JPH09258742A - Muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a muffler that can sufficiently reduce noise, propagated in a pipeline over a wide band. SOLUTION: A plurality of sound absorbing materials 80a are arranged in a pipeline connected to a pipeline 10 so as to form a plurality of pipelines 10a, and an ANC(active noise control device) 44 is provided for each pipeline 10a. In the ANC 44, noise is detected by a detecting microphone 46, and sound opposite in phase but with the same sound volume as the sound wave of the noise is emitted from a speaker 48 by a controller 52. The controller 52 further performs feedback control of the emitted sound from the speaker 48 so as to minimize the sound detected by an evaluating microphone 50. Noise is reduced over a wide band by the synergetic effect of the sound absorbing material 80a and ANC 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer for reducing noise propagating in a pipeline such as an air conditioning duct.

[0002]

2. Description of the Related Art For example, in an air-conditioning duct that guides an airflow generated by an airflow generator such as a fan indoors or outdoors, the driving sound of the airflow generator propagates in the duct as unnecessary noise. Therefore, in order to reduce this noise, on the inner wall of the duct near the airflow generator, that is, the noise source,
2. Description of the Related Art A device for lining a sound absorbing material made of a porous material such as glass wool to passively reduce noise has been widely used.

On the other hand, conventionally, there has been proposed a device that actively reduces noise by propagating sound having a phase opposite to that of the noise propagating from a noise source. This is because the noise is picked up by the detection microphone on the downstream side of the noise source and the sound wave is detected, and the sound of the opposite phase to the noise is emitted from the speaker on the downstream side of the detection microphone. Further, there is also known a technique of controlling the sound to be generated by the speaker while checking the mute state with an evaluation microphone installed on the downstream side of the speaker.

[0004]

The former passive silencer tends to be inferior in the sound deadening effect particularly in the low frequency range, and if the aim is to improve the sound deadening effect, the pressure loss of the air flow increases or noise is generated by itself. This leads to problems such as In the latter active muffling device, the muffling effect may be insufficient depending on the shape of the pipe and the state of the inner surface, and particularly the muffling effect in the high frequency range is inferior.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a silencer capable of sufficiently reducing the noise propagating in the pipe over a wide band.

[0006]

The present invention has been made to achieve the above object, and a sound deadening device according to a first aspect of the present invention is a sound absorbing device provided inside a duct through which a primary sound wave propagates. A material and an active noise reduction control device having a sound wave generating means for emitting a secondary sound wave having a phase opposite to that of the primary sound wave and having substantially the same volume as the primary sound wave propagating through the pipe. . According to this configuration, the low frequency range of the noise is reduced by the active noise reduction control device, and the high frequency range is reduced by the sound absorbing material, so that the noise is reduced over a wide band.

A sound deadening device according to a second aspect is the sound deadening device according to the first aspect, characterized in that an active sound deadening control device is provided in the sound absorbing material. With this configuration, the synergistic effect of the sound absorbing material and the active sound deadening control device is enhanced, the sound deadening effect is further improved, and the sound deadening device is made compact.

A sound deadening device according to a third aspect of the present invention is the sound deadening device according to the second aspect, wherein a plurality of sound absorbing materials are arranged at intervals in the transverse direction of the pipe, and the sound absorbing material forms a pipe. It is characterized in that it is formed and an active muffling control device is provided for each pipeline. According to this configuration, the sound deadening effect of the sound absorbing material improves as the surface area and volume of the sound absorbing material increase.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The silencer according to the present invention will be described below.
Embodiments will be described with reference to the drawings. (1). First embodiment A. Configuration of the first embodiment FIG. 1 includes a silencer according to a first embodiment of the present invention.
Shows the broken pipeline. Reference numeral 10 in the drawing indicates an air conditioning duct or the like.
It is a pipeline. This conduit 10 has a rectangular cross section and
On the left side in the figure in the passage 10, there is a ventilation suction fan.
An airflow generator or noise source is present. This
Various equipment such as crab, refrigerator, automobile, heat pump, etc.
It is also possible to apply the present invention to the pipeline used for.
Although the noise source is not shown, the driving sound is
Propagate from left to right in the road 10. Where the noise transmission
Based on the sowing direction, the left side of the pipeline is "upstream" and the right side is
It is defined as "downstream side".

The silencer of the present embodiment is provided in the middle of the pipeline 10 on the downstream side of the noise source. This muffler includes a short pipe 70 having a pipe wall that is continuous with the pipe wall of the pipe 10, and a plurality of sound absorbing materials 8 provided in the pipe 70.
0a, 80 and an active noise reduction control device (Active Noise
Controller (hereinafter abbreviated as “ANC”) 44.

