JPH0772873A - Active muffler - Google Patents

Abstract

PURPOSE:To efficiently supply a muffler sound wave into a duct by respectively providing openings on the wall surfaces of the duct opposite to respective microphones and speakers and covering these openings with plate material with ventilation. CONSTITUTION:When an air stream (a) flows from the upper stream of the duct 1, a noise is detected by a noise detection microphone through the opening 1a and the plate material 10a with ventilation to be supplied to the speaker, and to be converted to the muffler sound wave, and to be emitted into the duct 1 through the plate material 10b with ventilation and the opening 1c. The sound wave interferes with the noise in the air stream (a), and acts so as to reduce the noise and muffle. Then, the sound wave is detected by a muffler error detection microphone through the opening 1b and the plate material 10b to be converted to a muffler error signal, and a noise signal detected by the microphone and the muffler error signal are operated based on the prescribed operational relation by a control part, and a muffler correction signal is formed, and the muffler sound wave is emitted from the speaker again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active muffler suitable for reducing noise from pipes such as blowers and engines.

[0002]

2. Description of the Related Art An active muffler utilizes the principle of radiating an additional sound having the same sound pressure and an opposite phase with respect to noise propagated from a sound source, and muffling by sound wave interference. However, even if established in principle, there are many problems with practical means for stabilizing and practically improving the silencing effect, particularly with respect to the method of attaching the sound wave detecting means and the additional sound generating means in the pipeline. ing.

In particular, in order to put active muffling into practical use in the air flow path of an air conditioner or the like, a method that considers the generation of secondary noise due to air flow and the characteristic deterioration due to the influence of heat, humidity, pressure, dust, etc. This is an extremely important technology because it leads to a stable muffling effect for a long time. In consideration of this point, US Pat. No. 4,665,549 and JP-A-3-76
No. 499 and the like disclose a method for installing noise detecting means and additional sound radiating means in the pipeline, and in the silencer proposed in Japanese Patent Application No. 3-157990, which is related to the applicant's application, the inner surface of the pipeline is disclosed. A material with a high sound absorption effect is attached to the high frequency to eliminate the turbulence of the air flow and improve the sound deadening effect.

[0004]

However, in the muffling device of the former two cases, the cold / warm airflow in the pipeline directly hits the detecting means and the secondary additional sound generating means, and the inside / outside of the pipeline. Condensation may occur due to the temperature difference between the above, and the problem may not be solved because the characteristics are deteriorated due to the influence of dust and moisture inside the pipeline. Further, the fastening means for the parts causes the turbulence of the air flow, the generation of the secondary noise and the air flow hitting the noise detection range, which leads to the deterioration of the silencing effect.

Further, in the latter sound deadening device, it is difficult to attach the material having the sound absorbing effect to the inner surface, and there are various problems in assembling. Also, when the signal from the pipe noise detection means is processed to generate additional sound, it is necessary to electrically amplify the pipe noise detection signal. The effect is reduced. However, in Japanese Patent Application No. 3-157990, there is no countermeasure against this problem, and a solution to this problem has been desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been provided to solve the above-mentioned problems of the prior art, and detects noise contained in an air flow flowing in a duct by a noise detection microphone to generate a noise signal. The noise signal is converted and subjected to a predetermined process in the signal processing control unit and supplied to the speaker, and at the same time, the speaker emits a silencing sound wave having the opposite phase and the same amplitude as the noise to interfere with the noise. In addition, the noise that has received this interference action is detected by a muffling error detection microphone and converted into a muffling error signal, and is also supplied to the signal processing control unit to be compared with the noise signal by the signal processing control unit. A noise reduction correction signal based on the relationship is output, and the noise in the airflow is reduced by causing the speaker to emit a muffling sound wave having an opposite phase and the same amplitude as the noise. Out microphone, a speaker and mute error detecting microphone on an outer wall surface of the duct, sequentially arranged along a direction of flow of the air stream, and,
An active muffling device is provided in which openings are provided in the wall surface of the duct facing the microphones and the speakers, and the openings are covered with a sound-permeable plate material.

Further, according to the present invention, the signal processing control section is provided in a control box provided on the duct, the speaker is provided in a speaker box provided on the duct, and the noise detection microphone is provided. An active muffling device is provided in which the mute error detection microphone is attached to the control box and the speaker box.

Further, the present invention provides an active muffling device in which the output of the noise detecting microphone and the output of the muffling error detecting microphone are respectively amplified by an amplifier and supplied to the signal processing control section. .

[0009]

According to the present invention, since the opening is covered with the plate material having good sound permeability, the noise in the duct can be efficiently detected by the noise detection microphone and the silencing error detection microphone, and the speaker can be effectively used. The sound-deadening sound waves emitted as a result can be efficiently supplied into the duct.

Further, in the present invention, since the signal processing control section, the speaker, and the noise / silence error detection microphone are housed in the control / speaker box, it is possible to appropriately arrange the duct.

