JP5161801B2 - Omnidirectional condenser microphone unit and omnidirectional condenser microphone - Google Patents

Description

  The present invention relates to an omnidirectional condenser microphone unit and an omnidirectional condenser microphone in which a diaphragm is not greatly displaced when there is a large pressure fluctuation.

  The omnidirectional condenser microphone unit operates with the pressure difference between the pressure inside the unit, that is, the pressure in the back space, and the pressure outside the unit, that is, the sound pressure, with the back space of the diaphragm being sealed or nearly sealed. To do. Hereinafter, a conventional omnidirectional condenser microphone will be described with reference to FIG.

  In FIG. 4, the portion corresponding to the bottom plate of the bottomed cylindrical unit case 1 is the front portion (upper portion in FIG. 4) of the microphone unit, and a hole is formed in the bottom plate 12. It has become. In the unit case 1, a diaphragm holding ring 2, a diaphragm 3, a spacer 4, a fixed electrode 5, a conductive cylinder 7, and a circuit board 8 are disposed in order from the front side. An insulating tube 6 is interposed between the outer peripheral surface of the conductive tube 7 and the inner peripheral surface of the unit case 1.

  The diaphragm 3 is made of a thin film, and an outer peripheral edge portion is fixed to the diaphragm holding ring 2 in a state where an appropriate tension is applied. A thin ring-shaped spacer 4 is interposed between the outer peripheral edge of the diaphragm 3 and the fixed electrode 5, and a gap having the same interval as the thickness of the spacer 4 is formed between the diaphragm 3 and the fixed electrode 5. Yes. The fixed electrode 5 is formed with an appropriate number of openings 51 connected to the space on the inner peripheral side of the conductive cylinder 7. The front end (the upper end in FIG. 4) of the conductive cylinder 7 is an outward flange 71. The front end portion of the insulating cylinder 6 has an inner peripheral surface cut away to form a stepped portion 62, and the outer peripheral side of the stepped portion 62 is a circular jetty 61 rising toward the diaphragm 3. The flange 71 of the conductive cylinder 7 and the fixed electrode 5 are located on the inner peripheral side of the jetty 61. The flange portion 71 of the conductive cylinder 7 is placed on the stepped portion 62. The protruding length of the jetty 61 from the step 62 is shorter than the dimension obtained by adding the thickness of the flange 71 of the conductive cylinder 7 and the thickness of the fixed electrode 5, and a gap is generated between the jetty 61 and the spacer 4. ing.

  The rear end of the unit case 1 is open, and the open rear end is bent inward to press the outer peripheral edge of the circuit board 8 toward the inner side in the axial direction of the case 1. By this pressing force, the insulating cylinder 6, the flange portion 71 of the conductive cylinder 7, the fixed electrode 5, the spacer 4, the diaphragm 3, and the diaphragm holding ring 2 are pushed in this order, and the diaphragm holding ring 2 is pushed above the unit case 1. By contacting the inner surface of the portion corresponding to the bottom plate 12, the built-in components are pressed and contacted with each other with an appropriate pressure. The fixed electrode 5 is electrically connected to an appropriate circuit pattern on the circuit board 8 via the conductive cylinder 7. The diaphragm 3 is electrically connected to the unit case 1 through the diaphragm holding ring 2, and the unit case 1 is electrically connected to an appropriate circuit pattern on the circuit board 8.

  The minute gap formed between the diaphragm 3 and the fixed electrode 5 is connected to the space on the inner peripheral side of the conductive cylinder 7 through the hole 51 of the fixed electrode 5. The space is almost sealed. Therefore, the diaphragm 3 vibrates according to the pressure difference between the pressure in the back space of the diaphragm 3 and the pressure outside the unit, that is, the sound pressure applied to the front surface of the diaphragm 3, and the sound signal is output after being electroacoustic converted. The directional characteristics are omnidirectional. The diaphragm 3 and the fixed electrode 5 constitute a capacitor using air as a dielectric. When the diaphragm 3 vibrates due to the pressure difference, the capacitance of the capacitor changes. The diaphragm 3 and the fixed electrode 5 constituting the capacitor electrode are connected to a circuit board 8, and a circuit for outputting the capacitance change as a voltage change, an impedance conversion circuit, and the like are incorporated in the circuit board 8. .

