JPH06266366A - Active noise canceller - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] In an active noise canceller, it is possible to determine the filter coefficient of a wraparound prevention filter without a sound source generator and without stopping the noise canceller. To do. A wraparound prevention filter 34 includes a path estimation filter unit 34a that estimates a transfer system of a backpropagation path that wraps around from a noise detection point side to an output end of an erasure filter 33 via a noise cancellation point, and a path estimation filter. A wraparound elimination filter section 34b that simulates a transfer system of a sneak path by setting an inverse filter coefficient of the filter coefficient of the section 34a.
The path estimation filter unit 34a receives the detection signal of the acoustoelectric converter 31 at the noise detection point as an input, and outputs the output signal of itself and the electroacoustic converter 32 at the noise elimination point side as an acoustoelectric converter. The filter coefficient is determined so as to eliminate the difference from the electric output signal obtained from it, and the output signal of the elimination filter 33 is input to the wraparound elimination filter section 34b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise canceling apparatus for canceling noise by creating a canceling sound having the same amplitude and opposite phase as the noise waveform and radiating the canceling sound.

Recently, in order to improve the working environment,
In particular, it is required to reduce the noise generated by the equipment installed and used near people. Conventionally, a passive noise elimination method is generally used as such a noise reduction method. This passive noise elimination method takes noise countermeasures by using sound absorbing materials, sound insulating materials, etc., but there is a problem that the sound absorbing materials, sound insulating materials, etc. are large in scale for low frequency noise. The need for active noise reduction is increasing.

[0003]

2. Description of the Related Art In the active noise canceling method, when noise generated by a device particularly occupies an aperiodic sound component, in order to cancel the noise, a transfer system of a noise propagation path from a noise source to a noise canceling point. Is simulated by using an erasing filter composed of an adaptive digital filter (hereinafter simply referred to as an adaptive filter), noise of these noise sources is detected by acoustic means such as a microphone, and the noise is passed through the erasing filter to be placed at the erasing point. The generated noise is given to the loudspeaker to generate a canceling sound having the same amplitude and opposite phase as the noise waveform, and the canceling noise cancels the noise to cancel the noise. To correct the tap coefficient of this erasure filter, a detection microphone for detecting the residual sound remaining after erasure is installed near the speaker, and the tap coefficient of the adaptive filter is modified based on the information of the residual sound. .

However, in such an adaptive noise canceling system, the canceling sound after radiation propagates in the opposite direction in the noise propagation path and wraps around to the microphone for detecting the noise source, and this wraparound sound enters the canceling filter. As a result, even if the sound is emitted and muted at a point to be erased, the sound cannot be erased accurately, so that the sound cannot be erased sufficiently.

[0005]

As an active noise canceling system for preventing the above, for example, a DSM (Double
Sensing Microphone) method or FILTERED
-There is a U configuration.

In the former DSM method, a wraparound sound detection microphone is provided at a position symmetrical to the noise detection microphone on the noise source side with respect to the noise source side microphone, and the wraparound sound detection microphone is used. The detected wraparound sound is subtracted from the noise detected by the noise detection microphone to cancel the wraparound sound in the detected noise. However, this method requires twice the total distance from the erasing speaker to the microphones for noise detection and wraparound sound detection, which requires a large installation space and bulk, and requires two microphones with uniform sensitivity. However, there are drawbacks such that the same level input cannot be input to both microphones due to the influence of standing waves. The latter FIL
The TERED-U configuration requires a filter longer than the tap length of the erasing filter as a dedicated filter for preventing wraparound, which is difficult to realize when the hardware scale is limited.

Therefore, as a simple method for preventing the wraparound sound, a wraparound prevention filter that simulates a transmission system from the erasing speaker to the noise detection microphone using an FIR filter or the like is provided, and an output signal of the sneak prevention filter is provided. Another solution is to subtract from the microphone output to detect the noise source.

FIG. 10 shows an active noise canceller having such a structure. In the figure, 1 is a noise source, 2 is a housing, 3 is a noise propagation path, 4a is a noise detection microphone on the noise source side,
Reference numeral 12 is a speaker for emitting an erased sound on the noise elimination point side, 4b
Is a microphone for detecting the residual sound after elimination, 9 is an elimination filter made of an adaptive filter, 8'is a wraparound prevention filter made of an adaptive filter, 13 is an output signal of the wraparound prevention filter 8'from the detection signal of the microphone 4a. A subtractor 20 for subtraction is a sound source generator for broadband noise or the like.

