JP3087967B2 - Microphone unit for electronic silencing in ducts - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone unit for electronic noise reduction in a duct, and more particularly to a wind noise in a ventilation path such as a duct and a plane wave transmitted from a noise source. The present invention relates to a microphone unit for electronic noise reduction in a duct that detects noise with a sensor microphone.

[Conventional technology]

2. Description of the Related Art Recently, an electronic noise reduction system for electronically reducing noise in a duct or the like has been receiving attention. An electronic silencing system detects noise by installing a microphone unit in the middle of an air duct such as a duct, radiates a load sound with the same sound pressure and opposite phase as the noise, and forcibly cancels the noise by sound wave interference. Cause it to occur.

In this way, noise generated from a ventilation fan or the like of the air conditioner is prevented from propagating in the ventilation path of the duct and to building equipment such as a concert hall that dislikes noise.

Conventionally, as shown in FIG. 6, a microphone unit used in the electronic silencing system has a sound receiving surface of a sensor microphone 10 installed in an air passage 12 corresponding to an air blowing direction (arrow direction). Detects the noise that propagates in the interior. The sensor microphone 10 is a streamlined nose-cone sensor microphone or a sensor microphone with a spherical windproof screen (not shown) attached thereto. The sound has been reduced.

[Problems to be solved by the invention]

However, the speed of the airflow flowing in the air duct is more than 10 m /
At higher speeds of more than a second, using the nose cone type sensor microphone described above or attaching a windproof screen to the sensor microphone has no effect, and if the airflow speed is fast, the wind noise will increase, and There is a drawback that the level of the sound originally contained is exceeded and noise cannot be detected.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a microphone unit for electronic silencing in a duct, in which a plane wave transmitted from a noise source is accurately detected by a sensor microphone without being affected by the speed of an airflow.

[Means for solving the problem]

The present invention, in order to achieve the above object, in a microphone unit for electronic silencing in a duct which detects a plane wave propagating in the air duct of the duct by a sensor microphone, a part of the wall surface of the air duct is opened. A box-like body attached to the outside of the air passage in communication with the opening, a sensor microphone attached to the inside of the box-like body, and a perforated plate attached to the opening, The sensor microphone is installed with the sound receiving surface facing in the transverse direction of the air passage, and the box-shaped body is filled with a sound-permeable material for preventing a resonance phenomenon.

[Action]

According to the present invention, focusing on the fact that the sound in the low-frequency sound range propagated in the duct has a uniform sound pressure distribution on the cross section of the air passage 12, the sound receiving surface 10a of the sensor microphone 10 is moved inside the air passage 12 Box mounted outside the air duct 12 not affected by the airflow
Among the noises installed in the duct in the transverse direction of the duct and propagating in the duct, the noise of the plane wave is detected by the sensor microphone for the purpose of silencing a plane wave (low-frequency noise) that propagates in a plane.

Further, since the box-shaped body 14 is filled with the sound-permeable material 24 and absorbs noise propagated in the box-shaped body 14, it is possible to prevent a resonance phenomenon occurring in the box-shaped body 14, thereby Thus, the noise can be transmitted to the sound receiving surface 10a of the sensor microphone 10 as it is.

〔Example〕

Hereinafter, a preferred embodiment of a microphone unit for electronic silencing in a duct according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a side sectional view showing a first embodiment of a microphone unit for electronic silencing in a duct according to the present invention,
The same or similar members as those in the conventional example shown in FIG. 4 will be described with the same reference numerals.

In FIG. 1, an air passage 12 is made of a zinc iron plate and has a rectangular cross section, and air sent from a fan (not shown) is sent in the direction of the arrow in the figure. Also, noise generated from the fan propagates in the same direction as the air.

A part of the upper surface of the air passage 12 is opened to a predetermined size, and a seal box 14 having one surface opened in the opening 12a is attached and sealed by packings 16, screws 18, 18,. . The seal box 14 has a ceiling surface 14
The sensor microphone 10 is attached to a via a vibration-proof elastic body 20.

Further, the sensor microphone 10 has a sound receiving surface 10a having the air passage 12a.
The air passage 12 is inserted into the seal box 14 attached to the opening 14a of the air passage wall which is not affected by the speed of the airflow flowing through the inside.
, The plane wave (low-frequency noise) that is a plane wave of noise propagating in the duct is detected.

Further, a perforated plate (an airflow shielding plate or a finely woven wire mesh 22 or a perforated metal) is attached below the sensor microphone 10, and the perforated plate is attached to the seal box 14 as shown in FIG. It is stretched over the opening 14a. Therefore, the airflow entrained from the air passage 12 into the opening 14a of the seal box 14 is finely crushed by the perforated plate, so that no vortex sound is generated due to the entrainment of the airflow. Thus, only the noise propagating in the air passage is detected by the sensor microphone.

Next, the operation of the microphone unit for electronic silencing in a duct configured as described above will be described.

Among the noises generated in the air passage 12, sound in a high-frequency sound range of several hundred hertz or more is attenuated and muted, so that only noise in the low-frequency sound region propagates through the air passage 12. Further, when the sound in the low-frequency sound range propagates through the air passage 12, since the diameter of the air passage is L and the sound speed is C, the sound is a low-frequency sound lower than the frequency C / 2L. Only the mode of plane wave propagation, which is a pressure distribution, can be taken. Therefore, the noise in the low-frequency range can be detected if the sound receiving surface of the sensor microphone 10 is installed so as to face the air passage 12 in the transverse direction.

