JPH06332468A - Active silencer - Google Patents

Abstract

PURPOSE:To simultaneously silence a periodic sound and a wide band random sound without enlarging a silencer, in an active silencer using a adaptive type FIR filter. CONSTITUTION:This device is provided with adaptive filters 5, 6 by which a periodic sound and a random sound in noise in a duct space 12 are taken out respectively and which generate individually inverse sound signals for each noise signal, an adder circuit 18 which adds this inverse sound signals, a speaker 14 which radiates inverse sound into the duct space 12 based on signals which are summed up in the adder circuit 18, and a monitor microphone 15 which detects a level of a reduced sound after silencing and updates a filter coefficient in each adaptive filter 5, 6 based on the feedback signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates unsteady broadband noise in a sound wave propagation passage such as a space in a duct by applying a reversal sound having an opposite phase and the same amplitude. The present invention relates to improvement of an active muffling device that performs

[0002]

2. Description of the Related Art Generally, an active muffler of this type has a phase opposite to that of an unsteady broadband noise in a sound wave propagation path, such as a space in a duct, and an inversion of the same amplitude. There is an active muffling device that generates a sound to muffle the sound. As this active silencer,
An adaptive FIR (Finite Impulse Response) filter is used, and after generating a reversal sound signal of the same amplitude in antiphase by the adaptive FIR filter with respect to the noise signal in the space output from the detection microphone, the reversal sound signal Is output to the speaker to emit a reverse sound to the space, and a monitor microphone arranged at a predetermined observation point in this space detects a synthesized sound of the noise and the reverse sound emitted from the speaker at the observation point. , The synthetic sound is input as a reduced sound level, and the adaptive F is used to reduce the reduced sound level.
It is known that the sound pressure level around the observation point is reduced by successively updating the filter coefficient of the IR filter (for example, 1988 EA-88- of the Technical Research Report of the Institute of Electronics, Information and Communication Engineers). 29).

[0003]

By the way, as a mode of use of such an active muffler, a periodic noise (hereinafter referred to as a periodic sound) such as a compressor in an air conditioner is targeted, and the periodic sound is generated. When the sound is to be muted (for example, when the compressor noise as disclosed in Japanese Patent Laid-Open No. 3-88600 is muted), or a random sound over a wide band such as a fan in an air conditioner (hereinafter,
It is generally known that a wideband random sound) is targeted and the wideband random sound is muted. However, in these two types of noise, that is, in a space where a periodic sound and a wideband random sound are simultaneously propagated. On the other hand, when the active silencer as described above is provided, the following problems occur. That is, in the space where the two types of noise are simultaneously propagated, the periodic sound component is often projected as a peak, and the periodic sound component is dominant in the entire noise. Therefore, if such active noise is to be silenced by the active muffling device, the adaptive FIR filter is sufficiently adapted to the periodic sound component to mute the periodic sound component. However, it may not be able to sufficiently adapt to a wide band random sound, and as a result, a situation may occur in which only the wide band random sound remains unmuted. Further, as a configuration capable of muting the wide band random sound, it is conceivable to dispose two systems so as to mute the periodic sound and the wide band random sound individually, but this is a large-scale device. However, there is a problem in terms of practicality.

The present invention has been made in view of the above circumstances, and provides an active muffling device capable of muffling a periodic sound and a wide band random sound at the same time without increasing the size of the entire device. With the goal.

[0005]