In this active noise canceller, in order to learn the filter coefficient of the wraparound prevention filter, the device that is the source of noise is stopped and the sound source generator 2 is used instead.
0 generates noise, and the speaker 12 causes the microphone 4
The filter coefficient is calculated so that the noise (a wraparound sound) that has passed through a and the noise (a wraparound elimination sound) that has passed through the sneak prevention filter become equal and the output of the subtractor 13 becomes zero.

However, since this wraparound prevention filter 8'is a fixed filter, if the filter coefficient deviates from the ideal value due to aging, deterioration of the erasing performance will occur. Further, in order to set the filter coefficient of the wraparound prevention filter 8 ′, it is necessary to include the sound source generator 20, which increases the hardware scale. Furthermore, when initializing or resetting the filter coefficient of the wraparound prevention filter 8 ′, it is necessary to stop the operation of the device or the like that is the noise source, which leads to a decrease in the operating rate of those devices.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a filter for a wraparound prevention filter without providing a sound source generator and without stopping a noise elimination target device. It is to be able to find the coefficient.

[0012]

FIG. 1 is a diagram illustrating the principle of the present invention. The active noise canceling apparatus of the present invention includes an acoustoelectric converter 31 arranged at a noise detection point on the noise source side of a noise propagation path, and an electroacoustic transducer arranged at a noise cancellation point separated in the noise propagation path direction from the noise detection point. An acoustoelectric converter is provided with a converter 32, an erasing filter 33 including an adaptive filter simulating a transfer system of a noise propagation path, and a sneak prevention filter 34 including an adaptive filter simulating a transfer system of a sneak sound propagation path. The detection signal of 31 is eliminated by the filter 3
3 is applied to the electro-acoustic transducer 32 to be applied to the propagating noise in the opposite phase and with the same amplitude to cancel the propagating noise, and the output signal of the canceling filter 33 is converted to the detection signal of the acousto-electric transducer 31 through the sneak filter 34. In the active noise canceller configured to remove the wraparound sound component in the detection signal by giving it, the wraparound prevention filter 34 is
Elimination filter 3 from the noise detection point side via the noise elimination point
The path estimation filter unit 34a that estimates the transfer system of the backward propagating path to the output terminal of 3 and the inverse filter coefficient of the filter coefficient of the path estimation filter unit 34a are set to simulate the transfer system of the detour path. The route estimation filter unit 3 is configured to include the wraparound elimination filter unit 34b.
4a receives the detection signal of the acoustoelectric converter 31 at the noise detection point as an input, and uses the output signal of itself and the electric output signal obtained from the electroacoustic converter 32 at the noise elimination point side as an acoustoelectric converter. The filter coefficient is determined so as to eliminate the difference, and the output signal of the elimination filter 33 is input to the wraparound elimination filter section 34b.

In the above-mentioned active noise canceller, a plurality of electroacoustic transducers are arranged at the noise canceling points by changing the direction in which the canceling sound is emitted. Corresponding to each of these electroacoustic transducers, a canceling filter and a wraparound prevention are provided. It can be configured such that a filter is provided.

Further, in the above-mentioned active noise canceller, temperature detecting means for detecting the atmospheric temperature in the noise propagation path is provided, and when the temperature fluctuation detected by this temperature detecting means exceeds a predetermined value, the electroacoustic transducer. It can be configured to correct the inverse filter coefficient of the anti-wraparound filter while stopping the sound generation by.

Further, in the above-mentioned active noise canceller, a monitoring means for monitoring the fluctuation of the filter coefficient of the canceling filter is provided, and when the filter coefficient of this canceling filter fluctuates from an optimum value to a certain value, the electroacoustic transducer. It can be configured to correct the inverse filter coefficient of the anti-wraparound filter while stopping the sound generation by. Further, in this active noise eliminator, a temperature detecting means for detecting the atmospheric temperature in the noise propagation path is provided, and when the temperature fluctuation detected by the temperature detecting means exceeds a predetermined value, the monitoring section filters the erasing filter. The coefficient may be read out.

Further, the above-mentioned temperature detecting means may be attached to a plurality of points in the noise propagation path, the average value of the detected temperatures of the temperature detecting means may be obtained, and the control may be performed based on the average temperature fluctuation. Good.

[0017]

The noise from the noise source passes through the noise propagation path and is output outside the path. This noise is taken out by the acoustoelectric converter 31 installed in the noise propagation path, and the erasing filter 3 is used.
Enter in 3.

