JP2610393B2 - Active noise control system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor device for an active noise control system which emits sound waves having the same sound pressure and opposite phase to noise in a noise propagation passage in a duct to mute the noise.

[0002]

2. Description of the Related Art Conventionally, as a method of silencing noise propagating in a duct, a passive silencing method such as a method of absorbing sound with a sound absorbing material adhered to the duct has been adopted. There are problems such as.

On the other hand, active studies have been actively conducted on active silencing methods in which sound waves having the same sound pressure and opposite phase to the sound waves of the noise propagated in the duct are simultaneously radiated into the duct, and the sound is silenced by interference between the sound waves. I have. However, many problems still remain.

[0004] Two sensors (microphones) used as means for detecting noise propagating in the duct and the state of silencing in the duct during operation of the system are installed by being exposed to a high-speed airflow in the duct. The air velocity in the duct is 5
m / s to 10 m / s, so that the vibrating part of the sensor reacts under the influence of the high-speed airflow and generates 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.

[0005] In particular, when the sensor is installed protruding into the duct, irregularities are formed on the duct wall surface, and turbulence of the air flow occurs at the portion, and the sensor detects the turbulence of the air flow as a noise signal. Therefore, high-precision noise control could not be performed.

[0006] The surface of the sensor is exposed to the space in the duct, and the secular change of performance due to dust and the like is inevitable. Therefore, regular maintenance is required, but the maintenance work is not easy if the sensor has a complicated structure.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to detect the low frequency region of the noise in the duct by reducing the influence of the air flow in the duct, and to perform the noise control with high accuracy. It is an object of the present invention to provide a sensor device of an active noise control system capable of performing a maintenance work and facilitating maintenance work.

[0008]

According to the present invention, there is provided a sensor device of an active noise control system according to the present invention, comprising: a filter portion provided at an opening of a duct wall and made of a porous material that transmits sound waves; A sensor unit for detecting a sound wave in the duct through the filter unit and converting an acoustic signal into an analog electric signal.

[0009]

According to the above-mentioned means, according to the present invention, since the sensor section is attached to the opening of the duct wall through the filter section, the air flow in the duct does not hit the sensor section, thereby preventing the sensor section from generating noise due to the air stream in the duct. A noise-canceling sound wave that does not include unnecessary noise can be generated, and highly accurate noise control can be performed.

[0010] Further, by forming the filter portion from a porous material, the attenuation in the middle and high frequency regions of the noise propagating in the duct can be increased and the attenuation in the low frequency region can be reduced. Further, by separately providing the filter section and the sensor section, maintenance work can be facilitated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a configuration explanatory diagram showing an example of an active noise control system to which the present invention is applied.

That is, noise propagating in the duct 1 is detected by the first microphone (first sensor) 2 and converted into an analog electric signal. The analog electric signal from the first microphone 2 is amplified by the microphone amplifier 5 and once passes through an analog frequency cutoff filter 8 by analog signal processing with gradual frequency cutoff characteristics without time delay. Further, the analog electric signal passing through the analog frequency cutoff filter 8 is converted into a digital electric signal by the analog-to-digital converter 11, and then the digital frequency cutoff filter 14 is formed by digital signal processing having a steep frequency cutoff characteristic without time delay. Pass through. By receiving the above processing, the information on the noise from the first microphone 2 becomes a digital electric signal including only a signal in a frequency region to be silenced.

On the other hand, a second microphone (second sensor) 4
From, information on the noise reduction status in the duct 1 indicating how much noise in the duct 1 has been reduced by operating the system can be obtained as an analog electric signal. The analog electric signal from the second microphone 4 is
Microphone amplifier 7, analog frequency cutoff filter 10 by analog signal processing, analog-digital converter 13, digital frequency cutoff filter 16 by digital signal processing
, A digital electric signal including only a signal in a frequency region to be silenced is obtained.

The arithmetic unit 19 does not simply generate an electric signal for radiating sound waves having the same sound pressure and opposite phase with respect to the propagation noise in the duct 1 obtained from the first microphone 2. The following calculation is performed in order to create a noise reduction signal so that the optimum noise reduction sound wave can be radiated at that time with respect to the sound wave of the noise in the duct 1 at the place where the noise reduction speaker 3 is installed.

