JP5268675B2 - Boundary microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent noise generation due to entry of a high-frequency current generated with an external electromagnetic wave into a microphone case even in such a case without impairing a vibration-noise preventing function. <P>SOLUTION: A boundary microphone constituted by storing a microphone unit 30, having an electrostatic type acousto-electric converter 32 and an impedance converter 33 in a metallic unit case 31, in a microphone case 1 including a metallic flat base portion 10 whose top surface side is made open and a metallic microphone cover 20 covering the top surface side thereof and having many openings, and then fixing the microphone unit 30 onto the base portion 10 with a fixing band 50 with an elastic member interposed uses conductive cloth 60 as the elastic member, and has at least an impedance converter storage portion 33a of the microphone unit 30 fixed onto the base portion 10 with the fixing band 50 in a state the impedance converter storage portion 33a is wrapped with the conductive cloth 60. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a boundary microphone, and more particularly to a technique for preventing noise from being generated by an external electromagnetic wave.

  Boundary microphones (planar sound pickup microphones) are also called surface mount microphones because they are installed on desks and floors in TV studios and conference rooms, for example. A flat microphone case as described in Document 1 is used. An example of this will be described with reference to FIGS. 4 is a cross-sectional view taken along line DD in FIG. 5, and FIG. 5 is a cross-sectional view taken along line CC in FIG.

  According to this, the microphone case 1 used for the boundary microphone basically includes a flat base portion 10 made of metal with an upper surface opened and a large number of openings attached to the base portion 10 so as to cover the upper surface. It consists of two parts of a metal microphone cover 20 having a (sound wave introduction hole).

  Usually, the base portion 10 is formed by casting such as zinc die casting, and a punching plate (perforated plate) is used for the microphone cover 20. Instead of the punching plate, a wire mesh body may be used.

  The microphone cover 20 is screwed to the base portion 10, but if it is screwed at multiple points, the appearance will be impaired, so it is usually set at one point.

  That is, a screw insertion hole 21 is formed in the approximate center of the microphone cover 20, and a boss 11 having a female screw as a counterpart is erected on the base portion 10, and a fixing male screw 22 is inserted from the screw insertion hole 21 to the boss. 11, and the microphone cover 20 is fixed to the base portion 10.

  Thereby, a shield space is formed between the base portion 10 and the microphone cover 20, and the microphone unit 30 and the circuit board 40 are accommodated therein.

  In the boundary microphone, the microphone unit 30 includes an electrostatic acoustoelectric converter 32 in which a diaphragm and a fixed pole are disposed opposite to each other in a metal unit case 31, and an impedance converter. A capacitor microphone unit including an FET (field effect transistor) 33 is used.

  Although not shown, a sound quality adjustment circuit, an audio signal output circuit, and the like are mounted on the circuit board 40. A microphone cord 41 is connected to the circuit board 40. The microphone cord 41 is pulled out from the base portion 10 via the cord bush 12 and connected to a phantom power source (not shown).

  By the way, the punching plate used for the microphone cover 20 is made of, for example, an iron plate having a large number of holes, cut into a predetermined shape, and then processed into a desired shape by a press. The peripheral end surface (cut surface) 20a in contact with 10 is asymmetric and jagged. Further, when the base portion 10 is also made of die casting, the casting surface is not necessarily flat.

  Therefore, although the electrical connection between the base unit 10 and the microphone cover 20 is a point contact at multiple points, when considering the influence of external electromagnetic waves, electromagnetic waves such as ordinary VHF and UHF bands used in broadcasting stations are used. Interference due to can be sufficiently dealt with by the shield by the base 10 and the microphone cover 20 described above.

  However, in the field of microphones, with the rapid spread of mobile phones in recent years, strong electromagnetic waves radiated from mobile phones (for example, commercial radio waves are generated in the city within a range of several centimeters to several tens of centimeters). The effect of the electric field strength reaching several tens of thousands of the electric field strength is a problem.

  That is, in the shield by the base part 10 and the microphone cover 20, the electrical contact is a point contact, and the part has an impedance with respect to a high frequency. The cover 20 acts as an antenna, which may cause noise.

  In order to solve this problem, the present applicant, as Patent Document 2, interposes a gasket made of a conductive cloth having both elasticity and conductivity between the abutting end faces of the base portion 10 and the microphone cover 20 to provide a microphone case. It is proposed to strengthen the shield of No. 1 to prevent the generation of noise due to electromagnetic waves emitted from a mobile phone.

  According to the invention described in Patent Document 2, an effective shielding action can be obtained if the high-frequency impedance between the butted end surfaces of the base portion 10 and the microphone cover 20 is low and uniform over the entire circumference.