Further, an electroacoustic converter 32 installed on the noise propagation system path behind the preceding acoustoelectric converter 31 when viewed from the noise propagation direction is used as an acoustoelectric converter, and an output signal of this acoustoelectric converter is used. , Sneak path estimation filter 34a
Take the difference from the output signal of. The filter coefficient of the path estimation filter 34a is set to LM so that this output difference is minimized.
The coefficient is determined by a coefficient estimation algorithm such as the S algorithm. As a result, the path estimation filter 34a simulates the propagation system from the acoustoelectric converter 31 to the output side of the elimination filter 33 through the electroacoustic converter 32 used as the acoustoelectric converter.

The electroacoustic transducer 32 on the noise elimination point side can be used as it is as an acoustoelectric transducer, and the electromechanical impedance and the mechanoelectric impedance in that case can be considered to be reversible. When the electroacoustic converter 32 is of a conductive type and is used as an acoustoelectric converter, the frequency characteristic can be corrected by a differentiating circuit or the like.

Also, the noise propagation path is not reversible unless the kind of noise is accompanied by an air flow and the noise propagation path is extremely short with respect to the noise wavelength.

Therefore, if the inverse filter of the path estimation filter 34a is obtained as the wrap-around elimination filter 34b, a propagation system in which the above system is driven from the reverse is simulated. In other words, this is a simulation of a propagation system in which the electroacoustic transducer 32 is electrically driven and the sound passes through the noise propagation system path and enters the acoustoelectric transducer 31. Therefore, it is the same as the simulation of the sneak path of the active noise canceller.

A plurality of electroacoustic transducers 32 are arranged at the noise elimination point by changing the direction of emission of the elimination sound, and an elimination filter and a wraparound prevention filter are provided corresponding to each of these electroacoustic transducers for control. If done, the noise can be two-dimensionally completely eliminated.

The temperature detection means is provided to detect the atmospheric temperature in the noise propagation path, and when the temperature fluctuation exceeds a predetermined value, the electroacoustic transducer stops sounding while the reverse of the wraparound prevention filter. If the filter coefficient is modified, noise can be eliminated by correctly simulating the sneak path even when the transfer characteristic of the propagation path fluctuates with temperature.

Further, a monitoring means is provided to monitor the fluctuation of the filter coefficient of the elimination filter, and when the filter coefficient fluctuates from an optimum value over a predetermined value, the electroacoustic transducer stops sounding, while wraparound occurs. If the inverse filter coefficient of the prevention filter is modified, even if the transfer characteristic of the sneak path is changed for some reason, it can be immediately detected and the sneak path can be correctly simulated to muffle noise. Further, the monitoring by the monitoring means can be performed when the temperature fluctuation by the temperature detecting means exceeds a predetermined value.

Further, the above-mentioned temperature detecting means may be attached to a plurality of places in the noise propagation path, and the average value of the temperature detected by each temperature detecting means may be obtained and the control may be performed based on the average temperature fluctuation. Good.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. Throughout the following drawings, circuits denoted by the same reference numerals have the same function.

FIG. 2 shows an active noise canceller as an embodiment of the present invention. In the figure, 1 is a noise source, 2 is a noise source 1
Reference numeral 3 denotes a noise propagation path such as a duct inside the housing 2 through which the noise of the noise source 1 propagates. Reference numeral 4a denotes a microphone arranged at a noise detection point in the noise propagation path 3 so as to detect noise on the noise source 1 side. After the device 7a and the subtractor 13,
It is configured to be input to the elimination filter 9 which is an adaptive filter.

Further, a speaker 12 of an electrodynamic type or the like for emitting an erasing sound is arranged at a noise erasing point which is separated by a predetermined length in the noise propagation direction on the noise propagation path 3 from the noise detection point. The point is provided with a microphone 4b for detecting the residual sound after the erasure. The residual sound detection signal of the microphone 4b is supplied to the amplifier 5b and the aliasing prevention filter 6
b, through the A / D converter 7b, and is inputted to the elimination filter 9 as a filter coefficient updating input. The output of the erasing filter 9 is branched into two, one of which is emitted as an erasing sound from the speaker 12 through the D / A converter 10, the aliasing prevention filter 6d, the amplifier 5d, and the switch 11a, and the other is a wraparound prevention filter described later. 8 is input.

Further, when the speaker 12 is used as an acoustoelectric converter, the detection signal is a switch 11a and an amplifier 5.
c, anti-aliasing filter 6c, differentiating circuit 17, A / D
It is input to the wraparound prevention filter 8 via the converter 7c, the switch 11b, and the subtractor 19. The wraparound prevention filter 8 is connected to the subtractor 13 side via a delay device 14.

