JPH09106289A - Active noise control device - Google Patents

Abstract

(57) [Abstract] An object of the present invention is to reduce the influence of the air flow in a duct and the vibration of the duct and to detect the noise in the duct with high accuracy.
Another object of the present invention is to provide an active noise control device capable of suppressing the sound in a wide frequency range even in a large-diameter duct by increasing the frequency of a standing wave composed of a sound deadening sound wave generated in the cross-sectional direction of the duct. According to the present invention, as a sensor for detecting noise propagating in a duct 11 or a sound deadening condition in the duct 11, the cross-sectional shape is connected to the inner space of the duct 11 and has a cross-sectional shape outside the inner space of the duct 11. A space having an isosceles triangle whose direction is one side is provided, and the sensor 16 is installed in this space. Further, speakers 671 and 672 are installed as face-to-face wall surfaces of the duct 11 as sound deadening speakers, respectively. However, the sound waves having the same phase and the same sound pressure are radiated from the speakers 671 and 672 into the duct to increase the frequency of the standing wave generated in the cross-sectional direction of the duct.

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 silencing noise by radiating sound waves having the same sound pressure in antiphase with the noise in the passage for propagating noise in the duct.

[0002]

2. Description of the Related Art In general, as a method of silencing noise propagating in an air conditioning duct, a passive noise silencing method such as a method of absorbing sound with a sound absorbing material adhered inside the duct has been employed. However, there are problems such as pressure loss and size. On the other hand, active sound silencing methods are being actively researched by simultaneously radiating sound waves of opposite phase and same sound pressure to the sound wave of noise propagating in the duct into the duct, and silencing the sound waves by the interference of both sound waves. However, many problems still remain.

FIG. 16 is a structural explanatory view showing a conventional active noise control system. That is, the first composed of a microphone
Information on noise propagating in the duct 62 is taken in by the sensor 61 as an analog electric signal, and further amplified through the amplifier 63 of the microphone amplifier.

First, the analog low-pass filter 6 is applied to the analog electric signal amplified by the amplifier 63.
Pass 4. After that, it is converted into a digital electric signal through an A / D (analog-digital) converter 65.

In this way, the digital electric signal containing only the signal in the low frequency region to be silenced is input to the digital arithmetic unit 66. Further, the situation of muffling in the duct 62 due to the operation of the system is detected by the second sensor 68 including a microphone installed on the downstream side of the muffling speaker 67 as viewed from the noise source. Similarly to the analog electric signal obtained from the first sensor 61, the analog electric signal obtained from the second sensor 68, which is the information on the muffling condition in the duct 62, is also similar to the analog electric signal obtained from the first sensor 61.
9. Pass the analog low-pass filter 70 for analog signal processing and the A / D (analog-digital) converter 71.

From the second sensor 68, information on how much the noise propagated in the duct 62 has been silenced by the operation of the system is input. The digital arithmetic unit 66 takes in the information and calculates an optimum coefficient based on the adaptive control algorithm 72 so that the signal always approaches zero, and the input signal from the first sensor 61 is used as the filter coefficient of the silence signal generation filter 73. Perform the operation of convolving with.

In this way, the digital arithmetic unit 66 performs a convolution operation on various signals into the input signal from the first sensor 61, and the adaptive control algorithm 72 sequentially updates the silencing signal generation filter 73 to create a silencing digital electric signal.

The digital electric signal for silencing is D / A
A (digital-analog) converter 74 converts the analog electric signal to an analog low-pass filter 75 by analog signal processing to finally obtain a sound-reducing analog electric signal containing only a signal in a low frequency region to be silenced.

This muffling analog electric signal is amplified by the amplifier 76 of the power amplifier to drive the muffling speaker 67 and radiate the muffling sound wave into the duct 62.
In this way, various signal processing is performed, and for the noise propagating in the duct 62, a sound wave for silencing having antiphase and same sound pressure is generated in the duct 6
2 radiated. The emitted sound wave for silencing is the duct 62.
A noise sound wave propagating in the interior interferes with each other and cancels each other out, resulting in a sound deadening effect.