(A) In the system, when a sound wave propagates in the duct 1 or a signal passes through the circuit, the transfer function is affected by a unique transfer function such as a time delay or a change in frequency characteristics. Is performed.

(B) From the information of the first microphone 2 and the second microphone 4, based on the adaptive control algorithm 18, the input signal from the second microphone 4 is brought close to zero (that is, the sound is effectively eliminated). ) Calculate the coefficient. The coefficient is used as a filter coefficient of the muffling signal generation filter 17 to perform convolution with the digital electric signal from the first microphone 2 to create a muffling digital electric signal.

The digital electric signal for silencing generated by the arithmetic unit 19 passes through a digital frequency cutoff filter 15 by digital signal processing, and is converted into an analog electric signal by the digital-analog converter 12. Further, the analog electric signal from the digital-analog converter 12 passes through the analog frequency cutoff filter 9 by the analog signal processing, and becomes a noise-reducing analog electric signal including only a signal in a low frequency region to be silenced. The silencing analog electric signal is amplified by the power amplifier 6 and the silencing speaker 3
Drive. The muffling speaker 3 converts the muffling analog electric signal into a muffling sound wave and radiates it into the duct.

As described above, the noise propagating in the duct 1 is simultaneously radiated into the duct 1 with the noise canceling sound having the same sound pressure and the opposite phase to the sound propagating in the duct 1 so that the two sound waves interfere with each other, thereby suppressing the noise propagating in the duct 1. I do.

FIG. 1 is a sectional view showing an example of the sensor device according to the present invention. That is, the opening 21 is provided on the wall surface of the duct 1.
The duct 1 is closed so as to close the opening 21.
The filter unit 22 is disposed on the outer wall surface of. The filter portion 22 is made of a porous material 20 made of, for example, high-density glass wool or the like, and is a plate-like holding member 2 having an appropriate aperture ratio, such as an aluminum plate having a large number of small holes.
It is configured by being sandwiched by three. The filter unit 2
The sensor unit 24 is disposed on the outer surface of the second unit 2. The sensor unit 24 is configured by holding the first microphone 2 by a spacer 25. The filter part 22 and the sensor part 24 are positioned by a positioning member 26, and the filter part 22, the sensor part 24 and the positioning member 26 are
And attached with screws 28.

Although the case where the first microphone 2 is attached has been described with reference to FIG. 1, the same configuration can be applied to the case where the second microphone 4 is attached.
The airflow velocity in the duct 1 is as fast as 5 m / s to 10 m / s, and the first microphone 2 and the second microphone 4 for detecting information on noise propagating in the duct 1 and the muffling state in the duct 1 react to the airflow. I do. If reacted, an unnecessary noise signal is generated, which has a bad influence on noise reduction.

Therefore, as shown in FIG. 1, the porous material 20 is sandwiched between plate-like holding members 23 having an appropriate aperture ratio in the openings 21 on the wall surface of the duct 1 where the two microphones 2 and 4 are installed.

When glass wool having a high density is used as the porous material 20, resistance to the air flow is generated, and the influence of the microphones 2 and 4 from the air flow in the duct 1 is reduced. In addition, glass wool absorbs sound in the mid- to high-frequency range, but transmits sound in the low-frequency range without absorbing it, so that sound in the low-frequency range to be silenced is attenuated without any change. Microphone 2 without
Reach 4 Since the filter portion 22 is sandwiched between holding members 23 such as an aluminum plate, the surface is flat and can be set on the same plane as the wall surface of the duct 1. Therefore, the wall surface of the duct 1 is smoothed without irregularities, so that the turbulence of the air flow in the duct 1 can be prevented.

Therefore, the first microphone 2 and the second microphone 2
The microphone 4 can accurately take in information of noise propagating in the duct 1 and a muffling state in the duct 1 into the system. That is, the first microphone 2 and the second microphone 4 can generate a noise-reducing sound wave that does not include unnecessary sound by preventing generation of a noise signal due to high-speed airflow, and can perform highly accurate noise control.