The conduit 70 has the same cross section as the conduit 10,
Both end faces are airtightly connected to the conduit 10. Sound absorbing material 8
0a and 80 have a half-size sound absorbing material 80a formed in a rectangular shape having a semi-elliptical cross section obtained by cutting an elongated ellipse at a major axis portion and having a size corresponding to the length and height of the duct 70. Is the basic element. A combination of two half-size sound absorbing materials 80a, which are flat surfaces and are fixed to each other, is used as the full-size sound absorbing material 80. In this case, the conduit 70
Half-size sound absorbing material 80a is fixed to both side surfaces inside with their flat surfaces aligned, and two full-size sound absorbing materials 80 are arranged between them along the length direction of the conduit 70. There is. Between the half-size sound absorbing materials 80a on both sides and the full-size sound absorbing materials 80 adjacent to them, and between the full-size sound absorbing materials 80, the actual pipeline 1 through which the air flow flows
It is formed as 0a, and the widths of these three conduits 10a are set to be the same.

Further, both ends of the sound absorbing material 80a are chamfered so that the cross section has an appropriate R, and in this case, the downstream side is formed more gently than the upstream side. As the sound absorbing material 80a, for example, a material in which glass wool is surrounded by perforated punching metal is used, and the thickness related to the sound absorbing property is appropriately set.

As shown in FIGS. 1 to 3, the ANC 44 emits a detection microphone 46 for detecting a sound wave of noise propagating in each duct 10a and a secondary sound wave into the duct 10a. A speaker (sound wave generating means) 48,
And an evaluation microphone 50. These are 1
One set is provided for each pipeline 10a, and in this case, as shown in FIG. 1, the sound absorbing material 80a on both sides facing the pipelines 10a on both sides and the middle pipeline 10a are provided. The detection microphone 46, the speaker 48, and the evaluation microphone 50 are incorporated in this order from the upstream side to the downstream side in one of the facing sound absorbing materials 80a at appropriate intervals. These are then connected to a single controller 52, as shown in FIGS. As the detection microphone 46, a unidirectional microphone is used because only the noise from the upstream side is detected without being influenced by the sound emitted from the speaker 48, and the evaluation microphone 50 uses ambient sound waves. For detection, it is preferable to use an omnidirectional one.

As shown in FIG. 2, the controller 52 is provided with an interface 53, a CPU 62, a digital filter 60, and a memory 64. The interface 53 includes an A / D converter 54, a D / A converter 56, and an A / D converter 58. Under such a configuration, the output signal of the detection microphone 46 is A
The data is converted by the / D converter 54 and can be taken into the CPU 62 and the digital filter 60.
The output signal of the evaluation microphone 50 is converted by the A / D conversion unit 58 and taken into the CPU 62.

The CPU 62 has the microphones 46, 5 respectively.
Based on the detection signal of 0, the transfer function parameters for control stored in the memory 64 are called, and these transfer function parameters are supplied to the digital filter 60.
The digital filter 60 creates a drive signal based on the given transfer function parameter and the detection signal of the detection microphone 46 input from the A / D conversion unit 54. Then, the D / A converter 56 converts this drive signal and supplies it to the speaker 48. The speaker 48 generates a secondary sound wave based on the drive signal, and emits this secondary sound wave into each duct 10a.

B. Operation of First Embodiment Next, the operation of the silencer will be described. B-1. When the noise source (passive noise reduction) noise source driven by the sound absorbing material is driven, the noise that is the driving sound propagates from the left to the right in FIG. Each pipeline is divided by 10
Propagate in a. The noise propagating in the pipeline 10a is absorbed by the sound absorbing material 80a and is reduced on the downstream side of the pipeline 10a.

B-2. Mute by ANC44 (Acty
Bed mute) Next, in ANC44, detecting microphone 4
6 outputs a detection signal based on the sound wave in the conduit 10a.
In the second controller 52, the A / D converter 54 converts the detection signal of the detection microphone 46 into a digital signal, which is then converted into a digital filter 60 and the CPU 6.
Feed to 2. The CPU 62 calls the transfer function parameter from the memory 64 based on the converted detection signal of the detection microphone 46, and the digital filter 60
To supply. The digital filter 60 creates a drive signal based on the transfer function parameter and the detection signal of the detection microphone 46 input from the A / D conversion unit 54.

This drive signal is sent to the D / A converter 5
It is converted by 6 and transmitted to the speaker 48, whereby the speaker 48 generates a secondary sound wave having the same amplitude and frequency as the primary sound wave but opposite phase, and the secondary sound wave is transmitted through the conduit 1.
Release into 0a. As a result of canceling the secondary sound wave from the speaker 48 and the primary sound wave from the noise source 12, the noise is significantly reduced on the downstream side of the speaker 48 in the conduit 10a.

