JP2015158542A - Noise reduction method in closed space, and noise reduction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise reduction system for actively cancelling all sounds in a closed space where a number of reflection sounds are superposed on noise.SOLUTION: The noise reduction system includes: a microphone 1 which collects a sound within a room that is a closed space, and generates a first acoustic signal S1 representing the sound; band pass filters 21-2N each having a predetermined bandwidth defining a resonant frequency for each mode of separately calculated standing waves within the room as a central frequency, for extracting specific frequency components from the first acoustic signal S1, respectively, and generating second acoustic signals S21-S2N; phase adjusting means 31-3N for adjusting phases and gains of the second acoustic signals S21-S2N for generating third acoustic signals S31-S3N cancelling the standing waves, respectively; an adder 4 which adds the third acoustic signals S31-S3N, respectively, to generate a fourth acoustic signal S41; and a speaker 6 which emits cancellation sounds of the standing waves into the room on the basis of the fourth acoustic signal S41.

Description

  The present invention relates to a noise reduction method and a noise reduction system in a closed space, and is particularly useful when applied to reduce noise that enters a room from an outdoor noise source such as a wind turbine of wind power generation.

  A wind power generation system is attracting attention as one of the technologies for providing renewable energy. At the same time, there is a problem that wind turbines constituting the wind power generation system become noise sources due to the generation of wind noise. Thus, appropriate noise reduction measures using a windmill as a generation source are an urgent issue to be solved in order to promote the spread of wind power generation systems.

  On the other hand, various active noise reduction techniques have already been proposed, but most of them deal with a continuous spectrum of sound with a bandwidth, and mute for a specific environment and specific equipment (for example, Non-patent document 1). That is, (a) When producing anti-phase sound in a place close to the noise source itself (example: silence of a gas turbine, diesel generator, etc.), (b) The positional relationship between the noise source and the listener and the surrounding environment are fixed. (Example: reduction of siren noise heard by ambulance drivers, silence of helicopter cabin), (c) noise propagation path is fixed (example: silence in air conditioning ducts and exhaust ducts), (d ) In case of reflected sound control (example: active sound insulation wall of highway), (e) In case of silence only in ear (example: commercially available noise canceling earphone), etc.

  By the way, the sound audible in the room is superimposed on the sound reflected from the wall or the like in addition to the direct sound from the noise source entering from the window or the like, and the phase cannot be predicted. Noise can be canceled by measuring the sound at the position of the ear and generating the opposite phase sound there as in the above-mentioned prior art (the principle of noise canceling earphones), but a number of reflected sounds are superimposed on the incident sound. It is not possible to actively cancel all the sounds of the entire room.

  Further, in the method of detecting the acoustic signal representing the noise radiated from the noise source as in the above prior art and radiating another acoustic signal opposite in phase to the acoustic signal to suppress the noise, the noise at a specific position is Even if it can be reduced, the sound generated by the acoustic signal different from the noise source is generated, so that there is a problem that the amount of noise increases at a position outside a specific position.

  Recently, a noise canceller (see Non-Patent Document 2) called “Sono” has been proposed as a device for preventing external noise from being attached to a window of a house. This is because the device attached to the window emits vibrations in the opposite phase to the noise, making the window itself a large noise-cancelling speaker and reducing outdoor noise.

  However, the basic principle that the noise canceller basically reduces noise by using a sound having a phase opposite to that of the noise is not different from the conventional noise canceling method. Therefore, it has the same problem as described above. Furthermore, there is no effect on noise entering through a route other than windows.

  Further, as a measure for preventing noise entering from the outside, measures such as making the window of the house a double window are taken, but in this case, there is an inconvenience that the window cannot be opened.

Masaharu Nishimura, Atsushi Usagawa, Shiro Ise, Active Noise Control, Corona, 2008 Speaker "Sono" shuts out outside noise just by attaching to the window, URL; see www.gizmodo.jp/2013/11/sono.html

  In view of the above prior art, the present invention provides a noise reduction method and a noise reduction system in a closed space that can actively cancel the sound of a specific closed space in which a number of reflected sounds are superimposed on the noise itself. With the goal.

