secondary sound wave generating means and the evaluation sound wave detecting means, and generates a secondary sound wave based on the corrected transfer function. The active muffling apparatus according to claim 4, wherein the secondary sound wave generating means generate the secondary sound waves.