The evaluation microphone 50 also outputs a detection signal based on the reduced noise. A / D
The conversion unit 54 converts the detection signal into a digital signal and supplies the digital signal to the CPU 62. Based on this, C
The PU 62 changes the transfer function parameter called from the memory 64 in order to correct the amplitude or frequency of the secondary sound wave from the speaker 48. That is, the CPU 62
Feedback control is performed so that the detection signal of the evaluation microphone 50 becomes less than the allowable value. Thus, ANC
By performing feedback control at 44, the secondary sound wave that minimizes the propagating noise is emitted from the speaker 48, and the noise is made extremely small on the downstream side of the conduit 10a.

C. Effects of First Embodiment According to the muffling device of the first embodiment, first, the noise of the noise source is absorbed by each sound absorbing material 80a as it propagates in the pipe 10a, and the noise is absorbed in the pipe 10. It is decreasing when it reaches. Further, the ANC 44 allows the sound absorbing material 80a
The noise that is being reduced by is further reduced, and as a result,
The noise passing through the silencer is greatly reduced.

Further, since the microphones 46, 50 of the ANC 44 and the speaker 48 are built in the sound absorbing material 80a, the synergistic effect of sound deadening by the sound absorbing material 80a and the ANC 44 is enhanced, and the sound deadening effect is further improved.
The silencer can be made compact.

FIG. 4 shows the presence or absence of the sound absorbing material 80a and the ANC 44.
The results of measuring the volume of noise from the low sound range to the high sound range at the outlet and the inlet of the pipe line 10a in the four cases in which the on / off of 4 are combined (the sound absorbing material 80a is provided in the first embodiment and the ANC 44 is on) Is shown. How much the volume measured at the entrance is attenuated at the exit is a problem, but first, if the silencer is not installed,
That is, in the case of "no sound absorbing material 80a, ANC44 is off", the noise propagates to the outlet while naturally attenuating, and the attenuation amount is small from the low sound range to the high sound range.

Next, in the case of "no sound absorbing material 80a, ANC44 is on", the sound is effectively attenuated in the low sound range, but the attenuation amount is not so large in the high sound range. Further, in the case of "the sound absorbing material 80a is present and the ANC 44 is off", the amount of attenuation in the low tone range is not so large, and it is effectively attenuated in the high tone range. That is, the sound absorbing material 80a has a characteristic that it does not contribute much to the attenuation in the low range and attenuates it in the high range. On the contrary, the ANC 44 has a large attenuation effect in the low range and does not contribute much to the attenuation in the high range. Can be said to have. Therefore, according to the case of "there is the sound absorbing material 80a and the ANC 44 is on", which is the specification of the muffling device of the present embodiment, they mutually complement the frequency regions in which it is difficult to muffle each other.
It can be seen that the noise is reduced over a wide band.

In addition, FIG.
Only the contribution by NC44 was taken out and compared with the case with and without sound absorbing material 80a. The sound deadening by ANC44 is 125H in the case with sound absorbing material 80a.
In the low sound range below z, it becomes large as shown by the diagonal lines. That is, it is better to use the sound absorbing material 80a together.
It is shown that the noise reduction effect of the ANC 44 becomes large in the frequency band where it is difficult to mute only with 0a.

(2). Second Embodiment Next, a second embodiment of the present invention will be described. A. Configuration of the Second Embodiment FIG. 6 shows a pipeline provided with a silencer according to the second embodiment. The silencer of the second embodiment has a configuration in which a vibration suppressing device 14 is added to the silencer of the first embodiment. In FIG. 6, the upstream side (left side) of the pipeline 10
A noise source 12 is shown in the figure. In this case, the pipe 70 separate from the pipe 10 is omitted, and the sound absorbing material 80 is provided in the pipe 10.
And ANC 44 are provided. Note that, in FIG. 6, the illustration of the sound absorbing material 80 that partitions the inside of the pipeline 10 is omitted.
The sound absorbing material 80 extends to the upstream side as compared with the case of the first embodiment, and the vibration suppressing device 14 is provided on the pipe wall of that portion.

The vibration suppressing device 14 includes a vibration detecting pickup 16 for detecting the vibration (primary vibration) of the pipe wall of the pipe 10 propagating from the upstream side, one or a plurality of actuators 18, and a vibration detecting device. The evaluation pickup 20 and the same evaluation pickup 20 are provided. The vibration detection pickup 16, the actuator 18, and the evaluation pickup 20 are arranged in this order from the upstream side to the downstream side of the pipeline 10, and are connected to a single first controller 22. The controller 52 of the first embodiment will be referred to as a second controller 52.