FIG. 3 shows a more detailed structure around the wraparound prevention filter 8. As shown in the figure, the wraparound prevention filter 8 has two filter parts, that is, a sneak path estimation filter 8a and a sneak sound elimination filter 8
b, and the detour route estimation filter 8a has an A / D
The output signal of the converter 7a is input through the delay device 14a,
The filter output signal is input to the subtractor 19. The switching unit 11b is connected to the other input terminal of the subtractor 19. Further, the output signal of the canceling filter 9 is inputted to the wraparound sound canceling filter 8b, and the filter output signal is inputted to the subtracter 13 via the delay device 14b.

The wrap-around prevention filter 8 and the elimination filter 9 are adaptive digital filters, and DS
It is realized by P (Digital Signal Processor).

The operation of the apparatus of this embodiment will be described below.
Noise is output from the noise source 1 existing inside the housing 2 such as a computer or an electronic device through the noise propagation path 3 to the outside of the housing 2. First, the operation of obtaining the filter coefficient of the wraparound prevention filter 8 will be described. At this time, the switching device 11
Both a and 11b can be switched to the side.

The noise generated by the noise source 1 is taken out by the microphone 4a placed at the noise detection point, and the noise detection signal is amplified by the amplifier 5a and the anti-aliasing filter 6.
a, the A / D converter 7a, and the delay device 14a, and is input to the sneak path estimation filter 8a.

Since the electrodynamic speaker 12 installed on the noise propagation path 3 behind the microphone 4a as viewed from the noise propagation direction also operates as an acoustoelectric converter because of its reversibility of operation, this speaker 12 is used. It is used as an acoustoelectric converter, and its detection signal is used as a switch 11a, an amplifier 5c,
It is led to the subtractor 19 through the aliasing prevention filter 6c, the differentiating circuit 17, the A / D converter 7c, and the switching device 11b.

Here, the differentiating circuit 17 is necessary for correcting the frequency characteristic when the electrodynamic speaker 12 is used as an acoustoelectric converter, and in the present embodiment, it is a stage preceding the A / D converter 7c. Although it is composed of analog elements,
It may be configured by software in the wraparound prevention filter 8 configured by a DSP in the subsequent stage of the converter 7.

The difference between the output signal of the A / D converter 7c and the output signal of the previous sneak path estimation filter 8a is taken by the subtractor 19 and the filter of the sneak path estimation filter 8a is made to minimize this output difference. The coefficients are determined by a coefficient estimation algorithm such as the LMS algorithm. Here, the noise detection signal from the microphone 4a side via the sneak path estimation filter 8a and the switcher 1 from the speaker 12 side.
The time of the delay device 14 is set such that the phase relationship with the noise detection signal passing through 1 becomes the same in the subtractor 19.

As a result, the sneak path estimation filter 8a
From the microphone 4a to the noise propagation path 3 and the speaker 1
2 via the switch 11a, the amplifier 5c, the anti-aliasing filter 6c, the differentiating circuit 17, the A / D converter 7
This means that the transmission system of the path (the reverse path of the so-called wrap-around path) passing through the switch 11b is simulated.

In the sneak path estimation filter 8a, the filter coefficient of this transmission system is obtained, and the inverse filter coefficient of the filter coefficient is obtained. This inverse filter coefficient can be regarded as the same as that simulating a propagation system in which the previous propagation system is driven from the reverse. Therefore, if this inverse filter coefficient is set in the wraparound sound elimination filter 8b, the wraparound sound elimination filter 8b becomes a filter simulating the wraparound path.

Next, the switches 11a and 11b are switched to the side to eliminate noise. The output signal from the erasing filter 9 is passed through the D / A converter 10, the aliasing prevention filter 6d, the amplifier 5d, and the switch 11a, and the speaker 12 for muffling.
Drive and emit an erasing sound for the propagated noise. Another microphone 4b for detecting the residual sound installed near the speaker 12 captures the residual sound that remains unerased at the mute point.

The residual sound detection signal from the residual sound detecting microphone 4b is input to the erasing filter 9 through the amplifier 5b, the aliasing prevention filter 6b and the A / D converter 7b. The elimination filter 9 determines a filter coefficient based on the residual sound information by a coefficient estimation algorithm such as an LMS algorithm.

