JP2006003756A - Three dimensional active silencer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively silence the control target sound generated from a sound source slender in a specific direction. <P>SOLUTION: The three-dimensional active silencer is equipped with a sensor 21 for detecting the signal having a correlation with the control target sound emitted from a sound source P having a length greater than the half wavelength of the control target sound emitted from the sound source having the length above the half wavelength of the control target sound along the specific direction, a plurality of additive sound sources 22 for use in control for outputting sound waves at prescribed amplitude and phase, a plurality of error sensors 23 for measuring the sound pressure level of a surrounding sound field, and a control circuit 24 for controlling the output of the additive sound sources 22 for control so as to simultaneously minimize the output signals of the plurality of the error sensors 23 based on the output signal of the sensor 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a three-dimensional active silencer that silences a control target sound generated from a sound source, and more particularly to an elongated sound source or a device that can mute a control target sound generated in a narrow space.

  A three-dimensional active silencing method is known in which the acoustic power of a control target sound (noise) generated from a sound source (noise source) is minimized by using an additional sound source for control, and the entire target space is silenced uniformly. In the three-dimensional active silencer, the distance between the sound source and the additional sound source for control needs to be close to about 以下 or less of the wavelength λ. For this reason, it is difficult to reduce the high frequency control target sound due to restrictions such as the size and shape of the product, and the mute control of the low frequency control target sound has been the focus.

In addition, since the target sound source can be approximated to a point sound source because of its mute principle, if the sound source is planar or linear, the sound pressure can be reduced, for example, by inserting a partition into the sound source radiation surface. The mute control is performed by creating a condition that can be approximated to a point sound source group having a uniform phase (see, for example, Patent Document 1). For high-frequency controlled sound, measures using a sound absorbing material or a sound insulating material are effective.
JP 2002-303114 A

  The above-described three-dimensional active silencer has the following problems. That is, in the case of a high-frequency control target sound, it is difficult to mute, for example, a peak sound or the like even when a sound absorbing material or a sound insulating material is used.

  In addition, the method of approximating a line sound source or a surface sound source to a point sound source group with uniform phase and sound pressure by measures such as insertion of ducts and partition plates is not always effective in all cases due to product shape and performance problems. Absent. In addition, the higher the frequency, the more complicated the sound pressure / phase distribution, so that it becomes difficult to divide into regions with uniform characteristics and approximate point sound sources.

  On the other hand, when the sound source is present in a narrow space, there are restrictions such that the installation space for the control speaker cannot be secured even if the frequency is low, or the sound-deadening effect is low due to acoustic reflection or the like. In particular, in the case of a blower, if a control speaker is installed in the vicinity of the sound source, the flow path of the wind is obstructed, and there is a possibility that a new secondary sound source due to a decrease in efficiency as a blower or turbulent flow may occur. .

  Accordingly, an object of the present invention is to provide a three-dimensional active silencer that can effectively silence a control target sound generated from a sound source elongated in a specific direction or a control target sound generated in a narrow space.

  In order to solve the above problems and achieve the object, the three-dimensional active silencer of the present invention is configured as follows.

(1) A reference sensor that detects a signal correlated with a control target sound emitted from a sound source having a length equal to or longer than a half wavelength of the control target sound along a predetermined direction, and outputs a sound wave with a predetermined amplitude and phase A plurality of additional sound sources, a plurality of error sensors for measuring sound pressure levels in a predetermined space separated from the sound source, and the output signals of the plurality of error sensors simultaneously minimized based on the output signals of the reference sensors Thus, a control circuit for controlling the output of the additional sound source is provided.

(2) The three-dimensional active silencer described in (1) above, wherein the sound source is formed in a straight line.

(3) The three-dimensional active silencer described in (1) above, wherein the sound source is formed in an annular shape.

(4) The three-dimensional active silencer described in (1) above, wherein the additional sound source is opposed to the sound source and is adjacently arranged at an interval within a half wavelength of the control target sound. And

(5) The three-dimensional active silencer described in (1) above, wherein the additional sound source has a flat phase characteristic and unidirectionality.