In order to achieve the above-mentioned object, the present invention provides a muffling signal corresponding to a noise in which a periodic sound and a wide band random sound are mixed and each sound is separated and taken out. Is generated. Specifically, claim 1
As shown in FIG. 1, the described invention outputs a periodic sound signal based on the periodic sound in the noise with respect to the noise transmitted through the noise transmission system (12) and having a mixture of the periodic sound and the random sound. Periodic sound signal output means (16), and a random sound signal output means for outputting a random sound signal based on the random sound in the noise (4a), (13), (17), the periodic sound signal A periodic sound deadening FIR filter (6b) which receives the periodic sound signal from the output means (16) and generates an inverted sound signal having the same amplitude and an opposite phase to the periodic sound signal, and the random sound signal output means (4
a random sound muffling FIR filter (5b) which receives the random sound signals from a), (13) and (17) and generates an inverted sound signal having the same amplitude and an opposite phase to the random sound signal; An adding means (18) for respectively receiving the inverted sound signal from the sound deadening FIR filter (6b) and the random sound signal from the random sound deadening FIR filter (5b) and summing up the respective inverted sound signals, and the adding means (18) ), The FIR filter for silencing the periodic sound
An additional sound source for radiating to the noise transfer system (12) a reversal sound based on a reversal sound signal obtained by adding up a reversal sound signal from (6b) and a reversal sound signal from a random sound deadening FIR filter (5b)
(14) and are provided. Further, monitor means arranged at a predetermined observation point of the noise transmission system (12), which detects the reduction sound level of the periodic sound and the reduction sound level of the random sound at the observation point, and outputs the respective reduction sound signals as feedback ( 15) and
The periodic sound signal from the periodic sound signal output means (16) and the reduced sound signal of the periodic sound fed back from the monitoring means (15) are received, and the periodic sound signal and the period around the observation point are generated by the reduced sound signal of the periodic sound. Periodic sound adaptive algorithm execution means (6c) for updating the filter coefficient of the periodic sound deadening FIR filter (6b) so as to reduce the sound pressure level of the sound, and the random sound signal output means (4a), (13) ), (17) and the reduced sound signal of the random sound fed back from the monitoring means (15) from the monitoring means (15), the sound pressure of the random sound around the observation point by the random sound signal and the reduced sound signal of the random sound. The random sound adaptive FIR algorithm (5b) for updating the filter coefficient of the random sound deadening FIR filter (5b) so as to reduce the level is provided.

According to a second aspect of the present invention, in the active noise suppressor according to the first aspect, random noise signal output means (4a), (13) and (17) detect all noises in the noise transmission system. Noise detection means (13) for outputting the noise signal and periodic sound signal recognition means for receiving the periodic sound from the periodic sound signal output means (16)
(4a), receiving the noise signal from the noise detection means (13) and the periodic sound signal from the periodic sound signal recognition means (4a), and removing only the random sound signal from the noise signal The sound signal extracting means (17) is provided.

[0007]

With the above construction, the present invention provides the following actions. In the invention according to claim 1, for the periodic sound in the noise transmitted through the noise transmission system (12), the periodic sound signal output means (16) outputs a periodic sound signal based on the periodic sound, This output is received by the periodic sound deadening FIR filter (6b), and an inverted sound signal having the same amplitude and an opposite phase to the periodic sound signal is generated. On the other hand, for the random sound in the noise transmitted through the noise transmission system (12), the random sound signal output means (4a), (13), (17) outputs a random sound signal based on this random sound. Then, this output is received by the random sound muffling FIR filter (5b), and an inverted sound signal having the same amplitude and an opposite phase to the random sound signal is generated. Then, after these inverted sound signals are added up by the adding means (18), the signals are transmitted to the additional sound source (14) and radiated from the additional sound source (14) to the noise transfer system (12). Further, the monitoring means (15) detects the reduced sound level at the observation point, the reduced sound signal of the periodic sound is applied to the adaptive algorithm execution means (6c) for the periodic sound, and the reduced sound signal of the random sound is adapted for the random sound. Type algorithm execution means (5d), and each algorithm execution means (6d
c) and (5d) are the corresponding FIR filters (6
The filter coefficients of b) and (5b) are updated sequentially. This allows
Both periodic and random tones will be silenced in one system.