As shown in FIG. 1, if the filter unit 22 and the sensor unit 24 are housed in one by the holder 27 and installed in the duct 1, the filter unit 2 and the sensor unit 24 can be used for maintenance work.
2 and the sensor unit 24 can be removed separately,
Maintenance work becomes easy.

[0025]

As described above, according to the present invention, since the sensor section is attached to the opening of the duct wall via the filter section, the air flow in the duct does not hit the sensor section. It is possible to generate noise-muffling sound waves that do not include unnecessary noise by preventing the generation of noise in the section, and perform highly accurate noise control.

Further, by forming the filter portion from a porous material, the attenuation in the middle and high frequency regions of the noise propagating in the duct can be increased, and the attenuation in the low frequency region can be reduced. Further, by separately providing the filter section and the sensor section, maintenance work can be facilitated.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a configuration explanatory diagram showing an example of an active noise control system to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Duct 2 ... 1st microphone (1st sensor), 3
… Speaker for noise reduction, 4… Second microphone (second sensor), 5… Microphone amplifier, 6… Power amplifier, 7
... microphone amplifier, 8 ... analog frequency cutoff filter, 9 ... analog frequency cutoff filter, 10 ... analog frequency cutoff filter, 11 ... analog-digital converter, 12 ... digital-analog converter, 13 ... analog-digital converter, 14: Digital frequency cutoff filter, 15: Digital frequency cutoff filter, 16
... Digital frequency cutoff filter, 17 ... Mute signal generating filter, 18 ... Adaptive control algorithm, 19 ... Calculation unit, 20 ... Porous material, 21 ... Opening unit, 22 ... Filter unit, 23 ... Holding member, 24 ... Sensor unit 25: spacer, 26: positioning member, 27: holder, 28: screw.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Asayama 2-4-10 Higashinakanobu, Shinagawa-ku, Tokyo Timeware Co., Ltd. (56) References JP-A-5-223335 (JP, A) JP-A Heisei 6-130968 (JP, A) JP-A-5-341917 (JP, A) JP-A-5-67948 (JP, A) JP-A 6-19482 (JP, A) Jpn. U) Japanese Utility Model Application Hei 4-75398 (JP, U) Japanese Utility Model Application Hei 4-20098 (JP, U)

Claims (1)

(57) [Claims] 1. A first sensor for detecting a noise propagating in a duct and converting an acoustic signal into an analog electric signal, and a second sensor for detecting a muffled state in the duct and converting the acoustic signal into an analog electric signal. An analog frequency cutoff filter by analog signal processing having a gradual frequency cutoff characteristic for passing only a signal in a frequency range to be silenced from each analog electric signal from the first sensor and the second sensor; An analog-to-digital converter for converting each analog electric signal from the analog frequency cutoff filter into a digital electric signal by signal processing; and a signal in a frequency domain to be silenced from each digital electric signal from the analog-to-digital converter. Digital signal processing with a sharp frequency cutoff A digital frequency cutoff filter; an arithmetic unit for creating a digital electric signal for silencing from the information of the first sensor and the second sensor passed through the digital frequency cutoff filter by the digital signal processing; and a silencing unit created by the arithmetic unit. A digital frequency cutoff filter by digital signal processing having a steep frequency cutoff characteristic that allows only a signal in a frequency range to be silenced from the digital electric signal to pass; A digital-analog converter for converting a signal into an analog electric signal; and a gradual frequency cutoff characteristic for passing only a signal in a frequency range to be silenced from the analog electric signal for silencing from the digital-analog converter. For analog signal processing That the analog frequency cutoff filter, the analog signal processing speaker more configured active noise control for emitting a sound-absorbing sound waves in the duct and converts the silencing analog electrical signal passed through the analog frequency cutoff filter in the acoustic signal by In the system , a filter portion made of a porous material which is provided at an opening of a duct wall surface and which absorbs sound in a frequency range from a middle range to a high range but hardly absorbs sound in a low frequency range and transmits the sound. An active noise control system comprising: a sensor unit that detects a sound wave in a duct through the sensor and converts an acoustic signal into an analog electric signal.