  However, for example, if there is a portion with a high frequency impedance in part due to the material of the gasket (conductive cloth) to be used, a high frequency current enters the microphone case 1 from that portion and is detected by the FET 33. Noise can be generated.

  As another problem, the microphone unit 30 is fixed to the base unit 10 by the fixing band 50. However, since the boundary microphone is installed on a desk or a floor surface, it is susceptible to vibration.

  Therefore, as a measure for preventing the occurrence of noise due to vibration, as shown in FIG. 5, vibration absorbing members (between the microphone unit 30 and the base unit 10, and between the fixed band 50 and the microphone unit 30, respectively). As the damper material, elastic bodies 51a and 51b made of, for example, butyl rubber are interposed.

  According to this, since the microphone unit 30 and the base unit 10 are electrically insulated, it is necessary to connect the ground (unit case 31) of the microphone unit 30 to the ground of the circuit board 40 via the lead wire 34. There is.

  In this case, since the wiring space of the lead wire 34 is narrow and the wiring dimension is short, a shield-coated wire cannot be used for the lead wire 34.

  Therefore, when the lead wire 34 operates as an antenna that takes in a high-frequency current, and the high-frequency current enters the microphone case 1, the high-frequency current flows to the FET 33 through the lead wire 34, and a large noise is generated. Problems arise.

Utility Model Registration No. 2515812 JP-A-2005-333180

  Therefore, an object of the present invention is to provide a boundary microphone that can prevent generation of noise caused by a high-frequency current due to an external electromagnetic wave entering the microphone case without impairing the vibration noise prevention function. There is.

In order to solve the above-described problems, the present invention includes a microphone case including a flat metal base portion whose upper surface side is open and a metal microphone cover having a number of openings covering the upper surface side of the base portion. In the microphone case, a microphone unit having an electrostatic acoustoelectric converter and impedance converter in a metal unit case is stored in a horizontal state with its sound collection axis parallel to the base part. is, in a boundary microphone that is fixed on the base portion by a fixing band the microphone unit via the elastic member, the conductive cloth is used as the elastic member, the conductive cloth, on of the microphone unit comprising a cylindrical portion enclosing an impedance converter housing part whose serial impedance converter is housed, the At least a portion of the cylindrical portion that contacts the base portion extends over the entire length of the unit case, and a tongue piece disposed between the unit case and the base portion is continuously provided. The impedance converter housing portion is fixed on the base portion by the fixing band in a state of being wrapped with the conductive cloth.

  According to the present invention, at least the impedance converter housing portion in which the impedance converter is housed of the microphone unit is fixed on the base portion by the fixing band in a state of being wrapped with the conductive cloth, and the impedance transducer housing portion is Is electrically connected to the base via a conductive cloth, so that even if high-frequency current due to external electromagnetic waves enters the microphone case, it does not flow to the impedance converter (FET) and is caused by the high-frequency current. Generation of noise can be prevented. Moreover, since the conductive cloth has elasticity, generation of vibration noise can be prevented.

Sectional drawing which shows the boundary microphone of this invention (BB sectional view taken on the line of FIG. 2). Sectional drawing which shows the boundary microphone of this invention (AA sectional view taken on the line of FIG. 1). The perspective view which shows the structural example of the electrically conductive cloth applied to this invention. Sectional drawing which shows the conventional boundary microphone (DD sectional view taken on the line of FIG. 5). Sectional drawing which shows the conventional boundary microphone (CC sectional view taken on the line CC of FIG. 4).

  Next, an embodiment of the present invention will be described with reference to FIGS. In the description of this embodiment, the same reference numerals are assigned to components that may be regarded as the same as or the same as those of the conventional example described with reference to FIGS.

  As shown in FIG. 1 and FIG. 2, also in the boundary microphone of the present invention, the microphone case 1 is attached so as to cover the upper surface and the flat base portion 10 whose upper surface side is opened as a basic configuration. And a metallic microphone cover 20 having a large number of openings (sound introduction holes).

  The base portion 10 is preferably formed by casting such as zinc die casting, but other than this, a molded product of a metal press may be used. In addition, a punching plate (perforated plate) is usually used for the microphone cover 20, but a wire net may be used instead of the punching plate. Moreover, in order not to make a main body inconspicuous, paintings, such as black, may be given.

  The microphone cover 20 is screwed to the base portion 10, but since the appearance is impaired when screwed at multiple points, a screw insertion hole 21 is drilled at one central location of the microphone cover 20. A boss 11 having a female screw is erected on the base portion 10, a fixing male screw 22 is screwed into the boss 11 from the screw insertion hole 21, and the microphone cover 20 is fixed to the base portion 10 at one point. preferable.

  Thereby, a shield space is formed between the base portion 10 and the microphone cover 20, and the microphone unit 30 and the circuit board 40 are accommodated therein.