Here, as the pickups 16 and 20, for example, piezoelectric elements can be used.
Moreover, as the actuator 18, for example, a piezoelectric element, an electromagnetic element, a ferroelectric element, or the like can be used. Alternatively, a hydraulic actuator may be used as the actuator 18, and the valve of this hydraulic actuator may be controlled by the first controller 22.

As shown in FIG. 7, the first controller 2
The configuration of No. 2 is almost the same as that of the second controller 52. That is, the first controller 22 is provided with the interface 23, the CPU 32, the digital filter 30, and the memory 34. The interface 23 includes an A / D converter 24, a D / A converter 26, and an A / D converter 28. Under this configuration, the output signal of the vibration detection pickup 16 is A / D.
The conversion unit 24 is A / D-converted and then taken into the CPU 32 and the digital filter 30, and the output signal of the evaluation pickup 20 is A / D-converted by the A / D conversion unit 28 and taken into the CPU 32. It is designed to be used.

The CPU 32 controls the pickups 16 and 20.
The transfer function parameters for control stored in the memory 34 are called up (the transfer function itself is known) based on the detection signal of (1), and these transfer function parameters are supplied to the digital filter 30. Digital filter 3
0 creates a drive signal based on the given transfer function parameter and the detection signal of the vibration detection pickup 16 input from the A / D converter 24. And D / A
The conversion unit 26 converts this drive signal, and the actuator 1
8 The actuator 18 causes a secondary vibration based on the drive signal, and transmits this secondary vibration to the pipe wall of the pipe line 10.

B. Operation of Second Embodiment Next, the operation of the second embodiment will be described. Here, when the noise source 12 is driven, not only the noise generated by the noise source 12 propagates in the pipeline 10 but also the noise source 1
The vibration accompanying the driving of 2 propagates on the pipe wall of the pipe 10.

First, in the vibration suppressing device 14, the vibration detecting pickup 16 outputs a detection signal based on the vibration of the pipe wall. In the first controller 22, the A / D conversion unit 24 converts the detection signal of the vibration detection pickup 16 into a digital signal, which is then converted into a digital filter 30.
And CPU 32. The CPU 32, based on the converted detection signal of the vibration detection pickup 16,
The transfer function parameter is called from the memory 34 and supplied to the digital filter 30. Digital filter 30
Generates a drive signal based on the transfer function parameter and the detection signal of the vibration detection pickup 16 input from the A / D converter 24.

Then, this drive signal is applied to the D / A converter 2
6 is converted and transmitted to the actuator 18, whereby the actuator 18 causes a secondary vibration of the same amplitude and frequency as the primary vibration but of opposite phase, and the secondary vibration is transmitted to the pipe wall of the conduit 10. To do. As a result of canceling the secondary vibration by the actuator 18 and the primary vibration by the noise source 12, the actuator 1 in the pipeline 10 is canceled.
On the downstream side of 8, the vibration of the pipe wall is significantly reduced.

The evaluation pickup 20 also outputs a detection signal based on the reduced vibration. The A / D converter 24 converts the detection signal of the evaluation pickup 20 into a digital signal and supplies it to the CPU 32. Based on this, the CPU 32 changes the transfer function parameter called from the memory 34 in order to correct the amplitude or frequency of the secondary vibration by the actuator 18. That is, the CPU 32 performs feedback control so that the detection signal of the evaluation pickup 20 becomes less than the allowable value. Thus, by performing the feedback control in the vibration suppressing device 14, the vibration of the pipe wall of the pipe 10 is made extremely small on the downstream side of the actuator 18.

The operation of the ANC 44 is exactly the same as that of the first embodiment, and the second controller 52 emits a secondary sound wave having a phase opposite to that of the noise detected by the detection microphone 46 and having the same volume from the speaker 48. In addition, the sound of the speaker 48 is feedback-controlled so that the volume detected by the evaluation microphone 50 is minimized.

C. Effect of Second Embodiment In the second embodiment, the actuator 18 of the vibration suppression device 14 generates the secondary vibration of the opposite phase with the amplitude and frequency substantially the same as the primary vibration of the pipe wall of the pipe 10. By applying to the pipe wall to damp the vibration propagating through the pipe wall, A
The detection microphone 46 of the NC 44 can detect substantially only the primary sound wave from the noise source 12, and the evaluation microphone 50 substantially detects the primary sound wave from the noise source 12 and the secondary sound wave from the speaker 48. Only the superposed (i.e. canceled) sound waves of can be detected.

