JP2791510B2 - Active silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device, and more particularly to an active noise reduction device for reducing noise of a blower, an engine, or the like by using interference of sound waves.

[0002]

2. Description of the Related Art There is an active silencer as a device for suppressing noise of a blower, an engine or the like. The active silencer is 180 degrees out of phase with the sound wave contained in the noise,
The noise is suppressed by radiating sound waves having the same amplitude from the speaker and causing sound wave interference.

FIG. 5 is a schematic diagram showing a configuration of a conventional active silencer. Referring to FIG. 5, the active silencer is provided near one end 11 in pipe 2 having one end 11 coupled to sound source 1 and open end 12, A microphone 3 for detecting a sound wave generated from the sound source 1 and propagating through the conduit 2, and a microphone provided in the conduit 2 at a predetermined distance from the microphone 3 on the side of the open end 12, for transmitting sound for silencing. A speaker 4 for radiating into the channel 2, and a loudspeaker 4 provided near the opening end 12 in the pipe 2, which receives sound wave interference generated by the sound source 1 and generated by the speaker 4, and is muted. A microphone 6 for outputting a muffling error signal by detecting a sound wave, and connected to the microphones 3, 6 and the speaker 4, and performing predetermined processing on the output of the microphone 3, Give a signal to generate sound waves for silencing In response to the mute error signal, and a signal processing circuit 14 for controlling the speaker 4 so as to reduce the muffling error signal.

The microphone 3 and the speaker 4 are separated from each other by a predetermined distance, and the speaker 4 and the microphone 6 are separated from each other by a predetermined distance.

[0005] The active silencer shown in FIG. 5 operates as follows. The sound wave generated from the sound source 1 passes through the conduit 2, causes sound wave interference with the sound wave generated from the speaker 4, and is emitted from the open end 12. Microphone 3 is sound source 1
A sound wave from the speaker 4 and a sound wave from the speaker 4 are detected, and a signal corresponding to the sound pressure of the detected sound wave is supplied to the signal processing circuit 14.

The signal processing circuit 14 performs a predetermined process on the signal supplied from the microphone 3 so as to generate a sound wave having a waveform opposite in phase to the sound wave generated from the sound source 1.
A signal is sent to the speaker 4. At this time, the signal processing circuit 14
In the signal processing performed in step (2), the sound wave emitted from the sound source 1 propagates along the distance from the position of the microphone 3 to the position of the speaker 4, and the sound wave output from the speaker 4 reaches the microphone 3 again. This is performed in consideration of characteristics such as acoustic feedback caused by the operation.

A sound wave emitted from a sound source 1 and a speaker 4
As described above, sound waves radiated from the above cause sound wave interference. Therefore, the sound wave after the interference that passes through the microphone 6 is
The sound wave is weaker than the sound wave generated from the sound source 1. However, in order to further improve the silencing performance of the active silencer, the sound pressure of the sound wave passing through this portion, detected by the microphone 6, is used for controlling the signal processing circuit 14 as a silencing error signal. That is, the microphone 6 detects the sound pressure of the sound wave after the interference, and supplies the sound pressure to the signal processing circuit 14 as a noise reduction error signal. The signal processing circuit 14 is controlled so that the silencing error signal becomes smaller. As the signal processing circuit 14, an adaptive digital filter is often used.

[0008]

According to the active silencer shown in FIG. 5, the silencing error sound pressure level detected by the microphone 6 can be reduced to some extent. However, it is difficult to make the overall value of the silencing error sound pressure level smaller than a certain value. On the other hand, there is still a strong demand that the influence of noise emitted from the silencer to the outside be reduced.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an active silencer capable of reducing the influence of noise emitted outside even when it is difficult to further reduce the overall value of the silencing error sound pressure level. It is to provide.

