JP5053626B2 - Condenser microphone unit and condenser microphone - Google Patents

Description

  The present invention relates to a condenser microphone unit and a condenser microphone, and more particularly to a configuration for switching a low-frequency pass characteristic after assembly and a configuration for equalizing pressure inside and outside the condenser microphone unit.

  A condenser microphone unit includes a film-like diaphragm that vibrates in response to sound waves, and a fixed electrode (also referred to as a “back plate”) that is disposed opposite to the diaphragm with a predetermined gap therebetween. And other components for fixing and holding the diaphragm and the fixed electrode in the unit holder. A capacitor is constituted by the diaphragm and the fixed electrode, and when the diaphragm receives a sound wave and vibrates, the capacitance of the capacitor changes. Therefore, the change in capacitance is output as a change in electric signal.

  As the diaphragm of the condenser microphone unit, for example, a synthetic resin film made of polyphenylene sulfite (PPS) having a thickness of 2 μm is used as a base, and a conductive metal film such as gold is deposited thereon. Therefore, if there is a difference between the air pressure before and after that, the diaphragm is displaced. When the atmospheric pressure is lowered, the diaphragm may bulge outward like a balloon, and the diaphragm may be destroyed. When the atmospheric pressure increases, the diaphragm is pushed inward, and the diaphragm may come into contact with the fixed electrode. For this reason, in a condenser microphone unit having a structure in which a pressure difference occurs before and after the diaphragm, a configuration that eliminates the pressure difference before and after the diaphragm is employed. Eliminating this pressure difference is called pressure equivalence.

  As a condenser microphone unit having a structure in which a difference in atmospheric pressure occurs between the front and rear of a diaphragm, there are a non-directional microphone unit and a variable directional microphone unit in which a pair of front and rear condenser microphone elements are arranged in parallel back to back. In the omnidirectional condenser microphone unit, the front side of the diaphragm communicates with the atmosphere, and the rear side of the diaphragm is a sealed air chamber. The variable directivity condenser microphone unit has a structure in which two microphone elements each having a diaphragm and a fixed electrode as main components are combined together in a back-to-back manner as described above. The back side of each diaphragm of the element is a sealed air chamber. The omnidirectional condenser microphone unit and variable directional condenser microphone unit are airtight on the back side of the diaphragm as described above, so if measures for pressure equivalence are not taken, the diaphragm will be Deform. Not only the condenser microphone unit of the above type but also a condenser microphone unit of a type in which a pressure difference may occur before and after the diaphragm requires pressure equivalence.

  Since the atmospheric pressure changes slowly, the configuration for pressure equivalence only needs to be able to cope with the slowly changing atmospheric pressure. Therefore, pressure equalization is performed by forming minute holes in the diaphragm at positions that do not affect the acoustic characteristics. In order to provide a pressure equivalent opening in the diaphragm, the present applicant has proposed a method of applying heat by spark discharge to a predetermined portion of the diaphragm (see, for example, Patent Document 1). According to this method, since no burr is generated at the periphery of the opening, it is possible to prevent generation of noise due to contact of the conductive metal film of the diaphragm with the fixed electrode, and variation in the diameter of the opening is relatively small. There are advantages that can be done.

  Furthermore, the present applicant has previously filed a patent application regarding an acoustic resistance measurement device and an acoustic resistance adjustment method (see Patent Document 2). The invention described in Patent Document 2 includes a first pipe in which one end is connected to a compressed air supply source and a reference acoustic resistance material is arranged at the other end, and one end is connected to the compressed air supply source and the other end is an acoustic resistance to be measured. A second pipe in which the material is disposed, an air throttle part provided in the middle of each of the first pipe and the second pipe, and the first pipe and the second pipe connected downstream of the air throttle part in the air flow direction. And a differential pressure gauge that is provided in the bridge pipe and measures a pressure difference between the first pipe and the second pipe. Since the measurement apparatus and the measurement method described above can measure the acoustic resistance of a diaphragm in which minute holes are formed by a method as described in Patent Document 1, a diaphragm having an appropriate acoustic resistance is selected. In the case of a variable directivity condenser microphone unit, it is possible to reduce variations in acoustic resistance of the diaphragms that make a pair.