  The configuration of the present invention that achieves the above object is based on the following knowledge. For example, if wind power generation becomes widespread in the future, there is a possibility that it will be installed in the vicinity of a house. In this case, no matter how much measures are taken on the windmill side, noise generation cannot be made zero. On the other hand, a slight sound or sometimes a pleasant sound may be a serious unpleasant sound by a person. In this way, there are many problems that cannot be solved only by cutting off the noise source in various societies, and complete silence is not always required. Therefore, in the process of thinking that there are no other mitigation measures on the victim side other than sound insulation and sound absorption, I came up with the idea of removing resonance in the room.

  As a result of simple basic experiments, it was found that very low frequency resonances and their extreme enhancement can easily occur even in houses of general size due to the standing wave of various modes and the principle of Helmholtz resonance. I understood.

  If it is resonance, the phase of the entire room is synchronized, so there is a possibility that the noise of the entire room can be reduced with a canceling sound from one place. On the other hand, it is difficult to target the entire space with the conventional active noise control. In addition, while the application range of the conventional active noise control technology is effective at a wavelength of about 500 Hz or less, the wavelength does not significantly affect the cancellation accuracy when the synchronized phase is handled. It was found that there is a possibility of being applicable to frequencies around 1 KHz.

The first aspect of the present invention based on such knowledge is as follows:
A first step of obtaining a resonance frequency for each mode of each standing wave related to sound in a closed space targeted for noise reduction by calculation or measurement,
A second step of obtaining a first acoustic signal representing the sound by detecting the sound of the space with sound collecting means installed at a position other than the nodes of the standing waves in the space;
By inputting the first acoustic signal to each band-pass filter whose center frequency is adjusted in advance to each resonance frequency, the second acoustic signal in a predetermined band included in each band-pass filter is input to each of the band-pass filters. A third step of obtaining the output of the bandpass filter;
A fourth step of obtaining a third acoustic signal by adjusting a gain of the third acoustic signal so that each standing wave corresponding to each resonance frequency is canceled;
A fifth step of emitting a canceling sound of the standing wave into the space by driving a control sound source arranged at a position antinode of each standing wave in the space with the third acoustic signal; There is a noise reduction method in a closed space, characterized by comprising:

The second aspect of the present invention is:
In the noise reduction method in the closed space described in the first aspect,
In the fourth step, the third acoustic signal is obtained by adjusting the phase as well as the gain of the third acoustic signal so that each standing wave corresponding to each resonance frequency is canceled. The feature is a noise reduction method in a closed space.

The third aspect of the present invention is:
In the noise reduction method in a closed space described in the first or second aspect,
A sixth step of obtaining the fourth acoustic signal by adding the third acoustic signals by the adding means, respectively;
The control sound source is a noise reduction method in a closed space, which is driven by the fourth acoustic signal to radiate the standing wave canceling sound in the space.

The fourth aspect of the present invention is:
In the noise reduction method in a closed space described in any one of the first to third aspects,
The method of reducing noise in a closed space, wherein the first acoustic signal in the second step is detected by sound collecting means disposed at a corner where each side in the three-dimensional direction of the space intersects. It is in.

According to a fifth aspect of the present invention,
In the noise reduction method in a closed space described in any one of the first to third aspects,
The first acoustic signal in the second step is obtained by averaging the acoustic signals detected by a plurality of sound collecting means respectively disposed on each side in the three-dimensional direction of the space, or of the space The noise reduction method in a closed space is characterized in that the sound signals detected while moving the sound collecting means along each side in the three-dimensional direction are obtained on average.

The sixth aspect of the present invention is:
In the noise reduction method in a closed space described in any one of the first to fifth aspects,
In the noise reduction method in a closed space, the canceling sound is radiated from a control sound source arranged at the corner of the space.

The seventh aspect of the present invention is
A sound collecting means that is disposed at a position other than the nodes of each standing wave related to sound in a closed space that is a target for noise reduction, and that collects the sound and generates a first acoustic signal representing the sound. When,
A specified bandwidth having a center frequency that is a resonance frequency for each mode of each standing wave in the space obtained by calculation or measurement, and the center frequency is different based on the first acoustic signal. A plurality of band-pass filters that extract the frequency components of and generate a second acoustic signal;
A plurality of gain adjusting means for adjusting the gain of the second acoustic signal to generate a third acoustic signal for canceling each standing wave;
A control sound source that is disposed at a position that is antinode of each standing wave in the space and that is driven by the third acoustic signal to emit the canceling sound of the standing wave in the space. The feature is in a noise reduction system in a closed space.

