JPH04318897A - Active acoustic attenuator - Google Patents

Abstract

PURPOSE:To offer the active acoustic attenuator which can have optimum frequency resolution in a frequency band of an actual object sound and obtain excellent acoustic attenuation characteristics at all times. CONSTITUTION:This active acoustic attenuator is equipped with a detector 3 which detects a sound 2 propagating in a duct 1 in one direction, an A/D converter 8 which performs the A/D conversion of the sound signal detected by the microphone 3, a controller 12 which finds the phase and level of the sound signal, frequency by frequency, according to the converted digital signal of the A/D converter 8, a speaker 4 which is provided in front of the microphone 3 in the sound propagation direction and outputs a sound in phase and of the same loudness with the sound at the position according to the phase and level of the sound signal found by the controller 12, and a variable oscillator 13 which varies the sampling period of the A/D converter 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attenuator for attenuating noise and noise, and more particularly to an active acoustic attenuator which obtains a damping effect by applying an acoustic signal having a phase opposite to that of the noise.

0002

BACKGROUND OF THE INVENTION Conventionally, this type of active acoustic attenuator includes a microphone for detecting an acoustic signal, an A/D converter for converting the detected signal from analog to digital.
D converter, CPU that calculates the phase and magnitude of the acoustic signal,
and a speaker that outputs new sound to cancel out the sound. The sampling period is defined by the calculation time and the control time, and is usually fixed.

0003

[Problem to be Solved by the Invention] However, when the sampling period is fixed, if the band frequency to be controlled as acoustic attenuation changes, for example, it was 0 to 2 kHz at the time of design, but it changed from 0 to 1 kHz at the time of actual on-site installation. When changes are made to attenuate sound, the frequency resolution decreases compared to the design, and the sound attenuation performance deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to be able to provide optimum frequency resolution to the frequency band of the sound that is actually targeted, and to always provide good frequency resolution. An object of the present invention is to provide an active acoustic attenuator that can obtain excellent acoustic attenuation characteristics.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention employs the following configuration.

That is, the present invention provides an active acoustic attenuator that includes:
A detection microphone that detects sound propagating in a predetermined direction, an A/D converter that A/D converts the sound signal detected by the microphone, and an A/D converter that converts the sound signal detected by the microphone into an A/D converter. A controller that determines the phase and magnitude of each frequency of the signal, and a controller that is installed at a position in front of the microphone in the direction of sound propagation, and that calculates the phase and magnitude of the acoustic signal at the position opposite to that of the sound based on the phase and magnitude of the acoustic signal determined by the controller. The present invention is characterized in that it includes a speaker that outputs sound of the same loudness, and means for varying the sampling period of the A/D converter or the controller. Here, the following three configurations can be considered as means for changing the sampling period. (1) The sampling period of the computer system is changed by changing the period of the sampling command to the A/D converter using hardware. (2) The sampling period is changed by changing the frequency of the operating clock that is the basis of the computer system. (3) The sampling period is changed by externally changing the value of the internal periodic timer of the computer system.

[0007]

[Operation] In the case of an active acoustic attenuator, the number of filter taps is determined by software in the computer system, and the sampling period is determined from the sum of the calculation time and control time. At this time, this number of taps becomes the resolution of the frequency band for acoustic attenuation control, and (1) the greater the number of taps set, (2) the greater the number of taps within the frequency band, the more

[0008] The controllable resolution becomes finer, and better sound attenuation characteristics can be obtained. However, it is difficult to change the number of filter taps depending on the target. For this reason, by freely changing the sampling period, the resolution of the frequency band to be controlled can be optimized, and the maximum attenuation performance can be expected.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram showing a schematic configuration of an active acoustic attenuator according to a first embodiment of the present invention. In the figure, 1 is a duct, and within this duct 1, a detection microphone 3, a speaker 4, and a monitor microphone 5 are installed along the direction in which sound (noise) 2 propagates.