  There is also known an omnidirectional condenser microphone capable of obtaining a pressure equivalent effect as a result of having a low frequency pass characteristic (see, for example, Patent Document 3). The sound groove provided between the capsule case and the holder (a member that supports the back plate), the outer side of the capsule case corresponding to the unit case and the side facing the back plate of the diaphragm corresponding to the diaphragm, It is acoustically coupled through a through hole provided in the holder and a small hole provided in the back cavity and back plate, and has a frequency characteristic in which the low frequency gain over a certain band is attenuated by the impedance of the acoustic coupling. It is characterized by that.

JP-A-9-84195 JP 2005-328347 A Japanese Utility Model Publication No. 60-98994

  According to the invention described in each patent document, it is possible to appropriately set the pass characteristic of a low frequency when the condenser microphone unit and the condenser microphone are designed or assembled. However, once assembled as a unit or microphone, the low-frequency pass characteristics cannot be switched, and once assembled, the low-frequency sound waves are fixed in a state that is easy to pass through or May be fixed in a state where it is difficult for sound waves to pass through. If fixed in a state where low-frequency sound waves are easy to pass through, the low-frequency sound cannot be picked up. As described above, the fluctuation of the atmospheric pressure causes the diaphragm to bulge outward or to be pressed inward to come into contact with the fixed electrode.

  The present invention has been made in view of the prior art as described above, and can change the pass characteristic of a low frequency after assembly, and can respond immediately even if there is a sudden change in atmospheric pressure. Another object of the present invention is to provide a condenser microphone unit and a condenser microphone that can perform pressure equivalency before and after the diaphragm.

The present invention relates to a diaphragm that vibrates in response to sound waves, a fixed electrode that is opposed to the diaphragm with a predetermined gap and constitutes a capacitor, and a rear air chamber formed behind the fixed electrode A condenser microphone unit comprising: an air hole that communicates with the rear air chamber and opens the rear air chamber to the outside; and a piezoelectric element that varies a rear acoustic resistance by changing an air flow degree of the air hole ; A sensor that can measure the atmospheric pressure outside the condenser microphone unit, and a controller that opens the air hole by applying a voltage to the piezoelectric element when the sensor detects a change in atmospheric pressure. This is the main feature.

The piezoelectric element can change the degree of air flow through the air holes by changing the voltage applied to the piezoelectric element and the direction thereof, thereby changing the rear acoustic resistance. When a voltage is applied to the piezoelectric element to increase the acoustic resistance and the opening of the air hole is closed, a sound wave having a very low frequency can be collected.
As described above, the piezoelectric element can vary the low-frequency limit depending on the applied voltage. The low frequency limit of the frequency response can be lowered by controlling the voltage applied to the piezoelectric element so that the piezoelectric element operates in the direction to open the opening of the air hole. Therefore, deformation of the diaphragm can be prevented.

  Embodiments of a condenser microphone unit and a condenser microphone according to the present invention will be described below with reference to the drawings. The embodiment shown in the figure is an example of a unidirectional condenser microphone unit, but the present invention is also applicable to an omnidirectional condenser microphone unit and other condenser microphone units.

  In FIGS. 1 and 2, reference numerals 10 and 20 denote first and second condenser microphone elements, respectively. The first and second condenser microphone elements 10 and 20 are assembled symmetrically in parallel with each other at both the front and rear (left and right in FIG. 1) of the insulating seat 30 with the insulating seat 30 interposed therebetween. Two condenser microphone elements 10 and 20 are arranged back to back. The first condenser microphone element 10 has a diaphragm 11 that is also called a diaphragm in the form of a film. The outer peripheral edge of the diaphragm 11 is fixed to one end face of a ring-shaped diaphragm holder 12 and is held by the diaphragm holder 12. The diaphragm 11 faces the fixed electrode 13 with a predetermined minute gap. The fixed electrode 13 is fixed to the insulating seat 30.

  The insulating seat 30 is a disk-like member as a whole, and circular recesses are formed in two steps before and after the insulating seat 30. Steps 36 and 38 are formed between the two steps of the recesses. Circular jetties 31 and 32 are formed at the outer periphery of the end. The fixed electrode 13 is fitted on the inner peripheral side of the jetty 31 on the front side of the insulating seat 30, and the outer peripheral edge of the rear end of the fixed electrode 13 is in contact with the stepped portion 36 on the front side of the insulating seat 30. The projecting dimension of the jetty 31 from the stepped portion 36 is smaller than the plate thickness dimension of the fixed electrode 13, and therefore the front part of the fixed electrode 13 projects to the front side of the insulating seat 30. A ring-shaped spacer 16 made of a thin film or the like is stacked on the front surface side of the fixed electrode 13, and the diaphragm 11 is stacked on the spacer 16 while being held by the diaphragm holder 12. Therefore, a minute gap corresponding to the thickness dimension of the spacer 16 is formed between the diaphragm 11 and the fixed electrode 13. The diaphragm holder 12 is arranged with the diaphragm 11 at the back side, and a ring-shaped terminal plate 14 is superimposed on the front surface of the diaphragm holder 12. The terminal board 14 has a terminal 14 </ b> A that protrudes forward from a part on the inner peripheral side.

