JPH03188798A - Electronic silencing system - Google Patents

Abstract

PURPOSE:To install a electronic silencing system even in a pipe duct in which the installation space of a straight pipe cannot be ensured by adopting a curved pipe for a pipeline in which a propagation sound wave is propagated in the system silencing the propagation sound wave from a noise source by radiating the sound wave of opposite phase but a same sound pressure. CONSTITUTION:A propagation sound wave from a fan 20 being a noise source is detected by a 1st sensor microphone 38 and a speaker 40 provided between the 1st sensor microphone and a 2nd sensor microphone 44 installed at down- stream of the 1st sensor microphone 38 so as to minimize the noise generates a sound wave of an opposite phase and same sound pressure with respect to the propagation sound wave to silence the propagation sound wave by means of sound wave interference. A pipeline including a curved pipe 24 is used for a pipe line of a prescribed length from the position of the 1st sensor microphone 38 to the position of the 2nd sensor microphone 44. A controller 42 in provided above the speaker 40. Since the noise level of air flow in the curved pipe 24 does not so much disturb the linear sound field in the curved pipe, even when more or less disturbance takes place, the sound wave from the speaker is enough to silence the noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electronic silencing system, and more particularly to an electronic silencing system for silencing propagating sound waves propagating in a pipe by using sound wave interference.

[Conventional technology]

2. Description of the Related Art Conventionally, passive silencers have been widely put into practical use, which muffle noise propagating in a pipe by utilizing phenomena such as interference by a pipe structure or sound absorption by a porous material lined inside the pipe. However, there are many demands for improvements in the size and pressure loss of such passive silencers.

On the other hand, as another method for silencing pipe noise, an active muffler has been proposed for a long time, that is, it emits a sound wave with the opposite phase and same sound pressure to the sound wave propagating from the noise source. However, electronic silencing systems that forcibly produce a silencing effect using sound wave interference are attracting attention.

Regarding this electronic silencing system, the present applicant has already disclosed a system configuration for practical use in Japanese Patent Laid-Open No. 164400/1983.

As shown in FIG. 4, such an electronic silencing system
With the speaker 16 as a reference, two sensor microphones 12 and 14 detect propagating sound waves propagating in the direction of the arrow in the figure.
They are installed at the upstream and downstream positions, respectively. On the other hand, the controller 18 controls the speaker 16 based on the human power signals from the two sensor microphones 12.14.
Outputs a signal to control the That is, the propagating sound waves emitted from the noise source in the conduit 10 are transmitted to the sensor microphone 12.1.
4, this sensor microphone 12.14
Detection signals are inputted to the controller 18 respectively. The controller 18 takes into account changes in propagation characteristics due to disturbances in the conduit 10 and changes in the characteristics of each electroacoustic transducer itself, measures a transfer function that indicates these characteristics, and uses the transfer function on the downstream side based on this transfer function. A drive signal is created such that the output signal of the sensor microphone 14 is minimized. The drive signal is output to the speaker 16, thereby causing the speaker 1 to
6 emits a sound wave for canceling the propagating sound wave.

As a result, at the installation position of the sensor microphone 14, the propagating sound waves are muffled by sound wave interference, and the propagating sound waves from the noise source are no longer propagated downstream from the installation position of the sensor microphone 14 in the conduit 10.

Further, the electronic silencing system is premised on the control of a -dimensional sound field. Concerning this, Koto Honde wrote in Japanese Unexamined Patent Publication No. 62-1
It has already been disclosed in Japanese Patent No. 64400.

[Problem to be solved by the invention]

However, based on the recognition that conventional electronic silencing systems cannot be installed in curved pipes where there is a risk of disturbing the one-dimensional sound field due to the self-flow of air passing through the pipe, the electronic silencing system was installed in a straight line. This required a straight pipe approximately 3m in length. Therefore, there is a problem that an electronic silencing system cannot be installed in a conduit having a length of about 3 m that does not have a straight pipe, that is, a conduit constructed by connecting a large number of curved pipes.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide an electronic muffling system capable of muffling propagating sound waves even in curved pipes.

[Means to solve problems]

In order to achieve the above object, the present invention detects propagating sound waves from a noise source propagating in a pipe with a first sensor microphone,
The propagating sound wave is emitted from a speaker provided between the first sensor microphone and the second sensor microphone so that the noise is minimized at the position of the second sensor microphone installed downstream of the first sensor microphone. In an electronic sound damping system that generates sound waves with the same sound pressure in an inverted position and muffles the propagating sound waves by sound wave interference, the sound waves are moved from the position of the first sensor microphone to the second
The present invention is characterized in that a conduit including a curved pipe is used as the conduit of a predetermined length to the position of the sensor microphone.

[Effect]

According to the present invention, the noise level of the airflow in the curved pipe (24) does not disturb the one-dimensional sound field in the curved pipe very much, and even when some disturbance occurs, the sound waves from the speaker It has been confirmed through experiments that the sound can be sufficiently silenced by
A conduit including a curved pipe (24) can be used as the conduit having a predetermined length from the position of the first sensor microphone (38) to the position of the second sensor microphone (44).