(6) Reference for detecting a signal correlated with the control target sound in a three-dimensional active silencer that reduces the acoustic power caused by the control target sound emitted from a sound source arranged in a space having an acoustic reflection surface inside A sensor, an additional sound source arranged in the space and outputting a sound wave with a predetermined amplitude and phase, an error sensor for measuring a sound pressure level in the space, and the error sensor based on an output signal of the reference sensor A control circuit for controlling the output of the additional sound source and an acoustic reflection suppression unit for preventing acoustic reflection by the acoustic reflection surface.

(7) The three-dimensional active silencer described in (6) above, wherein the acoustic reflection suppression unit is formed of at least one of a sound absorbing material, a sound insulating material, and a vibration damping material. .

  According to the present invention, it is possible to effectively mute a control target sound generated from a sound source that is elongated in a specific direction or a control target sound generated in a narrow space.

  FIG. 1 is a cross-sectional view schematically showing a blower 10 incorporating a three-dimensional active silencer 20 according to the first embodiment of the present invention, and FIG. FIGS. 3 to 6 are graphs showing control results in the three-dimensional active silencer.

  The blower 10 includes a casing 11 that is elongated in the horizontal direction, and an axial fan 12 that has a horizontal rotation axis C in the casing 11. Wind noise, sliding sound, and the like generated by the rotation of the axial fan 12 become the sound source P. The sound source P has a characteristic of being elongated in the horizontal direction, and the length L in the rotation axis direction of the sound source P is longer than a half wavelength of the control target sound generated by the sound source P.

  The three-dimensional active silencer 20 employs a multi-channel adaptive control method, detects a signal correlated with the sound source P installed in the housing 11, and inputs an input signal to the control circuit 24 described later. Sensor 21, a plurality of control additional sound sources 22 for generating control sounds, and the sum of the sound emitted from these control additional sound sources 22 and the sound emitted from sound source P are regarded as error signals. A plurality of error sensors 23, a control circuit 24 for calculating the amplitude and phase of the control sound, and an acoustic reflection suppressing unit 25 for preventing reflection by the casing 11 are provided. The control circuit 24 performs an operation for generating a control sound having an amplitude / phase that minimizes the sound pressure signal of the error sensor 23.

  Here, the numbers of the additional sound source 22 for control and the error sensor 23 are determined from the relationship between the length of the sound source P and the wavelength of the sound to be controlled. That is, the distance between adjacent control additional sound sources 22 is equal to or less than a half wavelength with respect to the wavelength of the control target sound.

  In the three-dimensional active silencer 20 configured as described above, silence is performed as follows. That is, a signal correlated with the sound source P detected by the sensor 21 is input to the control circuit 24, and the amplitude and phase of the control sound are calculated based on this signal and emitted from the control additional sound source 22. The sum of the control additional sound source 22 and the control target sound from the sound source P is detected as an error signal, processed again in the control circuit 24, and an independent control signal is sent to each control additional sound source 22. At this time, control signal sound waves having different amplitudes and phases are generated from the control additional sound source 22. As a result, the sound pressure at each error sensor 23 is minimized and the acoustic power is also minimized. In the case of spatial control, error sensor sound pressure minimization and acoustic power minimization do not necessarily match, but the acoustic power minimization is derived by error microphone sound pressure minimization based on the following principle.

FIG. 2 shows a case where there is one sound source P and one additional sound source 22 for control. The optimum amplitude q _S of the control additional sound source 22 that minimizes the acoustic power is the amplitude of the sound source P q _p , the transfer function between the sound source P and the error sensor 23 Zp, and between the control additional sound source 22 and the error sensor 23. If the transfer function is Zs, and the distance between the sound source P and the control additional sound source 22 is d,

  At this time, in the error sensor 23, it is necessary to reduce the sound pressure by 10 dB at least, and when the sound pressure reduction amount is 10 dB from Equation 1, it is necessary that at least kd ≦ 0.8.

Here, under the condition of kd ≦ 0.8,
q _S = −q _P (2)
In other words, if an additional sound having substantially the same amplitude and opposite phase as the sound source P is given, the acoustic power can be minimized. Here, the expression of the additional sound identified by setting the sound pressure Pe of the error sensor 23 located at a position away from the sound source P and the control additional sound source 22 to zero is the following expression (4).

