JPH0836391A - Active muffler - Google Patents

Abstract

PURPOSE:To provide an active muffler which reduces the noise of a device in a three dimensional space by employing a simple constitution. CONSTITUTION:The signals detected by a first sensor 33 located on a wall surface 32 of an objective device 31 and a second sensor 35 which detects the vibration of the vibrating surface of a speaker 34 are added in an adding section 40 and a power amplifier 44 of the speaker 34 is controlled so that an error signal 43, which is the sum of the signals, becomes zero or a minimum by an adaptive control section 36. By this control, the strength of the radiated sound of the speaker 34 is made to coincide with the strength of the sound radiated by the wall surface 32 of the device 31. Moreover, since the speaker 34 is directly placed on the surface 32, the radiated sound of the speaker 34 adds in a reversed phase. Thus, the radiated acoustic power of the surface 32 of the device 31 is reduced and the noise in three dimensional space is also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reducing the noise of equipment, and more particularly to an active silencer suitable for equipment placed in a three-dimensional space such as a transformer.

[0002]

2. Description of the Related Art One of conventional active silencers is one that is used for a case where sound propagates one-dimensionally, such as an air conditioning duct, which is widely used. FIG.
Is a schematic configuration diagram showing the first conventional example, in which the sound pressure propagated from the sound source 2 on one end side of the air conditioning duct 1 is to be reduced to zero at the outlet 3 on the other end side. Is.

This is a detection microphone 4 for obtaining a sound signal in the air conditioning duct 1 on the sound source 2 side of the air conditioning duct 1.
And an evaluation microphone 5 for obtaining a sound signal in the air conditioning duct 1 on the outlet 3 side, and a speaker 6 for outputting a sound in the air conditioning duct 1 between the microphones 4 and 5. There is.

Reference numeral 7 denotes an adaptive control section based on the Filtered-X LMS algorithm used in a general adaptive control system, which is a transfer function compensating filter 8,
Fixed FIR (Finite Impulse Resp)
onse) filter 9, adaptive FIR filter 1
It is configured by connecting 0s. Further, the output signal of the detection microphone 4 is the transfer function compensation filter 8 and the fixed FIR.
The output signal of the evaluation microphone 5 is input to the filter 9, and the adaptive FIR filter 10 outputs the output signal.
The output of the fixed FIR filter 9 is added to the speaker 6. And
The adaptive control unit 7 automatically determines the control coefficient so that the sound pressure becomes zero at the position of the evaluation microphone 5.

In such a system, an opposite-phase sound is emitted from the speaker 6 based on the sound detected by the detection microphone 4, and the sound is interfered with the sound in the air conditioning duct 1 propagating from the sound source 2 to the evaluation microphone. The sound pressure is set to zero while being evaluated with 5. If there is a point where the sound pressure is zero, the sound is reflected at that point due to the difference in acoustic impedance and does not propagate toward the outlet 3.

However, this is to reduce the sound pressure of the noise to zero by interference when the noise propagates one-dimensionally like the air conditioning duct 1, and is not applicable to the noise propagating three-dimensionally. Absent.

On the other hand, when the sound source is placed in a three-dimensional space, a method for reducing the overall noise of the device is to surround the device that is the sound source with many additional sound sources and There is a method of radiating the sound and reducing the sound leaking to the outside of the surrounding surface as much as possible. This is an extension of the above-described air-conditioning duct method in which sound propagates one-dimensionally to a three-dimensional space.

Next, an apparatus for realizing this method will be described with reference to FIG. 4 as a second conventional example. 4 is a schematic configuration diagram. In FIG. 4, a plurality of additional sound sources 13 are provided on the surrounding surface 12 equidistant from the device 11 which is the sound source.
Are arranged, and evaluation microphones 14 are arranged in the vicinity of these additional sound sources 13, respectively.

Further, each evaluation microphone 14 is connected so that an output signal is input to a control section 15 for driving and controlling the additional sound source 13. A signal having a correlation with the sound emitted from the device 11, for example, a reference signal such as a wall vibration signal is input to the control unit 15 via a signal line 16.

