JPS6126673B2 - - Google Patents

Description

[Detailed Description of the Invention] For example, boilers and cupolas generate low-frequency noise as fuel burns, which shakes houses in the surrounding area, rattling glass doors, and causing disease symptoms in humans. creating a risk of causing

The present invention aims to provide a device that attenuates the sound pressure of such low-frequency noise, and is intended to provide a device for attenuating the sound pressure of such low-frequency noise. When propagating into the atmosphere, a pressure wave that is 180 degrees out of phase with the waveform of the low-frequency noise is generated by an electrically driven pressure wave generator, and this is sent into the low-frequency noise to cancel out both pressure waves. This action attenuates the low frequency noise.

Conventionally, as a method of attenuating low frequency noise, as shown in Fig. 1, a resonance chamber 2 with a depth of 1/4 of the wavelength of the target noise is opened in the middle of a conduit 1, and the sound waves reflected from the depths of the resonance chamber 2 and Methods have been used to attenuate the noise by offsetting the noise passing through the conduit. However, this method uses part of the noise energy to generate antiphase sound waves and causes interference, so the attenuation effect is weak, and at most only a few dB of attenuation can be obtained.

It is also known to send pressure waves of opposite phase into the noise to be attenuated, thereby canceling out the two waves and attenuating the target noise. Figures 2 and 3 are
This type of silencing device is shown, and the device shown in FIG. 5, and a microphone 7 for detecting noise is installed at an appropriate position in the conduit 1, and based on the signal output from this microphone, an electromagnetic reciprocating type drive machine 4 is operated to drive the pressure generating plate 5, and the pressure generation plate 5 is opened. Sends pressure waves of opposite phase into the noise that reaches the vicinity,
In the device shown in FIG. 3, which cancels out both waves and attenuates the target noise, a chamber 3 is opened near where the conduit 1 exits.

The present invention provides such an electromagnetic reciprocating drive machine,
The present invention provides a low frequency silencing device that automatically drives a pressure generating plate in response to the frequency of noise and performs good silencing.

FIG. 4 shows the configuration of the low frequency muffling device of the present invention.

The output of the microphone 7, which senses the noise to be silenced, is filtered through a filter circuit 8, which passes only the current at the noise frequency to be attenuated, and a phase delay circuit (Phaes) corresponding to this frequency, as shown in Fig. 4.
Shifter), enters the amplifier 10, is amplified and sent to the driver 4. By using several sets of filter circuits and phase delay circuits in parallel,
It is possible to simultaneously exert a damping effect on several noise frequencies.

The driver 4 is operated by the output current of the amplifier 10 to drive the pressure wave generating plate 5, and when the pressure wave emitted from the plate 5 passes through the length L of the chamber 3 and reaches point B. , the phase delay circuit 9 shall be adjusted so that the phase difference with the pressure wave of the noise that has passed through the conduit 1 and reached point B is 180 degrees.

If the above length L is L = 0, a phase delay circuit is not required, but when high-temperature gas flows inside the conduit, L must be appropriately large to avoid high heat, so the circuit is It becomes necessary.

FIG. 5 shows an electromagnetically driven pressure wave generating drive machine used in the present invention. A coil 12 is fixedly wound around a shaft cylinder 11 connected to a pressure wave generating plate 5, and the shaft cylinder 11 is suspended by springs 13 and 14, and a magnet 15 is installed surrounding the shaft cylinder 11. When the output current of the amplifier 10 is passed through the coil 12, the shaft cylinder 11 and the pressure wave generating plate 5 reciprocate according to the frequency, thereby generating sound pressure waves. The space between the peripheral edge of the pressure wave generating plate 5 and the wall of the chamber 3 is closed with a flexible ring 16 as shown in FIGS. 6 and 7 to prevent gas leakage. In addition, a rear volume 17 of sufficient size is provided behind the pressure wave generating plate 5.
is provided and communicated with the outside through a small hole 18.

The muffling device of the present invention configured as described above has the following features:
The goal is to use it against low-frequency noise of approximately 50 to 100 hertz or less, and the lower the frequency, the more effective it is. In other words, in the low frequency range, the pressure waves emitted by the silencer have little directionality, so it is easy to balance them with the noise (incoming waves) to be attenuated, but as the frequency increases, the pressure waves have little directionality. Since the sound emitted from the incoming waves must be sent in from the front of the incoming waves, a sufficient effect cannot be obtained, which makes the construction of the silencing device difficult.

As described above, the low frequency muffler of the present invention is a muffler of the type in which a pressure wave of opposite phase is strongly generated by a pressure wave generator and sent to a target noise to attenuate the noise. Out of the output, multiple filter circuits corresponding to the noise of multiple frequencies to be silenced are provided to extract the output corresponding to the frequency and magnitude of the target noise, and when the gas containing the noise is high temperature. Since the microphone output is amplified through the phase delay circuit 9 and the drive unit 4 is operated, it is possible to powerfully muffle the noise of the target frequency according to its magnitude, which is difficult to achieve in the past. It is also possible to effectively attenuate noise of several tens of hertz or less, which is called low frequency.

[Brief explanation of the drawing]

1 to 3 are side views schematically showing three examples of conventional silencers, FIG. 4 is a block diagram showing the electric circuit of the present invention, FIG. 5 is a schematic longitudinal sectional view of an electromagnetic drive machine, and FIG.
The figure is a schematic vertical cross-sectional view showing the airtight structure around the pressure wave generating plate, and FIG. 7 is a schematic vertical cross-sectional view showing the rear volume. 1: conduit, 4: driver, 5: pressure wave generation plate,
7: Microphone, 8: Filter circuit, 9: Phase delay circuit, 10: Amplifier.

Claims (1)

[Claims] 1 A pressure generating plate 5 driven by an electromagnetic reciprocating drive type drive machine 4 is provided at the back of the chamber 3, including the case of zero depth, with the entrance facing the low frequency noise passing through the conduit 1, and an amplifier 1 through a plurality of filter circuits 8 that pass noises of different frequencies, which attempt to mute the output of the microphone 7 that senses the size.
0, connect the output of the amplifier 10 to the driver 4, and if the length L of the chamber 3 is not zero,
A low frequency muffler characterized in that a phase delay circuit 9 is interposed between each filter circuit 8 and an amplifier 10.