JPH05313671A - Silencer for opening of building - Google Patents

Abstract

PURPOSE:To improve the silencing effect of the silencer to be provided in the suction and exhaust port, etc., of a building. CONSTITUTION:A duct 3 is provided in the opening 2 of the building 1. A speaker 6 is installed in the duct 3. A first microphone 4 is disposed near the end of the duct 3 on the inner side of the room and a second microphone 5 is disposed near the end on the outer side of the room. A computer 8 drives an amplifier 11 in the antiphase from the noise collected by the first microphone 4 and negates the noise by outputting sound waves from a speaker 6. The remaining noise is collected by the second microphone 5. The computer 8 controls the output, phase, frequency spectra, etc., so as to decrease the output of the second microphone 5 to zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler, and more particularly to a muffler for noise radiated to the outside from openings such as intake and exhaust ports of a building.

[0002]

2. Description of the Related Art Conventionally, as a method of reducing noise radiated to the outside from an opening such as an intake / exhaust port of a building, a method of absorbing noise by installing a muffling chamber or a maze type silencer in the opening is generally used. Target. There is also known an active muffling method in which noise is picked up by a microphone, the waveform of the noise is inverted, sound waves of opposite phase are emitted from a speaker, and the noise is interfered with to attenuate the noise.

[0003]

A conventional silencer that absorbs noise by means of a silencer chamber or the like has no effect on low-frequency noise because it hardly absorbs low-frequency sound.
Further, because of its structure, the intake / exhaust resistance is large, so that there is a problem that a large-capacity intake / exhaust device is required. On the other hand, in the method of canceling noise by emitting sound waves of opposite phase from the speaker, it is not easy to obtain low-frequency noise in a non-directional manner and obtain sufficient effects from the directivity of the speaker.

Therefore, technical problems to be solved in order to improve the attenuation of low frequency noise and to effectively muffle factory noises and prevent environmental deterioration, arise. The present invention aims to solve this problem.

[0005]

The present invention is proposed to achieve the above object, and a duct is installed in an opening of a building, and a first microphone is provided in the vicinity of the indoor opening of the duct. The second microphone is disposed near the outdoor side opening, the speaker is installed in the duct, the output signal of the first microphone is inverted and amplified by an amplifier to drive the speaker, and the amplifier is also provided. A control unit for controlling the output of the second microphone, the output of the second microphone is fed back to the control unit, and the silencer for the building opening for controlling the amplifier by setting the output target value of the second microphone to zero, and the duct. The present invention provides a muffler for a building opening in which a sound absorbing material is attached to the inner peripheral surface of the building.

[0006]

[Operation] Noise in the building propagates into the duct and becomes a plane wave traveling in the duct. The output signal of the first microphone arranged near the entrance of the duct is inverted and amplified, and emitted from the speaker in the duct as a sound wave having a phase opposite to the noise,
It interferes with and attenuates plane wave noise. The second microphone arranged near the outlet of the duct collects noise radiated outside the room without being canceled by the speaker and feeds it back to the control unit. The control unit sets the frequency of the speaker output, the phase, the output of the second microphone = 0 as a target value,
It controls the volume and reduces the noise emitted from the duct opening as much as possible.

According to the second aspect of the present invention, in addition to the above-mentioned function, the high frequency component of noise is further absorbed by the sound absorbing material in the duct. As a result, the noise in the high frequency band in which the active noise reduction effect is reduced due to the phase shift from the speaker sound due to the short wavelength is attenuated, and a good noise reduction effect is obtained over the entire frequency band.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. For convenience of explanation, technical matters that are conventionally known will be described at the same time. In FIG. 1, reference numeral 1 is a building. A duct 3 is attached to the intake / exhaust opening 2 of the building 1.
The duct 3 projects toward the indoor side, and the first microphone 4 for measuring the indoor noise is arranged near the end on the indoor side. On the other hand, in the vicinity of the outdoor opening of the duct 3, a second microphone 5 for measuring noise radiated to the outside is arranged. Further, a noise canceling speaker 6 is installed at an intermediate portion in the duct 3.