The eighth aspect of the present invention is
In the noise reduction system in a closed space described in the seventh aspect,
The noise in a closed space, wherein the gain adjusting means adjusts the phase together with the gain of the second acoustic signal to generate a third acoustic signal for canceling each standing wave. In the reduction system.

The ninth aspect of the present invention provides
In the noise reduction system in a closed space described in the seventh or eighth aspect,
The noise reduction system in a closed space is characterized by having addition means for generating a fourth acoustic signal for driving the control sound source by adding the third acoustic signals.

The tenth aspect of the present invention provides
In the noise reduction system in a closed space described in any one of the seventh to ninth aspects,
The sound collecting means is in a noise reduction system in a closed space, characterized in that the sound collecting means is disposed at a corner where each side in the three-dimensional direction of the space intersects.

The eleventh aspect of the present invention is
In the noise reduction system in a closed space described in any one of the seventh to ninth aspects,
The sound collecting means generates the first acoustic signal by averaging the plurality of acoustic signals respectively detected at a plurality of locations on each side in the three-dimensional direction of the space, or the three-dimensional direction of the space The noise reduction system in a closed space is characterized in that the first acoustic signal is generated by averaging the acoustic signals detected while being moved along the respective sides.

The twelfth aspect of the present invention provides
In the noise reduction method in a closed space described in any one of the seventh to eleventh aspects,
The control sound source is in a noise reduction system in a closed space, which is disposed at the corner of the space.

  The present invention selects and controls only the resonance frequency, focusing on the fact that the unique resonance in a closed space such as a house amplifies the noise. In resonance, the phase is synchronized in the whole space, and the maximum amplitude is always in the corner portion of the space, so that the resonance in the whole space can be controlled from the control sound source arranged in the corner. Since the resonance frequency is specific to a specific closed space, a number of target natural resonance frequencies are separated by the same number of bandpass filters, and only the sound of each resonance frequency is individually controlled, so that the standing wave of each mode is Amplitude can be individually reduced to reduce noise. In this case, the noise source is not limited to the outside of the space but may be in the space. In addition, since the resonance frequency and the sound of the frequency in the vicinity thereof are selected by the band pass filter, it is possible to avoid an increase in noise other than the resonance frequency. That is, the sound of other frequencies is not radiated as a cancel sound. As a result, for example, a window can be opened and the noise environment can be improved with a simple and inexpensive device.

  Furthermore, in a relatively high frequency band, there are many cases to deal with by absorbing noise with a normal sound absorbing material. However, since the sound absorbing material absorbs non-resonant frequencies in the same manner as the resonant frequency, the resonance sound is reduced. However, the non-resonant sound may attenuate more than necessary at the same rate, resulting in an acoustic environment with a feeling of pressure. In contrast, in the present invention, only the resonance frequency can be attenuated, so that a natural acoustic environment can be realized.

It is a conceptual diagram which shows the state which has arrange | positioned the sound collection means and the control sound source in the house which becomes the closed space to which the noise reduction system which concerns on embodiment of this invention is applied. It is a wave form diagram which shows the waveform of the standing wave of each mode of primary-tertiary. It is explanatory drawing which shows an example of the rectangular parallelepiped which imitated the room in the case of calculating the resonance frequency of the room (closed space) which reduces noise. It is explanatory drawing which shows an example of the combination of the rectangular parallelepiped and cylinder which imitated the room in the case of calculating the Holm Hertz resonance frequency in case the duct is attached to the room (closed space) for reducing noise. It is a block diagram which shows the noise reduction system which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a conceptual diagram showing a state in which sound collection means and a control sound source are arranged in a house that is a closed space to which a noise reduction system according to an embodiment of the present invention is applied. As shown in the figure, noise from a noise source 102 such as a windmill of a wind power generation system enters a room 101 of a house 100 forming a closed space through a window 101A or the like. Here, the noise source 102 need not be limited to the case where the noise source 102 is outside the room 101. It may be in the room 101. The house 100 may resonate and generate a loud sound due to noise intrusion. Resonance usually occurs when standing waves of a plurality of types of modes are generated in the room 101. In this embodiment, the sound generated in the room 101 including the standing wave SW (for the sake of simplicity, the standing wave of the lowest frequency is shown in FIG. 1) is collected by the microphone 1 to generate an acoustic signal, The acoustic signal is subjected to predetermined processing (described in detail later), and then supplied to the speaker 6, and the resonance sound is reduced by radiating the canceling sound of the standing wave SW from the speaker 6 into the room 101. Therefore, the microphone 1 in this embodiment is disposed near the ceiling 101B of the room 101 that becomes the antinode of the standing wave SW, and the speaker 6 is arranged near the floor surface 101C that also becomes the antinode of the standing wave SW. In this case, the arrangement positions of the microphone 1 and the speaker 6 do not need to be exactly the antinode positions. Also, the effect is inferior, but basically it is not necessary to be at the node position. However, the microphone 1 and the speaker 6 can be disposed on the antinode of the standing wave SW by being disposed at the end or corner of the room 101.