[0011] Sound (noise) 2 transmitted through the duct 1
is first detected by the detection microphone 3. The acoustic signal detected by the microphone 3 is passed through the bandpass filter 6, the amplification amplifier 7, and the A/D converter 8 to the controller 1.
Incorporated into 2. This controller 12 is equipped with a digital filter, and decomposes the frequency of the acoustic signal to calculate the phase and magnitude of each frequency.

From the controller 12, a D/A converter 9
, a low-pass filter 10 and a power amplifier 11 to provide the speaker 4 with an acoustic signal that cancels out the sound 2 in the duct. That is, when the sound 2 inside the duct reaches the position of the speaker 4, a sound of the same magnitude is output from the speaker 4 at the opposite position for each frequency, thereby canceling the sound 2.

At this time, the remaining sound that has not been canceled out is detected by the monitor microphone 5, and is taken into the controller 12 through the bandpass filter 6', amplification amplifier 7', and A/D converter 8', and the control coefficients are changed. Become an element. This repetition achieves optimal sound attenuation. however,
The positions of 6' and 7' may be either.

Further, in this embodiment, a variable oscillator 13 is provided as a method for changing the sampling period. When the controller 12 takes in the output of the amplifier 7 via the A/D converters 8, 8', the sampling period can be changed by changing the pulse output synchronization of the variable oscillator 13.

As described above, in this embodiment, the sampling period of the A/D converters 8, 8' is changed from the fixed sampling period to the active acoustic attenuator for reducing the noise 2 in the duct 1. This allows for optimal frequency resolution at the target frequency, making it possible to achieve the maximum sound reduction effect. In addition, the above-mentioned target frequency band makes it possible to save the effort of replacing parts for fixed sampling period generation or changing software due to changes in duct diameter and dimensions, and is extremely useful.

FIG. 2 is a functional block diagram showing a schematic configuration of an active acoustic attenuator according to a second embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the first embodiment described above only in the method of changing the sampling period. That is, in this embodiment, the variable oscillator 13 used as the operating clock or interrupt clock of the controller 12
This is a method that directly changes the sampling period by changing the pulse output synchronization of the pulse output. Even with such a configuration, the same effects as in the first embodiment can be obtained.

FIG. 3 is a functional block diagram showing a schematic configuration of an active acoustic attenuator according to a third embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the first embodiment described above in that, as a means for changing the sampling period, the controller 12 reads the value of the variable switch 14, and changes the sampling period by itself according to that value. There is a particular thing. Even with such a configuration, the same effects as in the first embodiment can be obtained.

It should be noted that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. In the embodiment, the present invention is applied to sound attenuation in a duct, but the present invention is applicable not only to a duct but also to anything in which sound propagates in one direction.

[0021]

[Effects of the Invention] As explained above, according to the present invention, since the sampling period can be changed freely,
It becomes possible to realize an active acoustic attenuator that can have an optimal frequency resolution for the frequency band of the sound that is actually targeted, and that can always obtain good acoustic attenuation characteristics.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing a schematic configuration of an acoustic attenuator according to a first embodiment of the present invention;

FIG. 2 is a functional block diagram showing a schematic configuration of a second embodiment of the present invention;

FIG. 3 is a functional block diagram showing a schematic configuration of a third embodiment of the present invention.

[Explanation of symbols]

1...Duct, 2...In-duct sound (noise), 3...Detection microphone, 4...Speaker, 5...Monitor microphone, 6, 6'...Band pass filter, 7, 7'...Amplification amplifier, 8, 8'...A/D converter, 9...D/A converter, 10...Low pass filter, 11...Power amplifier, 12...controller, 13...variable oscillator, 14...Variable switch.

Claims (1)

[Claims] Claims 1: A microphone that detects sound propagating in a predetermined direction, an A/D converter that A/D converts the acoustic signal detected by the microphone, and a digital signal converted by the A/D converter. a controller that calculates the phase and magnitude of each frequency of the acoustic signal based on the signal; and a controller that is provided at a position in front of the microphone in the sound propagation direction, and calculates the acoustic signal at the position based on the phase and magnitude determined by the controller. a speaker that outputs sound of the same magnitude in opposite phase to the A/
An active acoustic attenuator comprising: a D converter or means for varying the sampling period of the controller.