_{P e = q P Z P +} q S Z S → 0 ... (3)
q _S = − (Z _P / Z _S ) · q _P (4)
Here, when the sound source P and the additional sound source 22 for control are close to each other,

  Therefore, acoustic power minimization is realized under these conditions.

Next, the point that it is preferable to use a flat speaker as the control additional sound source 22 will be described. That is, in the three-dimensional active silencing, for example, when the number of the sound source P to be controlled and the control additional sound source 22 is one, the sound pressure decrease amount η [dB] is the wave number k, the control target sound and the control additional sound source Is calculated by the following equation (7).

  From this equation, for example, in order to reduce the control effect by 7 dB, it is necessary to satisfy the following condition (8).

kd ≦ 0.8 (8)
Here, if the frequency is f [Hz], the wave number k is given by k = 2πf. From this relational expression, in order to obtain a sufficient control effect, it is necessary to bring the sound source P closer to the control additional sound source 22 as the frequency increases.

  For example, when the control target sound is 800 Hz, the distance between the sound source P and the additional sound source 22 for control needs to be close to 0.02 m. When the sound source P is a linear sound source that is long in the horizontal direction, the additional sound source 22 for control needs to have a linear radiation characteristic that is as long as possible in the axial direction in order to satisfy this condition.

  Further, when the casing 11 is narrow, there are many cases where almost no extra space is left in the casing 11. Therefore, the control additional sound source 22 is required to be small and thin. In consideration of such a problem, it is preferable to use a flat speaker as the additional sound source 22 for control.

  As shown in FIG. 3, the planar speaker emits acoustic energy in a linear waveform, that is, emits a plane wave H as a surface sound source, and has a flat phase and sharp directivity. Therefore, the radiated sound exists only in the front direction with respect to the speaker vibration surface as shown in FIG. Therefore, if these flat speakers are installed at an interval that is equal to or less than a half wavelength with respect to the wavelength of the sound to be controlled, a linear sound source having a long radiation characteristic in the axial direction can be created. Therefore, the control additional sound source 22 is a thin flat speaker having a sharp directivity, a sound emission direction limited to only the front direction of the speaker, and a flat phase characteristic. It is also possible to control a line sound source.

  5 to 8 are diagrams showing simulation results of reduction effects when the number of control additional sound sources 22 is four and the frequency to be controlled is 800 Hz. As a result, a reduction effect of about 10 dB is obtained. 5 and 7 show the case where the distance between the error microphone 23 and the sound source P is 0 m, and FIGS. 6 and 8 show the case where the distance between the error microphone 23 and the sound source P is 0.02 m. In these drawings, α represents the sound pressure level of the sound source P, and β represents the sound pressure level at the position of the error microphone 23. It can be seen that the lower the sound pressure level, the greater the silencing effect.

  According to the three-dimensional active silencer 20 configured as described above, a plurality of control additional sound sources 22 are installed in accordance with the sound pressure / phase distribution of the sound source P, and each control additional sound source 22 is individually monitored. By performing multi-channel control that individually controls the error sensor 23 and those signals, measures such as installing a duct and inserting a partition plate are added even if the shape of the sound source P is a linear sound source that is long in the axial direction. It is possible to control without any problems.

  Further, in the case of a sound source P that has a high frequency such as a peak component and does not take measures for sound absorption and sound insulation, if control additional sound source 22 can be brought close to sound source P, control with three-dimensional active noise reduction is possible. It becomes. Further, if direct control is possible even when characteristics such as sound pressure and phase are not provided, it is possible to control a sound source having all distribution characteristics such as a line sound source and a plane sound source in addition to a point sound source.

  Furthermore, by using a planar speaker as the additional sound source 22 for control, it becomes possible to control even a high-frequency line sound source having a short wavelength. By using a small and thin flat speaker, it becomes possible to control without being restricted by the narrowness inside the housing 11.

  FIG. 9 is an explanatory diagram schematically showing a three-dimensional active silencer 30 according to the second embodiment of the present invention. In the present embodiment, the sound source P is an annular line sound source.