  The microphone unit 30 includes an electrostatic acoustoelectric transducer 32 in which a diaphragm and a fixed pole are arranged oppositely in a unit case 31 having a metal cylindrical shape, as in the conventional example. A capacitor microphone unit including an FET (field effect transistor) 33 as an impedance converter is used.

  In this embodiment, although not shown in detail, the microphone unit 30 has a front acoustic terminal on the front end surface of the unit case 31 and a rear acoustic terminal provided on the side peripheral surface of the unit case 31. This is a unidirectional microphone unit.

  Although not shown, a sound quality adjustment circuit, an audio signal output circuit, and the like are mounted on the circuit board 40. A microphone cord 41 is connected to the circuit board 40. The microphone cord 41 is pulled out from the base portion 10 via the cord bush 12 and connected to an unillustrated phantom power source or the like.

  The microphone unit 30 is disposed horizontally on the base unit 10 with its sound collection axis parallel to the base unit 10 and is fixed by the fixing band 50. In the present invention, the microphone unit 30 is a conductive cloth 60. It is fixed on the base portion 10 by the fixing band 50 in a state of being wrapped.

  Referring to FIG. 3, in this embodiment, conductive cloth 60 includes a cylindrical portion 61 and a tongue piece 62 that extends over the entire length of unit case 31 along the axial direction of cylindrical portion 61 from one end side of a portion of cylindrical portion 61. With.

  The inner diameter of the cylindrical portion 61 is substantially the same as the outer diameter of the unit case 31, and the impedance converter storage portion 33 a in which the impedance converter 33 of the microphone unit 30 is stored is fitted in the cylindrical portion 61. The The cylindrical portion 61 does not cover the rear acoustic terminal.

  As the impedance converter accommodating portion 33a is fitted into the cylindrical portion 61, the tongue piece 32 is disposed along the side peripheral surface of the unit case 31, and as shown in FIG. It is arranged on the base part 10 so as to sandwich the tongue piece 32 with the part 10 and is fixed by the fixing band 50.

  The conductive cloth 60 is, for example, a cloth material having both conductivity and elasticity obtained by weaving a silver-coated nylon fiber with a nickel-plated conductive fiber into a cloth shape or processing into a non-woven cloth. 10-70X can be used.

  In this embodiment, the fixed band 50 is a band member having substantially the same width as that of the cylindrical portion 61, is disposed on the cylindrical portion 61, and both ends thereof are attached to the base portion 10 with male screws 52 and 52. The fixing band 50 may be made of metal or synthetic resin, but is preferably made of metal.

  In the microphone unit 30, the ground (unit case 31) is connected to the ground of the circuit board 40 through the lead wire 34 as in the conventional example, but according to the present invention, the impedance converter housing portion 33 a is electrically conductive. Since the unit case 31 is encased in the cylindrical portion 61 of the cloth 60 and electrically connected to the base portion 10 via the conductive cloth 60, the lead wire 34 does not operate as an antenna, and the high frequency current Generation of noise due to is prevented.

  In addition, since the tongue piece 62 of the conductive cloth 60 is disposed between the microphone unit 30 and the base portion 10, external elasticity is not directly transmitted to the microphone unit 30 due to its elasticity, and generation of vibration noise is reduced. .

A conductive cloth similar to the conductive cloth 60 may be sandwiched between the end face 20 a of the microphone cover 20 and the base portion 10 .

DESCRIPTION OF SYMBOLS 1 Microphone case 10 Base part 20 Microphone cover 20a End surface 21 Screw insertion hole 22 Male screw 30 Microphone unit 31 Unit case 32 Electrostatic acoustoelectric converter 33 Impedance converter (FET)
33a Impedance converter housing portion 34 Lead wire 40 Circuit board 41 Microphone cord 50 Fixed band 60 Conductive cloth 61 Cylindrical portion 62 Tongue piece

Claims (1)

A microphone case including a metal flat base portion whose upper surface side is open and a metal microphone cover having a large number of openings covering the upper surface side of the base portion is provided, and a metal unit is provided in the microphone case. A microphone unit having an electrostatic acoustoelectric converter and an impedance converter is housed in a case in a horizontally placed state with its sound collection axis parallel to the base part, and the microphone unit is interposed via an elastic member. In the boundary microphone fixed on the base part by a fixed band,
Conductive cloth is used as the elastic member, the conductive cloth has a cylindrical portion enclosing an impedance converter housing portion upper Symbol impedance converter is housed within the microphone unit, at least one of the cylindrical portion The portion that contacts the base portion extends over the entire length of the unit case, and is provided with a tongue piece disposed between the unit case and the base portion, and the impedance converter housing portion is A boundary microphone characterized by being fixed on the base portion by the fixing band in a state of being wrapped with the conductive cloth.

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