JP3568365B2 - Active noise control system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active noise control system, and more specifically, a sound wave detector for detecting noise in a duct, and a sound wave having the same amplitude and opposite phase to the noise detected by the sound wave detector is radiated into the duct. The present invention relates to an active noise control system having a loudspeaker and a housing for housing the loudspeaker.
[0002]
[Prior art]
As a conventional technique related to the above active noise control system, an active noise control system in which small holes are formed in a speaker unit mounting plate in order to balance the static pressure in the duct and the static pressure in the space behind the diaphragm of the speaker. Japanese Patent Application Laid-Open No. HEI 6-129227 discloses a technique in which warm air enters the rear side of a diaphragm of a speaker through a small hole to cause dew condensation, thereby causing the speaker to malfunction or corrode. There is a need to solve the problem of causing damage.
As a first method for solving the above-mentioned phenomenon, there is described a structure in which an aluminum honeycomb that allows air to pass therethrough but does not easily transmit heat is provided in a small hole.
In the second method, a large temperature difference between the hot air in the duct and the surface of the speaker unit is regarded as an element of dew condensation, and a heating means for heating the speaker is provided to reduce the temperature difference. Is introduced.
In the third method, a vinyl film that separates the inside of the duct from the speaker unit is provided to prevent the warm air entering from the small holes from coming into direct contact with the speaker unit.
In the fourth method, a rubber elastic film or a bellows structure film is provided in the small hole. These films are used to separate the duct-side space and the speaker unit-side space from the pressure difference between the two spaces. Can be balanced, but the gas is blocked so as not to flow.
[0003]
[Problems to be solved by the invention]
In the first, third, and fourth methods of the prior art active noise control system exemplified above, it is possible to restrict the warm air in the duct from entering through the pressure-balancing small holes, but the speaker vibration Since a preventive effect cannot be obtained for a path that passes through the plate itself and reaches the rear surface of the speaker, there is a problem that the measures for preventing dew condensation are insufficient.
[0004]
Further, in the second method of the prior art, the speaker is overheated by the heat transmitted from the gas flowing through the duct to the speaker and the heat given to the speaker by the heater as the dew condensation preventing means, and the life of the speaker is shortened. In addition, there has been a problem that since the operation gas is likely to be defective, it can be used only for a duct in which the temperature of the flowing gas is relatively low.
[0005]
An object of the present invention is to prevent the high-humidity hot air in a duct from entering the rear surface of the speaker via the diaphragm itself of the speaker in view of the above-described problems in the related art, and It is another object of the present invention to provide an active noise control system that can more reliably prevent the formation of dew condensation and the like, and can be used for a duct having a relatively high temperature of flowing gas.
[0006]
[Means for Solving the Problems]
To achieve the above object, an active noise control system according to claim 1 of the present invention comprises:
It is characterized by having a pressurizing device for pressurizing the first space surrounded by the speaker and the housing to a pressure higher than the pressure in the duct.
[0007]
Due to the above-described features, in the active noise control system according to claim 1 of the present invention, the pressure Pe in the first space is always maintained higher than the pressure Pd in the duct at least during operation of the duct ( Since Pe> Pd), the high-humidity gas in the duct does not enter the first space, and the problem of condensation is eliminated. In other words, the high humidity hot air in the duct is also restricted from entering the path that passes through the diaphragm of the speaker and reaches the back of the speaker, so that an effect of more reliably preventing dew condensation can be obtained. . In addition, since a heater is not used as the dew condensation preventing means, the speaker is overheated, and the life of the speaker is less likely to be reduced and operation failure is unlikely. Therefore, it can be used for a duct having a relatively high temperature of flowing gas.
[0008]
As a specific configuration for always maintaining the pressure in the first space higher than the pressure in the duct during operation of the duct, a specific configuration for detecting the pressure in the duct as in the invention of claim 2 is provided. May be provided, and a control unit that adjusts the inside of the first space to a pressure not lower than the pressure in the duct detected by the pressure detector using a pressurizing device may be provided. In particular, when the pressure fluctuation in the duct is relatively large, such a control unit is effective.
