JP2513238Y2 - Microphone for active silencer - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a microphone for an active silencer, which is applied to mechanical products such as air conditioners and blowers.

[Prior Art] FIGS. 5 (a) and 5 (b) show a microphone installation diagram of a conventional active silencer.

In FIGS. 5 (a) and 5 (b), 1 is a duct, 02 is a microphone for detecting internal sound, 03 is a control microphone for monitoring whether the internal sound is suppressed, and 4 is a control for suppressing the internal sound. Speakers 5 are signal processing circuits.

In the active silencer, microphones 02, 03 and a speaker 4 are arranged as shown in the figure, and a detection microphone 02 detects an original sound propagating in the duct 1 together with an air flow, and a signal processing circuit 5 creates a signal having a phase opposite to the original sound. However, the speaker 4 outputs a sound to cancel the original sound and cancel the sound. The control microphone 03 monitors whether or not the internal sound is suppressed, and the signal processing circuit 5
Is adjusted so that the output of the control microphone 03 becomes zero.

The conventional microphones 02, 03 are flush mounted on the wall as shown in FIG. 5 (a), or (b).
It was installed by being inserted into the duct 1 as if to squeeze it.

[Problems to be solved by the device]

 The conventional device has the following problems.

(1) The self-noise of the microphone caused by the turbulence of the air flow is large, and the difference between the sound pressure signal and the noise signal is small. Therefore, the conventional device cannot reduce the noise signal, and as a result, the mute volume deteriorates.

(2) Since only the sound pressure of one section of the duct is detected,
A sound pressure signal having a frequency that becomes a node of the sound pressure at that position cannot be correctly evaluated, and the sound deadening level deteriorates.

 The present invention is intended to solve the above problems.

[Means for solving the problem]

The active silencer microphone of the present invention is an active silencer equipped with a microphone for detecting internal sound, a control speaker for suppressing internal sound, and a control microphone for monitoring suppression of internal sound in the duct. A slit is opened in the direction, a porous material is built in the outside, and a cylindrical container that communicates with the slit is installed, and a sound pressure-electric converter is installed at one end of the container for detection and control. It is characterized by the configuration of a microphone.

[Action]

In the above, pressure fluctuations on the slit surface are random, and because there is no correlation by position, they cancel each other when they enter the cylindrical container outside the slit, and do not reach the front surface of the sound pressure-electric converter, The sound pressure-electricity converter is less likely to detect pressure fluctuations due to air flow. On the other hand, the sound waves propagating in the duct and entering the cylindrical container do not cancel each other out, reach the sound pressure-electricity converter as they are, and the sensitivity to the sound pressure in the duct does not drop, and the S / N is improved. .

Also, since the slit is cut in the axial direction of the duct, the sound pressure-electricity converter contains not only the sound pressure of one cross section of the duct but also the information of the sound having a width in the axial direction of the duct. Even if one section of the part where the slits are installed becomes a node of sound pressure, the sound pressure does not become 0 because the information before and after that is entered in the sound pressure-electricity converter, and the active silencer for the sound of that frequency. The volume of the sound will not deteriorate.

Due to the above, the airflow noise generated by the turbulence of the airflow is reduced, the sound reduction effect is increased, and the sound pressure is transmitted and detected through the slit in the duct axial direction.
It is also possible to eliminate a phenomenon in which a predetermined volume reduction cannot be obtained due to the conventional microphone being located at the sound pressure node.

〔Example〕

 One embodiment of the present invention is shown in FIGS.

The detection microphone 2 and the control microphone 3 of the present embodiment shown in FIGS. 1 to 3 include a detection microphone 2 for detecting an internal sound, a control speaker 4 for suppressing the internal sound, and a control for the internal sound in the duct 1. In an active silencer equipped with a control microphone 3 for monitoring the temperature, a slit provided on the wall of the duct 1 along the axial direction of the duct 1.
21, a cylindrical container 22 provided outside the duct 1 and communicating with a slit 21 and containing a porous material 23 therein, and a sound pressure-electricity converter 24 provided at one end of the container 22.

