JPH07334167A - Sensor device for active noise control system - Google Patents

Abstract

(57) [Summary] [Object] The present invention can reduce the influence of air flow in a duct to perform highly accurate noise control, can detect a low frequency region of noise in a duct, and facilitate maintenance work. It is an object of the present invention to provide a sensor device for an active noise control system to be obtained. According to the present invention, a sound wave having the same sound pressure and an opposite phase to the sound wave of noise propagating in the duct 1 is simultaneously radiated into the duct 1 to cause both sound waves to interfere with each other, so that noise propagating in the duct 1 is silenced. In a sensor device of a noise control system, a filter section 22 made of a porous material 20 that allows sound waves to pass through is provided in an opening 21 on a wall surface of the duct 1, and a sound wave in the duct 1 is detected through the filter section 22. And a sensor section 24 for converting an acoustic signal into an analog electric signal.

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 silences noise by radiating sound waves having the same sound pressure and opposite phase to that of noise in a duct for propagating noise in a duct.

[0002]

2. Description of the Related Art Heretofore, as a method for silencing noise propagating in a duct, a passive silencing method such as a method of absorbing sound by a sound absorbing material attached to the duct has been used, but pressure loss and noise There are problems such as

On the other hand, active sound damping methods have been actively researched by simultaneously radiating sound waves of the same sound pressure and opposite phase to the sound waves of noise propagating in the duct into the duct and suppressing the sound by the interference of both sound waves. There is. However, many problems still remain.

Two sensors (microphones) used as means for detecting noise propagating in the duct and muffling conditions in the duct when the system is operating are installed by being exposed to a high-speed air flow in the duct. The wind speed in the duct is 5
m / s to 10 m / s, which causes the vibrating part of the sensor to react under the influence of the high-speed air flow and generate a noise signal. Therefore, when the acoustic signal in the duct is converted into an electric signal and taken in the system, this noise signal is also taken in. The arithmetic unit performs arithmetic processing on the signal including the noise signal. Therefore, since the generated silencing signal also includes an unnecessary signal, the unwanted sound is also emitted into the duct as a silencing sound wave. In particular, this noise signal contains many low-frequency components and overlaps with the low-frequency region targeted for noise reduction, so the noise reduction accuracy becomes 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 the portion, and the sensor detects the turbulence of the air flow as a noise signal. Therefore, highly accurate noise control cannot be performed.

Further, since the surface of the sensor is exposed in the space inside the duct, it is inevitable that the performance will change with time due to dust and the like. 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 that can perform the maintenance work and can easily perform the maintenance work.

[0008]

To achieve the above object, a sensor device of an active noise control system according to the present invention comprises a filter portion provided in an opening of a duct wall surface 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 is provided.

[0009]

According to the present invention, the air flow in the duct does not hit the sensor by mounting the sensor through the filter on the opening of the wall surface of the duct by the above means. Therefore, noise in the sensor due to the air flow in the duct is prevented. It is possible to generate a silenced sound wave that does not include unnecessary noise, and it is possible to perform highly accurate noise control.

Further, by constructing the filter portion from a porous material, it is possible to increase the attenuation in the middle and high frequency regions of the noise propagating in the duct and reduce the attenuation in the low frequency region. Furthermore, the maintenance work can be facilitated by providing the filter section and the sensor section separately.

[0011]

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

That is, the 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 then passes through the analog frequency cutoff filter 8 by analog signal processing having a gentle frequency cutoff characteristic without time delay. Further, the analog electric signal passed through the analog frequency cutoff filter 8 is converted into a digital electric signal by the analog-digital converter 11, and then the digital frequency cutoff filter 14 by digital signal processing having a steep frequency cutoff characteristic with no time delay. Pass through. By receiving the above processing, the noise information from the first microphone 2 becomes a digital electric signal including only the signal in the frequency domain to be silenced.

On the other hand, the second microphone (second sensor) 4
From the above, information on the muffling situation in the duct 1 indicating how much the noise in the duct 1 has been silenced by operating the system is obtained as an analog electric signal. The analog electric signal from the second microphone 4 is the first microphone 2
Like the analog electric signal from the 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
By passing through the signal, a digital electric signal containing only the signal in the frequency domain to be silenced is obtained.

The calculation unit 19 does not simply create an electric signal for radiating a sound wave having the same sound pressure and opposite phase to the noise propagated in the duct 1 obtained from the first microphone 2. The following calculation is performed in order to create a muffling signal so that the most appropriate muffling sound wave can be emitted with respect to the sound wave of the noise in the duct 1 at the location where the muffling speaker 3 is installed.

(B) In the system, when a sound wave propagates in the duct 1 or a signal passes through the circuit, it is affected by its own transfer function such as time delay and change in frequency characteristic. Therefore, the transfer function is corrected. Perform an operation to

(B) Based on the information of the first microphone 2 and the second microphone 4, the input signal from the second microphone 4 approaches zero on the basis of the adaptive control algorithm 18 (that is, the muffling is effectively performed). ) Calculate the coefficient. The coefficient is used as a filter coefficient of the muffling signal generation filter 17 to perform a calculation for convoluting the digital electrical signal from the first microphone 2 to create a mute digital electrical signal.

The noise-eliminating digital electric signal generated by the arithmetic unit 19 passes through the 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 analog signal processing and becomes a muffling analog electric signal containing only the signal in the low frequency region which is the target of the muffling. This mute analog electric signal is amplified by the power amplifier 6 and the mute speaker 3
To drive. The muffling speaker 3 converts the muffling analog electric signal into a muffling sound wave and radiates it into the duct.