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the electronic silencing system according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram showing an embodiment of a conduit to which an electronic silencing system according to the present invention is applied.

In FIG. 1, a single pipe 22 is connected to the fan 20,
This single pipe 22 is communicated with a single pipe 26 via a bent pipe 24. The single pipe 26 is communicated with a branch pipe 30 via a bent pipe 28. The branch pipe 30 has a plurality of openings (not shown) formed in the longitudinal direction, and blowoff pipes 34, 34, etc. each having an air blowout port 32 formed therein are attached to the openings. The single pipes 22, 26 used have an axial length l of 3 m or less.

Therefore, air from the fan 20 is sent into the branch pipe 30 in the direction of the arrow in the figure via the single pipe 22, bent pipe 24, single pipe 26, and bent pipe 28, and air is blown out from the opening of the branch pipe 30. The air is blown out from the air outlet 32 of the tube 34 into a desired space. Further, the noise from the fan 20 similarly propagates through the pipe system and is emitted from the air outlet 32.

A valve 36 is installed in the single pipe 22 to limit the amount of air that flows into the bent pipe 24 from the fan 20. On the downstream side of the single tube 22 and upstream of the curve B24a of the curved tube 24, a first sensor microphone 38 is attached with an open top surface of the single tube 22, as shown in FIG. The tip of the first sensor microphone 38 is installed in the center of the single tube 22 and is attached to face the propagating sound waves of the noise emitted from the fan 20.

A speaker 40 shown in FIG. 2 is attached to the downstream side of the curved portion 24a of the curved tube 24 with the upper surface of the curved tube 24 opened. Further, a controller 4 is provided above the speaker 40.
2 is installed. A second sensor microphone 44 is attached to the downstream side of the speaker 40. Note that the actions of the controller shown in FIG. 4 are omitted here, and the actions of the sensor microphones 38, 44 and the speaker 40 are also omitted.

Next, the operation of the electronic silencing system configured as described above will be explained.

Here, the disturbance of the one-dimensional sound field due to the self-flow of air in the curved pipe 24 and the disturbance of the linearity of the system due to the noise level of this self-flow were confirmed through experiments. According to the results, it has been found that even if the pipe 24 has a curved conduit, a one-dimensional sound field can be maintained within the curved pipe 24. It was also confirmed that the noise level of the self-airflow did not disturb the linearity of the system very much, and that these disturbances were caused by the controller 4.
It has also been found that the output control transmitted by No. 2 to the speaker 40 can sufficiently compensate for this.

As a result, it was previously believed that electronic silencing systems could not be installed on curved pipes, but the results of this confirmation test revealed that electronic silencing systems can be installed on curved pipes as well. Therefore, an electronic silencing system can be installed even in a conduit where an electronic silencing system cannot be installed because it does not have a straight pipe with a length of about 3 m.

FIG. 3 shows an embodiment in which the propagation path of sound waves propagating within the curved pipe 24 is improved to obtain a high silencing effect.

According to FIG. 3, curved vanes 46, 46, 46 are attached to the curved portion 24a in the curved tube 24 at equal intervals, and the propagation path of the curved tube 24 is divided. As a result, the speed of the air sent from the fan 20 shown in FIG.
Even when the air flow exceeds S, the air flow on the downstream side of the vanes 46, 46 can be maintained in a rectified state by passing through the vanes 46, 46, 46. Therefore, it is possible to prevent disturbance of the -dimensional sound field within the curved pipe 24.
4 may be equipped with an electronic sound deadening system.

[Effects of the Invention] As explained above, according to the electronic silencing system according to the present invention, a one-dimensional sound field can be formed even if the conduit through which the propagating sound waves propagate is a curved pipe, and the noise caused by self-airflow can be reduced. The level disturbs the linearity of the system too much! As we have confirmed through experiments that some disturbances in linearity can be muffled by speakers, electronic silencing systems can be installed in curved pipes even in pipes where there is no space for installing straight pipes. .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a conduit in which an electronic silencing system according to the present invention is installed, FIG. 2 is a perspective view showing the installation state of the electronic silencing system in FIG. 1, and FIG. 4 is a perspective view showing an embodiment in which a vane is installed in a curved pipe to which an electronic silencing system according to the present invention is installed, and FIG. 4 is a perspective view showing a state in which a conventional electronic silencing system is installed. 20...Fan, 24.28...Song 1 38.
...First sensor microphone, 40...Speaker, 4
2... Controller, 44... Second sensor microphone, 46... Vane.

Claims (1)

[Claims] (1) The first sensor microphone detects the propagating sound waves from the noise source propagating in the pipe, and the noise is minimized at the position of the second sensor microphone installed downstream of the first sensor microphone. electronic silencing, in which a sound wave having the opposite phase and the same sound pressure as the propagating sound wave is generated from a speaker provided between a first sensor microphone and a second sensor microphone, and the propagating sound wave is muffled by sound wave interference; An electronic silencing system characterized in that a conduit including a curved pipe is used as a conduit of a predetermined length from the position of the first sensor microphone to the position of the second sensor microphone.