The amplifiers 63 and 69, the analog low-pass filters 64 and 70, and the A / D converters 65 and 71 are A
The D / A converter 74 and the D / A converter 74 constitute the D / A converters 77 and 78.
And the analog low-pass filter 75 and the amplifier 76 are D
The / A converter 79 is configured.

[0011]

However, assuming that the sound field in the duct 62 is one-dimensional, the duct 62
There are two possible propagation directions of inward propagation noise: the + direction (noise source → downstream) and the − direction (downstream → noise source). Since the controller of the active noise control system performs the calculation when the sound wave input from the first sensor 61 propagates in the + direction, the propagation noise from the − direction (for example, the reflected sound from the downstream curved duct) is reduced to the first value. 1 sensor 61 and 2nd sensor 68
If it is input from, accurate control cannot be performed.

Further, as shown in FIG. 7, when the first sensor 61 detects a sound wave emitted from the speaker 67 in addition to the sound wave from the noise source, it is input / amplified again to the controller, and the digital operation unit 66 outputs. Mute signal generating filter 73
And is re-emitted from the speaker 67 as a sound wave other than the sound deadening sound wave. This not only deteriorates the control, but also leads to a howling phenomenon between the speaker 67 and the first sensor 61. Conventionally, in order to avoid this howling phenomenon, a howling cancellation filter 8 in the controller is used.
Howling was canceled by signal processing using 0. In FIG. 7, A is an acoustic transfer function between the speaker 67 and the first sensor 61 by the howling cancellation filter 80. By convolving the output signal of the speaker 67 with the acoustic transfer function of the howling cancellation filter 80, the sound sneaking into the first sensor 61 from the speaker 67 is predicted. In B, howling is avoided by subtracting the sound that wraps around the first sensor 61 from the speaker 67 that is predicted from the signal actually input from the first sensor 61.

Further, two sensors (microphones) used as means for detecting noise propagating in the duct and muffling condition in the duct during system operation are installed by being exposed to a high-speed air flow in the duct. The airflow in the duct has a wind speed of 5 m / s to 10 m / s, and therefore the vibrating part of the sensor reacts under the influence of the high-speed airflow to generate a noise signal. Therefore, when the acoustic signal in the duct is converted into an electric signal and taken into the system, this noise signal is also taken. The arithmetic unit performs arithmetic processing on the signal including the noise signal. For this reason, the generated noise-elimination signal also includes an unnecessary signal, and even an unnecessary sound is radiated into the duct as a noise-elimination sound wave. In particular, since this noise signal contains many low-frequency components and overlaps with the low-frequency region to be silenced, the accuracy of the silence is extremely poor.

In particular, when the sensor is installed so as to project into the duct, irregularities are formed on the wall surface of the duct, and turbulence of the air flow occurs at that portion, and the sensor detects the turbulence of the air flow as a noise signal. Therefore, high-precision noise control could not be performed.

Therefore, as shown in FIG. 4, the sensor 16 composed of a microphone having a unidirectional characteristic is installed in the microphone installation space inside the microphone installation section 14 'provided on the wall surface of the duct 11 so as not to be exposed to the air flow. Store. In this case, if the cross-sectional shape of the microphone installation portion 14 'is rectangular, the angle θ formed by the wall surface of the duct 11 and the inner wall surface of the microphone installation portion 14' becomes large, and when the sound wave propagating in the duct 11 enters the microphone installation space, a space is created. The noise that occurs in the + direction in the duct 11 cannot be accurately detected even if the sensor 16 of the unidirectional microphone is used, which causes a diffraction phenomenon that is an acoustic change associated with the change of the shape. Could not improve the accuracy of.

FIG. 14 shows a case where a single muffler speaker 67 is installed on the wall surface of the duct 11. Here, c is the speed of sound and l is the cross-sectional dimension of the duct. That is, the rectangular duct 1
When a single muffling speaker 67 is installed on one wall surface of No. 1 and a driving force is applied (when a particle velocity is applied), the sound pressure distribution in the cross section of the duct 11 is expressed as follows.

