JPS61234216A - Feedback compensation type silencer - Google Patents

Abstract

PURPOSE:To substantially attenuate an optional low frequency sound, by detecting a noise in a duct while generating a sound in a reverse phase to a sound source waveform and silencing the noise. CONSTITUTION:A silencer mounts a generated sound detecting microphone 3, duct output sound detecting microphone 2 and a silencing additional sound source 5 in a duct 1 communicating with a noise source 4. A detection signal from the generated sound detecting microphone 3 is input to a control signal arithmetic part 8 through a generated sound identification filter 6. The arithmetic part 8, inputting also a signal from the duct output sound detecting microphone 2 and calculating from these signals a sound in a reverse phase to a sound source waveform, drives the additional sound source 5 through a driving part 7. In this way, an optional low frequency sound can be effectively attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a device for significantly silencing low-frequency noise in a duct from an air blower, a ventilation fan, etc. before the intake and exhaust of an internal combustion engine or compressor.

Problems with the Prior Art Many studies have been published to date claiming that active mufflers are effective in attenuating low-frequency sounds without increasing the size of the muffler. (Cause, Ishii: 1981
(October, Acoustical Society of Japan) Theoretically, if the sound generated by the sound source can be completely identified and there is a speaker that can generate the opposite-phase sound, complete noise reduction is possible. However, since the microphone for detecting the waveform of the sound source is affected by the additional sound source, there is a possibility of oscillation occurring between the microphone and the speaker. This is the cause that prevents the practical use of active silencers. Therefore, in previous research, microphones,
We have been thinking about suppressing oscillation by modifying the speaker position and duct structure. However, this method has the disadvantage that it can only achieve a sound reduction effect of about 15 dB for sounds other than pure tones.

Purpose of the Invention In order to solve these drawbacks, the present invention utilizes noise identification and feedback of duct output sound to configure a control system that suppresses the effects of fluctuations in the noise source and oscillations between microphones and speakers. The purpose is to measure the attenuation of wave sound. The present invention
It can be used to significantly attenuate arbitrary low-frequency sounds emitted from compressors, boilers, etc.

Structure of the Invention The present invention provides an active muffler for eliminating sound in a duct, which includes a part of an identification filter that measures and identifies the waveform of the sound source, a microphone that detects the duct output sound, and a microphone that detects the sound source waveform and the duct output sound. It consists of an arithmetic unit that processes information and calculates signals to the drive unit necessary to generate sound with the opposite phase of the sound source waveform from the speaker.

The operation of the present invention will be explained in more detail using the operation diagram of the invention. 1st
The figure is a diagram of the principle of the present invention. 4 indicates a noise source such as a compressor or boiler, and the sound generated by it is emitted into the duct 1. The duct is equipped with a microphone 3 for detecting generated sound, a microphone 2 for detecting duct output sound, and an additional sound source 5 for muffling. Outside the duct, an additional sound source drive unit 7, a generated sound identification filter 6, and a control signal calculation unit 8 are arranged, and the configuration is such that effective noise reduction can be achieved based on duct output sound information and generated sound information. It has become. FIG. 2 is a block diagram showing the flow of information in this configuration. GO(S) is a transfer function from the additional sound source to the duct exit, F(s) is a generated sound identification filter, and usually F(s)=-1/Go(s).

If the compensator is Gc (s), the transfer characteristics from the noise d (s) and the detected sound d" (s) to the duct output sound y (s) are given by the following. Here, the denominator rational function Δ(s ) = 1- Go (s) If the gain 1Δ(s)1 of Gc (s) is made large, I y(s) l can be made small. In principle, 1Δ(s) I −OO makes ly( s) l -0, and the duct output sound can be completely eliminated. To achieve this, the gain I Ge(s) l of the compensator Gc (g) may be increased while suppressing oscillation.

This method has the advantage of being easy to implement with only slight modifications to conventional classical control methods, and can flexibly respond to changes in sound propagation characteristics.

Embodiment In the above description, an example was shown in which two microphones were used to obtain generated sound and duct output sound information. on the other hand,
If there is a flow of hot air along with sound in the duct, such as in the muffler of an internal combustion engine, the sound cannot be detected using a microphone. Therefore, as shown in FIG. 3, the above control system can be constructed using a sound pressure detection mechanism with four strain gauges mounted on a thin film. Using this, it becomes possible to perform noise reduction control even under extremely high temperatures.

Effects of the invention In order to compensate for the shortcomings of active mufflers and always demonstrate high muffling performance, this muffler mechanism effectively utilizes information on the generated sound and duct output sound, so it eliminates noise whose frequency changes arbitrarily. A high silencing effect can also be obtained.

[Brief explanation of drawings]

FIG. 1 shows a diagram of the principle of the present invention. Figure 2 is its block diagram. FIG. 3 shows a conceptual diagram of a sound pressure detection mechanism in place of a microphone. In the figure, 1 is a heat-resistant thin film, 2 is a strain gauge, 3 is a strain amplifier, and 4 is a frequency analyzer. Figure 1 Figure 3

Claims (1)

[Claims] In order to eliminate low-frequency sounds in the duct, a generated sound identification mechanism unit includes a microphone that collects the sound generated from the sound source and an identification filter that identifies the generated sound waveform, a microphone that collects the duct output sound, and generated sound information. and a feedback compensation mechanism section that processes output sound information, and a drive section that drives an additional sound source based on the signal from the feedback compensation mechanism section, and outputs the output sound from the additional sound source to the opposite phase sound of any generated sound. A feedback compensation type silencer characterized by following the following.