According to the second aspect of the invention, as the random sound signal detecting operation by the random sound signal output means, the noise detecting means (13) detects all noises in the noise transmission system, and the noise detecting means (13) ) Outputs a noise signal to the random sound signal extraction means (17). On the other hand, the periodic sound signal recognition means (4a) outputs the periodic sound signal based on the periodic sound from the periodic sound signal output means (16) to the random sound signal extraction means (17). Then, in the random sound signal extracting means (17), only the random sound signal is taken out by removing the periodic sound signal from the noise signal.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing a control system of the active silencer according to the present embodiment, and FIG. 3 shows an example of a specific configuration thereof. First, the control system of the active silencer will be described with reference to FIG. This system corresponds to the periodic sound and wide band random sound transmitted through a certain transmission system (1) corresponding to the noise from the periodic signal generator (2) and the wide band random signal generator, respectively. A wideband random signal based on the noise from (3) is obtained, and an inversion signal that cancels each signal is generated by the adaptive filters (4), (5), (6), so that each sound is transmitted through the transfer system. After passing through (1), they are each muted. Specifically, the periodic signal from the periodic signal generator (2) is the first adaptive filter (4) and the third adaptive filter (6).
And the wideband random signal from the wideband random signal generator (3) are transmitted to the first adder (7). Then, in the first adder (7), the periodic signal and the wideband random signal are added together, and the added signal is added to the second adder (8).
Have been sent to. Further, the periodic signal transmitted to the first adaptive filter (4) is transmitted from the first adaptive filter (4) to the second adder unit (8), and in the second adder unit (8), The periodic signal is subtracted from the signal obtained by summing the wideband random signal, so that only the wideband random signal remains, and this wideband random signal is added to the second adding unit (8).
To the second adaptive filter (5). Then, in the second adaptive filter (5), a signal that cancels the wide band random signal based on the input wide band random signal, that is, an inverted signal of the same amplitude in the opposite phase with respect to the wide band random signal is generated. Is generated. On the other hand, in the third adaptive filter (6), a signal that cancels the periodic signal based on the input periodic signal, that is, an inverted signal of the same amplitude in opposite phase to the periodic signal is generated. . And the second and third adaptive filters
The inverted signals generated in (5) and (6) are transmitted to the third adder (9) so that the periodic signal and the wide band random signal transmitted through the transmission system are canceled by the inverted signal. It has become. Further, the noise signal state after the canceling operation of this signal is monitored, and the error signal of the periodic signal is the third adaptive filter.
In (6), the error signal of wideband random signal is fed back to the second adaptive filter (5), and each adaptive filter
The inverted signal generated in (5) and (6) is corrected with time so that the periodic signal and the wide band random signal are canceled well.

Next, with reference to FIG. 3, a specific configuration of the active silencer adopting the above-described control system will be described. The active muffling device of this figure is for muffling both the periodic sound and the broadband random sound transmitted in the duct of the air conditioner. Specifically, the periodic sound generated from the electric motor (M) arranged at the upstream end of the duct and the wide band random sound generated from the fan (F) are both silenced.

In this figure, (11) is a duct, inside which is a space (12) as a propagation path (noise transmission system) for noise sound waves from the noise sources (M) and (F) located at the left end in the figure. Are formed. Reference numeral (13) is a detection microphone as noise detection means arranged upstream of the noise propagation direction indicated by the arrow in the space (12) and adapted to detect the noise in the space (12). (14) is an addition for radiating to the space (12) of the duct (11), which is arranged downstream of the detection microphone (13) in the noise propagation direction and has a phase opposite to the noise and having the same amplitude. It is a speaker as a sound source. In the duct (11), a monitor microphone (15) as monitor means is arranged at a predetermined observation point on the downstream side of the speaker (14) in the noise propagation direction. The monitor microphone (15) is adapted to detect, at its observation point, a reduced sound level of noise reduced by the action of the inversion sound emitted from the speaker (14).

The speaker (14) is connected to a controller (21) for generating an inverted sound signal having a phase opposite to that of noise and having the same amplitude via a D / A converter (not shown) or the like. The output signals of the detection and monitor microphones (13), (15) are input to the controller (21) via an A / D converter (not shown) or the like.
A vibration pickup sensor (16) as a periodic sound signal output means is attached to the electric motor (M), and the output signal of the sensor (16) is also input to the controller (21). .

Next, the structure of the controller (21) will be described. The controller (21) includes first to third adaptive filters (4), (5) and (6) and two adder circuits (17) and (18). Then, the adder circuit (17) as a random sound signal extraction means receives the output signal of the detection microphone (13) and the output signal of the first adaptive filter (4), and outputs from the output signal of the detection microphone (13). First adaptive filter
The signal obtained by subtracting the output signal of (4) is transmitted to the second adaptive filter (5). An adder circuit (18) as an addition means receives the output signal of the second adaptive filter (5) and the output signal of the third adaptive filter (6), and sums these signals to produce a speaker (14). It is designed to be sent to.

Next, the adaptive filters (4), (5) and (6) will be described. The first adaptive filter (4) recognizes the vibration signal received from the vibration pickup sensor (16) and generates a periodic sound signal based on the vibration signal. The adaptive FIR filter (4a) as a periodic sound signal recognition means. ) And an algorithm execution unit (4b) for adaptive control. The algorithm execution unit (4b) is a least mean square (LMS; Lea) method.
st Mean Square) adaptive control is performed so that the signal obtained by subtracting the periodic sound signal from the output signal of the detection microphone (13) in the adding circuit (17) becomes an accurate wide band random sound signal. The filter coefficient of the adaptive FIR filter (4a) is updated as a control parameter of the LMS.