[0017]

(Equation 1) However, the reflection is complete reflection, k is the wave number, ω is the angular frequency, and φ is the phase. From the condition of perfect reflection on the wall surface of the duct, the sound pressure is 2P at x = 1,

[0018]

(Equation 2) Therefore, the sound pressure and the particle velocity are expressed by the following equations.

[0019]

(Equation 3) In this formula, the particle velocity at the driving end of x = 0 is U ₀ sin ω
Given the condition t

[0020]

(Equation 4) Therefore,

[0021]

(Equation 5) From the above, the sound pressure distribution in the cross-sectional direction when a single muffling speaker is installed on one wall surface of the duct is

[0022]

(Equation 6) The relationship between the length of the duct side and the wavelength λ, and the positions of the antinode and the node of the sound pressure are as follows.

Kl = mπ l = m × λ / 2 (m = ± 1, ± 2, ± 3 ...) Antinode k (x-1) = mπ, x = l + m × λ / 2 k (x-1) = (2m + 1) × π / 2, x = 1 +
(2m + 1) × λ / 4 However, in the case of an antinode or a node, x is 0 or more and 1 or less,
m is only -1, -2, -3 ...

FIG. 10 shows the shapes of the primary, secondary, and tertiary standing waves and the frequencies at that time. In the case of muffling the noise propagating in the duct by the active control, the upper limit frequency at which the noise can be muffled is up to the frequency of the first standing wave generated in the duct cross section direction, and this frequency is determined by the dimension of the duct side. Therefore, when active control is applied to a large duct, there is a problem that noise that can be silenced is narrowed down to a very low band.

The present invention has been made in view of the above circumstances, and it is possible to accurately detect the noise in the duct by reducing the influence of the air flow in the duct and the vibration of the duct, and to use the sound wave for silencing generated in the transverse direction of the duct. Another object of the present invention is to provide an active noise control device capable of suppressing the noise in a wide frequency range even in a large-diameter duct by increasing the frequency of the standing wave.

[0026]

In order to achieve the above object, an active noise control device of the present invention comprises a first sensor for detecting noise propagating in a duct and a second sensor for detecting a muffling condition in the duct. The sound wave generated in the duct is controlled by the sensor and the detection outputs of the first sensor and the second sensor, and the sound wave having the opposite phase and the same sound pressure is radiated from the sound wave generator into the duct to muffle the sound wave propagated in the duct. In the active noise control device, as the first sensor or the second sensor, a space having an isosceles triangle whose cross-sectional shape is one side in the duct length direction is provided outside the duct internal space and communicates with the duct internal space. It is characterized in that a sensor is installed.

Further, the active noise control system of the present invention includes a first sensor for detecting noise propagating in the duct, a second sensor for detecting a muffling condition in the duct, the first sensor and the second sensor. In the active noise control device for suppressing the propagation noise in the duct by radiating the sound wave of the antiphase same sound pressure to the propagation noise in the duct controlled by the detection output of the inside of the duct from the sound wave generation unit, as the sound wave generation unit, At least one pair of sound wave generators are installed opposite to each other on the wall surface facing the duct, and sound waves of the same phase and the same sound pressure are radiated into the duct from the sound wave generators facing each other, and the frequency of the standing wave generated in the cross-sectional direction of the duct is determined. It is characterized by making it higher.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. As an embodiment of the present invention, a sensor device used in the active noise control system of FIG. 16 will be described. That is, the first sensor 61 that detects noise propagating in the duct 62, the second sensor 68 that detects the muffling condition in the duct 62, and the first sensor 6
The detection outputs of the first and second sensors 68 are converted into A / D conversion units 77,
A signal is input to the digital calculation unit 66 via 78, and a sound wave having an antiphase same sound pressure with respect to the noise propagated in the duct 62 which is controlled by the digital calculation unit 66 is radiated from a speaker in the duct 62 to propagate in the duct 62. An active noise control device that silences noise is used.