In this way, the noise propagating in the duct 1 is silenced by simultaneously radiating the silencing sound waves having the same sound pressure and the opposite phase to the sound wave of the noise propagating in the duct 1 into the duct 1 and causing both sound waves to interfere with each other. To do.

FIG. 1 is a sectional view showing an example of a sensor device according to the present invention. That is, the opening 21 is formed on the wall surface of the duct 1.
The duct 1 is provided so as to close the opening 21.
The filter portion 22 is arranged on the outer wall surface of the. The filter portion 22 is made of, for example, a porous material 20 made of high density glass wool or the like and has a plate-like holding member 2 such as an aluminum plate having a large number of small holes.
It is configured by sandwiching with 3. The filter unit 2
A sensor unit 24 is arranged on the outer surface of the second unit 2. The sensor unit 24 is configured by holding the first microphone 2 with a spacer 25. The filter portion 22 and the sensor portion 24 are positioned by a positioning member 26, and the filter portion 22, the sensor portion 24 and the positioning member 26 are held by a holder 27.
Attached by means of screws 28.

Although the case where the first microphone 2 is attached has been described with reference to FIG. 1, the case where the second microphone 4 is attached can be similarly configured.
The air velocity in the duct 1 is as high as 5 m / s to 10 m / s, and the first microphone 2 and the second microphone 4 that detect information on noise propagating in the duct 1 and the muffling situation in the duct 1 respond to the air flow. To do. When it reacts, it generates an unnecessary noise signal, which adversely affects the muffling.

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

When glass wool having a high density is used as the porous material 20, it becomes a resistance to the air flow and the influence of the air flow in the duct 1 on the microphones 2 and 4 is reduced. 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. Microphone 2 without
Reach 4. Since the filter portion 22 is sandwiched by holding members 23 such as aluminum plates, the surface thereof is flat and can be set flush with the wall surface of the duct 1. Therefore, since the unevenness of the wall surface of the duct 1 is eliminated and the duct 1 is smooth, 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 on noise propagating in the duct 1 and the muffling situation in the duct 1 into the system. That is, the first microphone 2 and the second microphone 4 can prevent noise signals from being generated by a high-speed airflow and can generate a sound-deadening sound wave that does not include unnecessary sound, and can perform highly accurate noise control.

Further, as shown in FIG. 1, when the filter portion 22 and the sensor portion 24 are put together into one by the holder 27 and installed in the duct 1, the filter portion 2 is used when performing the maintenance work.
2 and the sensor part 24 can be removed separately,
Maintenance work becomes easy.

[0025]

As described above, according to the present invention, since the air flow in the duct does not hit the sensor by mounting the sensor in the opening of the wall surface of the duct via the filter, the sensor by the air flow in the duct It is possible to prevent the generation of noise in a part and generate a silenced sound wave that does not include unnecessary noise, and perform highly accurate noise control.

Further, by constructing the filter portion from a porous material, it is possible to increase the attenuation in the middle and high frequency regions of the noise propagating in the duct and reduce the attenuation in the low frequency region. Furthermore, the maintenance work can be facilitated by providing the filter section and the sensor section separately.

[Brief description of drawings]

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

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

[Explanation of symbols]

1 ... duct, 2 ... first microphone (first sensor), 3
... mute speaker, 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 number 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 ... arithmetic unit, 20 ... porous material, 21 ... opening, 22 ... filter unit, 23 ... holding member, 24 ... sensor unit, 25 ... Spacer, 26 ... Positioning member, 27 ... Holder, 28 ... Screw.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Asayama 2-4-10 Higashi Nakanobu, Shinagawa-ku, Tokyo Inside Timewear Co., Ltd.

Claims (2)

[Claims] 1. A sensor of an active noise control system that silences noise propagating in a duct by simultaneously radiating sound waves of the same sound pressure and opposite phase to the sound wave of noise propagating in the duct into the duct to cause both sound waves to interfere with each other. In the device, a filter section made of a porous material that is provided for the opening of the wall surface of the duct and transmits the sound wave, and a sensor section that detects the sound wave in the duct through this filter section and converts the acoustic signal into an analog electric signal. A sensor device for an active noise control system, comprising: 2. An active noise control system comprising: a first sensor for detecting noise propagating in a duct and converting an acoustic signal into an analog electric signal; and a mute condition in the duct for detecting an acoustic signal as an analog electric signal. A second sensor for converting into an analog frequency, and an analog frequency by analog signal processing having a gradual frequency cutoff characteristic that allows passage of only a signal in a frequency range to be silenced from each analog electric signal from the first sensor and the second sensor A cutoff filter, an analog-digital converter for converting each analog electric signal from the analog frequency cutoff filter by the analog signal processing into a digital electric signal, and a target for silencing from each digital electric signal from the analog-digital converter Also has a sharp frequency cutoff characteristic that allows only signals in the frequency domain A digital frequency cutoff filter by digital signal processing, a calculation unit that creates a silencing digital electric signal from the information of the first sensor and the second sensor that have passed through the digital frequency cutoff filter by digital signal processing, and the calculation unit From the created digital electric signal for noise reduction, a digital frequency cutoff filter by digital signal processing having a sharp frequency cutoff characteristic that passes only the signal in the frequency domain to be muted, and a digital frequency cutoff filter by the digital signal processing A digital-analog converter for converting the sound-deadening digital electric signal into an analog electric signal, and a gentle frequency for passing only the signal in the frequency range to be muted from the sound-absorbing analog electric signal from the digital-analog converter Shut off An analog frequency cut-off filter by analog signal processing having, and a speaker that converts a sound deadening analog electric signal that has passed through the analog frequency cut-off filter by analog signal processing into an acoustic signal and emits a sound deadening sound wave into the duct. The sensor device for an active noise control system according to claim 1, wherein the configured active noise control system is used.