  In the arrangement relationship of each member as described above, the holding ring 15 is fitted on the outer periphery of the front side of the insulating seat 30 and is fixed to the insulating seat 30 integrally. The holding ring 15 integrally has an inward flange on the front side, and the inward flange pushes the terminal plate 14 backward, and the pressing force applied to the terminal plate 14 causes the diaphragm holding body 12 and the diaphragm to be pressed. 11. The fixed electrode 13 is pushed backward in this order, and the fixed electrode 13 is pressed against the insulating seat 30. Thus, each member is substantially integrally fixed to the insulating seat 30 by the pressing force applied to each member. Behind the fixed electrode 13, a rear air chamber 17 is formed by forming the recessed portion in the insulating seat 30. A hole 39 that penetrates the insulating seat 30 in the thickness direction (front-rear direction) is formed at the center of the insulating seat 30, and the hole 39 communicates with the rear air chamber 17. The rear acoustic resistor 18 of the first condenser microphone element 10 is disposed in the hole 39.

  The second condenser microphone element 20 is configured in the same manner as the first condenser microphone element 10. However, since the first and second condenser microphone elements 10 and 20 are arranged in opposite directions, the second condenser microphone element 20 has the right side in FIG. 1 as the front and the left side as the rear. explain. The second condenser microphone element 20 has a film-like diaphragm 21. The outer peripheral edge of the diaphragm 21 is fixed to one end surface of a ring-shaped diaphragm holder 22 and is held by the diaphragm holder 22. The diaphragm 21 is opposed to the fixed electrode 23 with a predetermined minute gap. The fixed electrode 23 is fixed to the insulating seat 30.

  The fixed electrode 23 is fitted on the inner peripheral side of the jetty 32 on the rear side (right side in FIG. 1) of the insulating seat 30, and the outer peripheral edge of the rear end of the fixed electrode 23 is the step on the rear side of the insulating seat 30. 38. The projecting dimension of the jetty 32 from the step portion 38 is smaller than the plate thickness dimension of the fixed electrode 23, and therefore the front part of the fixed electrode 23 projects from the insulating seat 30. A ring-shaped spacer 26 made of a thin film or the like is stacked on the front surface side of the fixed electrode 23, and the diaphragm 21 is stacked on the spacer 26 while being held by the diaphragm holder 22. Therefore, a minute gap corresponding to the thickness dimension of the spacer 26 is formed between the diaphragm 21 and the fixed electrode 23. The diaphragm holder 22 is arranged with the diaphragm 21 at the back side, and a ring-shaped terminal plate 24 is superimposed on the front surface of the diaphragm holder 22. The terminal plate 24 has a terminal 24A that protrudes forward from a part on the inner peripheral side.

  In the arrangement relationship of each member as described above, the pressing ring 25 is fitted to the outer periphery of the rear side (right side in FIG. 1) of the insulating seat 30 and is integrally fixed to the insulating seat 30. The holding ring 25 integrally has an inward flange on the front side, and the inward flange pushes the terminal plate 24 backward, and the pressing force applied to the terminal plate 24 causes the diaphragm holding body 22 and the diaphragm to be pressed. 21, the fixed electrode 23 is pushed backward in this order, and the fixed electrode 23 is pressed against the insulating seat 30. Thus, each member is substantially integrally fixed to the insulating seat 30 by the pressing force applied to each member. A rear air chamber 27 is formed behind the fixed electrode 23 by forming the recessed portion in the insulating seat 30. The rear air chamber 17 communicates with the hole 39. A rear acoustic resistor 28 of the first condenser microphone element 20 is disposed in the hole 39.