  Here, the position of the microphone 1 for picking up the sound does not have to be the same corner as that of the canceling speaker 6, but in this case, the phase of the sound to be radiated depends on the resonance mode such as the primary and secondary modes. Since it is different in the reverse phase mode and also varies depending on the time delay of the signal processing system caused by the frequency, individual control for each frequency is required.

  FIG. 2 is a waveform diagram showing an example of each mode of standing waves generated in the room. FIG. 4A shows a standing wave having the lowest resonance frequency (primary mode), FIG. 5B shows a standing wave having a resonance frequency that is twice that of the standing wave (secondary mode), and FIG. (Tertiary mode). In such a standing wave, the resonance frequency becomes an integral multiple every time the mode order increases. Incidentally, when the wind turbine of the wind power generation system is used as the noise source 102, the frequency of the standing wave in the primary mode may be 10 or more Hz lower than the audible frequency. The purpose of this embodiment is to cancel a standing wave in a low frequency range of about 10 Hz to 100 Hz. However, there is no need to limit the frequency band. An appropriate selection can be made according to the resonance frequency to be canceled.

If the shape (dimension) of the room 101, generally the shape (dimension) of the closed space is determined, the resonance frequency of the standing wave generated in the room 101 is uniquely specified by calculation or actual measurement. A method for calculating the resonance frequency when the room 101 (closed space) is a rectangular parallelepiped will be described with reference to FIG. As shown in FIG. 3, given the dimensions of the vertical L ₁ , horizontal W, and height H of the room 101 that is the object of calculation in this case, the resonance frequency in the room 101 is given by the following equation (1).

[Equation 1]
f = (c / 2) {(n _x / L ₁ ) ² + (n _y / W) ² + (n _z / H) ² } ^1/2 (1)

Here, _nx , _ny , and _nz are integers, and c is the speed of sound. The lowest resonance frequency is usually the primary mode of the longest side, and is 17 Hz if the longest side is 10 m. If a corridor is included, this condition can be satisfied even in ordinary houses, and there are a large number of resonance frequencies.

Furthermore, as shown in FIG. 4, if the length L ₂ and the opening diameter d is and ventilation tower number m, it is conceivable to resonate at the Helmholtz resonance frequency. The Helmholtz resonance frequency at this time is given by the following equation (2).

[Equation 2]
f = dc / {4 (πVL ₂ ) ^1/2 } (2)

However, this expression (2) is an approximate expression, L ₂ is the length of the ventilation tower, d is the opening diameter, and V is the volume of the space. For example, if the duct length is 2 m in a space of 3 m × 5 m × 2.4 m, f to 6d (Hz) becomes the resonance frequency, and resonance of 10 Hz or less can also occur. That is, it is suggested that these resonance phenomena may amplify an ultra-low frequency below the audible band, which is often a problem in wind power generation.

  Regardless of which resonance occurs, the resonance oscillation is synchronized in phase throughout the space. This is a big difference from the case of handling unresonant sound. In the standing wave, the resonance of any mode always becomes the maximum sound pressure amplitude portion at the corner of the room 101.

  The noise reduction method according to the present embodiment uses these properties, first measures the resonance frequency with the microphone 1 placed in advance in the corner of the room 101, passes through a band-pass filter that passes only that frequency, and then passes through the room 101. The resonance of the entire interior of the room 101 is canceled by emitting a sound having a phase opposite to that of the resonance sound from the corner. Specifically, the following processes are included.

1) The resonance frequency for each mode of each standing wave related to the sound in the room 101, which is a closed space that is a target for noise reduction, is obtained by calculation or measurement. At the same time, each center frequency of the bandpass filter prepared corresponding to the resonance frequency to be canceled is adjusted to each resonance frequency. Here, the calculation of the resonance frequency is performed using the formula (1) or the formula (2) described based on FIG. 3 or FIG. In the actual measurement, it is desirable to collect the sound in each traveling route while moving the microphone along each side of the room 101 and average the levels of the collected acoustic signals. As a result, it is possible to eliminate the influence of reflected sound interference different from the resonance phenomenon.