  The three-dimensional active silencer 30 employs a multi-channel adaptive control system, detects a signal correlated with the sound source P, and generates a control sound with a sensor 31 used as an input signal to a control circuit 34 to be described later. And a plurality of additional sound sources for control 32 arranged in an annular shape for detecting the sum of the sound emitted from these additional sound sources for control 32 and the sound emitted from sound source P, and regarded as an error signal A plurality of error sensors 33 arranged and a control circuit 34 for calculating the amplitude and phase of the control sound are provided. The control circuit 34 performs an operation for emitting a control sound having an amplitude / phase that minimizes the sound pressure signal of the error sensor 33.

  Here, the numbers of the additional sound source 32 for control and the error sensor 33 are determined from the relationship between the length of the sound source P and the wavelength of the sound to be controlled. That is, the distance between adjacent control additional sound sources 32 is equal to or less than a half wavelength with respect to the wavelength of the control target sound.

  In the three-dimensional active silencer 30 configured as described above, silence is performed as follows. That is, a signal correlated with the sound source P detected by the sensor 31 is input to the control circuit 34, and the amplitude and phase of the control sound are calculated based on this signal and emitted from the control additional sound source 32.

  The sum of the control additional sound source 32 and the control target sound from the sound source P is detected as an error signal, processed again in the control circuit 34, and an independent control signal is sent to each control additional sound source 32. At this time, control signal sound waves having different amplitudes and phases are generated from the control additional sound source 32. As a result, the sound pressure at each error sensor 33 is minimized and the acoustic power is also minimized.

  FIG. 10 is an explanatory diagram schematically showing a case where the above-described three-dimensional active silencer 30 is applied to the axial fan device 40. Since the sound source P exists between the tip portion of the rotating impeller 41 and the casing 42 along the inner periphery of the blower, it is considered to be an annular linear sound source. In this case, the frequency f [Hz] of the sound to be controlled is expressed by the following equation where n is a positive integer, where N is the number of blades of the impeller 41, fr [Hz] is the rotation frequency, and c is [m / s]. It is indicated by (9).

f = n · N · fr [Hz] (9)
In this case, the control additional sound source 32 is installed so as to surround the impeller 41, and the interval Δd [m] between the adjacent control additional sound sources 32 is controlled by the following equation (10). Arrange it so that it is less than half the wavelength of the sound.

  By arranging in this way, it is possible to control the annular sound source P.

  As described above, also in the three-dimensional active silencer 30 according to the second embodiment, the control target sound can be silenced in the same manner as the three-dimensional active silencer 20 described above.

  FIG. 11 is an explanatory diagram showing a configuration of a turbo blower 50 incorporating a three-dimensional active silencer 60 according to the third embodiment of the present invention.

  The turbo blower 50 includes a casing 51 and a turbo fan 52. A tongue 53 protruding inside is formed on a part of the casing 51 in the circumferential direction.

  The three-dimensional active silencer 60 employs a multi-channel adaptive control method, detects a signal correlated with the sound source P, and generates a control sound with a sensor 61 that is used as an input signal to a control circuit 64 described later. A plurality of additional sound sources for control 62 arranged in an annular shape for detecting the sum of the sound emitted from the additional sound source for control 62 and the sound emitted from the sound source P, and regarded as an error signal A plurality of error sensors 63 arranged and a control circuit 64 for calculating the amplitude and phase of the control sound are provided. The control circuit 64 performs an operation for emitting a control sound having an amplitude and phase that minimizes the sound pressure signal of the error sensor 63.

  Here, the numbers of the additional sound source for control 62 and the error sensor 63 are determined from the relationship between the length of the sound source P and the wavelength of the sound to be controlled. That is, the distance between the adjacent control additional sound sources 62 is equal to or less than a half wavelength with respect to the wavelength of the control target sound.

  In the turbo blower 50, in addition to the sound generated at the blade tip portion, the peak sound caused by the periodic air compression / expansion between the blade blade tip portion and the casing tongue portion becomes dominant. . For this reason, in order to perform efficient control, the acoustic power can be minimized by installing the control additional sound source 62 on the tongue 53. At this time, if the additional sound source 62 for control is installed to disturb the air flow path at the tongue 53, the efficiency of the blower is reduced and the secondary sound source is generated due to the turbulent flow. By adopting a thin flat speaker as the additional sound source 62, the air flow in the tongue 53 is not obstructed.