The control unit 15 controls so that the sound pressure in the evaluation microphone 14 is minimized.
The amplitude and phase of the additional sound source 13 are determined so that the sum of squares of the sound pressure in the evaluation microphone 14 is minimized.

However, in the case of such a configuration,
A large number of additional sound sources 1 for each evaluation microphone 14
Since the sounds from 3 are mixed in, the control system must be constructed in consideration of their influence, and the control system including the control unit 15 becomes complicated. Furthermore, it is necessary to set the interval between the additional sound sources 13 within 1/2 of the wavelength of the sound to be reduced, and if the surrounding surface 12 is set away from the sound source device 11, a large number of additional sound sources 13 are required. There is a problem such as

As another method, assuming that a device as a sound source is a set of discrete sound sources, the intensities and phases of those sound sources are obtained in advance, and when the additional sound sources are arranged in the surroundings, This is a method of controlling the intensity and phase of the sound source of the additional sound source so that the sound power of is minimized. Here, the strength of a sound source is the volume velocity emanating from the sound source, and is the integral of the vibration velocity over the area. The acoustic power is energy emitted from a sound source per unit time.

Next, an apparatus for realizing this method will be described with reference to FIG. 5 as a third conventional example. FIG. 5 is a schematic configuration diagram. In FIG. 5, 17 is a device that is a sound source, and each wall surface 18 of the device 17 is provided with an additional sound source 20 that is drive-controlled by a control unit 19.

Further, in the control section 19, it is assumed that a discrete sound source is present on each wall surface 18 from the vibration of each wall surface 18 measured in advance, and a database section 21 which has prepared the data in advance is provided. It is connected. Then, in the control unit 19,
The phases and sound intensities of the respective additional sound sources 20 are calculated so that the total sound power is minimized when the sounds of the original sound source 17 and the additional sound source 20 are added, and the addition results are calculated. The sound source 20 is drive-controlled.

However, in the case of such a configuration,
It is necessary to find the strength and phase of the original sound source in advance, and it takes a lot of effort to actually do this. further,
If there is a change such as a change in the amplitude or phase of the original sound source on the way, there is a problem that it is necessary to redo the setting, and it has not been put to practical use.

[0016]

As described above, the conventional device has various problems, and the device for reducing the total noise of the device in the three-dimensional space has not been put to practical use. The present invention has been made in view of such a situation, and its object is not to require a large number of additional sound sources, the control system does not become complicated, and the automatic control is performed with a simple configuration. An object of the present invention is to provide an active silencer capable of reducing the overall noise of equipment in a three-dimensional space.

[0017]

SUMMARY OF THE INVENTION An active silencer of the present invention detects a vibration surface of a target device or an additional sound source arranged near the vibration surface and driven by an amplifier, and a vibration of the vibration surface of the target device. Vibration of the additional sound source such that the first sensor, the second sensor that detects the vibration of the vibrating surface of the additional sound source, and the signals from the first and second sensors are added and calculated so that the sum becomes zero or minimum. And a control unit that sets the amplitude and phase of the amplifier, and further sets the amplification factor of the amplifier so that the strengths of both the additional sound source and the sound source of the vibration surface of the target device are equal. Further, the amplification factor of the amplifier is set so that the product of the area of the vibration surface of the additional sound source and the vibration amplitude becomes equal to the product of the equivalent area of the vibration surface of the target device and the vibration amplitude. It is characterized by .

[0018]

The active silencer configured as described above corresponds to each vibration detected by the first sensor on the vibration surface of the target device and the second sensor for detecting the vibration on the vibration surface of the additional sound source. The signals are subjected to addition calculation, and the control unit controls so that the sum becomes zero or minimum. With this control, the intensity of the sound emitted by the additional sound source matches the intensity of the sound emitted by the vibration surface of the target device, and the additional sound source is placed directly on or near the vibration surface of the target device. The sound radiated by the additional sound source is added to the opposite phase. For this reason, the radiated acoustic power from the vibrating surface of the target device can be reduced, and noise can be reduced even in a three-dimensional space.