  In the omnidirectional condenser microphone unit configured as described above, if there is no fluctuation in external pressure, that is, atmospheric pressure, the distance between the diaphragm 3 and the fixed electrode 5 is kept at a predetermined distance. Therefore, when the diaphragm 3 receives a sound wave and vibrates according to its sound pressure, it is converted into an audio signal with a predetermined sensitivity and output. However, when the atmospheric pressure fluctuates, the difference between the pressure inside the unit that is sealed and maintained at a constant pressure and the atmospheric pressure fluctuates, and the distance between the diaphragm 3 and the fixed electrode 5 fluctuates, and the microphone unit Sensitivity varies. When the atmospheric pressure rises, as shown by an arrow P in FIG. 4, positive pressure is applied to the diaphragm 3, and the diaphragm 3 is pushed toward the fixed electrode 5 at atmospheric pressure. The capacitance of the configured capacitor increases, and the sensitivity of the microphone unit increases. On the contrary, when the atmospheric pressure decreases, as shown by an arrow N in FIG. 4, a negative pressure is applied to the diaphragm 3, and the diaphragm 3 is pushed away from the fixed electrode 5 by the internal pressure, and fixed to the diaphragm 3. The capacitance of the capacitor formed by the electrode 5 is reduced, and the sensitivity of the microphone unit is reduced.

  In order to prevent such positional fluctuations of the diaphragm 3 due to atmospheric pressure fluctuations, a capillary tube is attached or a narrow gap is provided to slightly open the space behind the diaphragm 3 so that the pressure difference between the inside and outside is gradually increased. The structure can be eliminated. Eliminating the pressure difference between the inside and outside in this way is called pressure equivalent. By performing pressure equivalence, a very low frequency, eg, 0. The sensitivity is designed to be lowered with respect to sound waves of several Hz to several Hz.

  However, if the pressure fluctuates abruptly, such as when the train fluctuates on a subway platform, or when the door opens or closes in a closed room, the pressure equalization Even if the configuration is provided, the diaphragm 3 is largely displaced until the pressure is equivalent, and the sensitivity of the condenser microphone unit varies greatly. For example, when the atmospheric pressure suddenly rises and positive pressure is applied to the diaphragm 3, the diaphragm 3 is displaced toward the fixed electrode 5 and the sensitivity is increased. In an extreme case, the diaphragm 3 may come into contact with the fixed electrode 5 and generate a large noise. When the atmospheric pressure rapidly decreases and a negative pressure is applied to the diaphragm 3, the diaphragm 3 is displaced in a direction away from the fixed electrode 5, and sensitivity is lowered. In any case, if the displacement of the diaphragm 3 is large, the diaphragm 3 may be broken. Further, when the diaphragm 3 is a plastic film, creep may occur due to a large displacement, and the diaphragm 3 may not return to its original state.

  As prior arts related to the invention according to the present application, there are inventions described in Patent Document 1 and Patent Document 2. The invention described in Patent Document 1 is a variable directional condenser microphone that is switched to omnidirectional when the rear acoustic terminal is blocked, and includes an air chamber that supplements the omnidirectional component on the rear acoustic terminal side. It is said. In the invention described in Patent Document 2, a condenser microphone main body having a pair of opposing sound wave inlets is housed in a casing, and external communication paths corresponding to the pair of sound wave inlets are provided in the casing, The present invention relates to a microphone for a mobile phone that is provided with an open / close switch that opens and closes an external passage of the mobile phone and can select directivity and omnidirectionality.

JP 2006-332928 A Japanese Patent Laid-Open No. 10-290491

  The inventions described in Patent Document 1 and Patent Document 2 have a different purpose from the present invention described later. However, since the invention is common to the present invention only by opening and closing the sound wave entrance, the prior art is disclosed. Patent Literature 1 and Patent Literature 2 are cited as the literatures that are included.