Further, according to the present invention, since the outputs of the noise detection microphones and the muffling error detection microphones are amplified by the amplifier and supplied to the signal processing control section, noise can be reduced more efficiently.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the active muffler according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of a main part of an active silencer according to the present invention, and FIGS. 2 and 3 are transverse cross-sectional views at different parts during assembly thereof.

In these figures, 1 is a duct,
An air flow accompanied by noise is configured to flow in the direction of the arrow a inside thereof. And on the upper surface of this duct 1,
The control box 2 and the speaker box 7 are placed via the plate members 10a and 10b along the direction in which the air flow flows, and fixed with the screws 16. In short, the control box 2 is arranged on the upstream side of the air flow as compared with the speaker box 7.

The plate members 10a and 10b are both materials having excellent sound permeability, heat insulation, and airtightness, for example, open-celled soft urethane foam having these three properties, or sound permeability and airtightness. It is composed of a material in which a film and glass wool or felt having sound-transmitting and heat-insulating effects are laminated. The plate 10a corresponding to the control box covers the opening 1a provided on the upper surface of the duct 1, and the plate material 10b corresponding to the speaker box covers the opening 1b and the opening 1c provided on the upper surface of the duct 1, respectively.
It is provided on the upper surface and is screwed together with each box by a screw 16 as shown in FIGS.

The control and speaker boxes 2 and 7 are provided with flanges 2a and 7a on the lower edge of a box whose bottom is opened, and the screws 16 are fastened to the duct 1 by the flanges. The one control box 2 is provided with a microphone holding portion 2b having a support hole 2c penetrating in the vertical direction on the flange portion 2a, and the noise detection microphone 3 is supported in the support hole 2c so as to face the opening 1a. is doing. Further, the control box 2 is provided with a noise signal amplifier 4 for amplifying a noise signal detected by the microphone 3 on the inner surface of the ceiling wall thereof, and the noise signal amplified by the amplifier 4 is provided on the support bar 2d bridged between the inner surfaces of the side walls. A signal processing controller 5 for processing is provided. The microphone, the amplifier 4 and the signal processing controller 5 are electrically connected by a lead wire 6.

On the other hand, the speaker box 7 is provided with a microphone holding portion 7b having a support hole 7c penetrating in the vertical direction on the collar portion 7a, and the support hole 7c is muted so as to face the opening 1b. Error detection microphone 8
I support you. Further, the speaker box 7 is provided with a muffling error signal amplifier 9 for amplifying a noise signal detected by the microphone 8 on the inner surface of the ceiling wall thereof, and a speaker 11 so that a support bar 7d bridged between the inner surfaces of the side walls faces the opening 1c. Is provided.

The speaker 11 has its sound emitting surface opposed to the opening 1c through the plate member 10b. or,
The noise and silencing error detection microphones 3 and 8 face the openings 1a and 1b through the plate members 10a and 10b, respectively.

Both the microphones 3, 8, the amplifier 4,
9, the signal processing controller 5 and the speaker 11 are electrically connected by lead wires 6, 12 and 13, respectively, as shown in FIG. When the microphones 3 and 8 are supported in the support holes 2c and 7c, 14 and 15 are anti-vibration materials that are interposed between them to prevent the influence of vibration from the duct 1 on the microphones and This is to prevent leakage to the outside.

Since the present invention is constructed as described above, when an air flow a accompanied by noise flows from the upstream side of the duct 1 toward the control box 2, the noise is generated by the opening 1.
The noise is detected by the noise detection microphone 3 via a and the plate member 10a, converted into an electric signal, and amplified by the noise signal amplifier 4.

The noise signal amplified by the amplifier 4 is subjected to predetermined signal processing by the signal processing control section 5 and supplied to the speaker 11, where it is converted into a silenced sound wave. Then, this silenced sound wave is emitted into the duct 1 through the plate material 10b and the opening 1c.

The emitted sound-deadening sound wave interferes with the noise in the air flow a, and acts to reduce the noise and muffle it. The noise that has been interfered by the sound deadening sound waves is then detected by the sound deadening error detection microphone 8 through the opening 1b and the plate member 10b, and converted into a sound deadening error signal. The mute error signal is amplified by the amplifier 9 and then input to the signal processing control section 5. Along with the input of the muffling error signal, the control section 5 calculates the noise signal detected by the microphone 3 and the muffling error signal based on a predetermined calculation formula, creates a muffling correction signal, and again the speaker 11 More mute sound waves are emitted.

Thereafter, this signal processing is repeated, and the airflow b with reduced noise can be sent downstream of the duct 1 by the adapted acoustic wave interference having the opposite phase and the same amplitude.

The present invention is constructed as described above, but if the plate materials 10a and 10b are further described, the materials 10a and 10b having the sound permeability, the heat insulating property, and the airtightness effect.
However, when the flexible urethane foam is used, not only all the effects can be achieved with one material, but also the materials 10a and 10b vibrate due to the pressure fluctuation of the air flow inside the duct and the pressure fluctuation due to the sound wave emitted from the speaker. Two
Generation of secondary noise can be prevented. Further, in a boiler, an engine, or the like in which the duct internal temperature is high, a heat-resistant sheet (mica, glass, etc.) laminated with glass wool also corresponds to the embodiment of the present invention.