Elimination filter 9 output to speaker 12
The elimination sound signal of is also directly input to the wraparound sound elimination filter 8b. The wraparound sound canceling filter 8b generates a wraparound sound canceling signal simulating the wraparound sound based on the canceling sound signal, and the sneak canceling sound signal is inputted to the subtracter 13 through the delayer 14b, and the subtractor 13 At, the difference is obtained from the noise detection signal detected by the microphone 4a. As a result, the wraparound sound included in the noise detection signal (the erased sound emitted from the speaker 12 wraps around the microphone 4a following the noise propagation path 3 in the opposite direction) is canceled by the wraparound erased sound signal. Therefore, the output signal of the subtractor 13 can be considered as a noise detection signal from which the wraparound component has been removed, and this noise detection signal is input to the elimination filter 9. Accordingly, the elimination filter 9 can generate an accurate elimination sound signal, and the propagation noise can be sufficiently eliminated by the elimination sound emitted from the speaker 12 at the noise elimination point.

Various modifications are possible in carrying out the present invention. For example, although the differentiating circuit 17 in the above-described embodiment is configured by an analog element in the front stage of the A / D converter 7, it is configured by software in the sneak prevention filter 8 formed of the DSP in the rear stage of the A / D converter 7. You may.

The delay unit 14 may be formed of a logic circuit using analog elements, but may be formed of software in the wraparound prevention filter 8 formed of a DSP at the subsequent stage.

The subtracter 19 may also be provided digitally by providing a hardware subtraction circuit as in the embodiment, but may be constructed by software in the wraparound prevention filter 8 composed of a DSP.

When a piezoelectric acoustoelectric converter is used as the speaker 12, the differentiating circuit 17 is unnecessary.

The subtractor 13 may be configured digitally based on a logic circuit, but may be configured by software in the sneak prevention filter 8 or the elimination filter 9. The output signal after subtraction is transferred to the erasure filter 9 when it is configured by software in the wraparound prevention filter 8, and the output after subtraction is transferred to the wraparound prevention filter 8 when it is configured by software in the cancellation filter 9. Configure as follows.

Also, in the above embodiment, the speaker 1
In order to reduce that the erasing sound output by 2 becomes a rounding sound and enters the microphone 4a,
The directivity of “a” may be a unidirectional directivity that faces the noise source 1 and forms a blind spot with respect to the speaker 12 direction. To do this, take the difference between the output signals of the two omnidirectional microphones,
Directivity may be provided by adding a time constant having a constant delay time to the output signal of one of the two microphones.

Further, the radiation characteristic of the speaker 12 may be given a directivity so that the microphone 4a has a unidirectional directivity which is a blind spot. To that end, a structure may be adopted in which a time constant having a constant delay time is added to the output signals of a plurality of omnidirectional speakers to give directivity.

FIG. 4 shows an active noise canceller as another embodiment of the present invention. In the sound deadening process in the above-described embodiment, since the propagation path 3 is longer in the lateral direction than the wavelength of noise, erasing of one-dimensional sound waves is sufficient and only one erasing speaker is required. This means that when the noise component is composed of two-dimensional components in the vertical direction and the horizontal direction, only one of the components is erased, that is, one-dimensionally. In the embodiment shown in FIG. 4, the noise when the propagation path of the noise is longer not only in the horizontal direction but also in the vertical direction as compared with the wavelength,
This is a two-dimensional erasure for more complete noise erasure.

That is, in FIG. 4, the noise propagation path 3
At the noise elimination point in the inside, a speaker 12t is provided in a direction perpendicular to the speaker 12, and another sneak-in prevention filter 8, an elimination filter 9 and their associated circuit systems are provided separately from that of the speaker 12. To drive the speaker 12t.

The operation of the apparatus of this embodiment is basically the same as that of the above-mentioned embodiment. The difference is that the speaker 12 system circuit generates an erasing sound so as to eliminate the vertical component of the propagation noise, while the speaker 12t system circuit eliminates so as to eliminate the horizontal component of the propagation noise. It is generating sound.

FIG. 5 shows another embodiment of the present invention. Generally, the transfer characteristic of the noise propagation path 3 changes under the influence of temperature change. Therefore, in order to perform accurate noise elimination, it is necessary to correct the filter coefficients of the wraparound prevention filter 8 and the elimination filter 9 with respect to the temperature change. The apparatus of the embodiment shown in FIG. 5 is an active noise canceller having a filter coefficient correction function for such temperature changes.