  FIG. 12 is an explanatory diagram showing a configuration when the three-dimensional active silencer 50 according to the fourth embodiment of the present invention is applied to the cross-flow fan device 70. 12, the same functional parts as those in FIG. 11 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The crossflow fan device 70 includes a casing 71 and a crossflow fan 72. At two locations in the circumferential direction of the casing 71, tongues 73 and 74 protruding inside are formed.

  Note that the control additional sound source 62 of the three-dimensional active silencer 60 has two tongue portions 73 and 74 along the air flow, and therefore the control additional sound source 62 is installed in each portion. Thereby, acoustic power can be reduced effectively. Even if there are two tongue portions 73 and 74, if the sound pressure level is biased, a sufficient effect can be obtained even if the sound pressure level is uneven.

  13 and 14 are diagrams showing a comparison of sound pressure levels before and after control at a point 1 m away from the sound source P. FIG. In this case, it is shown that a reduction effect of 20 dB was obtained before and after the control with respect to the 800 Hz peak sound among the control target sounds.

  FIG. 15 is an explanatory diagram showing the configuration of the blower 100 in which the three-dimensional active silencer 110 according to the fifth embodiment of the present invention is incorporated.

  The blower 100 includes a housing 101 that is elongated in the horizontal direction, and an axial fan 102 that has a rotation axis C in the horizontal direction in the housing 101. Wind noise, sliding sound, and the like generated by the rotation of the axial flow fan 102 become the sound source P.

  The three-dimensional active silencer 110 detects a signal having a correlation with the sound source P installed in the housing 101 and uses the sensor 111 as an input signal to the control circuit 114 described later, and a control for generating a control sound. Additional sound source 112, error sensor 113 that detects the sum of the sound emitted from control additional sound source 112 and the sound emitted from sound source P and regards it as an error signal, and calculates the amplitude and phase of the control sound Control circuit 114 and an acoustic reflection suppression unit 115 for preventing reflection by the casing 101.

  The control circuit 114 performs an operation for emitting a control sound having an amplitude and phase that minimizes the sound pressure signal of the error sensor 113. A planar speaker is used as the control additional sound source 112. The acoustic reflection suppression unit 115 is made of, for example, a sound absorbing material, a sound insulating material, or a vibration damping material.

  In the three-dimensional active silencer 110 configured as described above, silence is performed as follows. That is, a signal correlated with the sound source P detected by the sensor 111 is input to the control circuit 114, and the amplitude and phase of the control sound are calculated based on this signal and emitted from the control additional sound source 112.

  The sum of the control additional sound source 112 and the control target sound from the sound source P is detected as an error signal, processed again in the control circuit 114, and an independent control signal is sent to each control additional sound source 112. At this time, control signal sound waves having different amplitudes and phases are generated from the control additional sound source 112. Thereby, the sound pressure at the error sensor 113 is minimized and the acoustic power is also minimized.

At this time, the control additional sound source 112 emits sound only in the front direction of the vibration surface (plane wave H). For this reason, it is necessary to completely face the sound source P. Further, when the control target sound emitted from the sound source P is reflected by the inner wall of the housing 101, a secondary virtual sound source P1 is generated at a location different from the radiation direction of the control additional sound source 112. For example, as shown in FIG. 16, when the casing 101 in the vicinity of the sound source P has a parabolic curvature, the reflected sound wave concentrates on the focal point of the parabola at a position different from the position of the sound source P, and is secondary. Therefore, the sound from the virtual sound source P1 is also superimposed and input to the error sensor 113, and the above-described kd ≦ 0.8 cannot be satisfied. For this reason, the amplitude and phase output from the control additional sound source 112 are shifted, and effective active silencing cannot be controlled.