2) As shown in FIG. 1, a sound in the room 101 is detected by the microphone 1 installed at a position that becomes an antinode of each standing wave in the room 101 to obtain a first acoustic signal representing the sound.

3) By inputting the first acoustic signal to each bandpass filter whose center frequency is adjusted in advance to each resonance frequency, the second acoustic signal in a predetermined band of each bandpass filter is input to each bandpass filter. Get as filter output.

4) The third acoustic signal is obtained by adjusting the phase and gain of the third acoustic signal so that each standing wave corresponding to each resonance frequency is canceled.

5) A third acoustic signal is added by an adder to obtain a fourth acoustic signal.
6) As shown in FIG. 1, the speaker 6 disposed at the position where the antinode of each standing wave in the room 101 is driven by the fourth acoustic signal, and the canceling sound of each standing wave is emitted into the room 101. To do.

  Thus, according to the present embodiment, standing waves in each mode due to noise whose phases are synchronized in the entire room 101 can be suppressed satisfactorily.

  Such a noise reduction method can be realized, for example, in the noise reduction system shown in FIG. FIG. 5 is a block diagram showing a noise reduction system according to the embodiment of the present invention. As shown in the figure, the noise reduction system according to the present embodiment includes a microphone 1, a plurality of band pass filters 21, 22,..., 2N, a plurality of phase adjusting means 31, 32,. A unit 4, an amplifier 5, and a speaker 6.

  Here, the microphone 1 is a closed space that is a target for noise reduction, for example, at a position that becomes an antinode of each standing wave related to the sound generated in the room 101 of the house (see FIG. 1; the same applies hereinafter). The first sound signal S1 representing the sound is generated by collecting the sound. A plurality of bandpass filters 21, 22,..., 2N corresponding to each of the first to Nth modes are predetermined with the resonance frequency of each standing wave mode in the room 101 as the center frequency. Specific frequency components having different center frequencies based on the first acoustic signal S1 are extracted to generate second acoustic signals S21, S22,... S2N.

  The phase adjusting means 31, 32, ..., 3N adjust the phase and gain of the second acoustic signals S21, S22, ..., S2N to cancel each standing wave S31, S32,..., S3N are generated. Thereby, the time delay can be adjusted.

  The adder 4 adds the third acoustic signals S31, S32,..., S3N to generate a fourth acoustic signal S4 that becomes a cancel signal for each standing wave.

  The speaker 6 serving as a control sound source is disposed at the corner of each standing wave in the room 101 and is driven by the fourth acoustic signal S4 to emit a canceling sound of each standing wave into the room 101.

  In this embodiment, the phase and gain of the second acoustic signals S21, S22,..., S2N are adjusted by the phase adjustment means 31, 32,. Thus, the noise caused by the standing wave in the room 101 is attenuated by setting the canceling sound to the optimum phase and gain. Here, when adjusting the gain, by adjusting the gain so that it gradually increases from the lowest level, the predetermined adjustment can be performed satisfactorily without causing inconvenience such as howling in the room 101. Can be implemented.

  In the above embodiment, the same number of phase adjusting means 31, 32,..., 3N are provided corresponding to the bandpass filters 21, 22,. .., 2N when the time delay between the first acoustic signal S1 and the second acoustic signals S21, S22,. Not necessarily required. However, when the band-pass filters 21, 22,..., 2N are constituted by digital circuits, a predetermined delay is always generated during signal processing, so that the phase adjusting means 31, 32,. Phase adjustment by 3N is required. Further, the gain is basically set to 1 or less as long as howling can be prevented. Therefore, it is not always necessary to adjust the gain once for each noise reduction operation by the noise reduction system.

  In addition, a third acoustic signal (phase adjusting means 31 is an output signal of the phase adjusting means 31, 32,..., 3N (or the bandpass filters 21, 22,..., 2N when not provided). , 32,..., And 3N are not added by the adder 4 and are input individually to the plurality of speakers 6 without being added by the adder 4, and the cancellation sounds are emitted from the plurality of speakers 6. It can also be configured to.

  INDUSTRIAL APPLICABILITY The present invention can be used in the industrial field of manufacturing and selling noise reduction equipment that reduces environmental noise and contributes to the realization of a comfortable society.

