JP4934532B2 - Condenser microphone unit - Google Patents

Description

  The present invention relates to a condenser microphone unit, and more particularly, to a dustproof metal net (metal mesh) attached to an opening forming a front acoustic terminal.

  Referring to FIG. 3, the condenser microphone unit includes a unit case 10 and an electrostatic acoustoelectric converter 20 as a basic configuration.

  The unit case 10 is formed in a cylindrical shape with a bottom made of, for example, an aluminum material, and a front acoustic terminal 11a including an opening is provided on one end surface side 11 corresponding to the bottom surface. The other end surface side of the unit case 10 is opened to accommodate the acoustoelectric converter 20. Although only one front acoustic terminal 11a is shown in FIG. 3, a plurality of front acoustic terminals 11a are usually provided as small holes.

  The acoustoelectric converter 20 is disposed, for example, with a diaphragm 22 made of a synthetic resin film having a metal vapor deposition film on one side and a diaphragm 22 via a spacer ring 23, and a kind of capacitor is provided together with the diaphragm 22. The fixed pole 24 to be formed is included.

  The diaphragm 22 is stretched on one surface of a support ring (also referred to as a diaphragm ring) 21 in a state where a predetermined tension is applied. The support ring 21 is made of metal.

  The fixed pole 24 is supported on one surface side of an insulating seat 25 made of synthetic resin. The circuit board 40 is disposed on the other surface (back side) of the insulating seat 25. An FET (field effect transistor) 50 as an impedance converter that is electrically connected to the fixed electrode 24 is mounted on the circuit board 40.

  Since the condenser microphone unit shown as this conventional example is unidirectional, the circuit board 40 is provided with a rear acoustic terminal 41 having an opening.

  In relation to this, the insulating seat 25 is provided with a sound hole 25a extending from the rear acoustic terminal 41 to the back air chamber 26 formed on the back side of the fixed pole 24, and in the sound hole 25a. An acoustic resistance material 27 made of a nonwoven fabric or the like is provided.

  As described in Patent Document 1, the front acoustic terminal 11a is provided with a dust-proof metal net 30 for preventing foreign matters such as dust from entering the unit case 10 through the opening. It is done. In the following description, the metal net may be referred to as a metal mesh.

  This condenser microphone unit is housed in the unit case 10 in the order of a metal mesh 30, a support ring 21 with a diaphragm 22 stretched, a spacer ring 23, an insulating seat 25 having a fixed pole 24, and a circuit board 40. The unit case 10 is assembled by caulking the peripheral edge on the other end surface side.

  The metal mesh 30 is firmly tightened by the caulking pressure at this time, the support ring 21 and the unit case 10 are reliably electrically connected, and the acoustic-electric conversion is performed by the repulsion force of the metal mesh 30 and the caulking pressure. The container 20 is fixed in the unit case 10.

  By the way, the opening (the density of the eyes) of the metal mesh 30 is preferably finer in order to prevent intrusion of fine foreign matter, and usually about 100 mesh is used. There is a problem that the high frequency response is degraded by acoustic resistance.

  This will be described with reference to the machine equivalent circuit of FIG. P1 is a sound source for the front acoustic terminal 11a, P2 is a sound source for the rear acoustic terminal 41, rf is an acoustic resistance of the metal mesh 30, sf is an air stiffness of the front air chamber 12 existing between the metal mesh 30 and the diaphragm 22, mo is the mass of the diaphragm 22, so is the stiffness of the diaphragm, ro is the braking resistance of the diaphragm 22 due to the thin air layer 13 existing between the diaphragm 22 and the fixed pole 24, and s 1 is the air in the back air chamber 26. The stiffness r1 is an acoustic resistance by the acoustic resistance material 27 that gives directivity to the rear acoustic terminal 41.

  In the mechanical equivalent circuit, since the stiffness is expressed by a capacitor, if the volume of the front air chamber 12 existing between the metal mesh 30 and the diaphragm 22 is large, the acoustic resistance rf of the metal mesh 30 and the front air chamber 12 are large. Since the air stiffness sf causes the CR filter to be configured acoustically, the frequency response particularly at high frequencies is degraded.

  As another problem, in the condenser microphone unit, the diaphragm 22 and the back air chamber 26 constitute a resonance circuit. Normally, the braking resistance (acoustic resistance) of the thin air layer 13 between the diaphragm 22 and the fixed pole 24 is used for braking the resonance circuit.