FIG. 1 is a sectional view showing an example of a sensor device according to the present invention. That is, for example, the duct 1 made of zinc iron plate or the like
A rectangular opening 12 having a long side in the length direction of the duct 11 is provided on the wall surface of the duct 1. A microphone installation portion 14 made of, for example, a lead plate is opened in the opening 12 so as to close the opening 12. The unit 12 is attached so as to provide a microphone installation space having an isosceles triangular cross section with one side in the length direction. The microphone installation part 14 is formed to be inclined from the upstream end of the propagation noise and the downstream end of the propagation noise of the opening 12 to the center between both ends. A porous material 15 made of, for example, glass wool is provided in the microphone installation space in the microphone installation section 14. This porous material 15
For example, a sensor 1 including a unidirectional microphone
6 is held in the microphone installation space with the sound receiving surface facing the noise source.

That is, assuming that the sound field in the duct 11 is one-dimensional, the propagation directions of the noise propagated in the duct 11 are two directions, that is, the + direction (noise source → downstream) and the − direction (downstream → noise source). Conceivable. Since the controller of the active noise control system performs the calculation when the sound wave input from the sensor 16 propagates in the + direction, the noise propagated from the-direction (for example, the reflected sound from the downstream curved duct) is detected by the sensor 16. If input, accurate control cannot be performed. Therefore, FIG.
As shown in FIG. 5, by providing the sensor 16 with a unidirectional characteristic that only detects sound waves from the direction of the noise source, the control accuracy of the controller of the active noise control system can be improved.

Further, as shown in FIG. 5, by making the microphone installation space of the microphone installation section 14 into an isosceles triangular cross section having a small base angle θ, the sound wave propagating in the duct 11 penetrates into the microphone installation space. In this case, it is possible to realize a microphone installation space in which the diffraction phenomenon is prevented and the unidirectional characteristics of the unidirectional microphone can be utilized.

When the sensor detects not only the sound wave from the noise source but also the sound wave emitted from the speaker, it is input to the controller again, amplified, and processed by the sound deadening signal generation filter of the digital arithmetic unit to be muted from the speaker. Re-emitted as sound waves other than sound waves. This not only deteriorates the control, but also leads to a howling phenomenon between the speaker and the sensor. In the past, in order to avoid this howling phenomenon, a howling cancellation filter in the controller was used to cancel the howling sound by signal processing.
Therefore, as shown in FIG. 6, by installing the sensor 16 of the unidirectional microphone toward the noise source in C, howling can be avoided without detecting the radiated sound of the speaker 67. That is, the sensor 16
It is possible to omit the howling canceling filter in the controller by providing a single directional characteristic to and not detecting the sound emitted from the speaker 67.

Further, the air velocity in the duct 11 is as high as 5 m / s to 10 m / s, and the sensor 16 including a microphone for detecting the information of noise propagating in the duct 11 and the muffling condition in the duct 11 changes the air flow. react. If reacted, an unnecessary noise signal is generated, which has a bad influence on noise reduction. Therefore, the porous material 15 is held by the microphone installation portion 14 in the opening 12 on the wall surface of the duct 11 in which the sensor 16 including the microphone is installed.
A sensor 16 composed of a microphone is held inside. When glass wool is used as the porous material 15, it becomes a resistance to the air flow, and the air flow in the duct 11 is not directly applied to the sensor 16 including the microphone, and the sensor 16 causes the duct 11 to operate.
The influence of the internal air flow is small. Glass wool absorbs sound in the mid- to high-frequency range but transmits sound in the low-frequency range with almost no absorption, so the sound in the low-frequency range to be silenced is almost unchanged and attenuated. Without reaching, the sensor 16 including the microphone is reached. Since the porous material 15 can be set on the same surface as the wall surface of the duct 11, the wall surface of the duct 11 is smooth and smooth, and turbulence of the air flow in the duct 11 can be prevented. Further, the porous material 15 absorbs the vibration of the duct 11. Therefore, the sensor 16 can accurately capture the information of the noise propagating in the duct 11 and the silencing condition in the duct 11 into the system.
That is, the sensor 16 prevents the generation of a noise signal due to a high-speed air flow and absorbs the vibration of the duct 11, so that it is possible to generate a silenced sound wave that does not include unnecessary sound, and highly accurate noise control can be performed. it can.