  For this reason, in this Embodiment, in order to prevent the acoustic reflection by the housing | casing 101, the acoustic reflection suppression part 115 is provided. Even if this acoustic reflection suppression unit 115 does not directly contribute to the reduction of the radiated acoustic power from the sound source P, it prevents the generation of secondary virtual sound sources by providing it on the curvature surface of the housing 62. The condition of kd ≦ 0.8 is satisfied, and the reduction and deterioration of the sound power can be suppressed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

Explanatory drawing which shows the structure of the air blower in which the three-dimensional active silencer which concerns on the 1st Embodiment of this invention was integrated. Explanatory drawing which shows the silencing theory of the same three-dimensional active silencer. The side view which shows the planar speaker as an additional sound source for control incorporated in the same three-dimensional active silencer. Explanatory drawing which shows the silencing theory of the same plane speaker. Explanatory drawing which shows the silencing effect in the same three-dimensional active silencer. Explanatory drawing which shows the silencing effect in the same three-dimensional active silencer. Explanatory drawing which shows the silencing effect in the same three-dimensional active silencer. Explanatory drawing which shows the silencing effect in the same three-dimensional active silencer. Explanatory drawing which shows the structure of the three-dimensional active silencer which concerns on the 2nd Embodiment of this invention. Explanatory drawing which shows the structure which applied the same three-dimensional active silencer to the axial flow fan apparatus. Explanatory drawing which shows the structure of the turbo type air blower in which the three-dimensional active silencer which concerns on the 3rd Embodiment of this invention was integrated. Explanatory drawing which shows the structure of the crossflow fan apparatus incorporating the three-dimensional active silencer which concerns on the 4th Embodiment of this invention. Explanatory drawing which shows the sound pressure level before control in the same three-dimensional active silencer. Explanatory drawing which shows the sound pressure level after control in the same three-dimensional active silencer. Explanatory drawing which shows the air blower incorporating the three-dimensional active silencer which concerns on the 5th Embodiment of this invention. Explanatory drawing which shows the control principle of the same three-dimensional active silencer.

Explanation of symbols

  10, 100 ... blower, 12 ... axial fan, 20, 30, 60, 110 ... three-dimensional active silencer, 21, 31, 61, 111 ... sensor, additional sound source for control 22, 32, 62, 112 ..., error Sensors 23, 33, 63, 113 ..., 24, 34, 64, 114 ... control circuit, 25, 35, 65, 115 ... acoustic reflection suppression unit, 50 ... turbo blower, 70 ... cross-flow fan device.

Claims (7)

A reference sensor for detecting a signal correlated with the control target sound emitted from a sound source having a length equal to or longer than a half wavelength of the control target sound along a predetermined direction;
A plurality of additional sound sources that output sound waves with a predetermined amplitude and phase;
A plurality of error sensors for measuring a sound pressure level in a predetermined space separated from the sound source;
And a control circuit for controlling the output of the additional sound source so as to simultaneously minimize the output signals of the plurality of error sensors based on the output signal of the reference sensor. .   The three-dimensional active silencer according to claim 1, wherein the sound source is formed in a linear shape.   The three-dimensional active silencer according to claim 1, wherein the sound source is formed in an annular shape.   2. The three-dimensional active silencer according to claim 1, wherein the additional sound source is opposed to the sound source and is adjacently arranged at an interval within a half wavelength of the control target sound.   The three-dimensional active silencer according to claim 1, wherein the additional sound source has a flat phase characteristic and a unidirectional characteristic. In the three-dimensional active silencer for reducing the acoustic power due to the sound to be controlled emitted from the sound source arranged in the space having the acoustic reflection surface inside,
A reference sensor for detecting a signal correlated with the control target sound;
An additional sound source arranged in the space and outputting a sound wave with a predetermined amplitude and phase;
An error sensor for measuring the sound pressure level in the space;
A control circuit for controlling the output of the additional sound source so as to minimize the output signal of the error sensor based on the output signal of the reference sensor;
A three-dimensional active silencer, comprising: an acoustic reflection suppression unit that prevents acoustic reflection from the acoustic reflecting surface.   The three-dimensional active silencer according to claim 6, wherein the acoustic reflection suppressing unit is formed of at least one of a sound absorbing material, a sound insulating material, and a vibration damping material.

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