Further, in the present invention, the microphones 3 and 8 are used.
Since there is no protrusion on the upstream side of the microphones, turbulence does not occur on the upstream side of these microphones. Therefore, the turbulence hits the openings 1a and 1b facing the respective microphones 3 and 8 and the local 2 There is no concern that secondary noise will be generated and unnecessary noise will be input to the microphone.

[0025]

Since the present invention is configured as described above, the speaker can be installed outside the duct without being affected by heat, dust, moisture, secondary noise, etc. inside the duct, and therefore, it is accurate. The anti-phase / same amplitude characteristic can be retained stably for a long period of time, and the silencing effect can be maintained for a long period of time. In addition, since the sound deadening error detection microphone can be installed in the box-shaped body where the speaker is installed, it is not necessary to install the sound deadening error detection microphone directly in the duct, and the work of connecting to the duct can be rationalized, and a low-cost active sound deadening device can be installed. Can be provided. In addition, since the mute level difference detection microphone can be installed outside the duct without being affected by heat, dust, moisture, secondary noise, etc. inside the duct, it is possible to accurately and stably detect the muffling error for a long period of time. The muffling effect can be maintained for a long time.

Further, according to the present invention, since the amplifier for electrically amplifying the mute error signal can be installed in the speaker box in which the speaker is installed, the influence of external noise on the mute error signal is reduced, and the mute error is reduced. Since it can be detected accurately, the silencing effect can be maximized.

Furthermore, since the noise detection microphone can be installed outside the duct without being affected by heat, dust, moisture, secondary noise, etc. inside the duct, noise can be accurately and stably detected for a long period of time. The muffling effect can be maintained for a long time. In addition, because the noise detection microphone can be installed in the control box that installs the control unit that performs signal processing,
Since it is not necessary to install a noise detection microphone directly on the duct, the work for fastening to the duct can be rationalized, and a low-priced active silencer can be provided.

Further, according to the present invention, since the amplifier for electrically amplifying the noise signal can be installed in the control box in which the control section for controlling the signal is installed, the influence of the external noise on the noise signal is reduced. Since noise can be detected accurately, the silencing effect can be maximized.

Further, regarding the positional relationship between the speaker box equipped with the speaker, the control box equipped with the control unit for performing signal processing, and the duct, the muffling error detection microphone and the noise detection microphone are separated from each other in the airflow direction of the duct. Since it is installed so as to be positioned, the airflow is not affected by the secondary airflow noise that hits the fastening parts and the like, so that the silencing error and noise can be accurately detected, and the silencing effect can be maximized.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of an active silencer according to the present invention.

FIG. 2 is a cross-sectional view of a control box portion of the active silencer according to the present invention.

FIG. 3 is a cross-sectional view of a speaker box portion of the active silencer according to the present invention.

FIG. 4 is an electric circuit diagram showing electrical connections of a noise detection microphone, a silence error detection microphone, a signal processing control unit, and a speaker in the active silencer according to the present invention.

[Explanation of symbols]

 1 Duct 1a, 1b, 1c Opening 2 Control box 3 Noise detection microphone 4 Noise signal amplifier 5 Signal processing control unit 7 Speaker box 8 Silence error detection microphone 9 Silence error signal amplifier 10a Plate material 10b Plate material 11 Speaker

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G10K 11/16

Claims (3)

[Claims] 1. A noise detection microphone detects noise contained in an air flow flowing in a duct to convert it into a noise signal, and the signal processing control unit performs a predetermined process on the noise signal and supplies it to a speaker. At the same time, a noise canceling sound signal having a phase opposite to that of the noise and having the same amplitude as that of the noise is emitted to interfere with the noise, and the noise affected by the interference is detected by the noise canceling error detection microphone to detect the noise canceling error signal. And the signal processing control unit to output a silencing correction signal based on the relationship with the noise signal, and again from the speaker the phase and amplitude of the noise opposite phase. In a device for reducing the noise in the airflow by emitting a sound deadening sound wave, the noise detecting microphone, the speaker, and the sound deadening error detecting microphone are placed on the outer wall surface of the duct. And are sequentially arranged along the flow direction of the airflow, and openings are provided in the wall surface of the duct facing the microphones and speakers, respectively, and the openings are covered with a sound-permeable plate material. An active silencer characterized by. 2. The signal processing control section is provided in a control box provided on the duct, the speaker is provided in a speaker box provided on the duct, and the noise detection microphone is provided in the control box. The active muffling apparatus according to claim 1, wherein the muffling error detection microphone is attached to the speaker box. 3. The output of the noise detection microphone and the output of the silence error detection microphone are amplified by an amplifier, respectively.
The active muffler according to claim 1, wherein the active muffler is supplied to the signal processing control unit.