  An air hole 35 communicating with the hole 39 is formed in the insulating seat 30 so as to penetrate the insulating seat 30 in the radial direction, and the air hole 35 is opened on the outer peripheral surface of the insulating seat 30. A piezoelectric element support 40 is fixed to the outer peripheral surface of the insulating seat 30 at the opening position of the air hole 35. In the example shown in FIG. 1, the piezoelectric element support 40 is fixed to the lower part of the insulating seat 30. The piezoelectric element support 40 has an inverted T-shaped cross section. The piezoelectric element support 40 has an air hole 41 that passes through the piezoelectric element support 40 in the vertical direction and communicates with the air hole 35 of the insulating seat 30, and the air hole 41 opens at the lower end surface of the piezoelectric element support 40. . The lower part of the piezoelectric element support 40 extends in a wing shape in the front-rear direction (left-right direction in FIG. 1), and the lower surface of the piezoelectric element support 40 is interposed by spacers 43, 43 that are paired in the front-rear direction. The piezoelectric element 8 is attached in parallel with the lower surface of the piezoelectric element support 40. A gap corresponding to the thickness of the spacers 43, 43 is formed between the lower surface of the piezoelectric element support 40 and the piezoelectric element 8, and this gap is formed on the left and right wings of the piezoelectric element support 40 in the thickness direction. It communicates with intake and exhaust holes 42, 42 formed therethrough.

  As the piezoelectric element 8, a bimorph type vibrator can be used. FIG. 4 shows an outline of a bimorph-type vibrator. Two piezoelectric elements 81 and 82 extending and contracting in the length direction are overlapped and joined, and a voltage is applied between both piezoelectric elements, whereby one piezoelectric element is obtained. The other piezoelectric element is configured to be contracted when is extended. In any piezoelectric element, the polarization direction is the thickness direction. FIG. 4A shows a parallel type, in which two overlapping electrodes of the piezoelectric elements 81 and 82 are used as an intermediate electrode 85, and a voltage is generated between the intermediate electrode 85 and the other electrode of the piezoelectric elements 81 and 82. A source is connected to apply a voltage to the two piezoelectric elements 81 and 82 in parallel. FIG. 4B shows a series type in which a voltage source is connected between the electrodes outside the two piezoelectric elements 81 and 82 that overlap each other, and voltage is applied to the two piezoelectric elements 81 and 82 in series. It is a thing. In any case, when a voltage is applied, one piezoelectric element is expanded, and the other piezoelectric element is contracted, whereby the piezoelectric element 8 is bent upward or downward in FIG.

  According to the embodiment shown in FIGS. 1 and 2, the rear acoustic resistance of each condenser microphone element 10, 20 can be made variable by controlling the voltage applied to the piezoelectric element 8. FIG. 3 shows an example in which the rear acoustic resistance of the condenser microphone elements 10 and 20 is increased. By applying a DC voltage between the terminals of the piezoelectric element 8, the piezoelectric element 8 is brought into the opening of the air hole 41. It approaches and the air circulation degree of the air hole 41 is made low. In this state, the air flow between the rear air chambers 17 and 27 of the condenser microphone elements 10 and 20 and the outside is restricted, and the acoustic resistance of the rear acoustic terminals of the condenser microphone elements 10 and 20 is increased. The illustrated embodiment is a variable directivity microphone unit in which a pair of front and rear condenser microphone elements are arranged back to back, and the air hole 41 is closed by a piezoelectric element 8, and the rear acoustic terminals of both elements 10 and 20 are connected. By increasing the acoustic resistance to the maximum, it is possible to pick up extremely low frequency sound waves.

  However, when the air hole 41 is closed, the diaphragms 11 and 21 are deformed by the difference between the front and rear pressures as described above due to fluctuations in the atmospheric pressure, so that pressure equivalence is required. The pressure equivalent is preferably such that a slight gap is generated between the opening of the air hole 41 and the piezoelectric element 8 by controlling the DC voltage applied to the piezoelectric element 8. This is because the change in the external air pressure is gradual, so that pressure equivalence is performed only by forming a slight gap between the opening of the air hole 41 and the piezoelectric element 8.

  However, depending on the use conditions of the microphone, the external air pressure may change abruptly. For example, when wind noise, vibration noise, door opening and closing, etc. are performed, the atmospheric pressure changes rapidly. When the atmospheric pressure changes abruptly as described above, these are detected by an appropriate sensor and input to the control unit. In the control unit, the piezoelectric element 8 operates so as to open the opening of the air hole 41. The voltage applied to 8 is controlled to lower the low frequency limit of the frequency response. By doing so, pressure equivalence before and after the diaphragms 11 and 21 is performed, and deformation of the diaphragms 11 and 21 can be prevented.