The second adaptive filter (5) generates an inverted sound signal to be transmitted to the speaker (14) and then generates the inverted sound signal.
A predetermined transfer function that delays the output signal from the adder circuit (17) for a predetermined time by the propagation time required for the inverted sound radiated from the speaker (14) due to the output to the monitor microphone (15) is input. The first filter (5a), which is an FIR filter, and the noise signal received from the adder circuit (17) are basically opposite in phase and adapted as a random noise canceling FIR filter for generating an inverted sound signal of the same amplitude. Type F
An IR filter (5b) and an F having a predetermined transfer function in order to prevent the inverted sound radiated from the speaker (14) from propagating to the detection microphone (13) and causing howling.
A second filter (5c) including an IR filter and an algorithm execution unit (5d) as an adaptive algorithm execution unit for random sound for adaptive control are provided. The algorithm execution unit (5d) is similar to that of the first adaptive filter (4) in the least mean squares method (LMS; Least Mean Square).
e) Adaptive control using an algorithm, which is based on a signal obtained by delaying a noise signal received through the first filter (5a) and a reduced sound signal fed back from a monitor microphone (15), L) to reduce the sound pressure level of the broadband random sound around the observation point
Adaptive FIR filter (5
The filter coefficient of b) is updated and the inverted sound signal is adaptively controlled and corrected. The second adaptive filter (5) also includes a subtraction circuit (5e) that subtracts the output signal of the second filter (5c) from the output signal of the addition circuit (17).

The third adaptive filter (6) is the motor (M).
Propagation time required for the periodic sound emitted from the speaker to reach the installation position of the speaker (14) and for the reduced sound produced by the inverted sound emitted from the speaker (14) to be input to the monitor microphone (15). The third filter (6a), which is an FIR filter having a predetermined transfer function that delays the output signal of the vibration pickup sensor (16) for a predetermined time, and the periodic signal received from the vibration pickup sensor (16) are basically Adaptive FIR filter (6b) as a FIR filter for silencing periodic sound that generates an inverted sound signal having the opposite phase and the same amplitude
And an algorithm execution unit (6c) as an adaptive algorithm execution means for periodic sound for adaptive control.
The algorithm execution unit (6c), like the first and second adaptive filters (4) and (5), uses the least mean squares method (LM).
S; Least Mean Square) algorithm is used for adaptive control, based on the delayed signal of the noise signal received through the third filter (6a) and the reduced sound signal fed back from the monitor microphone (15). , Update the filter coefficient of the adaptive FIR filter (6b) as the LMS control parameter so as to reduce the sound pressure level of the periodic sound around the observation point in the duct (11), and adaptively control the inverted sound signal. It is supposed to be corrected.

Therefore, with such a configuration, an inverted sound signal that cancels a wide band random signal is generated in the second adaptive filter (5), and a periodic sound signal that cancels a periodic sound signal is generated in the third adaptive filter (6). Inverted sound signals are generated, the inverted sound signals are added up in the adder (18) and transmitted to the speaker (14), and then the inverted sound is radiated from the speaker (14) into the duct space (12). The periodic sound and the wide band random sound in the duct (11) are cancelled, and the inverted sound signals are corrected so that the error signal level from the monitor microphone (15) approaches 0. It has become so. In other words, the correspondence between the specific configuration of the active silencer shown in FIG. 3 and the block diagram of FIG. 2 is that the duct internal space (12) is the transmission system.
In (1), the motor (M), which is one of the noise sources, is connected to the periodic signal generator (2), and the fan (F), which is the other noise source.
Is the wideband random signal generator (3), the detection microphone (13) is the first adder (7), and the adder circuit (17) is the second adder.
The speaker (14) and the monitor microphone (15) correspond to the third adder (9), respectively (8).