In FIG. 5, reference numeral 15 is a temperature detecting sensor for detecting the atmospheric temperature of the noise propagation path 3, and the temperature detection signal is inputted to the CPU 16 via the A / D converter 7e. The CPU 16 is also supplied with the output signal of the subtractor 19 for updating the filter coefficient of the sneak path estimation filter 8a, and can instruct the elimination filter 9 to operate / stop the correction of the filter coefficient. It is like this.

The basic operation of the apparatus of this embodiment shown in FIG. 5 is the same as that of the above-mentioned embodiment. In this example device,
Normally, active noise cancellation is performed with the switch 11 being switched to the side.

The temperature detecting sensor 15 detects the atmospheric temperature in the noise propagation path 3, the CPU 16 reads the temperature change, and when the temperature change exceeds a certain value, the CPU 16 stops the correction of the filter coefficient of the erasing filter 9, Next, the switch 11 is operated to switch from side to side to stop the emission of the erasing sound by the speaker 12 and prepare to correct the filter coefficient of the wraparound prevention filter 8.

When the coefficients of the wraparound prevention filter 8 are modified, the CPU is also in a state in which the filter coefficient modification is gradually converged.
The CPU 16 monitors based on the output signal of the subtractor 19, and when the filter coefficient is in a converged state, the CPU 16 switches the switching device 11 from side to side. As a result, the speaker 12 again generates an erasing sound to perform the erasing operation, the erasing filter 9 corrects the filter coefficient based on the residual sound detection signal from the microphone 4b, and the active noise erasing operation is performed.

FIG. 6 shows another embodiment of the present invention. In the apparatus of the embodiment shown in FIG. 5 described above, there is only one temperature detection sensor for temperature correction, and only one temperature can be detected, but in general, the temperature in the noise propagation path 3 is biased depending on the location. There is a high possibility that The embodiment of FIG. 6 is adapted to cope with such a temperature deviation.

That is, in FIG. 6, the noise propagation path 3
Temperature detecting sensors 15a to 15e are provided at a plurality of locations (five in the embodiment) inside, and the temperature detection signals are respectively guided to the multi-channel A / D converter 21, and the multi-channel A / D converters are provided. The converter 21 converts it into a serial signal and inputs it to the CPU 16.

The basic operation of the apparatus of this embodiment shown in FIG. 6 is the same as that of the embodiment shown in FIG. As a difference, in the apparatus of this embodiment, the temperature detection sensors 15a to 15e detect temperatures at a plurality of points in the noise propagation path 3, and the CPU 16 reads the temperature changes respectively, and the CPU 16 outputs the detection sensor output. When the temperature change reaches a certain value, the coefficient correction of the erasing filter a is stopped, and then the switch 11 is operated to switch from side to side, and the speaker 12 produces a sound. And prepare to correct the filter coefficient of the wraparound prevention filter 8.

When the filter coefficient of the wraparound prevention filter 8 is modified, the CPU 1 shows a state in which the coefficient modification converges.
6 monitors, and when the coefficients are in a converged state, CPU 1
Reference numeral 6 switches the switching device 11 from side to side. As a result, the speaker 12 again generates an erasing sound and performs the erasing operation, the filter coefficient of the erasing filter 9 is corrected, and the active noise erasing operation is performed.

FIG. 7 shows another embodiment of the present invention. The propagation characteristics of the noise propagation path 3 may change due to various factors other than the above-mentioned temperature change. In this embodiment, such a change in propagation characteristic can be dealt with.

In FIG. 7, in this embodiment, the temperature detecting sensor is not provided, and the CPU 16
It is possible to monitor the convergence of the coefficient of the wraparound prevention filter 8 based on the output signal of the subtractor 19, and to monitor the fluctuation of the filter coefficient of the elimination filter 9.

The basic operation of the apparatus of this embodiment is the same as that of the embodiment of FIG. That is, normally, the active noise elimination is performed with the switch 11 being switched to the side. During the active noise elimination, the CPU 16 monitors the variation of the filter coefficient of the elimination filter 9 via the parallel interface directly connected to the CPU 16.

The detection signal of the microphone 4b input to the erasing filter 9 is the residual sound component at the erasing point. The filter coefficient of the elimination filter 9 when the residual sound component is the minimum is stored in the CPU 16, and when a certain constant coefficient variation occurs from the stored elimination filter coefficient,
While stopping the generation of the erasing sound by the speaker 12,
Switching from side to side for the switch 11,
The filter coefficient of the wraparound prevention filter 8 is corrected.