  The illustrated embodiment is an example of a variable directional condenser microphone unit, but the present invention can also be applied to an omnidirectional condenser microphone unit having a single microphone element and having a rear air chamber sealed. . In the omnidirectional condenser microphone unit, since the rear air chamber is sealed, when the external air pressure fluctuates, a pressure difference is generated before and after the diaphragm, and the diaphragm is deformed. Therefore, an air hole communicating with the rear air chamber is provided, and the piezoelectric element is disposed so as to face the opening of the air hole to the outside air. In a normal use state, the opening of the air hole is closed by the piezoelectric element or very little. Allow air to circulate one by one. When a sensor that detects the air pressure before and after the diaphragm is arranged and the air pressure difference between the front and rear is detected, the control unit controls the DC voltage applied to the piezoelectric element, opens the air hole and opens the air pressure before and after the diaphragm. Try to eliminate the difference.

  As described above, the example in which the present invention is applied to the variable directional condenser microphone unit and the example in which the present invention is applied to the omnidirectional condenser microphone unit have been described. However, the present invention is also applicable to a condenser microphone unit having other directional characteristics. Can do.

  By incorporating the condenser microphone unit according to the present invention into a microphone case and incorporating necessary electrical components such as a microphone connector and a circuit board into the microphone case, a condenser microphone having the effects described so far can be obtained.

  The condenser microphone according to the present invention may be stored with the opening of the air hole opened by a piezoelectric element. This is because even if the atmospheric pressure fluctuates, pressure equivalence is achieved and the diaphragm does not deform. In use, a power source for driving a microphone, for example, a phantom power source may be used as a DC voltage source to be applied to the piezoelectric element to close the opening of the air hole.

It is a longitudinal cross-sectional view which shows the Example of the condenser microphone unit which concerns on this invention. It is the front view which abbreviate | omitted a part of the said Example. It is a longitudinal cross-sectional view which shows the operation | movement aspect of the said Example. The example of the piezoelectric element applicable to this invention is shown, (a) is a schematic diagram of a parallel type, (b) is a schematic diagram of a series type.

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 Piezoelectric element 10 Microphone element 11 Diaphragm 12 Diaphragm holder 13 Fixed electrode 16 Spacer 17 Rear air chamber 18 Rear acoustic resistor 20 Microphone element 21 Diaphragm 22 Diaphragm holder 23 Fixed electrode 26 Spacer 27 Rear air chamber 28 Rear Acoustic resistor 30 Insulating seat 35 Air hole 40 Piezoelectric element support body 41 Air hole 42 Air inlet / outlet hole 43 Spacer

Claims (7)

A condenser having a diaphragm that vibrates in response to a sound wave, a fixed electrode that is opposed to the diaphragm with a predetermined gap and constitutes a condenser, and a rear air chamber formed behind the fixed electrode A microphone unit,
An air hole communicating with the rear air chamber and opening the rear air chamber to the outside;
A piezoelectric element that varies the degree of air flow in the air holes and makes the rear acoustic resistance variable ;
A sensor that can measure the atmospheric pressure outside the condenser microphone unit;
When this sensor detects a change in atmospheric pressure, a controller that opens the air hole by applying a voltage to the piezoelectric element;
Condenser microphone unit with. The condenser microphone unit according to claim 1, wherein the piezoelectric element is disposed so as to face the opening of the air hole and changes a degree of air flow to the opening. The piezoelectric element is supported by a piezoelectric element support, the piezoelectric element support has a second air hole communicating with the air hole, and the piezoelectric element is disposed so as to face the opening of the second air hole. 2. The condenser microphone unit according to 2. The microphone unit is a variable directional microphone unit in which a pair of front and rear condenser microphone elements are arranged back to back, and the pair of condenser microphone elements are integrally held by a common insulating seat. 2. The condenser microphone unit according to claim 1, wherein an air hole is formed to open the chamber to the outside. The condenser microphone unit according to claim 1, wherein the piezoelectric element is capable of closing an air hole. A condenser microphone comprising a condenser microphone unit incorporated in a microphone case, wherein the condenser microphone unit is a condenser microphone unit according to any one of claims 1 to 5 . The condenser microphone according to claim 6 , wherein a power source for driving the microphone is used as a DC voltage source to be applied to the piezoelectric element.

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