Next, a silencing operation for silencing the noise in the duct (11) using the above active silencing device will be described. First, the noise in the space (12) in the duct (11) is detected by the detection microphone (13) and transmitted to the addition circuit (17). On the other hand, the vibration signal of the electric motor (M) detected by the vibration pickup sensor (16) is transmitted to the first adaptive filter (4) and the third adaptive filter (6), respectively. Then, in the first adaptive filter (4), a periodic sound signal is generated based on the vibration signal from the vibration pickup sensor (16), and this periodic sound signal is transmitted to the adding circuit (17). Then, in the adder circuit (17), the periodic sound signal is subtracted from the output signal of the detection microphone (13), so that only the wide band random sound signal is transmitted to the second adaptive filter (5). . Then, the second adaptive filter (5) generates an inverted sound signal that cancels the wideband random signal, while the third adaptive filter (5)
At (6), an inverted sound signal that cancels the periodic sound signal based on the output signal of the vibration pickup sensor (16) is generated. Then, the inverted sound signals generated in each of the adaptive filters (5) and (6) are summed in the adder circuit (18), and then output to the speaker (14) to emit the sound emitted from the speaker (14). Thus, both the periodic sound and the broadband random sound are muted. Further, at the observation point, the reduced noise level, that is, the reduced sound level is detected by the monitor microphone (15), and this reduced noise signal, that is, the reduced sound signal, is output by the second adaptive filter (5) and the third adaptive filter ( 6)
The adaptive FI is fed back to each algorithm execution unit (5d), (6c) of
The filter coefficients of the R filters (5b) and (6b) are sequentially updated. By updating this filter coefficient, the adaptive FIR
The inversion signal generation by the filters (5b) and (6b) is
The noise in 1) is accurately measured over time, and the sound pressure level around the observation point in the duct is reduced best. As described above, according to the configuration of this example, with respect to the noise in which the periodic sound and the wide band random sound are mixed, the respective sounds are separated and extracted, and the muffling signals corresponding to the respective sounds are generated. One system can perform the silencing operation for two types of noise, and can mute the periodic sound and the broadband random sound at the same time without increasing the size of the entire device.

It should be noted that the present invention is not limited to the case where the devices that generate the periodic sound and the wide band random sound are individual devices, but for a device that emits all of these noises. Is also applicable.

(Modification) Next, a modification of the active silencer according to the present invention will be described. In this example, not only a peak sound of a single frequency but also a peak sound of a harmonic composed of a plurality of periodic sounds is emitted from the source of the periodic sound.
For example, this is a configuration considered in the case of muffling noise from a compressor of an air conditioner or the like. That is, a plurality of types of periodic sounds (noise from the compressor, etc.) and broadband random sounds (noise from the fan, etc.) are simultaneously silenced, and the basic configuration is the same as that of the control system shown in FIG. However, since only the generation part of the periodic signal is different, this example describes only the generation part of the periodic signal.

As shown in FIG. 4, in the control system of this example, for a device (M ') that emits a peak sound due to a harmonic,
As means for detecting individual periodic sounds, a vibration pickup sensor (16) is provided and the power supply frequency of this device is detected. In other words, the vibration signal from the vibration pickup sensor (16) is converted into the rotation frequency signal generation circuit (25).
The rotation frequency signal generation circuit (25)
Generates a periodic signal corresponding to a periodic sound based on the rotation frequency, while the power frequency is changed to the power frequency signal generation circuit (2
6) so that the power supply frequency signal generation circuit (2
By 6), the periodic signal corresponding to the periodic sound based on the power supply frequency is generated. Then, the periodic signal generated by each of the signal generation circuits (25) and (26) is input to the harmonic generation circuit (27), and a new harmonic signal is generated by the harmonic generation circuit (27). The first harmonic signal
The signals are transmitted to the adaptive filter (4) and the third adaptive filter (6), respectively. Other configurations are similar to those of the control system shown in FIG.

With such a structure, it is possible to muffle noises in which a wide band random sound and a peak sound due to a harmonic are mixed, respectively, and it is possible to greatly expand the application of the active muffling apparatus. it can.

In this modification, the vibration pickup sensor (16) is adopted as the means for detecting the peak sound due to the harmonics based on the rotation frequency, but a non-contact type vibration detection device or the like is adopted. You can also do it. In the case of adopting the vibration pickup sensor (16),
The mounting position is to be directly mounted on the electric motor or attached to an outer plate or the like attached thereto.

[0024]

As described above, according to the active muffler of the present invention, the following effects are exhibited. According to the invention described in claim 1, the periodic sound signal and the random sound signal are generated by the periodic sound signal output means (16) and the random sound signal output means (4a), (13), (17) in one system. Individually take out each inverted sound signal for silence
After generating by the IR filters (6b) and (5b) and summing up by the adding means (18), the inverted sound based on this inverted sound signal is radiated from the additional sound source (14) to the noise transmission system. It is possible to mute the periodic sound and the broadband random sound at the same time without increasing the overall size.