The CPU 16 also monitors the state where the correction of the filter coefficient of the wraparound prevention filter 8 is converged. When the filter coefficient is converged, the CPU 1
Reference numeral 6 switches the switching device 11 from side to side. The speaker 12 again generates an erasing sound by the output signal of the erasing filter 9 in which the filter coefficient at the time of the previous erasing operation is stored and starts the erasing operation, and the wraparound sound is generated by the corrected coefficient of the wraparound prevention filter 8. While removing the noise, the active noise canceling operation is performed while correcting the filter coefficient of the canceling filter 9 based on the residual sound detection signal of the microphone 4b.

FIG. 8 shows still another embodiment of the present invention. In this embodiment, the embodiment of FIG. 5 and the embodiment of FIG. 7 are combined, that is, the variation of the adaptive filter coefficient described above is monitored when the atmospheric temperature value detected by the temperature detection sensor varies. It was done like this. Therefore, in this embodiment, the temperature detection sensor 15 is provided,
The detected temperature value is input to the CPU 16 via the A / D converter 7e.

The basic operation of the apparatus of this embodiment is the same as that of the embodiment of FIGS. That is, normally the switching device 1
Active noise cancellation is performed while 1 is switched to the side.

The CPU 16 monitors the coefficient variation of the elimination filter 9 via a parallel interface directly connected to the CPU 16. On the other hand, the residual sound component at the erasing point is detected by the microphone 4b and input to the erasing filter 9.

The CPU 16 stores the filter coefficient of the erasing filter 9 when the residual sound component is the minimum, and stops the sounding by the speaker 12 when the coefficient variation of a certain constant value occurs from the stored filter coefficient, while switching. The device 11 is switched from side to side to correct the filter coefficient of the wraparound prevention filter 8.

However, the CPU 16 stores the filter coefficient of the elimination filter 9 when the residual sound is minimum and constantly checks whether or not a certain constant coefficient variation occurs from the stored adaptive filter coefficient. When shared with other devices, there is a drawback that the load of software processing of the CPU 16 is increased and the efficiency is reduced.

Therefore, in the apparatus of this embodiment, the CPU 16 reads the temperature change detected by the temperature detecting sensor 25 installed in the noise propagation path 3, and the CPU 16 finds that the temperature change has a certain value. Only when the determination is made, the coefficient variation of the elimination filter 9 is monitored via the parallel interface directly connected to the CPU 16. As a result, the CPU 16 only needs to read the temperature information, so that the load on the CPU 16 can be reduced.

The CPU 16 also monitors the state in which the correction of the temperature change coefficient is converged. When the coefficient is converged, the CPU 16 switches the switching unit 11 from side to side. The speaker 12 again performs the erasing operation by generating an erasing sound by the output signal of the erasing filter 9 while the coefficient of the previous erasing operation is stored, and the active noise erasing operation is performed by the corrected coefficient of the erasing filter 9. Be seen.

FIG. 9 shows an apparatus according to still another embodiment of the present invention. In this embodiment, the embodiment of FIG. 8 is further improved so that the variation of the filter coefficient is monitored when the average value of the detected temperatures of the plurality of temperature detecting sensors for detecting the atmospheric temperature changes. is there. Therefore, in the device of the present embodiment, a plurality of temperature detecting sensors 15a to 15e are arranged at a plurality of positions in the noise propagation path 3, and the temperature detected values thereof are sent to the CPU 16 via the multi-channel A / D converter 21. It is designed to be input to.

The basic operation of the apparatus of this embodiment is the same as that of the embodiment of FIG. As a difference, the CPU monitors the filter coefficient of the erasing filter 9 when the average value of the temperatures detected by the plurality of temperature detecting sensors 15a to 15e exceeds a certain value.

That is, the detection outputs of the temperature detecting sensors 15a to 15e arranged at a plurality of positions in the noise propagation path 3 are multiplexed by the A / D converter 21 and taken into the CPU 16, and the average value of the detected temperatures is obtained. Is calculated and the average temperature change is monitored in the CPU 16. The CPU 16 monitors the filter coefficient variation of the erasing filter 9 via a parallel interface directly connected to the CPU 16 only when the average temperature change reaches a certain value. Other operations are the same as in the case of the apparatus of the embodiment shown in FIG.