[0010]

According to the first aspect of the present invention, there is provided an active silencer having one end through which a sound wave from a sound source is introduced, and the other end which is an opening end through which the sound wave is emitted. A pipe in which the sound wave propagates, a sound wave detecting means for detecting the sound wave propagating in the pipe, a sound wave generating means for generating a sound wave in the pipe, a sound wave from a sound source and a sound wave generating means A post-interference sound wave detection means for detecting a post-interference sound wave obtained by interfering with a sound wave from the apparatus, and a predetermined frequency-based weighting of an output signal of the post-interference sound wave detection means based on human auditory characteristics Weighting means for outputting an error signal representing an error of the post-interference sound wave from a desired state, and the value of the error signal is a predetermined value in response to the output of the sound wave detection means and the error signal. Sound wave as approaching And a adaptive control means for adaptively controlling the generation of waves by stages. The active silencer according to the invention according to claim 2 has one end where a sound wave from a sound source is introduced, and another open end where the sound wave is emitted, and a pipe through which the sound wave propagates. A sound wave detecting means for detecting a sound wave propagating in a pipe, a sound wave generating means for generating a sound wave in the pipe, a sound wave from a sound source, and a sound wave from the sound wave generating means interfering with each other. A post-interference sound wave detecting means for detecting the obtained post-interference sound wave, and correcting the output signal of the post-interference sound wave detection means based on the transfer characteristic of the pipe from the post-interference sound wave detection means to the other end of the pipe. Performing, estimating the state of the post-interference sound at the other end, outputting an error signal representing an error from a predetermined state of the estimated post-interference sound, and outputting the error signal and the error signal of the sound wave detecting means. The value of the error signal in response to And a adaptive control means for adaptively controlling the generation of waves by the sound wave generator so as to approach the prescribed value. An active silencer according to the invention according to claim 3 has one end through which a sound wave from a sound source is introduced, and another open end through which the sound wave is emitted, and a pipe through which the sound wave propagates. A sound wave detecting means for detecting a sound wave propagating in a pipe, a sound wave generating means for generating a sound wave in the pipe, a sound wave from a sound source, and a sound wave from the sound wave generating means interfering with each other. A post-interference sound wave detecting means for detecting the obtained post-interference sound wave, and weighting the output signal of the post-interference sound wave detection means according to a predetermined frequency based on human auditory characteristics; To the other end of the pipeline based on the transfer characteristic of the pipeline to estimate the state of the post-interference voice at the other end, and an error signal representing an error of the estimated post-interference voice from a predetermined state. To output Comprising a weighting means, responsive to the output and the error signal of the acoustic wave detection means, and adaptive control means for adaptively controlling the generation of waves by the sound wave generator so as to approach a value the value of the error signal determined in advance.

[0011]

In the active noise reduction apparatus according to the first aspect of the present invention, the signal indicating the sound pressure of the sound wave after the interference detected by the post-interference sound wave detection means is given a predetermined weight based on the human auditory characteristics. Thus, an error signal is obtained. The sound wave generating means operates so as to minimize the error signal, and the sound wave generating means generates a sound wave which causes interference with the sound wave from the sound source. By determining the weighting in advance so as to obtain a desired result, it is possible to control the distribution of the frequency component of the sound wave after the interference so as to be in a state favorable to human hearing. In the active noise reduction device according to the second aspect of the present invention, the signal indicating the sound pressure of the sound wave after interference detected by the sound wave after interference detection means includes:
Correction is performed based on the transfer characteristics of the pipeline from the post-interference voice detection means to the other end of the pipeline, and the post-interference voice at the other end is estimated. Then, an error signal from the predetermined state of the post-interference voice is obtained. The sound wave generating means operates so as to minimize the error signal, and the sound wave generating means generates a sound wave which causes interference with the sound wave from the sound source. By preliminarily determining the weighting so as to obtain a desired result, it is possible to control the distribution of the frequency component of the sound wave after the interference at the other end of the pipeline. In the active silencer according to the third aspect of the present invention, the signal indicating the sound pressure of the sound wave after interference detected by the sound wave after interference detection means is given a predetermined weight based on human auditory characteristics. Further, correction based on the transfer characteristic of the pipeline from the post-interference voice detection means to the other end of the pipeline is performed, and the post-interference voice at the other end is estimated. Then, an error signal from the predetermined state of the voice after the interference is obtained. The sound wave generating means operates so as to minimize the error signal, and the sound wave generating means generates a sound wave which causes interference with the sound wave from the sound source. By determining this weighting in advance so as to obtain a desired result, it is possible to control the distribution of the frequency component of the sound wave after the interference at the other end of the conduit so as to be in a state that is preferable for human hearing. .

