JP2003186478A - Device and method for noise control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a proper secondary sound even in the presence of another noise source in a duct by a device or method which radiates a proper secondary sound for noise propagated in the duct and radiated to reduce the noise by interference. <P>SOLUTION: A noise detection microphone 3 is provided nearby a noise source and a signal processing part 4 generates a control signal according to its detection signal to radiate a secondary sound from a secondary-sound radiation speaker 5. The control signal is optimized to nearly the same amplitude with and the opposite phase from the noise and information on that is obtained by computing the noise propagated from the noise source to a muting point by a duct inside passing noise simulating means 11 and computing the secondary sound through the simulation of a secondary sound simulating means 13. An error signal simulating means 14 adds the computed simulated noise and secondary sound and the control signal is so adjusted as to minimize their error component. Consequently, a decrease in interference by noise generated in the duct 2 can be evaded. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control device for reducing a noise by generating a secondary sound having substantially the same amplitude as the noise but an opposite phase.

[0002]

2. Description of the Related Art As a method of reducing noise, there is known a method of utilizing sound interference. As one of them, a noise source is covered with a long cylindrical box called a duct, and a secondary sound with almost the same amplitude and opposite phase as the noise propagating inside the duct is radiated into the duct, and it is positively influenced by the interference of these sounds. There is an active noise control device that effectively reduces noise. In this device, the noise propagating in the duct is regarded as a one-dimensional plane wave,
Secondary sound that interferes with this is emitted from an acoustic speaker mounted on the wall surface of the duct. The secondary sound radiated from the acoustic speaker is generated in the signal processing device in consideration of the acoustic transfer characteristics inside the duct. Also,
In order to maintain the optimum noise reduction effect even if there is a change in the acoustic transfer characteristics due to a temperature change in the duct or a change in the characteristics of the acoustic speaker that emits secondary sound, the calculation coefficient in the signal processing device is changed to the above characteristic changes. Corresponding adjustments are being made.

FIG. 2 is a schematic block diagram showing an example of a conventionally known active noise control device. In this noise control device, a duct 22 that surrounds the noise source 21 and is open at one end is provided to limit the propagation of sound waves generated from the noise source 21 in one direction (direction toward the open end of the duct 22). . The cross-sectional dimension of the duct 22 is set sufficiently smaller than the wavelength of the noise so that the noise propagating inside the duct 22 can be regarded as a primary plane wave.

The noise source 21 inside the duct 22
A noise detection microphone 23 (noise detection means) that detects noise generated from the noise source 21 and converts the noise into an electric signal is installed near the. The detection signal S11 obtained by the noise detection microphone 23 is sent to the signal processing unit 24, and in the signal processing unit 24, according to a calculation coefficient preset according to the acoustic transfer characteristics in the duct 22 and the like. The control signal S12 is calculated by adding arithmetic processing to the detection signal. The calculated control signal S12 is radiated from the secondary sound emission speaker 25 into the duct 22 as a secondary sound, and interferes with the noise propagating in the duct 22 from the noise source 21.
At this time, if the secondary sound and the noise are completely in the same amplitude and opposite phase relationship, the two cancel each other out, and the sound pressure after interference becomes'zero '. Since there is some error between them, the sound pressure does not become'zero 'even after the interference. Therefore, the error detection means 26 for detecting the sound pressure left as an error is provided closer to the opening end side of the duct 22 than the secondary sound emission speaker 25. Then, the calculation coefficient is calculated in the adaptive estimation unit 27 so that the error signal S13 detected by the error detection unit 26 is minimized, and the new calculation coefficient is fed back to the signal processing unit 24 to be updated. By continuing such signal processing, the error detected by the error detection microphone 26 is minimized and a sufficient silencing effect is obtained.

The adaptive estimator 27 is supplied with the detection signal S11 detected by the noise detection microphone 23, which is subjected to the fixed processing by the filter processor 27, and calculates the calculation coefficient based on the signal. It is like this. The filter processing section 27 multiplies the detection signal S11 by the same frequency response characteristic as the electroacoustic transfer characteristic from the output of the signal processing section 24 to the error detecting means 26, and outputs it.
By calculating the calculation coefficient based on the signal thus filtered, the transfer characteristic from the control signal S12 output from the signal processing unit 24 until being detected as the secondary sound by the error detection microphone 26 is canceled. , Which has a good correlation with the noise propagated in the duct 22. The adaptive estimation unit 28 uses the Filtered-X LMS algorithm (B.Widrow and
SD, Stearns, “Adaptive signal processing”, Prent
Ice-Hall, New Jersey, 1985) and the like are known.