As shown in FIG. 2, a thick panel duct 11 'made of gypsum board or the like may be used. In this case, the panel duct 11' has an opening 1a.
2'is provided, and the microphone installation part 14 is provided on the inner surface side of the panel duct 11 'so as to project into the opening 12'.
A lid-shaped protector 13 may be provided on the outer surface side of the panel duct 11 '. Reference numeral 15 is a porous material provided in a microphone installation space having an isosceles triangular cross section, and 16 is a sensor. Also in this case, the same effect as the above-mentioned embodiment is obtained.

FIG. 8 is a sectional view showing an example of the speaker device according to the present invention. That is, the pair of muffling speakers 67
1, 672 are installed facing each other on the opposite wall surfaces of the duct 11, and the speakers 671, 672 are connected to a controller 80 as shown in FIG. 9, and the controller 80 has a first sensor 61 and a second sensor 68. Are connected. As shown in FIG. 16, the controller 80 includes a digital operation section 66 and A / D conversion sections 77, 78.
And a D / A converter 79, the digital calculator 66 is composed of an adaptive control algorithm 72 and a silence signal generation filter 73, and the A / D converter 77 is an amplifier 63, an analog low-pass filter 64 and an A / D.
The D / A conversion unit 78 includes a converter 65, the A / D conversion unit 78 includes an amplifier 69, an analog low-pass filter 70, and an A / D converter 71, and the D / A conversion unit 79 includes a D / A converter.
It is composed of a converter 74, an analog low-pass filter 75, and an amplifier 76.

That is, the opposing speakers 671, 67
Sound waves having the same phase and the same sound pressure are radiated into the duct 11 from 2 to double the frequency of the primary standing wave generated in the cross-sectional direction of the duct 11.

FIG. 15 shows a pair of muffling speakers 671, 6
This is the case where 72 are installed on the wall surfaces of the ducts 11 facing each other. That is, when a pair of noise elimination speakers 671 and 672 are installed on the opposite wall surfaces of the rectangular duct 11 and a driving force of the same phase is applied (when a particle velocity is applied), the sound pressure distribution of the duct cross section is expressed as follows. To be done.

[0038]

(Equation 7) From this equation, the antinode and node of the standing wave are determined as follows.

[0039]

(Equation 8) In addition, since the sound pressure is maximized near the driving points at both ends (at the driving point, "particle velocity is not 0" and therefore "sound pressure is not maximum"), the shape of the standing wave and the frequency at that time are approximately It becomes like FIG.

Further, the pair of muffling speakers 671 and 672 separated by the distance l has a frequency of c / 2l × m (m = 1, 2).
,) Has a special radiation directivity as shown in FIG. In the case of a single sound source, looking at the directional characteristics at the frequency c / 2l that produces a primary standing wave in the duct cross-section direction, no sound waves are emitted in the duct cross-section direction, and the longitudinal cross-section of the duct (duct length It can be seen that it radiates only in (direction).
(See FIG. 13) The sound waves are radiated in the duct cross-section direction at a frequency of c / l, and a standing wave in the duct cross-section direction is first generated at this frequency.

From the above theory, it is possible to raise the frequency at which a standing wave is generated in the duct cross-sectional direction by installing two or more pairs of in-phase dual sound sources facing each other on the opposing wall surfaces of the duct. The frequency range that can be muted can be expanded.

As described above, by arranging a pair of or more in-phase dual sound sources facing each other on the duct facing wall surface, the frequency of the primary standing wave generated in the duct cross-section direction is doubled. It is possible to muffle the sound in a wide frequency range even in a large-diameter duct.

Further, since the number of sound sources of the sound wave generator is two or four, the control sound output from one sound source is reduced, so that the load applied to one speaker is reduced. Further, it becomes possible to cope with a large propagation noise.