[0012]

FIG. 1 is a schematic diagram of an active silencer according to a first embodiment of the present invention. The active silencer according to the first embodiment is intended to further enhance the effect of the active silencer on human perception.
Human hearing is several kilohertz compared to low frequency sound of several hundred Hz.
It is known that it has a characteristic of being sensitive to sound having a high frequency of z. Therefore, even if the overall value of the silencing error sound pressure level obtained by the effect of the active silencer is constant, it is more quiet for a human to attenuate higher-frequency sound waves more.
For this purpose, this embodiment performs weighting on the frequency axis of the silencing error sound pressure level so as to further enhance the effect on human hearing.

Referring to FIG. 1, an active silencer according to a first embodiment of the present invention includes a pipe 2 having one end 11 connected to a sound source 1, an open end 12, and a pipe 2 A microphone 3 provided as a sound wave detecting means for detecting a sound wave emitted from the sound source 1 and provided in the pipe 2 at a distance L1 from the microphone 3 on the side of the open end 12; A speaker 4 as sound wave generating means for generating a sound wave for silencing by interfering with a sound wave emitted from 1;
A sound wave generated after the sound wave generated from the sound source 1 and the sound wave generated from the speaker 4 interfere with each other is provided in the pipe 2 at a distance L2 from the speaker 4 and closer to the opening end 12, and a sound-absorbing error sound pressure level is detected. And a microphone 6 serving as a post-interference sound wave detecting means for outputting a signal indicating the following. A signal having an A characteristic as shown in FIG. An audibility correction filter 7 as a weighting means for weighting the signal output from the microphone 6 on the frequency axis as shown in FIG.
And a speaker connected to the microphone 3, the microphone 6, and the speaker 4 so that the speaker 4 generates a sound wave having a waveform substantially opposite in phase to the sound wave generated from the sound source 1 based on a signal output from the microphone 3. A signal for driving the speaker 4 is generated, and a waveform for driving the speaker 4 is
A signal processing circuit 5 for controlling the value of the error signal 8 to be small.

The signal processing circuit 5 gives a signal having a waveform opposite in phase to the output of the microphone 3 to the speaker 4 based on the output waveform of the microphone 3, causing the speaker 4 to interfere with the sound wave from the sound source 1. The digital filter 9 is connected to the output of the microphone 3 and the output of the audibility correction filter 7, and is connected to, for example, an LMS (Least).
And an adaptive algorithm 10 for successively updating the filter coefficients of the adaptive digital filter 9 by a Mean Square algorithm or the like so as to minimize the root mean square value of the error signal 8.

In driving the loudspeaker 4 by the adaptive digital filter 9 and the adaptive algorithm 10, transmission characteristics when a sound wave emitted from the sound source 1 propagates over a distance L 1 from the position of the microphone 3 to the position of the speaker 4,
Signal processing is performed in consideration of characteristics such as acoustic feedback that occurs when a sound wave output from the speaker 4 reaches the microphone 3 again. Also in the processing by the adaptive algorithm 10, processing in which the transfer characteristics from the output of the adaptive digital filter 9 to the output of the audibility correction filter 7 are considered is performed.

The active silencer shown in FIG. 1 operates as follows. The sound wave generated from the sound source 1 enters the duct 2 from one end 11 and is detected by the microphone 3 first. The microphone 3 detects the sound pressure level of the passing sound wave,
The signal is given to the adaptive digital filter 9. The adaptive digital filter 9 generates a sound wave having a waveform opposite in phase to the sound wave generated from the sound source 1 in consideration of the transfer characteristics of the sound wave while the filter coefficients are sequentially updated by the adaptive algorithm 10. To be,
A drive signal is given to the speaker 4.

The sound wave generated from the speaker 4 and the sound wave generated from the sound source 1 cause interference in the pipe 2 and pass through the microphone 6. The microphone 6 detects the sound pressure level of the passing sound wave and gives the signal to the audibility correction filter 7. The audibility correction filter 7 weights the input signal on the frequency axis according to the characteristics as shown in FIG. The adaptive algorithm 10 sequentially updates the filter coefficients of the adaptive digital filter 9 according to the above-mentioned LMS algorithm so that the root mean square value of the error signal 8 is minimized.