The active noise control device as described above is used to reduce the noise of the blower generated from the air conditioning duct, the cooling duct, etc., and is relatively large in commercial buildings, movie theaters, music halls and the like. Has been put into practical use in. In addition, it can be applied to ducts used for internal cooling of office equipment and home appliances. However, such a duct is originally used for blowing air, and often turbulence occurs in the interior of the duct. In particular, ducts used for office automation equipment and home appliances have a length of several tens of centimeters at the most, and the cross-sectional dimensions cannot be sufficiently taken, so that it becomes difficult to flow the wind smoothly, and noise caused by wind disturbance is generated. Is often occurring. When an active noise control device is applied to a duct blowing system that has noise due to such wind turbulence, there is a problem that the correlation between the secondary sound for noise control and the noise propagating in the duct is impaired. It has been pointed out.

Several proposals have been made for such a problem. For example, in Japanese Patent Laid-Open No. 2-280599, a microphone installed inside a duct is provided with a streamlined cowl,
Those that eliminate the effects of wind have been proposed. In addition,
Japanese Patent Laid-Open No. 5-188976 proposes a wire mesh provided between the fan for blowing air and the noise detecting means for rectifying the wind inside the duct.

[0008]

However, the above-mentioned conventional countermeasures have the following problems.
The place where the wind is disturbed inside the duct and noise is generated,
It is not always on the upstream side of the noise detection means. For example, in the case of ducts for internal cooling of OA equipment and home appliances, in order to miniaturize the device, it is necessary to make the duct not a simple rectangular parallelepiped but a complicated shape that bends or changes the diameter inside. There is also. Then, the wind inside the duct collides with the bent portion or the place where the diameter changes, and the flow is disturbed, which causes new noise. In addition, the noise detection means and the error detection means are usually provided with a distance between them in order to secure time for adaptive identification and secondary sound generation. Therefore, when the duct itself has a bend or changes in diameter, a new noise generation location exists between the noise detection means and the error detection means.

As described above, when there is a new noise generation source between the position where the noise detecting means is provided and the position where the error detecting means is provided, the error detecting means detects the noise propagating from the blower. A synthetic wave of sound, which is composed of two factors of noise newly generated at the bent portion and the diameter changing portion, is detected. On the other hand, the noise detected by the noise detection means is almost limited to that propagated from the blower, the linear relationship between the signals obtained by both detection means is destroyed, and the coherence is significantly lowered.

FIG. 3 shows a result of simulating such a phenomenon as to how loud the noise of the blower is, how much noise is added between the two detecting means to lower the coherence. From this result, it has been confirmed that coherence can easily be reduced even with extremely small noise (a noise level of 10 dB or less).

When the coherence of the sound inside the duct is lowered in this way, even if the secondary sound is adaptively estimated on the basis of the noise signal by the noise detecting means and the error signal by the error detecting means, the difference between the two is generated. Since the correlation is low, an appropriate calculation coefficient cannot be obtained.

The invention according to the present application has been made in view of the above problems, and an object thereof is to radiate an appropriate secondary sound with respect to noise emitted by propagating in a duct. An object of the present invention is to provide an active noise control device and a noise control method capable of reducing noise by a good interference effect.

[0013]

In order to solve the above problems, the invention according to claim 1 provides a duct for guiding noise generated from a noise source to an opening end, and a noise source near the noise source from the noise source. Noise detection means for detecting generated noise; signal processing means for generating a control signal for controlling noise from the noise source by calculation based on a signal obtained from the noise detection means; and the signal processing means. From the position where the secondary sound emission speaker that radiates the control signal generated in step 1 as a sound wave into the inside of the duct and the position where the noise detection means is provided, the duct opening side from the position where the secondary sound emission speaker is provided. The data that reaches the acoustic transfer characteristics inside the duct up to the sound deadening point set in is held, and the frequency response processing based on the acoustic transfer characteristics is performed on the detection signal obtained by the noise detection means. Holding a duct internal pass-by noise simulator means for simulating the noise reaching the mute point, the data corresponding to the electro-acoustic transfer characteristic up to the silencing point via the secondary sound radiating loudspeaker from the output of said signal processing means,
Secondary sound simulating means for simulating a secondary sound reaching the silencing point by performing frequency response processing by the electroacoustic transfer characteristic on the output signal of the signal processing means, and an output signal of the secondary sound simulating means. And an output signal of the duct internal passage noise simulating means, and an error signal simulating means for simulating an error component remaining as a result of interference between noise and a secondary sound at a sound deadening point, and an output signal of the error signal simulating means. And a adaptive control processing means for calculating a calculation coefficient of the signal processing means from the detection signal of the noise detection means so that the output of the error signal simulation means is minimized.

In the above noise control device, the noise generated from the noise source propagates inside the duct to the opening end. At the same time, the signal is converted into a signal by the noise detection means provided near the noise source, and a predetermined processing is performed by the signal processing means and output as a control signal. Then, based on this control signal, it is radiated into the duct as a sound wave from the secondary sound radiation speaker,
Interferes with the noise propagating in the duct. Therefore, the noise is effectively reduced by adjusting the control signal so that the secondary sound has substantially the same amplitude and opposite phase as the noise propagating in the duct. Then, the calculation coefficient when the control signal is generated by the signal processing means is set so as to minimize these errors based on the simulation signals generated by the duct internal passage noise simulation means and the secondary sound simulation means. It That is, the error between the noise actually propagated in the duct and the secondary sound actually radiated in the duct is not minimized. Therefore, noise from other factors between the noise source in the duct and the opening end, for example, noise generated by turbulence during ventilation, is excluded and only noise from the noise source originally considered is considered. Secondary sounds can be generated and interfered.

Such a secondary sound interferes with the noise generated in the noise source and propagating to the sound deadening point in the duct, and the detection signal obtained by the noise detecting means to generate the secondary sound. Has a good correlation with the noise propagating in the duct, and a secondary sound having good coherence can be generated by the processing in the signal processing unit. In other words, based on the noise signal detected near the original noise source, new noise uncorrelated with this noise signal tries to generate a secondary sound corresponding to the added noise in the duct. You can avoid the decline.

The interference due to the secondary sound as described above cannot reduce the noise generated by the turbulence of the wind in the duct, but the noise level is lower than that of the original noise source, and By generating the secondary sound that interferes well with the generated noise, the noise can be effectively reduced as a whole. The acoustic transfer characteristics inside the duct and the electroacoustic transfer characteristics from the output of the signal processing means to the sound deadening point can be obtained in advance by experiments or the like.

According to a second aspect of the present invention, a duct for guiding the noise generated from the noise source to the opening end is formed, and the noise generated from the noise source is detected in the vicinity of the noise source. Based on the acoustic transfer characteristics inside the duct, the noise reaching the muffling point set near the opening end of the duct is calculated as a duct internal passage simulated noise, and the noise source is calculated based on the signal obtained from the noise detecting means. Generating a control signal for controlling the noise from the, and generating the control signal and the electroacoustic transfer characteristics until the control signal is radiated from the secondary sound emission speaker to the inside of the duct and reaches the silencing point. Based on this, a secondary sound that interferes with the noise at the muffling point is calculated as a simulated secondary sound, and the simulated secondary sound and the duct interior passing simulated noise are added, and the residual error as a result of the interference at the muffling point is calculated. Minute is calculated as a simulated error signal, the calculation coefficient for generating the control signal is calculated so that the simulated error signal is minimized, and based on the control signal calculated using the calculated coefficient, A noise control method for radiating a secondary sound from a secondary sound radiation speaker into the duct.

In this noise control method, the secondary sound generated based on the noise propagating from the noise source to the muffling point and the detection signal detected in the vicinity of the noise source are respectively calculated as simulated sounds, and these errors are calculated. Since the control signal of the secondary sound is generated by feedback so as to minimize it, even if there is another uncorrelated noise source in the duct from the noise source to the silencing point, the noise from the original noise source It is possible to generate a secondary sound that interferes well with.

According to a third aspect of the present invention, in the noise control method according to the second aspect, the acoustic transfer characteristic generates a sound near the noise source, and the sound is generated near the noise source and at the silencing point. It is calculated based on a detection signal, and the electroacoustic characteristic is calculated based on the control signal and a detection signal at a silencing point of a secondary sound radiated by the control signal.

According to this method, it is possible to easily and surely obtain the acoustic transmission characteristic in the duct and the electroacoustic transmission characteristic from the control signal to the propagation to the silencing point as a secondary sound.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a noise control device according to an embodiment of the present invention. This noise control device is provided so as to surround a blower 1 that is a noise source, and a duct 2 that is provided so as to guide an air flow and noise from this position to an opening end, and a noise that detects noise generated by the blower 1. A detection microphone 3 (noise detection means), a signal processing unit 4 that outputs a control signal S2 for generating a secondary sound from the detection signal S1 detected by the noise detection microphone 3, and a secondary sound is radiated into the duct 2. The secondary sound emission speaker 5, the internal passage noise simulation unit 11 for calculating the noise generated in the blower 1 and propagating to the virtually deadening point 9 near the opening end of the duct 2, and the signal processing unit. Four
The secondary sound simulating means 13 for calculating the secondary sound reaching the virtual silencing point 9 and the signal S3 calculated by the duct internal passage noise simulating means 11 and the secondary sound simulating means 13 are calculated. An error signal simulating means 14 for calculating an error signal at the virtual silence point 9 from the signal S4 and an adaptive estimating section 8 for controlling the signal processing section 4 so that the error amount output from the error signal simulating means 14 is minimized. The filter processing unit 7 performs a filter process on the signal detected by the noise detection microphone 3 and inputs the signal to the adaptive estimation unit 8.

The duct 2 is set so that its cross-sectional dimension is sufficiently smaller than the wavelength of noise to be silenced so that the sound wave emitted from the blower 1 can be regarded as a plane wave.

The noise detecting microphone 3 is provided in the vicinity of the blower, detects noise generated from the blower 1, and converts it into an analog electric signal.

The signal processing unit 4 receives the detection signal S1 of the noise detection microphone 3 and generates a control signal S2 of a secondary sound that interferes with the noise in the duct based on the detection signal S1. The signal processing unit 4 converts the input analog signal into digital data sampled at a predetermined interval, and calculates the control signal S2 according to a calculation coefficient set from this data. The above-mentioned calculation coefficient is determined by the noise propagating from the blower 1 which is a noise source to the muffling point 9 according to the acoustic transfer characteristic 10 in the duct 2 and the noise propagating to the muffling point 9 in the duct based on the control signal S1. The next sound is set to have substantially the same amplitude and opposite phase, and is updated by the output from the adaptive estimation unit 8 at any time.

The secondary sound emission speaker 5 converts the control signal S2 output from the signal processing unit 4 into sound and radiates it into the duct 2, and is provided on the wall surface near the opening end of the duct 2. There is.

The secondary sound simulating means 13 is set with a calculation coefficient having the same frequency characteristic as the electroacoustic transfer characteristic from the control Shinkyo S2 which is the output of the signal processing section 4 to the virtual muffling point 9, and this coefficient is set. According to the above, the output of the signal processing unit 4 is subjected to calculation processing, and the secondary sound reaching the muffling point 9 is calculated as a simulated sound. Regarding the electroacoustic transfer characteristic 12, the microphone is installed at the sound deadening point 9 before the operation of this device, and the input signal to the secondary sound emitting speaker 5 and the virtual sound deadening point 9 are set at the sound deadening point 9 by using an FFT analyzer or the like. It can be obtained as a frequency response function between these two points from the output signal of the installed microphone. Then, this is converted into a numerical model such as a FIR filter model or an IIR filter model, and each coefficient of this model is used as an arithmetic coefficient to perform arithmetic processing on the output signal of the signal processing unit 4, so that the mute point 9 is actually subjected to a microphone. This is to obtain a signal corresponding to the secondary sound obtained by installing.

The above-mentioned passage noise simulating means 11 is
Data corresponding to the acoustic transfer characteristic 10 between the position where the noise detection microphone 3 is provided and the muffling point 9 is held as a calculation coefficient, and the detection signal S detected by the noise detection microphone 3 is held.
1 performs frequency response processing based on the acoustic transfer characteristic 10. As a result, the noise generated from the blower 1 propagates through the duct 2 and reaches the muffling point 9 as a simulated noise by calculation. As for the acoustic transfer characteristic 10, a microphone is installed at the muffling point 9 so that noise generated from the blower is detected by the noise detecting microphone 3.
And a microphone provided at the muffling point 9 to detect the data, and spectrum analysis of these data can be performed. Alternatively, white noise may be generated near the noise detection microphone 3 and detected by the above two microphones.

The error signal simulating means 14 receives the simulated noise S3 calculated by the duct internal passage noise simulating means 11 and the simulated sound S4 calculated by the secondary sound simulating means 13, and adds them. An error component is calculated.
As for this error component, the noise that propagates inside the duct 2 and propagates to the muffling point 9 interferes with the secondary sound that is radiated into the duct 2 and propagates to the muffling point 9, and the component remaining after that is simulated by calculation. It is what I asked for.

The adaptive estimation unit 8 constitutes an adaptive arithmetic processing means together with the filter processing unit 7, calculates the arithmetic count of the signal processing unit 4 so as to minimize the error signal, and optimizes and updates it. It is something to do.

Data corresponding to the electroacoustic transfer characteristic 12 from the control signal S2 to the secondary sound propagating to the muffling point 9 is set in the filter processing unit 7, and the detection signal S1 from the noise detection microphone 3 is set. The filtering process corresponding to the above characteristics is performed. The calculation coefficient is calculated by the adaptive estimation unit 8 based on the signal subjected to such filter processing, so that in the signal processing unit 4, the electroacoustic transfer characteristic 12 from the control signal S1 to the muffling point 9 is obtained. The control signal S2 including the characteristics to be canceled is generated. Therefore, the control signal S2 is set so that the error component is minimized at the muffling point 9, and a secondary sound that favorably interferes with the noise propagated in the duct 2 is generated.

In such a noise control device, when the blower 1 is driven, an air flow is generated in the duct 2, and along with this, noise is generated due to the turbulence of the air flow in the abruptly changing portion 15 of the cross section. This noise propagates to the open end of the duct 2 together with the noise generated from the blower 1. On the other hand, the noise generated by the blower 1 is detected by the noise detection microphone 3 and is input to the signal processing unit 4 and the duct internal passage noise simulation means 11 as the detection signal S1. Further, it is input to the adaptive estimation unit 8 via the filter processing unit 7. Then, in the duct internal passage noise simulation means 11, the noise propagating in the duct 2 to the muffling point 9 is calculated as simulated noise. Further, in the signal processing unit 4, a control signal S2 of a secondary sound that interferes with the noise propagating in the duct at the muffling point 9 is calculated based on the detection signal, and the control signal S2 is the secondary sound simulating means 13. Entered in. Then, in the secondary sound simulating means 13, the secondary sound arriving from the control signal S2 via the secondary sound radiating speaker 5 to the muffling point 9 is calculated as a simulated sound based on the electroacoustic transfer characteristic 12 obtained in advance. To be done.

The simulated noise S3 calculated by the duct inside passage noise simulating means 11 and the simulated sound S4 calculated by the secondary sound simulating means 13 are input to the error signal simulating means 14, and these are added to obtain an error component. To be Then, the control signal S2 that is input to the adaptive estimation unit 8 and is the output of the signal processing unit 4 is output.
The calculation coefficient of the signal processing unit 4 is calculated so that the error component is minimized with respect to the filtered signal having the same response characteristic as the electroacoustic transfer characteristic 12 from the sound deadening point 9 to the muffling point 9. The calculation coefficient obtained here is a calculation coefficient when signal processing is performed on the detection signal S1 by the noise detection microphone 3, and is output as the control signal S2 until it reaches the muffling point 9 as a secondary sound. And a characteristic corresponding to the acoustic transfer characteristic 10 inside the duct 2 are included. Therefore, when this control coefficient is fed back to the signal processing unit 4, and the control signal S2 output based on this is converted into the secondary sound by the secondary sound emission speaker 5 and propagated to the muffling point 9, the blower 1 outputs the control signal S2. The noise that propagates inside the duct and reaches the muffling point 9 has almost the same amplitude and opposite phase, and these sounds exhibit high coherence, and the noise is effectively reduced. That is, in the process of generating the secondary sound that interferes with the noise from the blower 1, the influence of new noise that is not correlated with the noise of the blower 1 such as the turbulence of the air flow in the duct 2 is eliminated, and the coherence is reduced. It is avoided and effective noise reduction is achieved.

[0033]

As described above, according to the active noise control device and the noise control method of the present invention, the information at the mute point is used as the information for optimizing the signal processing for the secondary sound generation. Since the error signal is calculated based on the acoustic transfer characteristics and electroacoustic transfer characteristics that have been obtained in advance, even if there are other noise sources from the noise source to the muffling point, there is high interference with the noise from the original noise source. It is possible to generate a secondary sound that indicates that the noise is effectively reduced.
Therefore, even when there is a concern that noise may be generated due to the flow of wind inside the duct, the bending and the diameter change of the duct can be allowed, which contributes to downsizing of the device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a noise control device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a conventional noise control device.

FIG. 3 is a diagram showing a change in coherence between signals detected by two microphones when a new noise source different from the original noise source is present in the duct in the noise control device shown in FIG. is there.

[Explanation of symbols]

1 Blower (noise source) 2 ducts 3 Noise detection microphone (noise detection means) 4 Signal processing unit 5 Secondary sound emission speaker 7 Filter processing unit 8 Adaptive estimation unit 9 silence points 10 Duct internal acoustic transfer characteristics 11 Duct internal passage noise simulation means 12 Electroacoustic transfer characteristics 13 Secondary sound simulation means 14 Error signal simulation means 15 Turbulent noise sources

Claims (3)

[Claims] 1. A duct for guiding noise generated from a noise source to an opening end, noise detection means for detecting noise generated from the noise source near the noise source, and a signal obtained from the noise detection means. A signal processing unit that generates a control signal for controlling noise from the noise source by calculation; a secondary sound emission speaker that emits the control signal generated by the signal processing unit into the duct as a sound wave; From the position where the noise detection means is provided, hold the data that reaches the acoustic transfer characteristics inside the duct from the position where the secondary sound emission speaker is provided to the silencing point set on the opening side of the duct, A duct internal passage noise simulating means for simulating noise reaching the muffling point by performing frequency response processing by the acoustic transfer characteristic on the detection signal obtained by the noise detecting means; Data corresponding to the electroacoustic transfer characteristic from the output of the processing means to the sound deadening point through the secondary sound emission speaker is held, and frequency response processing by the electroacoustic transfer characteristic is performed on the output signal of the signal processing means. The secondary sound simulating means for simulating the secondary sound reaching the muffling point, the output signal of the secondary sound simulating means and the output signal of the duct internal passage noise simulating means are added, and The error signal simulating means for simulating the residual error component as a result of the interference between the noise and the secondary sound, and the output of the error signal simulating means is the minimum from the output signal of the error signal simulating means and the detection signal of the noise detecting means. A noise control device comprising: an adaptive calculation processing means for calculating a calculation coefficient of the signal processing means. 2. A duct for guiding the noise generated from the noise source to the opening end is formed, the noise generated from the noise source is detected in the vicinity of the noise source, and the obtained detection signal and the acoustic transfer characteristic inside the duct. Based on the above, the noise reaching the muffling point set near the opening end of the duct is calculated as a duct internal passage simulated noise, and the noise from the noise source is controlled based on the signal obtained from the noise detecting means. Based on the generated control signal and the electroacoustic transfer characteristic until the control signal is radiated from the secondary sound emission speaker to the inside of the duct by the secondary sound emission speaker and reaches the silence point. A secondary sound to be interfered with the noise is calculated as a simulated secondary sound, the simulated secondary sound and the duct internal passage simulated noise are added, and the error component remaining as a result of the interference at the muffling point is simulated error signal. When And a calculation coefficient for generating the control signal is calculated so that the simulated error signal is minimized. Based on the control signal calculated using the calculation coefficient, the secondary sound emitting speaker outputs A noise control method comprising radiating a secondary sound into the duct. 3. The acoustic transfer characteristic is calculated on the basis of a detection signal of the sound generated near the noise source and at the noise source near the noise source, and the electroacoustic characteristic is calculated based on the control signal. And the detection signal at the silencing point of the secondary sound radiated by the control signal, the noise control method according to claim 2.