  However, adjusting this braking resistance is extremely difficult because it is necessary to change the distance between the diaphragm 22 and the fixed pole 24, or to change the size and number of sound holes provided in the fixed pole 24. . In addition, since the effective capacitance changes, other performance and specifications may change.

JP 2007-150995 A

  Accordingly, an object of the present invention is to prevent deterioration of the frequency response at high frequencies caused by the dustproof metal net attached to the front acoustic terminal and to easily adjust the braking resistance of the resonance circuit. It is in.

  In order to solve the above-mentioned problems, according to the present invention, as described in claim 1, the diaphragm stretched on the support ring and the fixed pole supported by the insulating seat are arranged to face each other with a spacer interposed therebetween. And a unit case made of metal having a front acoustic terminal having an opening on one end surface side, the other end surface side being opened, and housing the acoustoelectric transducer, and the unit case A dust-proof metal net disposed between the support ring and one end surface of the unit case so as to cover the front acoustic terminal therein, and a fixing provided on the other end surface of the unit case In the condenser microphone unit in which the acoustoelectric transducer is fixed in the unit case together with the metal net by means, the central portion of the metal net is formed of the metal net and the vibration. As reduce acoustic cavity volume between the plate, it is characterized by being recessed into a dish shape toward the diaphragm side.

  In the present invention, as described in claim 2, it is preferable that the central portion of the metal net is recessed in a dish shape so as to be substantially parallel to the diaphragm.

  According to the present invention, the central portion of the metal mesh body (metal mesh) attached to the front acoustic terminal is directed toward the diaphragm side so as to reduce the acoustic cavity volume between the metal mesh body and the diaphragm. The dish-shaped recess increases the air stiffness of the front air chamber existing in front of the diaphragm, and the pass band of the filter that attenuates the high range moves to the higher frequency side. It is possible to prevent the deterioration of the frequency response in the high range due to the metal net.

  Also, since the acoustic resistance of the metal net is connected in series with the impedance of the diaphragm, the damping resistance of the resonance circuit composed of the diaphragm and the back air chamber can be easily selected by selecting the acoustic resistance. Can be adjusted.

  Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing a condenser microphone unit according to an embodiment of the present invention, and FIG. 2 is a mechanical equivalent circuit diagram thereof. Components that may be regarded as the same as or the same as those in the conventional example described with reference to FIG.

  As shown in FIG. 1, the condenser microphone unit according to the present invention also includes a unit case 10 and an electrostatic acoustoelectric converter 20 as a basic configuration.

  The unit case 10 is made of metal and is formed into a bottomed cylindrical shape using, for example, an aluminum material, and an opening for forming the front acoustic terminal 11a is provided on one end surface side 11 corresponding to the bottom surface. The other end surface side of the unit case 10 is opened to accommodate the acoustoelectric converter 20.

  Although only one front acoustic terminal 11a is shown in FIG. 1, a plurality of front acoustic terminals 11a may be provided as small holes. The front acoustic terminal 11a may be formed as a plurality of rows of slits.

  The acoustoelectric converter 20 is disposed, for example, with a diaphragm 22 made of a synthetic resin film having a metal vapor deposition film on one side and a diaphragm 22 via a spacer ring 23, and a kind of capacitor is provided together with the diaphragm 22. The fixed pole 24 to be formed is included. An electret dielectric film may be applied to either the diaphragm 22 or the fixed pole 24.

  The diaphragm 22 is stretched on one surface of a support ring (also referred to as a diaphragm ring) 21 in a state where a predetermined tension is applied. The support ring 21 is made of metal.

  The fixed pole 24 is supported on one surface side of an insulating seat 25 made of synthetic resin. The circuit board 40 is disposed on the other surface (back side) of the insulating seat 25. An FET (field effect transistor) 50 as an impedance converter that is electrically connected to the fixed electrode 24 is mounted on the circuit board 40. The gate electrode of the FET 50 is connected to the fixed electrode 24.

  Since this condenser microphone unit is unidirectional, an opening as a rear acoustic terminal 41 is provided in the circuit board 40.