According to the second aspect of the present invention, the random sound signal output means (4a), (13) and (17) detect all noises in the noise transmission system and output the noise signal. (13),
The periodic sound signal recognition means (4a) that receives the periodic sound from the periodic sound signal output means (16), and the noise signal and the periodic sound signal from the periodic sound signal recognition means (4a) from the noise detection means (13). Since the random sound signal extracting means (17) for extracting only the random sound signal by removing the periodic sound signal from the noise signal is provided, the sound pressure level of the random sound in the whole noise is small. Even in this case, the random sound can be accurately detected and the random sound signal can be output, so that the silencing performance can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing a basic control system of an active silencer according to the present invention.

FIG. 3 is a diagram showing a specific configuration of an active silencer.

FIG. 4 is a view corresponding to FIG. 2 in a modified example.

[Explanation of symbols]

(4a) Adaptive FIR filter (periodic sound signal recognition means) (5b) Adaptive FIR filter (random sound mute F
(IR filter) (5d) Algorithm execution unit (adaptive algorithm execution means for random sound) (6b) Adaptive FIR filter (FIR for mute periodic sound)
Filter) (6c) Algorithm execution part (adaptive algorithm execution means for periodic sound) (12) Space (noise transfer system) (13) Detection microphone (noise detection means) (14) Speaker (additional sound source) (15) Monitor microphone (Monitoring means) (16) Vibration pickup sensor (periodic sound signal output means) (17) Addition circuit (random sound signal extraction means) (18) Addition circuit (addition means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03H 21/00 7037-5J

Claims (2)

[Claims] 1. A periodic sound signal output means (16) for outputting a periodic sound signal based on the periodic sound in the noise with respect to the noise transmitted through the noise transmission system (12) and mixed with the periodic sound and the random sound. ), And random sound signal output means (4a), (13), (17) for outputting a random sound signal based on the random sound in the noise, and the periodic sound signal from the periodic sound signal output means (16) Received,
A periodic sound deadening FIR filter (6b) for generating an inverted sound signal having the same amplitude and an opposite phase with respect to the periodic sound signal, and a random sound from the random sound signal output means (4a), (13), (17). A random sound muffling FIR filter (5b) for receiving a signal and generating a reversal sound signal having the same amplitude as the random sound signal, but a reversal sound signal and a random sound from the periodic sound muffling FIR filter (6b). Addition means (18) for receiving the inversion sound signals from the sound deadening FIR filter (5b) and summing up the respective inversion sound signals
And receiving the output of the adding means (18), the periodic sound deadening FIR
Reverse sound signal from filter (6b) and random sound mute FI
An additional sound source (14) for radiating to the noise transfer system (12) an inversion sound based on the inversion sound signal obtained by adding up the inversion sound signal from the R filter (5b), and a predetermined value of the noise transfer system (12). Monitor means (15) arranged at the observation point, which detects the reduced sound level of the periodic sound and the reduced sound level of the random sound at the observation point and outputs the respective reduced sound signals as feedback, and the periodic sound signal output means ( The periodic sound signal from 16) and the reduced sound signal of the periodic sound fed back from the monitoring means (15) are received, and the sound pressure level of the periodic sound around the observation point is reduced by the periodic sound signal and the reduced sound signal of the periodic sound. From the periodic sound adaptive algorithm executing means (6c) for updating the filter coefficient of the periodic sound deadening FIR filter (6b), and the random sound signal output means (4a), (13), (17) Feedback from random sound signal and monitoring means (15) Underwent reduction sound signal of the random noise, random noise signal and F for random sound muffling to reduce the sound pressure level of the random noise around the observation point by reduction sound signal of the random noise
An active silencer, comprising: an adaptive algorithm executing means (5d) for random sound for updating the filter coefficient of the IR filter (5b). 2. Random sound signal output means (4a), (13), (17)
Is a noise detecting means (13) for detecting all the noise of the noise transmission system and outputting the noise signal, and a periodic sound signal recognizing means (4a) for receiving the periodic sound from the periodic sound signal output means (16), Random sound signal extraction means for receiving the noise signal from the noise detection means (13) and the periodic sound signal from the periodic sound signal recognition means (4a) and extracting only the random sound signal by removing the periodic sound signal from the noise signal ( 17) The active silencer according to claim 1, further comprising: