WO2013114807A1

WO2013114807A1 - Active noise control device

Info

Publication number: WO2013114807A1
Application number: PCT/JP2013/000244
Authority: WO
Inventors: 昌鷹馬場; 敦仁矢野; 田崎　裕久
Original assignee: 三菱電機株式会社
Priority date: 2012-02-03
Filing date: 2013-01-21
Publication date: 2013-08-08
Also published as: JP2015079028A

Abstract

This invention reduces the influence of pipe resonance through a configuration provided with a helmholtz resonator for resonating at a frequency derived from the pipe resonance of an ventilation path. In particular, a high noise cancelling effect is realized through a configuration in which an error detection microphone (4) is disposed in a range near an antinode of a standing wave and a noise detection microphone (3) is disposed in a range near a node contiguous to near the antinode of the standing wave with a phase inverted from that of the antinode where the error correction microphone (4) is disposed. Additionally, an even higher noise cancelling effect is realized by disposing the helmholtz resonator near the antinode of the standing wave occurring due to pipe resonance in the ventilation path.

Description

Active noise control device

The present invention relates to an active noise control device for reducing noise propagating along an air flow along an air passage.

Conventionally, as a means for reducing noise propagating in the duct (or air passage) along with the air flow, a method has been employed in which a sound absorbing material is attached to the inner wall of the duct or combined with bending of the duct. However, it has been difficult to sufficiently reduce noise of 1 kHz or less. As a countermeasure, a method of reducing noise in the low frequency band in the duct by an active noise control technique has been taken. Patent Document 1 provides a detailed description of an active noise control device.

In active noise control, a noise detection microphone, error detection microphone, and control sound source are placed in the duct. The active noise control algorithm is driven using signals detected by the noise detection microphone and the error detection microphone. Specifically, a canceling sound is radiated from the control sound source based on the signal control so that the detection signal from the error detection microphone becomes small. As a result, the noise propagating through the duct and the noise radiated from the control sound source are canceled at the same sound pressure and opposite phase at the position of the error detection microphone, and the sound pressure at the error detection microphone is reduced.

In order to obtain a sufficient noise reduction effect in an actual environment, it is necessary that the detection signals of the noise detection microphone and the error detection microphone have substantially the same frequency characteristics without driving the active noise control. This is because the detection signal from the noise detection microphone is amplified and transmitted from the control sound source, but if the frequency characteristics of the error detection microphone are different, the noise is not successfully canceled at the position of the error detection microphone. In general, the correlation between the frequency characteristics of signals at two detection points is called “coherence”. A state where the coherence value is 1 represents a state where the frequency characteristics of the signals at the two detection points completely coincide.

In an actual environment, there is a problem that the linearity of noise is lost due to the turbulence and vortex of the fluid flowing in the duct, and the signal coherence at the noise detection microphone and the error detection microphone is reduced. Therefore, in Patent Document 1, a device for rectifying the fluid is provided on the upstream side of the active noise control configuration so as to bring the fluid close to a laminar flow state. Thereby, the coherence is improved, and a sufficient noise reduction effect can be obtained with respect to the noise in the duct by the active noise control.

JP 2000-352986 A

Since the conventional active noise control device rectifies the fluid flowing in the duct, it is considered that there is a certain effect on coherence reduction due to fluid turbulence and vortices. However, in the duct, resonance of sound waves occurs in the inside due to the shape of the tube. Due to the influence of the standing wave due to this resonance, depending on the positional relationship between the noise detection microphone and the error detection microphone, a decrease in coherence occurs at a specific frequency derived from tube resonance. As a result, there arises a problem that a sufficient noise reduction effect cannot be obtained.

On the other hand, regarding the arrangement of the noise detection microphone, the error detection microphone, and the control sound source in the duct, it takes time until the signal is amplified and transmitted by the control sound source after the noise is detected by the noise detection microphone. Therefore, it is necessary to take at least a certain distance in order to ensure the calculation delay time required for active noise control. Further, there is a distribution of fluid properties in the duct, and there is an intention to arrange a noise detection microphone and an error detection microphone so that coherence is as high as possible. Therefore, it is also an object of the present invention to dispose the noise detection microphone, the error detection microphone, and the control sound source at a position where the silencing effect of the active noise control device is easily exhibited.

The present invention has an object to solve the above-described problems and prevents a decrease in coherence at a specific frequency associated with duct resonance of a duct. The object is to sufficiently maintain the silencing effect of active noise control by preventing the reduction of coherence.

The active noise control device according to the present invention includes a noise detection microphone, an error detection microphone, and an active noise control device based on a control sound source, and further, a Helmholtz that resonates in the air passage at a frequency derived from tube resonance of the air passage. It is provided with a resonator. By reducing resonance in the tube by the Helmholtz resonator, the silencing effect of the active noise control device can be improved and the above-mentioned object can be achieved.

Furthermore, in another active noise control apparatus of the present invention, the Helmholtz resonator is arranged in the air passage near the antinode of the standing wave generated by the tube resonance. The Helmholtz resonator can effectively realize the silencing effect of the active noise control device.

Furthermore, in another active noise control apparatus of the present invention, the noise detection microphone and the error detection microphone are arranged in the vicinity of an antinode of a standing wave generated by the tube resonance in the air passage. The Helmholtz resonator can effectively realize the silencing effect of the active noise control device.

Furthermore, in another active noise control device of the present invention, a fur material is attached in the vicinity of or inside the port opening of the air passage surface in the Helmholtz resonator. With this feature, it is possible to construct a situation where the port opening is not directly exposed to the airflow, and to reduce the situation where the resonance frequency of the resonator is affected by a new sound source.

In the active noise control device according to the present invention, it is possible to improve the situation where the coherence is reduced between the noise detection microphone and the error detection microphone due to the influence of resonance generated in the duct (or the air duct). In particular, by installing the resonator at the closed end or the “antinode” of the standing wave accompanying the tube resonance, the influence of the tube resonance can be reduced, and the decrease in coherence can be prevented. In addition, in an environment where one of the noise detection microphone and the error detection microphone is installed on the “antinode” of the standing wave accompanying tube resonance, and the other is installed on the “node”, the influence of resonance can be effectively reduced. it can. By using a resonator in combination with the characteristic arrangement of the noise detection microphone 3 and the error detection microphone 4, a great silencing effect can be obtained.

In addition, by installing a fur material around the port opening of the resonator, a situation is created in which the port opening is not directly exposed by the airflow flowing through the duct (or air passage), and the generation of Karman vortices is suppressed. . In addition, a situation where a new sound source is generated and affects the resonance frequency of the resonator can be reduced.

Moreover, by installing a fur material around the port opening of the resonator and the inner wall of the port, it is possible to construct a situation where the port opening is not directly exposed to the airflow. As a result, the generation of Karman vortices is suppressed, and the situation where the resonance frequency of the resonator is affected by a new sound source can be reduced. In addition, the vibrational energy generated between the air column in the port portion and the internal volume increases in frictional resistance, whereby vibration energy is efficiently converted into heat. As a result, the sound absorption effect can be improved.

In addition, by making the cross-sectional area, port length, and internal volume of the resonator variable, it is easy to match the resonance frequency with the standing wave that occurs due to the closed tube resonance of the duct (or air passage). . As a result, the design flexibility of the resonator can be improved. In addition, it is easy to improve the reduction in coherence between the noise detection microphone and the error detection microphone, and the silencing effect can be effectively functioned.

1 is a basic configuration of an active noise control apparatus according to the first embodiment. The basic structure of the active noise control apparatus which showed the calculating means in the 1st step of this Embodiment 1. FIG. The basic structure of the active noise control apparatus which showed the calculation means in the 2nd step of this Embodiment 1. FIG. The basic structure of the active noise control apparatus which showed the calculating means in the 3rd step of this Embodiment 1. FIG. In the first embodiment, the state of the tube resonance and the resonance frequency when the duct (or the air passage) is regarded as a one-side closed tube structure. An actual measurement example 1 of sound pressure characteristics and coherence characteristics in the noise detection microphone 3 and the error detection microphone 4 in the first embodiment. Example 2 of actual measurement of sound pressure characteristics and coherence characteristics in the noise detection microphone 3 and the error detection microphone 4 in the first embodiment. An example of the structure of the resonator 13 according to the first embodiment and a resonance relational expression. The state of one side closed tube resonance when the resonator 13 is used in the first embodiment. A basic configuration of an active noise control apparatus according to the second embodiment. The situation of the single closed tube resonance when the resonator 14 is used in the second embodiment. The basic structure of the active noise control apparatus concerning this Embodiment 3. FIG. The state of one side closed tube resonance when the resonators 13, 14, 15, 16 are used in the third embodiment. 4 is a basic configuration of an active noise control device according to the fourth embodiment. In this Embodiment 4, the active noise control apparatus at the time of installing a fur material in a port inner wall. In the fifth embodiment, an example of a resonator structure in which the port cross-sectional area Sx and the port radius Rx can be made variable and a resonance relational expression. In Embodiment 5, an example of the structure of a resonator capable of making the port length Lx variable and the resonance relational expression. In this Embodiment 5, an example of the structure of the resonator which can make the internal volume Vx of a resonator variable, and a resonance relational expression.

Embodiment 1 FIG.
FIG. 1 shows the basic configuration of an active noise control apparatus according to the first embodiment of the present invention. The active noise control device is sometimes called a silencer. In the figure, reference numeral 1 denotes a duct (or an air passage) through which noise and air flow propagates, and reference numeral 2 denotes a fan noise source that sends the air flow to the duct (or air passage) 1. 3 is a noise detection microphone that detects noise in the duct (or air passage) 1, and 4 is an error detection microphone that similarly detects noise in the duct (or air passage) 1. The noise detection microphone 3 is located closer to the fan noise source 2 than the error detection microphone. Reference numeral 5 denotes a control sound source, which is suppressed so that noise propagating from the fan noise source 2 is canceled out at the position of the error detection microphone 4 by sound radiated from the control sound source 5.

Reference numerals

6 and 8 denote microphone amplifiers that amplify the detection signal, reference numerals 7 and 9 denote A / D converters, and reference numeral 11 denotes a D / A converter. Reference numeral 10 denotes calculation means for deriving a control sound to be radiated from the control sound source 5 based on the detection signal from the noise detection microphone 3 and the detection signal from the error detection microphone 4. Reference numeral 12 denotes a power amplifier that drives the control sound source 5, and 13 denotes a Helmholtz resonator that opens a port toward the inner surface of the duct (or air passage) 1 and resonates. The direction of the air flow by the fan noise source 2 is not limited to the direction of sending out to the duct (or air passage) 1, but may be the direction of sucking out from the duct (or air passage) 1. Further, in other embodiments including this embodiment, the noise propagating through the duct (or the air flow path) 1 may be noise without airflow.

2 to 4 are diagrams for explaining the operation of the computing means 10, and sequentially explaining the transition of the operation of the computing means 10 in FIG. The calculation means 10 of FIG. 1 stores all the functions shown in FIGS. 2 to 4, and only some functions of the calculation means 10 are shown in FIGS. 2 to 4.

FIG. 2 shows the state of the arithmetic means 10 in the first stage, and the internal arithmetic configuration used in this state is expressed as arithmetic means 10a. Reference numeral 10a1 denotes white noise generating means, 10a2 denotes first NLMS (Normalized LMS) algorithm means, and 10a3 denotes second NLMS algorithm means. Reference numeral 101 denotes a transfer characteristic “H” from the control sound source 5 to the noise detection microphone 3, and reference numeral 102 denotes a transfer characteristic “C” from the control sound source 5 to the error detection microphone 4. Here, the transfer characteristic is a parameter representing a transmission state in which a physical quantity such as electricity, heat, vibration, etc. of the object to be measured is transmitted, and is an important parameter for knowing the behavior and behavior of the object to be measured. At this stage, the fan noise source 2 is stopped, and noise and airflow are not generated in the delivery path 1.

As an operation, first, a white noise signal is output from the white noise generating means 10a1 and radiated from the control sound source 5 into the duct (or the air duct) 1 through the D / A converter 11 and the power amplifier 12. This white noise is captured by the noise detection microphone 3 and the error detection microphone 4 and input to the first NLMS algorithm means 10a2 and the second NLMS algorithm means 10a3, respectively. In the first NLMS algorithm means 10a2, the reference signal from the white noise generating means 10a1 and the detection signal from the noise detection microphone 3 are input, and the transfer characteristic “H” 101 in the duct (or air duct) 1 is identified. . Similarly, in the second NLMS algorithm means 10a3, the transfer characteristic “C” 102 in the duct (or air duct) 1 is identified.

Here, the LMS (Least Mean Square) algorithm will be briefly described. The LMS algorithm is a technique for determining a filter coefficient so as to minimize the mean square error between an input signal and a reference signal, and is widely used due to the advantage that the calculation amount is small. The NLMS (Normalized Least Mean Square) algorithm has a feature that the amount of calculation is larger than that of the LMS algorithm, but the convergence speed does not depend on the input signal amplitude. Both are used as general methods in active noise control.

FIG. 3 shows the state of the second stage of the calculation means 10, and the internal calculation configuration in this state is expressed as the calculation means 10b. At this stage, the control sound source 5 is stopped, the fan noise source 2 is steadily operated, and noise and airflow are propagated in the duct (or air duct) 1. Noise propagating through the duct (or air passage) 1 is captured by the noise detection microphone 3 and the error detection microphone 4. Further, the transfer characteristic until the noise detected at the noise detection microphone 3 point reaches the error detection microphone 4 point is identified as “R” 103.

FIG. 4 shows a third stage state of the computing means 10. This stage represents the steady operating state of active noise control. Noise propagating through the duct (or air passage) 1 is detected by a noise detection microphone 3. Thereafter, the transfer characteristic “R” is convoluted with the detection signal by the transfer characteristic R filter 10 c 3, and after passing through the inverter 10 c 4, is output as the operation means 10 c. The output of the computing means 10 c is sent to the control sound source 5, and the control sound is radiated into the duct (or air passage) 1. Further, the transfer characteristic H is convolved with the output of the computing means 10c, and the output of the transfer characteristic H is subtracted from the detection signal in the subtractor 10c1.

The computing unit 10c3 converts the detection signal from the noise detection microphone 3 into a signal at the position of the error detection microphone by convolving the transfer characteristic “R”. In addition, since the noise and phase at the four points of the error detection microphone are aligned as they are, the phase relationship between the sound emitted from the control sound source 5 and the noise is reversed via the inverter 10c4, and the duct. The active noise control state which cancels the noise which leaves (or the ventilation path) 1 is created. The reason for subtracting the output of the transfer characteristic H filter 10c2 in the subtractor 10c1 is to prevent howling. That is, the influence of the signal transmitted from the control sound source 5 to the noise detection microphone 3 is removed. With such a configuration, the noise transmitted from the fan noise source is canceled at the position of the error detection microphone 4 by the sound from the control sound source.

In order for active noise control to function to a high degree, it is necessary to keep the similarity in frequency characteristics of noise detected by the noise detection microphone 3 and the error detection microphone 4 high. This is because the noise transmitted from the fan noise source does not cancel each other out well with the sound from the control sound source unless the frequency characteristics are similar. Here, the correlation between the frequency characteristics of the sound at the two detection points is represented by a parameter called “coherence”, and a state where the coherence value is 1 represents a state where the frequency characteristics of the sound at the two detection points completely match. . According to the cited document 1, for example, there is shown a relationship in which the coherence value should be 0.8 or more in order to obtain the maximum reduction amount of −15 dB.

However, in actuality, the coherence value may decrease due to the influence of pipe resonance or the like in addition to the turbulence or vortex of the fluid flowing through the duct (or air passage) 1. FIG. 5 shows the state of tube resonance and the resonance frequency when the duct (or air passage) is regarded as a one-side closed tube structure. As shown in the figure, the noise transmitted from the noise source is reflected at the open end and the closed end, causing a resonance phenomenon. In FIG. 5, the resonance frequency is calculated with the duct (or air passage) length L being 1.9 m and the sound velocity v being 340 m / sec. For 1 × vibration, 44.7 Hz, for 3 × vibration, 134.2 Hz, for 5 × vibration, 223.7 Hz, for 7 × vibration, 313.2 Hz. In an environment in which a resonance phenomenon occurs, the sound amplitude varies depending on the position in the tube, and therefore, resonance causes a belly and a node. Since resonance occurs at a specific frequency in this way, there is a difference in frequency characteristics between the two microphones depending on the arrangement of the microphones. As a result, it is estimated that a state in which coherence is reduced occurs.

6 and 7 show actual measurement examples of sound pressure characteristics and coherence characteristics of the noise detection microphone 3 and the error detection microphone 4. 6 and 7, the position of the error detection microphone 4 is fixed in the vicinity of the opening end of the duct (or air passage) 1. In FIG. 7, the interval between the noise detection microphone 3 and the error detection microphone 4 is set wider than that in FIG. In FIG. 6, the dip of the detection signal in the noise detection microphone 3 is about 310 Hz corresponding to 7 times vibration, and the dip is shallow (about 5 dB). On the other hand, in FIG. 7, the dip of the detection signal in the noise detection microphone 3 is seen in the vicinity of 220 Hz corresponding to 5 times vibration, and the dip is deep (about 10 dB). Thus, the coherence changes depending on the position of the noise detection microphone 3. 6 and 7, no significant dip is observed in the signal on the error detection microphone 4 side.

In FIG. 6, the dip of the detection signal in the noise detection microphone 3 is about 310 Hz, which is close to the 7-fold vibration. The error detection microphone 3 is placed at a position deviated from the “antinode” of the standing wave, and a dip occurs in the sound pressure characteristics at the three points of the noise detection microphone. In FIG. 7, the dip is about 220 Hz, which is close to the above-mentioned 5 times vibration. An error detection microphone 4 is placed in the vicinity of the “antinode” of the standing wave at the opening of the tube, and a noise detection microphone 3 is placed in the vicinity of the “antinode” that has an opposite phase relationship to that.

6 and 7, there is a strong causal relationship between the occurrence of dip in the sound pressure characteristic, tube resonance, and microphone placement. In particular, when the noise detection microphone 3 and the error detection microphone 4 are in the vicinity of the “antinode” in which the resonance frequency is in an antiphase relationship, or from the “antinode” in which one is in the vicinity of the “antinode” and the other is in an antiphase relationship, When it is placed in the vicinity, it is easily affected by resonance and coherence is likely to decrease. Therefore, in such an environment, the arrangement of microphones for reducing the influence of resonance and maintaining coherence is important.

1 to 4 try to reduce the energy of tube resonance and reduce the occurrence of dip. This resonator is a silencer that applies Helmholtz's resonance principle to reduce a predetermined frequency component of a propagation sound propagating in the intake pipe. FIG. 8 shows an example of the structure of the resonator 13 and a resonance relational expression. When the radius R of the port corresponding to the opening, the cross-sectional area S of the port, the length L of the port, and the internal volume V are set to the frequency F0 based on the relational expression described in the lower part of FIG. Resonance occurs between the volume. As a result, energy is consumed as frictional heat with intense air movement, and a sound absorbing effect on the resonance frequency F0 is obtained.

FIG. 9 illustrates the state of one-side closed tube resonance when the resonator 13 is used, taking the case of 5 times vibration as an example. The amplitude in the amplitude direction indicates the intensity of the tube resonance frequency. In FIG. 9, the sound absorption effect of the resonator 13 suppresses reflection in the single closed tube and suppresses the strength of the standing wave. As a result, in FIG. 1 to FIG. 4, the degree of cancellation of the standing wave in the error detection microphone 4 is weakened, and the detection signal dip in the error detection microphone 4 becomes shallow. As a result, tube resonance is suppressed, and deterioration of coherence between the noise detection microphone 3 and the error detection microphone 4 is reduced.

As described above, it is possible to mitigate a decrease in coherence at a specific frequency due to the pipe resonance of the duct (or air passage). By installing the resonator 13 that selectively and effectively absorbs the frequency affecting the active noise control among the pipe resonances of the duct (or the air passage), the silencing effect can be maintained high.

In particular, the error detection microphone 4 is arranged at the position of the “antinode” of the resonance frequency, and the noise detection microphone 3 is located near the antinode of the standing wave whose phase is reversed from that of the antinode where the first noise detection means is arranged. When arranged in the vicinity of adjacent nodes, it is easily affected by resonance and the coherence tends to decrease. Further, the resonance amplitude is generally larger when the resonance frequency is smaller. Therefore, with respect to resonance having a relatively low resonance frequency such as 3 times, 5 times, and 7 times vibration, the phase of the error detection microphone 4 is inverted from that of the error detection microphone 4 and the phase of the noise detection microphone 3 is inverted from that of the error detection microphone 4. When placed in the range of “belly” to “node”, a large silencing effect can be obtained by using the resonator simultaneously. In this way, a large silencing effect can be obtained by using a resonator together with the characteristic arrangement of the noise detection microphone 3 and the error detection microphone 4.

Embodiment 2. FIG.
FIG. 10 shows a basic configuration of an active noise control apparatus according to the second embodiment of the present invention. A difference from FIG. 1 is that a resonator 14 is attached instead of the resonator 13. The other constituent elements are the same as those in FIGS. 1 to 4, and the description related to active noise control and the description related to tube resonance are the same as those in the first embodiment, and will be omitted.

FIG. 11 illustrates the attachment position of the resonator 14 in the example of 5 times vibration, and the resonator is arranged on the “antinode” of the standing wave of the tube resonance 5 times vibration. Also in this case, by making the resonance frequency F0 of the resonator coincide with the frequency of the tube resonance, the tube resonance can be suppressed by the sound absorption effect. As a result, the occurrence of dip causing deterioration of coherence is suppressed. Thereby, the effect of the active noise control device can be maintained high.

Embodiment 3 FIG.
FIG. 12 shows a basic configuration of an active noise control apparatus according to the third embodiment of the present invention. The difference from FIG. 1 is that a plurality of resonators, specifically, a resonator 14, a resonator 15, and a resonator 16 are attached in addition to the resonator 13. The other components are the same as those in FIGS. 1 to 4, and the description related to active noise control and the description related to tube resonance are the same as those in the first embodiment, and will be omitted. In FIG. 12, the resonators are installed at the top and bottom of the drawing, but they may be installed on the near side and the far side in the duct (or air passage) 1 as long as they are standing waves “belly”. The number of installed resonators is not limited to four, and may be any number.

FIG. 13 shows a state of 5 times vibration when the resonators 13 to 16 are attached. The resonators 14 to 16 are arranged at the position of the “antinode” of the standing wave of the tube resonance 5 times vibration. Also in this case, the resonance frequency F0 of the resonator is made to coincide with the frequency of the tube resonance, and a plurality of resonators are incorporated in the duct (or the air passage) 1. With this configuration, tube resonance is suppressed by the sound absorption effect, and a decrease in coherence can be prevented. Thereby, the silencing effect of the active noise control device can be maintained high.

Embodiment 4 FIG.
FIG. 14 shows a basic configuration of an active noise control apparatus according to the fourth embodiment of the present invention. A difference from FIG. 10 is that a fur material 17 is installed around the port opening of the resonator 14. Here, the fur material represents a material covered with soft hair. In a normal resonator, an air current hits the edge of the port opening, and a Karman vortex may be generated to become a new sound source. In addition, the Karman vortex may have a great influence on the resonance frequency of the resonator.

In FIG. 14, by providing the fur material 17 near the opening of the resonator 14, the airflow flowing inside the duct (or the air passage) can be decelerated. As a result, the edge of the port opening is not directly exposed to the airflow, so that the generation of Karman vortices is suppressed. Further, the influence of the resonator 14 on the resonance frequency is reduced.

In FIG. 14, the fur material 17 is installed around the port opening, but as shown in FIG. 15, the fur material 18 may be installed on the inner wall of the port of the resonator 14. When the configuration of FIG. 15 is used, the frictional resistance of the air vibration generated between the air column of the port portion and the internal volume is increased, and the sound absorption effect can be further improved.

Embodiment 5. FIG.
FIGS. 16 to 18 show an example of a cross-sectional structure of a resonator of an active noise control apparatus according to the sixth embodiment of the present invention. FIG. 16 shows the variability of the port cross-sectional area Sx and the port radius Rx of the resonator. In FIG. 16, by using an area variable resonator, the resonance frequency F0 can be increased by increasing the port cross-sectional area Sx, and F0 can be decreased by decreasing Sx. Adjustment of the port cross-sectional area Sx and the port radius Rx can be performed by using a plastic member or a movable mechanism. FIG. 17 shows the variability of the port length Lx of the resonator. In FIG. 17, if the port length Lx is increased, the resonance frequency F0 is decreased, and if Lx is decreased, F0 can be increased. The port length Lx can be adjusted by using a plastic member or a movable mechanism.

FIG. 18 shows the variability of the internal volume Vx of the resonator. In FIG. 18, if the internal volume Vx is increased, the resonance frequency F0 is decreased, and if Vx is decreased, F0 is increased. The internal volume Vx can be adjusted by moving the wall surface constituting the resonator.
A desired resonance state can be formed by the variation of the configuration shown in FIGS. 16 to 18 alone or the combination of these variations.

1 Duct (or air duct)
2 Fan noise source 3 Noise detection microphone 4 Error detection microphone 5 Control sound

source

6, 8 Microphone amplifier 7, 9 A / D converter
10 arithmetic means 10a1 white noise generating means 10a2 first NLMS algorithm 10a3 brother 2 NLMS algorithm 10b arithmetic means 10b1 transfer characteristic C filter 10b2 third NLMS algorithm 10c arithmetic means 10c1 adding circuit 10c2 transfer characteristic H filter 10c3 transfer characteristic R filter 10c4 inverter 11 D / A converter 12 power amplifiers 13, 14, 15, 16 resonators 17, 18

Claims

In the active noise control device provided in the air passage where the noise from the fan propagates,
First noise detecting means for detecting the noise;
Second noise detection means disposed at a position farther from the fan than the first noise detection means;
Control sound transmitting means for transmitting the control sound;
An arithmetic means for controlling the control sound based on the signals detected by the first noise detection means and the second noise detection means so that the amplitude of the detection signal in the second noise detection means is reduced;
An active noise control device comprising a Helmholtz resonator that resonates at a frequency derived from tube resonance of the air passage in the air passage.
The fan is provided at an end of the air passage,
The active noise control device according to claim 1, wherein the Helmholtz resonator is disposed at an end portion of the fan in the air passage.
The active noise control device according to claim 1, wherein the Helmholtz resonator is arranged near an antinode of a standing wave generated by the tube resonance in the air passage.
The first noise detecting means is arranged in the air passage near the antinode of the standing wave generated by the tube resonance,
The second noise detecting means is arranged in the air passage in a range from the vicinity of the antinode of the standing wave whose phase is inverted to the antinode where the first noise detecting means is arranged to the adjacent node. The active noise control device according to any one of claims 1 to 3, wherein
The first noise detecting means is arranged in the air passage near the antinode of the standing wave generated by the tube resonance,
The active noise according to any one of claims 1 to 3, wherein the second noise detecting means is disposed in the vicinity of a node of a standing wave generated by the tube resonance in the air passage. Control device.
The active noise control device according to any one of claims 1 to 4, wherein the Helmholtz resonator is configured to be able to adjust a resonance frequency by changing a port length.
The active noise control device according to any one of claims 1 to 4, wherein the Helmholtz resonator is mounted so as to adjust a resonance frequency by changing an internal volume.
The active noise control device according to any one of claims 1 to 6, wherein the Helmholtz resonator is provided with a fur material in the vicinity of a port opening on the air passage surface.
The active noise control device according to any one of claims 1 to 7, wherein the Helmholtz resonator has a fur material attached to an inner surface of the port.