  According to the conventional omnidirectional condenser microphone unit described with reference to FIG. 4, as already described, even if a configuration for pressure equivalence is added, if there is a sudden pressure fluctuation, the diaphragm is fixed. When the distance to the electrode fluctuates, the sensitivity fluctuates, and the pressure fluctuates greatly, there are problems such as vibration destruction, creep, and unpleasant noise.

  Accordingly, the present invention provides an omnidirectional condenser microphone unit and an omnidirectional condenser microphone that can avoid damage such as vibration destruction without causing a fluctuation in sensitivity even if there is a sudden pressure fluctuation. With the goal.

  The present invention includes an acoustic terminal, a diaphragm that vibrates by receiving the sound pressure of a sound wave that enters from the acoustic terminal, and a fixed electrode that is opposed to the diaphragm with a gap, and the back space of the diaphragm is A closed omnidirectional condenser microphone unit comprising an opening that communicates the back space of the diaphragm to the outside, and a valve that is displaced in a direction to open the opening due to an external pressure fluctuation. Is the most important feature.

  Although not particularly limited in the present invention, the valve is made of an elastic body, is provided in a cantilevered manner in the vicinity of the opening, and returns to its original state when the external pressure is stabilized, thereby sealing the opening. It is preferable to do.

  Further, although not particularly limited in the present invention, the opening is preferably provided in an end plate that seals the back space.

  Further, although not particularly limited in the present invention, the end plate is preferably a circuit board.

  Although not particularly limited in the present invention, the valve is preferably provided on the inner surface of the end plate facing the back space and on the outer surface opposite to the inner surface.

  Although not particularly limited in the present invention, the valve provided on the inner surface of the end plate opens the opening by applying positive pressure to the opening, and is provided on the outer surface of the end plate. The valve preferably opens the opening by applying a negative pressure to the opening.

  The present invention is also an omnidirectional condenser microphone in which an omnidirectional condenser microphone unit is housed in a microphone case, wherein the omnidirectional condenser microphone unit is the omnidirectional condenser microphone unit. .

  According to the present invention, since the diaphragm is not greatly displaced when there is a large pressure fluctuation, it is possible to effectively prevent breakage of the diaphragm, occurrence of creep, and generation of unpleasant noise.

It is a longitudinal section showing an example of an omnidirectional condenser microphone unit concerning the present invention. It is a longitudinal cross-sectional view which shows one operation | movement aspect of the said Example. It is a longitudinal cross-sectional view which shows another operation | movement aspect of the said Example. It is a longitudinal cross-sectional view which shows the example of the conventional omnidirectional condenser microphone unit

  Embodiments of an omnidirectional condenser microphone unit and an omnidirectional condenser microphone according to the present invention will be described below with reference to FIGS. In addition, the same code | symbol was attached | subjected to the same component as the structure of the prior art example shown in FIG.

  In FIG. 1, the bottom plate 12 side of the bottomed cylindrical unit case 1 is the front portion (upper portion in FIG. 1) of the microphone unit. Holes are formed in the bottom plate 12, and the holes serve as acoustic terminals 11 for introducing sound waves from the front side of the unit case 1. In the unit case 1, a diaphragm holding ring 2, a diaphragm 3, a spacer 4, a fixed electrode 5, a conductive cylinder 7, and a circuit board 8 are disposed in order from the front side. An insulating tube 6 is interposed between the outer peripheral surface of the conductive tube 7 and the inner peripheral surface of the unit case 1.

  The diaphragm 3 is made of a thin film made of plastic or the like, and an outer peripheral edge portion is fixed to the diaphragm holding ring 2 in an appropriate tension. A thin ring-shaped spacer 4 made of plastic or the like is interposed between the outer peripheral edge of the diaphragm 3 and the fixed electrode 5, and a gap having the same interval as the thickness of the spacer 4 is interposed between the diaphragm 3 and the fixed electrode 5. Is formed. The fixed electrode 5 is formed with an appropriate number of openings 51 connected to the space on the inner peripheral side of the conductive cylinder 7. The front end (the upper end in FIG. 1) of the conductive cylinder 7 is an outward flange 71. The front end portion of the insulating cylinder 6 has an inner peripheral surface cut away to form a stepped portion 62, and the outer peripheral side of the stepped portion 62 is a circular jetty 61 rising toward the diaphragm 3. The flange 71 of the conductive cylinder 7 and the fixed electrode 5 are located on the inner peripheral side of the jetty 61. The flange portion 71 of the conductive cylinder 7 is placed on the stepped portion 62. The protruding length of the jetty 61 from the step 62 is shorter than the dimension obtained by adding the thickness of the flange 71 of the conductive cylinder 7 and the thickness of the fixed electrode 5, and a gap is generated between the jetty 61 and the spacer 4. ing.