[0044]

As described above, according to the present invention, it is possible to reduce the influence of the air flow in the duct and the vibration of the duct for highly accurate noise control, and to eliminate the howling cancel filter between the sensor and the speaker. In addition, sound waves with the same phase and same sound pressure are radiated into the duct from the opposite sound wave generators to increase the frequency of the standing wave generated in the cross-sectional direction of the duct, and the sound can be silenced in a wide frequency range even in a large diameter duct. It is possible to provide an active noise control device that enables the above.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a sensor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing another example of the sensor device according to the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing an example of a single directivity characteristic of the sensor according to the present invention.

FIG. 4 is a cross-sectional view showing a sensor device compared with the present invention.

FIG. 5 is a sectional view showing an example of a sensor device according to the present invention.

FIG. 6 is a structural explanatory view showing an example of the operation of the active noise control system according to the present invention.

FIG. 7 is a configuration explanatory view showing an example of an operation of a conventional active noise control system.

FIG. 8 is a perspective view showing an example of a speaker device according to an embodiment of the present invention.

FIG. 9 is a block diagram showing an example of a speaker device according to an embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a standing wave in a transverse cross section of a duct in the case of a conventional single sound source.

FIG. 11 is an explanatory diagram showing an example of a standing wave in a transverse cross section of a duct in the case of an in-phase dual sound source according to the present invention.

FIG. 12 is a characteristic diagram showing an example of radiation directivity characteristics in the case of an in-phase double sound source according to the present invention.

FIG. 13: c / 2l of in-phase dual sound source in duct
It is a characteristic view which shows an example of the radiation directivity characteristic of [Hz].

FIG. 14 is an explanatory diagram for deriving a mathematical formula when a conventional single sound source is installed on one wall surface of a duct.

FIG. 15 is an explanatory diagram for deriving mathematical formulas when the in-phase dual sound sources according to the present invention are installed on mutually facing duct wall surfaces.

FIG. 16 is a structural explanatory view showing an example of an active noise control system.

[Explanation of symbols]

11 ... Duct, 12 ... Opening part, 13 ... Envelope, 14 ... Holder, 15 ... Porous material, 16 ... Sensor, 61 ... First sensor, 62 ... Duct, 63 ... Amplifier, 64 ... Analog low-pass filter, 65 ... A / D (analog-digital) converter, 66 ... Digital operation section, 67 ... Silencer speaker, 68 ... Second sensor, 69 ... Amplifier, 70 ... Analog low-pass filter, 71 ... A / D (analog-digital) Converter, 72 ... Adaptive control algorithm, 73 ...
Mute signal generating filter, 74 ... D / A (digital-analog) converter, 75 ... Analog low-pass filter, 7
6 ... Amplifier, 77, 78 ... A / D converter, 79 ... D / A
Converter, 80 ... Howling cancellation filter.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G10K 11/16 G10K 11/16 B (72) Inventor Masao Aoki 31 Arise Igawatani, Nishi-ku, Kobe-shi, Hyogo No. 1 206 Inside Aoki Applied Acoustics Co., Ltd.

Claims (2)

[Claims] 1. A first method for detecting noise propagating in a duct.
A sensor, a second sensor that detects a sound deadening condition in the duct, and a sound wave having an antiphase same-sound pressure with respect to the propagation noise in the duct, which is controlled by the detection outputs of the first sensor and the second sensor, from the sound wave generator. In an active noise control device that suppresses noise propagating in a duct by radiating it into the duct, the first sensor or the second sensor communicates with the duct inner space, and has a cross-sectional shape outside the duct inner space with one side in the duct length direction. An active noise control device characterized in that a space having an isosceles triangle is provided and a sensor is installed in this space. 2. A first detector for detecting noise propagating in a duct.
A sensor, a second sensor that detects a sound deadening condition in the duct, and a sound wave having an antiphase same-sound pressure with respect to the propagation noise in the duct, which is controlled by the detection outputs of the first sensor and the second sensor, from the sound wave generator. In an active noise control device that silences the noise propagating in the duct by radiating it into the duct, at least one pair of sound wave generating units are installed as the sound wave generating units facing each other on the wall surface facing the duct. An active noise control device characterized in that a sound wave having the same phase and same sound pressure is radiated into a duct to increase the frequency of a standing wave generated in the cross-sectional direction of the duct.