[0019]

EXAMPLES The concept underlying the present invention will be described prior to the description of the examples. First, attach an additional sound source to or near the vibration surface of the sound source that emits the sound to be reduced, and set it so that the phase of the vibration surface of the original sound source is in anti-phase and the intensity of the emitted sound matches. .

In principle, when the sound source and the additional sound source are close to each other, in order to minimize the radiation power from the sound source by using the additional sound source, the vibration speed of the sound source is v ₁ , the surface area is s ₁ , When the vibration velocity of the additional sound source is v ₂ and the surface area is s ₂ , | v ₁ | × s ₁ = | v ₂ | × s ₂ (1) and the phases of v ₁ and v ₂ are shifted by 180 degrees. Good.
However, here, it is assumed that both the vibration planes of the original sound source and the additional sound source are in translational motion, and equation (1) indicates that the sound intensity of the original sound source and the sound intensity of the additional sound source are equal. . In other words, the same amount of the fluid that has sprung from the original sound source is sucked in by the additional sound source. Strictly speaking, a slight deviation occurs depending on the distance between the sound sources and the frequency, but it generally holds when the distance between the sound sources is within ½ of the wavelength of the sound.

In order to realize this principle, the first thing to be considered is that the phase of the original sound source and the additional sound source is 180 degrees.
Secondly, the sound intensity of the additional sound source is adjusted to be equal to that of the original sound source.

Therefore, in the present invention, as a configuration embodying the above principle, a vibration detecting sensor is attached to the sound source vibrating surface and the additional sound source vibrating surface, and the signals are added so that the sum becomes zero. I do. If such control is performed, the phases of the original sound source and the additional sound source are shifted by 180 degrees.
However, as it is, the sound intensities do not match only with the phase shift.

Therefore, an amplifier for amplifying the vibration signal is provided, and either one or both are appropriately amplified and then added. The way of amplification is adjusted so that the intensities of both sounds match. With such a configuration, the sound intensity of the additional sound source can be set to match the sound intensity of the original sound source, and the phase can be set to be shifted by 180 degrees.

The sound intensity of the original sound source and the sound intensity of the additional sound source are as shown in the equation (1), and the sound intensity is made to coincide with each other by the area of the vibrating surface of the additional sound source and the vibration amplitude. This is done by determining (setting) the magnification of the amplifier so that the product becomes equal to the product of the equivalent area of the vibration surface of the original sound source and the vibration amplitude.

Next, embodiments of the present invention will be described with reference to the drawings. First, the first embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram. In FIG. 1, 31 is a target device that is a sound source, and a wall surface 32 of the device 31.
A first sensor 33 for detecting the vibration of the wall surface 32 is attached to the, and a speaker 34 as an additional sound source is attached in the vicinity of the first sensor 33. The speaker 34 has a second position for detecting the vibration of the vibration surface of the speaker 34.
Sensor 35 is attached.

The first and second sensors 33, 35 may be any sensors as long as they are capable of measuring vibrations, and for example, an acceleration pickup or a laser displacement meter can be used.

Further, 36 is a filter 3 for transfer function compensation.
7. Filtered-X configured by connecting a fixed FIR filter 38 and an adaptive FIR filter 39.
An adaptive control unit based on the LMS algorithm, and 40 is an addition unit. The first sensor 33 is connected to the transfer function compensation filter 37 and the fixed FIR filter 38 of the adaptive control unit 36 so that the output signal thereof is applied.

On the other hand, the addition unit 40 has a first sensor 33.
And the second sensor 35 are connected so that the respective output signals are amplified and input via the amplifiers 41 and 42, respectively. Further, the output from the adder 40, which is obtained by amplifying the output signals of the first sensor 33 and the second sensor 35 and performing the addition operation, is output as an error signal 43 by the adaptive FIR filter 3
9 is input. Further, the output of the fixed FIR filter 38 is added to the speaker 34 via the power amplifier 44.

As a result, the speaker 34, which is an additional sound source,
Is based on the output signals of the first sensor 33 and the second sensor 35.
The error signal 43, which is the output of, is controlled to be the minimum. That is, when the adaptive control unit 36 changes the control coefficient of the adaptive FIR filter 39 so as to make the error signal 43 zero and the error signal 43 approaches zero, the phase of the vibration of the speaker 34 of the additional sound source becomes the original. Device 31 that is a sound source
The phase of the wall surface 32 is shifted by 180 degrees.