  The rear end of the unit case 1 is open, and the open rear end is bent inward to press the outer peripheral edge of the circuit board 8 toward the inner side in the axial direction of the case 1. Reference numeral 13 denotes the bent portion of the unit case 1. By the pressing force of the bent portion 13, the insulating cylinder 6, the flange 71 of the conductive cylinder 7, the fixed electrode 5, the spacer 4, the diaphragm 3, and the diaphragm holding ring 2 are pushed in this order, and the diaphragm holding ring 2 is By contacting the inner surface of the end plate of the case 1, the built-in components are pressed and contacted with each other with an appropriate pressure. The fixed electrode 5 is electrically connected to an appropriate circuit pattern on the circuit board 8 via the conductive cylinder 7. The diaphragm 3 is electrically connected to the unit case 1 through the diaphragm holding ring 2, and the unit case 1 is electrically connected to an appropriate circuit pattern on the circuit board 8.

  The minute gap formed between the diaphragm 3 and the fixed electrode 5 is connected to the space on the inner peripheral side of the conductive cylinder 7 through the hole 51 of the fixed electrode 5. The space is almost sealed. Therefore, the diaphragm 3 vibrates according to the pressure difference between the pressure in the back space of the diaphragm 3 and the pressure outside the unit, that is, the sound pressure applied to the front surface of the diaphragm 3, and the sound signal is output after being electroacoustic converted. The directional characteristic of the microphone unit is omnidirectional. The diaphragm 3 and the fixed electrode 5 constitute a capacitor using air as a dielectric. When the diaphragm 3 vibrates due to the pressure difference, the capacitance of the capacitor changes. The diaphragm 3 and the fixed electrode 5 constituting the capacitor electrode are connected to a circuit board 8, and a circuit for outputting the capacitance change as a voltage change, an impedance conversion circuit, and the like are incorporated in the circuit board 8. .

  The configuration described so far is almost the same as the configuration of the conventional example shown in FIG. 4, but the present embodiment has a configuration having the following characteristics, and this point is different from the conventional example. .

  Two openings 14 are provided in the circuit board 8, and one valve 15 and 25 is provided for each opening 14 so as to seal the openings 14. One valve 15 is provided on the surface of the circuit board 8 facing the space on the inner peripheral side of the conductive cylinder 7, and the other valve 25 is opposite to the outer surface of the unit case 1 of the circuit board 8, that is, the mounting surface of the valve 15. It is provided on the side surface. These valves 15 and 25 are provided in a cantilevered manner in the vicinity of each opening 14. The valves 15 and 25 are made of a plate-like elastic body.

  In the normal natural state where no external force is applied, the valves 15 and 25 are in close contact with the circuit board 8 and seal the openings 14 as shown in FIG. For this reason, the gap formed on the back side of the diaphragm 3 and the air chamber connected thereto are almost sealed as described in the conventional example shown in FIG. 4, and the microphone unit according to this embodiment is used. The directivity characteristic of is omnidirectional.

  When the atmospheric pressure fluctuates rapidly and a positive pressure P is applied to the unit case 1, the inner valve 15 is pushed by the positive pressure P toward the space on the inner peripheral side of the conductive cylinder 7 as shown in FIG. It is deformed and the opening 14 is released. As a result, pressure equivalence between the external space of the unit case 1 and the space on the inner peripheral side of the conductive cylinder 7 can be quickly performed, so that the diaphragm 3 is prevented from being largely displaced, Thus, it is possible to prevent a problem that the diaphragm 3 cannot return to the current state due to the creep phenomenon.