As described above, the audibility correction filter 7 is used in FIG.
The error signal 8 has the A characteristic as shown in FIG.
Of the sound waves after the interference detected by the microphone 6, the components in the high frequency band are reflected more than the components in the low frequency band. The adaptive algorithm 10 and the adaptive digital filter 9 drive the speaker 4 so as to minimize the root mean square of the error signal 8. Therefore, even though the overall value of the signal output from the microphone 6 is equal to the conventional value, the high frequency band component which is relatively sensitive to humans among the sound waves passing through the microphone 6 is reduced, while the human beings are not so likely. The component of the low frequency band which has no influence becomes larger than before. Therefore, after the interference with the sound wave generated from the sound source 1 and generated from the speaker 4, noise in a frequency band particularly sensitive to human hearing is more efficiently silenced. Therefore, according to this active silencer, the silencing effect on the audibility can be enhanced, at least for humans, as compared with the conventional art.

In the active silencer shown in FIG. 1, the characteristics of the audibility correction filter 7 are A characteristics as shown in FIG. However, the frequency characteristics of the audibility correction filter 7 are not limited to those shown in FIG. For example, in the above-described first embodiment, the magnitude of the audible noise is reduced by selectively reducing the high frequency band component of the noise. However, the method is not limited to this method in order to enhance the silencing effect. For example, in the frequency spectrum of the noise that is the primary sound source, it is desirable to examine in advance how much frequency component sound should be attenuated to obtain a sound quality that is comfortable for humans, and to make the frequency component to be attenuated a comfortable sound quality. A filter having such characteristics as to allow the light to pass through can be used as the audibility correction filter 7. As a result, it is possible to selectively attenuate the frequency of the noise that makes the noise uncomfortable, thereby realizing an active noise reduction device that makes the sound quality of the noise more comfortable.

FIG. 3 is a schematic diagram of an active silencer according to a second embodiment of the present invention. This active silencer is based on the following concept.

In the conventional active silencer shown in FIG. 5, the characteristics of the signal processing circuit 14 are controlled so that the silencing error sound pressure level detected by the microphone 6 is reduced. However, actually, a standing wave generated by the sound wave reflected at the open end 12 at the open end 12 exists in the conduit 2. Therefore, the output waveform of the microphone 6 is different from the actual noise waveform radiated from the opening end 12 to the outside. In the prior art, as described above, the output signal of the microphone 6 is used as it is as a muffling error signal. Since the effect of the standing wave in the conduit 2 is not considered at all, it is not possible to perform the optimal noise reduction control on the sound wave radiated from the opening end.

In order to solve this problem, it is conceivable to install a microphone 6a as a noise reduction error detecting means outside the opening end 12, as shown in FIG. However, depending on the target to which the active silencer is applied, the microphone 6a cannot be installed outside the opening end 12 in many cases. In this embodiment, in an active silencer in which a microphone 6 as a post-interference sound wave detecting means is installed in the conduit 2, optimal silencing control for sound waves emitted from an open end is realized. is there.

The active silencer of the second embodiment shown in FIG. 3 is different from the active silencer of the first embodiment shown in FIG. 1 in that a microphone 6 is used instead of the audibility correction filter 7 shown in FIG. Is provided with a filter 13 as a weighting means for estimating the waveform of the noise radiated from the opening end 12 based on the noise canceling error signal output from. The output of the filter 13 is provided as an error signal 8 to the adaptive algorithm 10 of the signal processing circuit 5. Otherwise, the device shown in FIG. 3 and the device shown in FIG. 1 are identical. Identical parts are given identical reference numerals and names. Their functions are the same. Therefore, detailed description thereof will not be repeated here.

The characteristics of the filter 13 are determined as follows. Referring to FIG. 4, a sound wave detected by microphone 6 installed in conduit 2 is located behind microphone 6 at a distance L3 behind microphone 6.
In a, the distance L3 in the pipeline 2 is detected through the transfer characteristic H when the sound wave propagates. This transfer characteristic H can be measured for the pipe 2 in advance. By correcting the output of the microphone 6 installed in the conduit with this transfer characteristic H, it is possible to estimate a noise waveform detected by the microphone 6a installed outside the opening end 12. The characteristic of the filter 13 is selected so as to correct the signal output from the microphone 6 with the transfer characteristic H.