The first and second microphones 4 and 5 are A /
It is connected to the computer 8 via the D converter 7 and inputs a digitized audio signal to the computer 8. The computer 8 inverts the output signal of the first microphone 4, corrects the phase difference caused by the distance between the first microphone 4 and the speaker 6, drives the digital signal processor 9, and causes the D / A converter 10 and the amplifier 11 to operate. The speaker 6 is driven via the. From the speaker 6, a sound wave whose volume is almost the same as that of the noise picked up by the first microphone 4 is amplified. The noise propagating from the room into the duct 3 travels in the duct space as a plane wave that can be easily controlled, and is thus attenuated by being interfered with the sound wave of the opposite phase emitted from the speaker 6. The noise that is not eliminated is duct 3
Is detected by the second microphone 5 arranged near the exit of the, and is fed back to the computer 8 as an error amount. The computer 8 adds the output of the second microphone 5 to the output of the first microphone 4 to correct the volume, frequency spectrum and phase, and the output of the second microphone 5 is zero, that is, noise radiated to the outside. The output of the speaker 6 is controlled so that is zero.

In FIG. 2, the baffle 12 is provided so as to face the outdoor side opening of the duct 3 to reduce the amount of high frequency component radiation of noise in the direction facing the outdoor side opening of the duct 3. ing. Although the substantial duct length is extended by the baffle 12 and the outer wall surface 1a of the building 1, and the speaker 6 is installed in the extended duct space 3a, the present invention is not limited to this, and as shown in FIG. It may be in the duct 3 as shown. The silencer described above is very effective for noise composed of only low frequency components,
Due to the limitation of the computing speed of the computer 8, there is a limit to the controllability in the high frequency range, and the amount of attenuation decreases.

A second aspect of the present invention is a sound deadening device having improved sound deadening performance against high frequency noise. As shown in FIG. 3, a sound absorbing material 22 such as glass wool is attached to the inner surface of the elbow duct 21. The bass range is the speaker 6 described above.
And the high frequency range is attenuated by the sound absorbing material 22 and the bent shape of the duct.

FIG. 4 shows an experimental result of the silencer,
The outputs of the first and second microphones 4 and 5 are analyzed by a real-time analyzer. The vertical axis represents the noise attenuation amount (dB) obtained from the output difference between the first and second microphones 4 and 5, and the horizontal axis represents the frequency (Hz).
Is the attenuation performance line of the silencer according to claim 1, and the reference symbol B is that of the silencer according to claim 2. As shown in the figure, both of the silencers have a good silence performance of 20 dB below 125 Hz.

On the other hand, at 2 kHz, the amount of attenuation is 5 dB when the sound absorbing material is not used, and 9 dB when the sound absorbing material is used, which is a difference of 4 dB. . Therefore, it is desirable to select and use from two types of silencers depending on the frequency distribution of noise. The present invention can be variously modified without departing from the spirit of the present invention, and it goes without saying that the present invention covers those modifications.

[0014]

As described in detail in the above-mentioned embodiment, the present invention uses the duct provided in the opening of the building to convert the indoor noise, which is a diffused wave, into a plane wave that can be easily controlled, and has an opposite phase sound wave. Noise interference performance is significantly improved,
The emission noise can be reduced and the environment can be improved.

Further, according to the second aspect of the present invention, low frequency noise is silenced by sound waves of opposite phases, and noise in the high frequency range, which is difficult to be actively silenced due to the phase shift, is absorbed by the sound absorbing material. A high sound deadening effect can be obtained over a long period of time, and it is effective for a noise source including high frequency components.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a silencer according to claim 1.

FIG. 2 is a configuration diagram showing another embodiment of the silencer according to claim 1.

FIG. 3 is a configuration diagram of the silencer according to claim 2.

FIG. 4 is a graph showing sound wave attenuation of the silencer according to claims 1 and 2.

[Explanation of symbols]

 1 Building 2 Opening 3 Duct 4 First Microphone 5 Second Microphone 6 Speaker 8 Computer 11 Amplifier 21 Elbow Duct 22 Sound Absorbing Material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanao Owaki 1043 Shimoyama, Onigakeboji, Tsukuba, Ibaraki Prefecture Kumagai Technical Research Institute Co., Ltd. (72) Yotsugu Sugiki, 1043 Shimoyama, Onigakeku, Tsukuba, Ibaraki 1 Kumagai Gumi Research Institute Ltd.

Claims (2)

[Claims] 1. A duct is installed in an opening of a building, a first microphone is arranged near an indoor opening of the duct, and a second microphone is arranged near an outdoor opening of the duct. A speaker is installed in the space, an output signal of the first microphone is inverted and amplified by an amplifier to drive the speaker, and a control unit for controlling the output of the amplifier is provided, and the control unit controls the output of the second microphone. A silencer for a building opening, which feeds back an output and controls the amplifier by setting an output target value of a second microphone to zero. 2. The sound deadening device for a building opening according to claim 1, wherein a sound absorbing material is attached to an inner peripheral surface of the duct.