JP3725709B2 - Probe microphone device with flat frequency characteristics and electronic silencing system using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a probe microphone device in which a peak of a frequency response generated at a specific resonance frequency is suppressed, and an electronic silencing system using the probe microphone device.
[0002]
[Prior art]
FIG. 2 schematically shows a configuration of a general electronic silencing system, in which a reference microphone and an error microphone are arranged along an exhaust duct with a secondary sound source that generates a sound wave for silencing being interposed. The sound wave having a phase opposite to that of the sound is emitted from the secondary sound source into the duct to cancel the noise. In the figure, an exhaust duct 1 having one end connected to the noise source 2 is arranged in order from the side closer to the noise source 2 in the direction Y of the exhaust gas flowing in the exhaust duct 1, that is, from upstream to downstream. The reference microphone 3, the secondary sound source 4 and the error microphone 5 are arranged, and the output signals of the reference microphone 3 and the error microphone 5 are processed by the processing unit 6 and then given to the secondary sound source 4.
[0003]
In the processing unit 6, an analog signal representing a sound wave received by the reference microphone 3 is converted into a digital signal, then processed by the adaptive filter 7, converted into an analog signal, and given to the secondary sound source 4. Then, the sound is emitted into the exhaust duct 1 as a sound wave for silencing.
[0004]
A signal obtained by converting the output signal of the reference microphone 3 into a digital signal is also applied to the controller 8, and the controller 8 receives a signal obtained by digitally converting the analog output signal from the error microphone 5 as an error signal. The controller 8 determines the filter coefficient of the adaptive filter 7 so that the error signal is minimized.
[0005]
On the other hand, in the electronic mute system of FIG. 2, a so-called probe microphone in which an elongated probe tube (pipe tube) is connected to the tip of the microphone body to collect sound in the exhaust duct is used as the reference microphone 3 and the error microphone 5. May be used. When such an electronic silencing system is operated in a high temperature environment, in order to protect the reference microphone 3 and the error microphone 5 from high-temperature exhaust gas, the probe tube is lengthened as much as possible to sufficiently release heat near the microphone. It was like that.
[0006]
However, it is known that this probe microphone resonates by having a resonance frequency unique to the internal space of the probe tube, and has a frequency characteristic in which peaks occur at a plurality of frequencies as shown in FIG. Therefore, if such a frequency response peak is within the frequency to be silenced, there is a drawback that the silencing operation of the silencing system becomes unstable.
[0007]
One way to avoid this is to change the size of the probe tube so that the peak of the frequency response occurs on the higher frequency side and move the peak outside the frequency to be silenced. However, in order to move the peak to the higher frequency side, if the inner diameter of the probe tube is the same, the pipe length of the probe tube must be shortened. However, if the pipe length is shortened, heat radiation by the probe tube is not sufficiently performed, so that the higher the exhaust gas temperature, the higher the temperature of the microphone. In addition, since the protective case containing the microphone is also disposed near the high-temperature exhaust duct, the microphone is always kept at a high temperature, and as a result, the lifetime of the microphone is shortened.
[0008]
Therefore, in order to reduce the peak in the frequency response of the probe microphone as described above, Japanese Patent Laid-Open No. 8-33084 discloses a reference microphone 3 or an error at one end of the probe tube 12 as shown in FIG. It has been proposed to suppress the peak of the frequency response by fixing the microphone 5 and filling a sound absorbing material 13 such as glass wool in a portion of the inner hole of the probe tube 12 immediately before the microphone.
[0009]
Although this proposal is excellent in that it can suppress the peak in the frequency response of the probe tube, it simply fills the inner hole of the probe tube 12 with the sound absorbing material. There is a problem that the moisture of the exhaust gas is absorbed and the sound does not pass through the sound absorbing material.
[0010]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a microphone device that has good processability and can detect sound in a hot and humid place. And
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
The microphone body,
A hollow probe tube having one end fixed to the microphone body;
Sound absorbing means provided to fill at least a part of the internal space of the probe tube;
A film member provided to seal the inside of the probe tube at both ends of the probe tube;
A probe microphone, comprising:
I will provide a.
[0012]
The present invention also provides
A reference microphone, a secondary sound source, and an error microphone are installed in this order in the direction of the exhaust gas flow with respect to the exhaust duct, one end of which is connected to a noise source, and the sound waves received by the reference microphone and the error microphone are processed. An electronic silencing system for generating silencing sound waves from the secondary sound source,
At least one of the reference microphone and the error microphone is
The microphone body,
A hollow probe tube having one end fixed to the microphone body;
Sound absorbing means provided to fill at least a part of the internal space of the probe tube;
A film member provided to seal the inside of the probe tube at both ends of the probe tube;
An electronic muffler system characterized by comprising:
I will provide a.
[0013]
[Action]
The sound absorbing material filled in the probe tube suppresses the peak of the frequency response due to the natural frequency of the internal space of the probe tube. The first and second film members allow sound to pass but do not allow air or moisture to pass through. Thereby, the sound absorbing means is blocked from the outside, and the influence of moisture on the sound absorbing characteristics is removed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration when one embodiment of a probe microphone device according to the present invention is applied to a reference microphone of an electronic mute system. In FIG. 1, one end of a sound extraction pipe 15 is fixed to a through hole 14 formed in the wall surface of the exhaust duct 1 with screws or other appropriate means, and one end of a connection fitting 16 is appropriately connected to the other end of the sound extraction pipe 15. Attach by means of One end of the probe tube 17 is attached to the other end of the connection fitting 16 by an appropriate means, and the reference microphone 3 is fixed to the other end of the probe tube 17 by a fixing fitting 18. The probe tube 17 and the reference microphone 3 constitute a probe microphone. In order to protect the reference microphone 3, it is preferable to cover the outside of the reference microphone 3 with a protective case 19.