  When the positive pressure P disappears, the valve 15 returns to its original state as shown in FIG. 1 by its elastic force, and a normal electroacoustic conversion operation can be performed.

  Further, when the atmospheric pressure suddenly fluctuates and a negative pressure N is applied to the unit case 1, the outer valve 25 is pushed by the negative pressure N to the outside of the unit case 1, as shown in FIG. Opening 14 is released. As a result, pressure equivalence between the external space of the unit case 1 and the space on the inner peripheral side of the conductive cylinder 7 can be quickly performed, so that the diaphragm 3 is prevented from being largely displaced, Thus, it is possible to prevent a problem that the diaphragm 3 cannot return to the current state due to the creep phenomenon.

  When the negative pressure N disappears, the valve 25 returns to its original state as shown in FIG. 1 by its elastic force, and a normal electroacoustic conversion operation can be performed.

  In the embodiment shown in FIGS. 1 to 3, the inner valve 15 is provided in one of the two openings 14 formed in the circuit board 8, and the outer valve 25 is provided in the other. The valve may be provided with one valve that is in a neutral position in the natural state and closes the opening. The direction of displacement of this valve varies depending on whether the atmospheric pressure changes to positive pressure or negative pressure, and the valve releases the opening portion regardless of whether the pressure is positive or negative.

  The omnidirectional condenser microphone unit according to the present invention can constitute an omnidirectional condenser microphone by housing it in a microphone case. A connector for connecting a microphone cable may be provided in the microphone case as necessary.

  As an example of the use of the omnidirectional condenser microphone unit and the omnidirectional condenser microphone according to the present invention, there is a noise detecting microphone in an active noise canceling headphone. Active noise cancellation control in noise cancellation headphones includes feedforward control and feedback control. In the feedforward control, since the microphone is attached to the outside of the headphone, a problem occurs due to the atmospheric pressure fluctuation as described above. In the case of feedback control, since the microphone is attached to the inside of the headphones, the internal pressure fluctuates when the user wears the above-described problem. If the microphone unit or the microphone according to the present invention is employed as the noise detecting microphone in the active noise canceling headphones, such a problem can be solved.

DESCRIPTION OF SYMBOLS 1 Unit case 2 Diaphragm holding ring 3 Diaphragm 4 Spacer 5 Fixed electrode 6 Insulating cylinder 7 Conductive cylinder 8 Circuit board 11 Acoustic terminal 15 Valve 25 Valve

Claims (7)

An acoustic terminal, a diaphragm that vibrates by receiving the sound pressure of a sound wave entering from the acoustic terminal, and a fixed electrode that is opposed to the diaphragm with a gap therebetween, and the back space of the diaphragm is closed An omnidirectional condenser microphone unit,
An opening for communicating the back space of the diaphragm to the outside;
An omnidirectional condenser microphone unit including a valve that is displaced in a direction to open the opening due to an external pressure fluctuation.   2. The omnidirectional device according to claim 1, wherein the valve is made of an elastic body, is provided in a cantilevered manner in the vicinity of the opening, and returns to its original shape when the external pressure is stabilized to seal the opening. Condenser microphone unit.   The omnidirectional condenser microphone unit according to claim 1, wherein the opening is provided in an end plate that seals the back space.   4. The omnidirectional condenser microphone unit according to claim 3, wherein the end plate is a circuit board.   The omnidirectional condenser microphone according to claim 3 or 4, wherein the valve is provided on an inner surface of the end plate facing the back space and an outer surface opposite to the inner surface.   The valve provided on the inner surface of the end plate opens the opening by applying a positive pressure to the opening, and the valve provided on the outer surface of the end plate applies a negative pressure to the opening. 6. The omnidirectional condenser microphone unit according to claim 5, wherein the opening is opened as a result.   An omnidirectional condenser microphone unit comprising a omnidirectional condenser microphone unit housed in a microphone case, wherein the omnidirectional condenser microphone unit is the omnidirectional condenser microphone unit according to any one of claims 1 to 6. Omnidirectional condenser microphone.

Images