As a result, the phase of the vibration of the device 31 and the vibration of the speaker 34 of the additional sound source mounted on the wall surface 32 of the device 31 are 180 degrees out of phase by the automatic control, and the sound from the speaker 34 is transmitted from the device 31. The sound intensity can be made equal, and the radiated acoustic power of the device 31 can be reduced with a simple configuration. In the above description, the wall surface 32 is represented as the part of the device 31 that requires reduction of the radiated acoustic power, but the part of the device 31 that requires reduction of each radiated acoustic power is configured as described above. The same effect can be obtained without requiring a large number of speakers 34 of additional sound sources.

Next, a second embodiment will be described with reference to FIG. FIG. 2 is a schematic configuration diagram. In FIG. 2, reference numeral 51 denotes a target device that is a sound source, and a wall surface 52 of the device 51 has a first sensor 5 for detecting vibration of the wall surface 52.
3 is attached, and a speaker 55, which is an additional sound source driven by the power amplifier 54, is attached near the first sensor 53. Then, in the speaker 55,
Second sensor 5 for detecting vibration of the vibration surface of speaker 55
6 is attached.

Further, 57 is the first and second sensors 53, 5
6 is a control unit inserted between the output end of the power amplifier 6 and the input end of the power amplifier 54. The control unit 57 includes first and second amplifiers 58 and 59 and first and second frequencies such as low-pass filters. The filters 60 and 61, the addition unit 62, and the correction filter 63 form a positive feedback circuit. The output signals of the first and second sensors 53 and 56 are input to the first and second amplifiers 58 and 59 of the control unit 57, respectively.

The signals amplified by the first and second amplifiers 58 and 59 are fed to the first and second frequency filters 60 and 6 respectively.
It is added to the adder 62 via 1, and is added to the correction filter 63 after being added here. Further, the signal has its transfer characteristic improved by the correction filter 63 and is input to the power amplifier 54, where it is power-amplified and then the speaker 55.
Drive.

By increasing the amplification factor of the power amplifier 54 in such a process, the output signal of the adding section 62 approaches zero, and the phase of the vibration of the speaker 55 of the additional sound source is the device 51 which is the original sound source. 180 degrees out of phase with the wall surface 52.

As a result, also in this embodiment, the same effect as in the first embodiment can be obtained.

As in the first and second embodiments described above, the active noise suppressor of the present invention can reduce the total noise radiated in the three-dimensional space, so that the noise can be distributed around the housing like a transformer. It can be applied to equipment that emits noise.

[0037]

As is apparent from the above description, according to the present invention, a large number of additional sound sources are not required and the overall noise of the equipment in a three-dimensional space can be reduced with a simple structure. Play.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a first conventional example.

FIG. 4 is a schematic configuration diagram showing a second conventional example.

FIG. 5 is a schematic configuration diagram showing a third conventional example.

[Explanation of symbols]

 31 ... Equipment 32 ... Wall surface 33 ... First sensor 34 ... Speaker 35 ... Second sensor 36 ... Adaptive control unit 40 ... Addition unit 43 ... Error signal 44 ... Power amplifier

Claims (3)

[Claims] 1. A vibrating surface of the target device or an additional sound source arranged near the vibrating surface and driven by an amplifier, and a first sensor for detecting vibration of the vibrating surface of the target device.
A second sensor that detects the vibration of the vibrating surface of the additional sound source and the amplitude of the vibration of the additional sound source such that the signals from the first and second sensors are added and calculated so that the sum becomes zero or minimum. An active muffler comprising a control unit for determining a phase. 2. The active muffling apparatus according to claim 1, wherein the amplification factor of the amplifier is set so that the strengths of both the additional sound source and the sound source on the vibration surface of the target device are equal. 3. The amplification factor of the amplifier is set such that the product of the area of the vibration surface of the additional sound source and the vibration amplitude is equal to the product of the equivalent area of the vibration surface of the target device and the vibration amplitude. Item 1. The active silencer according to Item 1.