In this way, the microphones 46 and 50 are
Since the influence of the primary vibration on the pipe is reduced, the speaker 48 generates an accurate secondary sound wave based on the detection of each of the microphones 46 and 50, thereby improving the silencing performance in the conduit 10. It is possible to improve and maintain the silencing performance for a long time. Further, since the influence of the primary vibration, which is a disturbance, is substantially eliminated, it is possible to improve the control convergence speed, and it is possible to quickly mute the primary sound wave. Moreover, the vibration suppressing device 1 is provided by significantly damping the vibration of the pipe wall of the pipe line 10.
At a position farther from the noise source 12 than at 4, it is possible to suppress the induction of noise due to vibration.

Further, in the above structure, the vibration detecting pickup 16 and the actuator 1 are arranged from the side closer to the noise source 12 for generating the primary vibration and the primary sound wave to the side farther from the noise source 12.
8, evaluation pickup 20, microphone 4 for detection
By arranging 6, the speaker 48, and the evaluation microphone 50, the following effects are obtained. That is, first, it becomes easy to simultaneously cause the primary vibration detected by the vibration detection pickup 16 to reach the position of the actuator 18 and the actuator 18 to emit the secondary vibration corresponding to the primary vibration. It is possible to improve the excitation effect of the wall. Actuator 1
By providing the detection microphone 46 farther from the noise source 12 than the noise source 8, it is possible to reduce the influence of the primary vibration on the detection microphone 46 as compared with the opposite arrangement, and improve the sound deadening effect. It is possible to When the primary sound wave detected by the detection microphone 46 reaches the position of the speaker 48,
Simultaneously generates a secondary sound wave corresponding to the primary sound wave.

[0038]

As described above, according to the present invention,
The low frequency range of the noise is controlled by the active silencer controller,
The high frequency range is reduced by the sound absorbing material, and as a result, the noise is reduced over a wide band (claim 1). Further, the synergistic effect of the sound absorbing material and the active sound deadening control device is enhanced, the sound deadening effect is further improved, and the sound deadening device is made compact (claim 2). Further, as the surface area and volume of the sound absorbing material increase, the sound deadening effect of the sound absorbing material improves (claim 3).

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of an ANC (active muffling control device) according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of an ANC.

FIG. 4 is a diagram showing the results of measuring the relationship between the volume and frequency of noise at the outlet of a pipeline for each combination of a sound absorbing material and ANC.

FIG. 5 is a diagram comparing only the contribution by ANC from the sound deadening level shown in FIG. 4 and comparing the case with and without the sound absorbing material.

FIG. 6 is a cross-sectional view showing a conduit provided with a muffling device according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a vibration suppressing device according to a second embodiment of the present invention.

[Explanation of symbols]

 10, 10a, 70 Pipeline 44 Active silencer control device 48 Speaker (sound wave generating means) 80a Sound absorbing material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidenori Kenmochi 10-1 Nakazawa-machi, Hamamatsu-shi, Shizuoka Prefecture Yamaha stock company (72) Inventor Nei Shimizu 10-1 Nakazawa-machi, Hamamatsu-shi, Shizuoka Prefecture Yamaha stock company ( 72) Inventor Shinji Kishinaga 10-1 Nakazawa-machi, Hamamatsu-shi, Shizuoka Yamaha Stock Company (72) Inventor Kazutoshi Iijima 3-20-18 Asakusabashi, Taito-ku, Tokyo 8th Kikusei Tower Building 9F Japan Noise Control Co., Ltd. (72) Inventor Masaharu Hoshino 3-20-18 Asakusabashi, Taito-ku, Tokyo 8th Kikusei Tower Building 9F Japan Noise Control Co., Ltd. (72) Inventor Atsushi Nomiyama 3-20-18 Asakusabashi, Taito-ku, Tokyo 8th Kikusei Tower Building 9F Japan Noise Control Co., Ltd.

Claims (3)

[Claims] 1. A sound-absorbing material provided inside a pipe in which a primary sound wave propagates, and a sound wave having a phase opposite to that of the primary sound wave and having substantially the same volume with respect to the primary sound wave propagating in the pipe. An active muffling control device having a sound wave generating means for emitting a secondary sound wave. 2. The sound deadening device according to claim 1, wherein the active sound deadening control device is provided in the sound absorbing material. 3. A plurality of the sound absorbing materials are arranged at intervals in a transverse direction of the pipeline, the sound absorbing material forms the pipeline, and the active sound deadening control device is provided for each pipeline. The silencer according to claim 2, wherein the silencer is provided.