That is, a sound wave that can propagate in the air passage 12 having a rectangular cross section (having side lengths of a and b) is expressed by the following expression when its sound pressure is expressed by the expression.

(Λ is the wavelength of the sound wave in free space, m and n are integers) By the way, in the root of the above equation, A sound wave having a negative value is attenuated and cannot propagate through the air passage 12.

Therefore, Frequency f , That is, a sound wave in a mode of m = 0 and n = 0 can propagate. As shown in FIG. 4, the sound waves in such a mode become plane waves having a uniform sound pressure in the cross section of the air passage 12.

On the other hand, a sound wave having a frequency that can be propagated when m and n are other than zero, for example, when m = 0 and n = 1, propagates while reflecting in the air passage 12 as shown in FIG. Therefore, the sound pressure is not uniform on the cross section of the air passage 12. Moreover, in practice, the modes that can be propagated including m = 0 and n = 1 overlap and propagate in the air passage 12, so that the sound pressure distribution on the cross section of the air passage 12 becomes plural.

In the present invention, since the low-frequency noise that propagates in a plane as shown in FIG. 4 is to be silenced, the sound pressure of the sensor microphone 10 can be measured at any position on the cross section of the air passage 12. Can be.

The present invention pays attention to the above, and since the sensor microphone 10 is installed in the seal box 14 attached to the opening 12a of the airflow path 12, the generation of wind noise caused by the air current colliding with the sensor microphone 10 is generated. Can be prevented.

Also, since the sound receiving surface 10a of the sensor microphone 10 is mounted so as to be directed in the transverse direction of the air passage 12, the sensor microphone
Noise can be detected at the same level as a conventional microphone unit with 10 installed.

Further, since the sensor microphone 10 does not need to be specially processed as in the shape of a nose cone, the manufacturing cost can be reduced, and the sensor microphone 10 can be attached from the outside of the air passage, so that it can be easily attached. it can.

FIG. 3 is a sectional view showing a second embodiment of a microphone unit for electronic silencing in a duct according to the present invention.

In FIG. 3, the inside of the seal box 14 is filled with a sound-permeable material 24 such as felt or stainless steel wool. Further, in the sound-permeable material 24, the sensor microphone 10 is embedded by being covered with an anti-vibration elastic body 26.

Therefore, according to the second embodiment, since the seal box 14 is filled with the sound-permeable material, the noise in the air passage 12
When the noise propagates through the seal box 12a, the noise can be directly transmitted to the sensor microphone 10. As a result, a resonance phenomenon that occurs when noise propagates in the seal box 14 can be prevented, so that only noise in the air passage 12 can be accurately detected.

〔The invention's effect〕

As described above, according to the microphone unit for electronic silencing in a duct according to the present invention, the sound receiving surface of the sensor microphone is inserted into the box-shaped body attached to the opening of the duct's air passage wall in the cross direction of the air passage. The airflow noise can be reduced by accurately detecting the noise of the plane wave propagating in the duct in the plane, and the perforated plate can be attached to the opening of the air duct to prevent The airflow blown into the air passage is blocked, and only the noise propagating in the air passage can be detected by the sensor microphone. In addition, since the noise transmitted through the box is absorbed by the sound-permeable material filled in the box, resonance phenomena occurring in the box can be prevented, and the noise is directly received by the sensor microphone. Can be conveyed to the face.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a first embodiment of a microphone unit for electronic silencing in a duct according to the present invention, and FIG. 2 is a sectional view of a seal box applied to the microphone unit for electronic silencing in a duct according to the present invention. Perspective view showing an embodiment, third
FIG. 4 is a side sectional view showing a second embodiment of a microphone unit for electronic silencing in a duct according to the present invention, FIG. 4 is a schematic explanatory diagram of a plane wave of sound pressure propagating in an air passage, and FIG. FIG. 6 is a schematic explanatory view showing a state in which sound pressures propagating through the inside are superposed, and FIG. 6 is a perspective view of a main part showing a state of attachment of a sensor microphone applied to a conventional microphone unit. 10 ... sensor microphone, 12 ... air passage, 12a ... opening, 1
4 Seal box, 22 Wire mesh, 24 Sound-permeable material.

Continuing on the front page (72) Inventor Taku Kuribayashi 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Hitachi Plant Construction Co., Ltd. (72) Ryusuke Gotota 1-11-1 Uchikanda, Chiyoda-ku, Tokyo Hitachi Plant Construction Co., Ltd. (72) Inventor Tetsuo Shimada 2-1 Nissincho, Neyagawa-shi, Osaka Onkyo Co., Ltd. (56) References JP-A-62-206212 (JP, A) JP-A-50-62001 (JP) JP-A-2-192541 (JP, A) JP-A-62-119629 (JP, U) JP-A-49-63932 (JP, U)

Claims (1)

(57) [Claims] In a microphone unit for electronic noise reduction in a duct for detecting a plane wave propagating in an air passage of a duct by a sensor microphone, a part of a wall surface of the air passage is opened and communicated with the opening. A box attached to the outside of the air passage, a sensor microphone attached to the inside of the box, and a perforated plate attached to the opening. A microphone unit for electronic silencing in a duct, characterized in that the sound receiving surface is oriented in the transverse direction of the box and a sound-permeable material for preventing a resonance phenomenon is filled in the box-shaped body. .