[0009]
Further, as in the third aspect of the present invention, a conduit for communicating the second space between the speaker and the duct with the pressurizing device is provided, and the second space from the pressurizing device is lower in temperature than the gas in the duct. You may comprise so that air may be supplied. With such a configuration, the speaker can be cooled by the gas having a lower temperature than the atmosphere in the duct, such as the outside air, in the second space, so that the speaker and the housing are prevented from being shortened in life by the high-temperature gas in the duct. be able to.
[0010]
In order to obtain the necessary and sufficient dew condensation prevention effect, for example, as in the invention of claim 4, the pressurizing device raises the pressure of the first space in a range of 2 to 250 mm water column higher than the pressure in the duct. What is necessary is just to make it the structure which pressurizes so that it may become. Extremely high pressurization conditions are not only unnecessary, but also hinder the driving of the diaphragm of the speaker, and there is a concern that the original active noise control function that the speaker should have is hindered.
[0011]
Other features and advantages according to the present invention will become apparent from the following description of embodiments with reference to the drawings.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the active noise control system of the present invention will be described with reference to the drawings.
The active noise control system 2 of FIG. 1 is attached to a duct 80 connected to a gas engine 100 having an output of about 180 KW.
The duct 80 has a cylindrical shape with an inner diameter of about 150 mm, the gas flow rate is 20 to 30 m / s, and the conditions in the duct 80 during operation of the gas engine 100 are such that the pressure Pd is at most 95 mm water column, the relative humidity RH is 100%, In addition, the temperature is about 130 ° C., and the original noise in the duct 80 (before the active noise control system) is about 130 dB.
The active noise control system 2 is an enclosure 6 (an example of a housing) having a communication state with the inside of the duct 80 through a through hole 82 formed in a side wall of the duct 80, and is fixed inside the enclosure 6 so as to face the through hole 82. Speaker 4, first and second microphones 8a and 8b (both are examples of sound wave detectors) for detecting sound in duct 80, and detection results of first and second microphones 8a and 8b. And a control device 40 for radiating, from the speaker 4, a sound having the same amplitude as the noise in the duct 80 in the opposite phase.
The first microphone 8a is attached to the duct 80 via a through hole 84 formed on a side wall on the upstream side of the through hole 82 of the duct 80, and detects a propagated sound wave from a noise source (gas engine 100). I do. On the other hand, the second microphone 8b is attached to the duct 80 via a through hole 86 formed on the side wall on the downstream side with respect to the through hole 82 of the duct 80. An interference state with the emitted sound wave is detected. That is, the control device 40 determines the frequency and amplitude of the sound wave radiated from the speaker 4 so that the output signal from the second microphone 8b becomes zero.
[0013]
The active noise control system 2 has a pressurizing device for pressurizing the first space 10 surrounded by the rear part of the speaker 4 and the enclosure 6. The pressurizing device is, specifically, a pressurizing pump 14 having a maximum static pressure of 1500 mm water column. The pressurizing device sucks outside air having a lower temperature (20 to 40 ° C.) and lower humidity (RH 50%) than the atmosphere in the duct 80. Squeeze and expel the squeezed air from the outlet.
The exhaust port of the pressure pump 14 and the first space 10 of the enclosure 6 are connected by a first conduit 16 having an inner diameter of 6.5 mm. The first conduit 16 is provided with a valve 16a whose opening can be adjusted.
Further, a second conduit 18 extends from the exhaust port of the pressurizing pump 14, and the second conduit 18 branches into three branch pipes, each of which has a second space 20 between the speaker 4 and the duct 80, The space 22a is located between the first microphone 8a and the duct 80, and the space 22b is located between the second microphone 8b and the duct 80.