  In relation to this, the insulating seat 25 is provided with a sound hole 25a extending from the rear acoustic terminal 41 to the back air chamber 26 formed on the back side of the fixed pole 24, and in the sound hole 25a. An acoustic resistance material 27 made of a nonwoven fabric or the like is provided.

  The front acoustic terminal 11 a is provided with a dust-proof metal net (metal mesh) 30 for preventing foreign matters such as dust from entering the unit case 10 through the opening. In this example, the metal mesh 30 is a 100-mesh mesh body in which 100 wires having a diameter of 0.1 mm are incorporated within one inch, as in the above-described conventional example. It may be a body.

  This condenser microphone unit is housed in the unit case 10 in the order of a metal mesh 30, a support ring 21 with a diaphragm 22 stretched, a spacer ring 23, an insulating seat 25 having a fixed pole 24, and a circuit board 40. The unit case 10 is assembled by caulking the peripheral edge on the other end surface side, but a lock ring or the like that is screwed to the other end surface side of the unit case 10 may be used as the fixing means.

  The metal mesh 30 is firmly tightened by the caulking pressure at this time, the support ring 21 and the unit case 10 are reliably electrically connected, and the acoustic-electric conversion is performed by the repulsion force of the metal mesh 30 and the caulking pressure. The container 20 is firmly fixed in the unit case 10.

  As shown in FIG. 1, the metal mesh 30 has a peripheral portion sandwiched between the inner surface of the unit case 10 and the support ring 21, but in the present invention, the center corresponding to the front acoustic terminal 11 a of the metal mesh 30. The portion is recessed in a dish shape so as to be preferably substantially parallel to the diaphragm 22 toward the diaphragm 22 side.

  Thereby, since the acoustic cavity volume of the front air chamber 12 existing between the metal mesh 30 and the diaphragm 22 is reduced, the air stiffness of the front air chamber 12 is increased, and the filter for attenuating the high range is used. Since the pass band (resonance frequency) moves to a higher frequency side, it is possible to prevent the deterioration of the frequency response in the high region due to the metal net for dust prevention.

  Also, as shown in the mechanical equivalent circuit of FIG. 2, the acoustic resistance rf of the metal mesh 30 is connected in series with the impedance (mo, so, ro) of the diaphragm 22, so that the acoustic resistance rf is appropriately set. By selecting, the braking resistance of the resonance circuit composed of the diaphragm 22 and the back air chamber 26 can be easily adjusted.

  That is, as in the prior art, only the opening (mesh fineness) of the metal mesh 30 is selected without changing the distance between the diaphragm 22 and the fixed pole 24 and the size and number of sound holes provided in the fixed pole 24. As a result, the braking resistance of the resonance circuit composed of the diaphragm 22 and the back air chamber 26 can be easily adjusted.

Sectional drawing which shows the condenser microphone unit which concerns on embodiment of this invention. The machine equivalent circuit diagram of the condenser microphone unit of FIG. Sectional drawing which shows the conventional common condenser microphone unit. FIG. 4 is a mechanical equivalent circuit diagram of the condenser microphone unit of FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Unit case 11 One end surface side of unit case 11a Front acoustic terminal 12 Front air chamber 13 Thin air layer 20 Acoustoelectric converter 21 Support ring 22 Diaphragm 23 Spacer ring 24 Fixed pole 25 Insulating seat 26 Back air chamber 27 Acoustic resistance material 30 Metal mesh (metal mesh)
40 Circuit board 50 FET

Claims (2)

There is an acoustoelectric transducer in which a diaphragm stretched on a support ring and a fixed pole supported by an insulating seat are arranged oppositely via a spacer, and a front acoustic terminal consisting of an opening is provided on one end face side. The other end surface side is open, the metal unit case in which the acoustoelectric converter is accommodated, the support ring and the one end surface side of the unit case so as to cover the front acoustic terminal in the unit case; A dust-proof metal net disposed between the unit case and the acoustoelectric transducer in the unit case together with the metal net by a fixing means provided on the other end surface side of the unit case. In the condenser microphone unit
A central portion of the metal mesh body is recessed in a dish shape toward the diaphragm side so as to reduce an acoustic cavity volume between the metal mesh body and the diaphragm. Condenser microphone unit.   The condenser microphone unit according to claim 1, wherein a central portion of the metal net is recessed in a dish shape so as to be substantially parallel to the diaphragm.

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