[0015]
The internal space of each of the sound extraction pipe 15, the connection fitting 16 and the probe pipe 17 has an inner diameter necessary for extracting sound transmitted through the exhaust duct 1 and transmitting it to the reference microphone 3.
[0016]
As already described with reference to FIG. 3, the probe tube 17 has a resonance frequency unique to the inner space and resonates at a plurality of frequencies, and thus has a frequency characteristic in which peaks occur at a plurality of frequencies. If the peak of the frequency response is within the frequency to be silenced, the silencing operation of the silencing system becomes unstable. Therefore, for the purpose of suppressing the peak in such frequency characteristics, sound absorption of glass wool or the like is performed at an appropriate position in the internal space of the probe tube 17. An appropriate amount of material 20 is filled.
[0017]
Further, for the purpose of sealing the probe tube 17 and blocking the sound absorbing material 20 from the outside, a first polymer film 21 is provided in the connection fitting 16 so as to be in close contact with one end of the probe tube 17, and the probe tube The second polymer film 22 is disposed between the probe tube 17 and the reference microphone 3 with the second polymer film 22 in intimate contact with the other end of 17. The first polymer film 21 and the second polymer film 22 are made of a material that does not allow air and moisture to pass through and does not cause chemical and physical changes by exhaust gas but also has good sound permeability. It must be able to withstand high temperatures depending on the usage conditions. For example, Teflon, polyvinylidene chloride, polypropylene and the like are suitable as materials for the polymer films 21 and 22.
[0018]
By sealing both ends of the probe tube 17 with the first polymer film 21 and the second polymer film 22 having the above-described properties, the exhaust gas can be prevented from directly hitting the diaphragm, which is also called the life of the microphone. Can extend the lifetime of the microphone.
[0019]
As described above, in FIG. 1A, the probe microphone device seals the probe tube 17, the sound absorbing material 20 filling at least a part of the internal space of the probe tube 17, and the probe tube 17. Polymer films 21 and 22 provided at both ends of the probe tube 17 and a reference microphone 3 attached to one end of the probe tube 17 are provided. The frequency characteristics of the probe microphone device having such a configuration are as follows. The inner diameter of the probe tube 17 is 10 mm, the length of the probe tube 17 is 130 mm, the effective vibration diameter of the first polymer film 21 is 25 mm, and the second polymer film 22 When the effective vibration diameter was 20 mm, the thickness of the first and second polymer films 21 and 22 was 0.05 mm, and the material of the first and second polymer films 21 and 22 was Teflon, The result shown in 1 (B) was obtained. From this graph, it can be seen that the peak in the frequency response is effectively suppressed. Therefore, if the probe microphone device shown in FIG. 1A is used in an electronic silencing system, a desired silencing effect can be obtained. Moreover, since both ends of the probe tube 17 are sealed with the first polymer film 21 and the second polymer film 22 made of the above materials, the sound is not attenuated by these polymer films 21 and 22. Moreover, since the sound absorbing material 20 is blocked from the outside, the desired sound absorbing characteristics of the sound absorbing material 20 can be maintained over a long period of time.
[0020]
Actually, the exhaust gas may be cooled by the sound extraction pipe 15 or the connecting fitting 16 to generate water droplets. Therefore, for example, it is preferable to form the drain hole 23 in the connecting fitting 16 at an appropriate place.
[0021]
Up to this point, the installation location of the reference microphone 3 of the electronic mute system has been described. However, the same configuration as the installation location of the error microphone 5 can provide the same effect as that of the reference microphone.
[0022]
【The invention's effect】
As described above, as apparent from the description of one embodiment of the probe microphone device according to the present invention, since both ends of the probe tube are sealed with film members, the sound absorbing means is blocked from the outside, and the sound absorbing means There is an extraordinary effect that it is possible to maintain the desired sound absorption characteristics over a long period of time. Therefore, by applying the probe microphone device according to the present invention to the electronic muffling system, not only can the sound of the muffling target frequency be reliably muffled, but also the probe tube can be made longer, so that the exhaust gas has a high temperature. Even at times, high temperature can be prevented from being transmitted to the microphone.
[Brief description of the drawings]
FIG. 1A is a diagram schematically showing one embodiment of a probe microphone device according to the present invention, and FIG. 1B is a graph showing frequency characteristics thereof.
FIG. 2 is a diagram schematically showing a configuration of a conventional electronic silencing system.
FIG. 3A is a graph showing frequency characteristics of a conventional probe microphone device, and FIG. 3B is a diagram schematically showing a configuration of a known probe microphone device with improved frequency characteristics.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1: Exhaust duct, 3: Reference microphone, 14: Sound extraction port, 15: Sound extraction pipe, 16: Connecting metal fitting, 17: Probe pipe, 20: Sound absorption material, 21, 22: Polymer film

Claims (2)

The microphone body,
A hollow probe tube having one end fixed to the microphone body;
Sound absorbing means provided to fill at least a part of the internal space of the probe tube;
A film member provided to seal the inside of the probe tube at both ends of the probe tube;
A probe microphone characterized by comprising: A reference microphone, a secondary sound source, and an error microphone are installed in this order in the direction of the exhaust gas flow with respect to the exhaust duct, one end of which is connected to a noise source, and the sound waves received by the reference microphone and the error microphone are processed. An electronic silencing system for generating silencing sound waves from the secondary sound source,
At least one of the reference microphone and the error microphone is
The microphone body,
A hollow probe tube having one end fixed to the microphone body;
Sound absorbing means provided to fill at least a part of the internal space of the probe tube;
A film member provided to seal the inside of the probe tube at both ends of the probe tube;
An electronic muffler system comprising:

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