The output of the filter 13 is the adaptive algorithm 1
0 is given. As in the first embodiment, the adaptive algorithm 10 and the adaptive digital filter 9 drive the speaker 4 so that the root-mean-square of the error signal 8 is minimized. Therefore, a sound wave is generated from the speaker 4 so that the noise radiated outside the opening end 12 is optimally controlled, and interferes with the sound wave from the sound source 1. In other words, according to the active noise reduction device of this embodiment, the error signal output from the microphone 6 is corrected (weighted) in consideration of the transfer characteristics between the installation position of the microphone 6 and the opening end 12, so that the conventional device is used. The silencing effect can be further enhanced as compared with the device.

[0026]

As described above, according to the present invention, the output of the post-interference sound wave detecting means is corrected based on human auditory characteristics, and the state of the post-interference sound wave at the other end of the pipeline is estimated. Control the distribution of the frequency components of the sound waves (radiated noise) after interference by controlling the sound wave generator so that the sound waves after interference are minimized after performing both or both. Can be. By selecting a weighting that minimizes the effect on the surroundings according to the environment where the device is placed, the effect on the surroundings can be reduced even if the detected noise error sound pressure level is constant compared to the past. Can be reduced.

In other words, an active silencer capable of reducing the influence of noise on human hearing emitted to the outside of a pipeline even if the overall value of the silencing error sound pressure level cannot be reduced any more. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of an active silencer according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of the audibility correction filter of the first embodiment.

FIG. 3 is a schematic diagram of an active silencer according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a principle of correcting an error signal according to a second embodiment.

FIG. 5 is a schematic view of a conventional active silencer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sound source 2 Pipeline 3 and 6 Microphone 4 Speaker 5 Signal processing circuit 7 Perception correction filter 8 Error signal 9 Adaptive digital filter 10 Adaptive algorithm 12 Open end 13 Adaptive digital filter

Claims (3)

(57) [Claims] 1. One end to which a sound wave from a sound source is introduced;
A pipe having an open other end from which a sound wave is emitted and through which the sound wave propagates, sound wave detecting means for detecting a sound wave propagating through the pipe, and generating a sound wave in the pipe line Sound wave generating means for causing the sound wave from the sound source and the sound wave from the sound wave generating means to interfere with each other. Weighting means for outputting an error signal indicating an error from a predetermined state of the post-interference sound wave by performing weighting for each predetermined frequency based on human auditory characteristics to the output signal of the means, In response to the output of the sound wave detection means and the error signal,
And an adaptive control means for adaptively controlling the generation of the sound wave by the sound wave generating means so that the value of the error signal approaches a predetermined value. 2. One end to which a sound wave from a sound source is introduced,
A pipe having an open other end from which a sound wave is emitted and through which the sound wave propagates, sound wave detecting means for detecting a sound wave propagating through the pipe, and generating a sound wave in the pipe line Sound wave generating means for causing the sound wave from the sound source and the sound wave from the sound wave generating means to interfere with each other. The output signal of the means is corrected based on the transfer characteristics of the pipeline from the post-interference sound wave detection unit to the other end of the pipeline to estimate the state of the post-interference sound at the other end. Means for outputting an error signal indicating an error from a predetermined state of the estimated post-interference voice, and in response to the output of the sound wave detection means and the error signal,
And an adaptive control means for adaptively controlling the generation of the sound wave by the sound wave generating means so that the value of the error signal approaches a predetermined value. 3. One end to which a sound wave from a sound source is introduced,
A pipe having an open other end from which a sound wave is emitted and through which the sound wave propagates, sound wave detecting means for detecting a sound wave propagating through the pipe, and generating a sound wave in the pipe line Sound wave generating means for causing the sound wave from the sound source and the sound wave from the sound wave generating means to interfere with each other. The output signal of the means is weighted for each predetermined frequency based on human auditory characteristics, and further, correction based on the transfer characteristic of the pipeline from the post-interference sound wave detection unit to the other end of the pipeline is performed. Weighting means for estimating the state of the post-interference sound at the other end, and outputting an error signal indicating an error from a predetermined state of the estimated post-interference sound, and an output of the sound wave detection means. In response to said error signal,
And an adaptive control means for adaptively controlling the generation of the sound wave by the sound wave generating means so that the value of the error signal approaches a predetermined value.