That is, a part of the low-temperature, low-humidity high-pressure air obtained by the pressurizing pump 14 passes through the second conduit 18 and reaches the second space 20, the space 22a, and the space 22b, and each of the speakers 4 , The first microphone 8a and the second microphone 8b are cooled from the duct side (the pressure of the cooling air is naturally smaller than the pressure of the compressed air supplied to the first space). Another part of the high-pressure air is appropriately released from the three-way cock 16a of the first conduit 16, and the pressure Pe in the first space 10 is about 300 mm water column (that is, +205 mm from the pressure 95 mm water column in the duct 80). Water column). As described above, the relationship of Pe> Pd is maintained between the pressure Pe in the first space 10 and the pressure Pd in the duct 80, so that the high-humidity hot air from the duct 80 to the first space 10 Ingress is prevented. Here, the pressure difference between Pe and Pd is about 2 to 250 mm water column.
[0014]
In the active noise control system 2 of the present application, since the static pressure change in the target duct 80 is relatively small, a small hole for balancing the static pressure in the duct 80 and the space behind the diaphragm of the speaker 4 is unnecessary. And is not provided. Therefore, if the pressurizing device of the present application is not provided, the high-humidity gas in the duct 80 passes through the diaphragm (cone paper having a heat-resistant temperature of about 70 ° C.) of the speaker 4 and enters the back surface, that is, the first space 10. It is considered to be reached.
As a result of using the active noise control system 2 having the above-described configuration, the noise in a stage subsequent to the active noise control system 2 in the duct 80 is reduced to about 80 dB, and the relative humidity in the enclosure 6 is suppressed to about 70% RH. In addition, the temperature of the speaker 4 is maintained in the range of 30 to 40 ° C.
Since the driving of the active noise control system 2 is continued for about 10 minutes after the operation of the gas engine 100 is completed, the active noise control system 2 stays in the duct 80 for a while after the operation of the gas engine 100 is completed. The entry of the warm air into the first space 10 is also prevented.
[0015]
[Another embodiment]
<1> The pressurizing device is not limited to a pressurizing pump, but may be, for example, a sirocco fan (for example, a device having a maximum static pressure of about 30 mm around a water column).
[0016]
<2> For the duct 90 having relatively large pressure fluctuation, a pressure detector 50 for detecting the pressure in the duct 90 is further provided as shown in FIG. 2 instead of the above embodiment. It may be implemented in the form of the active noise control system 3. In this case, a control capable of controlling the pressure in the first space 10 by the pressurizing device 24 so that the pressure Pe in the first space 10 does not fall below the pressure Pd in the duct 90 detected by the pressure detector 50. The unit 70 (specifically, a control program as control means and its related devices) may be provided in the control device 40.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an embodiment of an active noise control system according to the present invention. FIG. 2 is a schematic diagram showing another embodiment of the active noise control system.
2, 3 Active noise control system 4 Speaker 6 Enclosure 8a First microphone 8b Second microphone 10 First space 14, 24 Pressurizing pump 16 First conduit 18 Second conduit 20 Second space 40 Control device 70 Control unit 80, 90 Duct 100 gas engine

Claims (4)

A sound wave detector for detecting noise in the duct, a speaker for radiating sound waves having the same amplitude in opposite phase to the noise detected by the sound wave detector into the duct, and a housing for housing the speaker An active noise control system,
An active noise control system comprising a pressurizing device for pressurizing a first space surrounded by the speaker and the housing to a pressure higher than a pressure in the duct. A pressure detector for detecting the pressure in the duct is provided, and the pressure in the first space is not reduced below the pressure in the duct detected by the pressure detector using the pressurizing device. The active noise control system according to claim 1, further comprising a control unit that adjusts the pressure. A conduit is provided for bringing the second space between the speaker and the duct into communication with the pressurizing device, and air having a lower temperature than the gas in the duct is supplied from the pressurizing device to the second space. An active noise control system according to claim 1 or 2 provided. The active noise control according to any one of claims 1 to 3, wherein the pressurizing device pressurizes the pressure in the first space to be higher than a pressure in the duct in a range of 2 to 250 mm water column. system.

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