In the above, the pressure fluctuation due to the air flow on the surface of the slit 21 is random, and there is no correlation by the position, so when they enter the cylindrical container 22 outside the slit 21, they cancel each other out, and the sound pressure-electricity converter 24 The sound pressure-electricity converter 24 is less likely to detect pressure fluctuations due to airflow. On the other hand, the pressure fluctuation of the sound wave propagating in the duct 1 has a correlation of 1 at each position of the slit 21, and the sound wave entering the cylindrical container 22 through the slit 21 is not canceled.
It reaches the sound pressure-electricity converter 24 as it is. Therefore, the sound pressure-electricity converter 24 installed as in the present embodiment is not sensitive to the sound pressure in the duct 1 and is insensitive to the pressure fluctuation due to the turbulence of the air flow, and the S / N ratio. Is improved, and the noise reduction effect becomes large as shown in FIG.

Further, since the slit 21 is cut in the axial direction of the duct 1, not only the sound pressure of one cross section of the duct but also the information of the sound having the width in the axial direction of the duct is stored in the sound pressure-electricity converter 24. Come in. Therefore, even if the slit 21 is installed
Even if the cross section becomes a node of sound pressure, the sound pressure does not become 0 because the sound pressure-electricity converter 24 contains the information before and after that, and the sound volume of the sound at that frequency is reduced as an active silencer. It doesn't get worse.

The porous material 23 built in the tubular container 22 is a slit.
An airflow is prevented from entering and exiting through the tubular container 22 and causing a pressure fluctuation due to a new airflow in the cylindrical container 22.

Furthermore, the sound of the frequency aimed at the sound reduction here is duct 1
Since a plane wave (with the same phase and sound pressure in the cross-sectional direction) is formed inside, there is no problem even if the sound pressure is detected on the duct wall.
By doing so, the turbulence generated in the wake of the upstream microphone is not received by the rear microphone and the airflow noise is not increased.

Due to the above, the airflow noise generated by the turbulence of the airflow is reduced, the sound reduction effect is increased, and the sound pressure is transmitted and detected through the slit in the duct axial direction.
It is also possible to eliminate the phenomenon that a predetermined sound volume cannot be obtained because the conventional microphone is located at the sound pressure node.

[Effect of device]

In the active silencer microphone of the present invention, the sound pressure-electricity converter provided at one end of the cylindrical container receives sound pressure from the inside of the duct through the slit and the inside of the cylindrical container, so that air flow noise is reduced. As the sound reduction effect is enhanced, it is also possible to eliminate the phenomenon that the conventional microphone is located at the sound pressure node and thus the volume reduction cannot be obtained.

[Brief description of drawings]

1 is an explanatory view of an active silencer according to an embodiment of the present invention, FIG. 2 is an explanatory view of a microphone of the above embodiment, FIG. 3 is a III-III arrow view of FIG. 2, and FIG. Is an explanatory view of the effect of the above-described embodiment, and FIG. 5 is an explanatory view of a conventional active silencer. 1 ... Duct, 2 ... Detection microphone, 3 ... Control microphone, 4 ... Control speaker, 5 ... Signal processing circuit, 21
… Slits, 22… cylindrical containers, 23… porous materials, 24… sound pressure −
Electrical converter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumio Aoi 1st Takamichi, Iwazuka-cho, Nakamura-ku, Nagoya, Aichi Mitsubishi Heavy Industries, Ltd. Nagoya Research Institute (72) Takanori Arai 2-chome, Niihama, Arai-cho, Takasago, Hyogo Prefecture No. 8-25 Takanishi Engineering Co., Ltd.

Claims (1)

(57) [Scope of utility model registration request] 1. An active silencer equipped with a microphone for detecting internal sound, a control speaker for suppressing internal sound, and a control microphone for monitoring suppression of internal sound in a duct, wherein a slit is provided in the duct wall in the axial direction of the duct. The detection and control microphones were constructed by opening a cylindrical container having a porous material on the outside and communicating with the slit, and installing a sound pressure-electrical exchanger at one end of the container. Microphone for active silencer, which is characterized.