DESCRIPTION OF SYMBOLS 1 Microphone 21-2N Band pass filter 31-3N Phase shifter 4 Adder 6 Speaker 100 House 101 Room 102 Noise source SW Standing wave

Claims (12)

A first step of obtaining a resonance frequency for each mode of each standing wave related to sound in a closed space targeted for noise reduction by calculation or measurement,
A second step of obtaining a first acoustic signal representing the sound by detecting the sound of the space with sound collecting means installed at a position other than the nodes of the standing waves in the space;
By inputting the first acoustic signal to each band-pass filter whose center frequency is adjusted in advance to each resonance frequency, the second acoustic signal in a predetermined band included in each band-pass filter is input to each of the band-pass filters. A third step of obtaining the output of the bandpass filter;
A fourth step of obtaining a third acoustic signal by adjusting a gain of the third acoustic signal so that each standing wave corresponding to each resonance frequency is canceled;
A fifth step of emitting a canceling sound of the standing wave into the space by driving a control sound source arranged at a position antinode of each standing wave in the space with the third acoustic signal; A noise reduction method in a closed space, characterized by comprising: In the closed space noise reduction method according to claim 1,
In the fourth step, the third acoustic signal is obtained by adjusting the phase as well as the gain of the third acoustic signal so that each standing wave corresponding to each resonance frequency is canceled. A characteristic noise reduction method in a closed space. In the noise reduction method in the closed space according to claim 1 or 2,
A sixth step of obtaining the fourth acoustic signal by adding the third acoustic signals by the adding means, respectively;
The method for reducing noise in a closed space, wherein the control sound source is driven by the fourth acoustic signal to radiate the canceling sound of the standing wave in the space. In the noise reduction method in the closed space as described in any one of Claims 1-3,
The method of reducing noise in a closed space, wherein the first acoustic signal in the second step is detected by sound collecting means disposed at a corner where each side in the three-dimensional direction of the space intersects. . In the noise reduction method in the closed space as described in any one of Claims 1-3,
The first acoustic signal in the second step is obtained by averaging the acoustic signals detected by a plurality of sound collecting means respectively disposed on each side in the three-dimensional direction of the space, or of the space A method for reducing noise in a closed space, characterized in that the sound signals detected while moving the sound collecting means along each side in a three-dimensional direction are averaged. In the noise reduction method in the closed space as described in any one of Claims 1-5,
The method for reducing noise in a closed space, wherein the canceling sound is radiated from a control sound source arranged at the corner of the space. A sound collecting means that is disposed at a position other than the nodes of each standing wave related to sound in a closed space that is a target for noise reduction, and that collects the sound and generates a first acoustic signal representing the sound. When,
A specified bandwidth having a center frequency that is a resonance frequency for each mode of each standing wave in the space obtained by calculation or measurement, and the center frequency is different based on the first acoustic signal. A plurality of band-pass filters that extract the frequency components of and generate a second acoustic signal;
A plurality of gain adjusting means for adjusting the gain of the second acoustic signal to generate a third acoustic signal for canceling each standing wave;
A control sound source that is disposed at a position that is antinode of each standing wave in the space and that is driven by the third acoustic signal to emit the canceling sound of the standing wave in the space. A noise reduction system in a closed space. The noise reduction system in a closed space according to claim 7,
The noise in a closed space, wherein the gain adjusting means adjusts the phase together with the gain of the second acoustic signal to generate a third acoustic signal for canceling each standing wave. Reduction system. The noise reduction system in a closed space according to claim 7 or claim 8,
A noise reduction system in a closed space, comprising addition means for generating a fourth acoustic signal for driving the control sound source by adding the third acoustic signals. In the noise reduction system in the closed space according to any one of claims 7 to 9,
The noise collection system in a closed space, wherein the sound collecting means is disposed at a corner where each side in the three-dimensional direction of the space intersects. In the noise reduction system in the closed space according to any one of claims 7 to 9,
The sound collecting means generates the first acoustic signal by averaging the plurality of acoustic signals respectively detected at a plurality of locations on each side in the three-dimensional direction of the space, or the three-dimensional direction of the space A noise reduction system in a closed space characterized in that the first acoustic signal is generated by averaging the acoustic signals detected while moving along each side of the. In the noise reduction method in the closed space as described in any one of Claims 7-11,
The noise reduction system in a closed space, wherein the control sound source is disposed at the corner of the space.

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