[0076]

As described above, according to the present invention, the distance from the erasing speaker to the microphone is shortened, the tap length of the dedicated filter for preventing the wraparound is shortened, and the broadband noise is reduced. It is not necessary to provide a sound source generator such as, etc.-Because the coefficient of the wraparound prevention filter can be determined without stopping the operation of the noise source device, it is possible to prevent the operating rate of the noise source device from decreasing. It has the effect of eliminating active noise, such as being able to mute sound regardless of whether it is a non-periodic sound or not, and it greatly contributes to maintaining a comfortable surrounding environment for equipment installed indoors.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a block diagram showing an active noise canceller as an embodiment of the present invention.

FIG. 3 is a block diagram showing a more detailed structure of a wraparound prevention filter portion in the embodiment apparatus.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing another embodiment of the present invention.

FIG. 6 is a block diagram showing another embodiment of the present invention.

FIG. 7 is a block diagram showing another embodiment of the present invention.

FIG. 8 is a block diagram showing another embodiment of the present invention.

FIG. 9 is a block diagram showing another embodiment of the present invention.

FIG. 10 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Noise Source 2 Housing 3 Noise Propagation Path 4a Noise Detection Microphone 4b Residual Sound Detection Microphones 5a, 5b, 5c, 5d Amplifiers 6a, 6b, 6c, 6d Anti-Folding Filters 7a, 7b, 7c A / D Converter 8 Wrap Prevention filter 8a Detour route estimation filter 8b Detour elimination filter 9 Elimination filter 10 D / A converter 11, 11a, 11b Switcher 12 Speaker 13 Subtractor 14, 14a, 14b Delay device 15, 15a-15e Temperature detection sensor 16 CPU (Central processing unit) 17 Differentiating circuit 19 Subtractor 20 Sound source generator 21 Multi-channel A / D converter

Claims (6)

[Claims] 1. An acoustoelectric transducer (31) arranged at a noise detection point on a noise source side of a noise propagation path, and an electroacoustic conversion arranged at a noise elimination point separated from the noise detection point in the noise propagation path direction. And a canceling filter (33) including an adaptive filter simulating the transfer system of the noise propagation path,
And a wraparound prevention filter (34) that is an adaptive filter that simulates a transmission system of a propagation path of a sneak sound, and applies a detection signal of the acoustoelectric converter to the electroacoustic converter through the elimination filter to reverse propagation noise. Propagation noise is eliminated by applying the same phase and amplitude, and the output signal of the elimination filter is given to the detection signal of the acoustoelectric converter through the sneak filter to remove the sneak sound component in the detection signal. In the active noise canceller configured as described above, the sneak prevention filter (34) estimates a transfer system of a sneak back propagation path from the noise detection point side to the output end of the erasure filter via the noise cancellation point. The path estimation filter unit (34a) and an inverse filter coefficient of the filter coefficient of the path estimation filter unit are set to simulate the transfer system of the sneak path. The path estimation filter unit receives the detection signal of the acoustoelectric converter at the noise detection point as an input, and outputs the output signal thereof and the electroacoustic converter on the noise cancellation point side. Is used as an acoustoelectric converter, the filter coefficient is determined so as to eliminate the difference from the electric output signal obtained from the acoustoelectric converter, and the output signal of the cancellation filter is input to the sneak cancellation filter unit. Noise canceler. 2. A plurality of electroacoustic transducers are arranged at the noise canceling points by changing the direction in which the canceling sound is emitted, and an erasing filter and a sneak prevention filter are provided corresponding to each of these electroacoustic transducers. The active noise canceller according to claim 1, which is provided. 3. A temperature detecting means for detecting an atmospheric temperature in a noise propagation path is provided, and when the temperature variation detected by the temperature detecting means exceeds a predetermined value, the electroacoustic transducer stops producing sound. On the other hand, the active noise canceller according to claim 1 or 2, wherein the inverse filter coefficient of the wraparound prevention filter is corrected. 4. A monitoring means is provided for monitoring the variation of the filter coefficient of the elimination filter, and when the variation of the filter coefficient of the elimination filter exceeds a predetermined value, the electroacoustic transducer stops sounding. 3. The active noise canceller according to claim 1 or 2, wherein the inverse filter coefficient of the wraparound prevention filter is modified while being made to do so. 5. A temperature detecting means for detecting an atmospheric temperature in a noise propagation path is provided, and when the temperature variation detected by the temperature detecting means exceeds a predetermined value, the monitoring section determines the filter coefficient of the erasing filter. The active noise canceller according to claim 4, which is adapted to read out. 6. The temperature detecting means is attached to a plurality of points in a noise propagation path, an average value of detected temperatures of the temperature detecting means is obtained, and control is performed based on the average temperature fluctuation. Item 7. The active noise canceller according to item 3 or 5.