JP4560424B2 - Condenser microphone - Google Patents

Description

  The present invention relates to a condenser microphone, and more specifically to a technique for reducing noise generated due to an external electromagnetic wave.

  As shown in FIG. 2, the condenser microphone 10 is usually used by connecting to an external device 30 such as a phantom power source or a mixer circuit via a microphone cable 20 made of a balanced shield cable.

  The condenser microphone 10 in this example includes a cylindrical microphone casing 11 made of, for example, a brass alloy that functions as a shield, and the condenser microphone unit 12 is covered with a protective cover 13 made of a metal mesh on one end side of the microphone casing 11. It is supported in the state. Although not shown, the condenser microphone unit 12 has a built-in FET (field effect transistor) as an impedance converter.

  The microphone housing 11 includes a circuit board 14 including an audio output circuit. When the microphone cable 20 is detachable, male connectors 21 and 21 are provided at both ends of the microphone cable 20, and female connectors 15 and 31 are provided at the other end side of the microphone casing 11 and the external device 30 side. Provided.

  These connectors are 3-pin type connectors defined by JEITA (Japan Electronic Machinery Manufacturers Association) RC-5236 “Latch Lock Round Connector for Acoustic Equipment”, and although not shown, The first pin, the second pin on the hot side of the signal, and the third pin on the cold side of the signal are provided.

  Each first pin of the male-side connectors 21 and 21 is connected to the shield-coated wire of the microphone cable 20. The first pin of the female connector 15 on the microphone 10 side is connected to the microphone casing 11, and the first pin of the female connector 31 on the external device 30 side is connected to the ground of the external device 30.

  Therefore, when the condenser microphone 10 is connected to the external device 30 via the microphone cable 20, the microphone casing 11 functions as a shield together with the shield covered wire of the microphone cable 20.

  However, when a strong electromagnetic wave is applied to the microphone casing 11 or the microphone cable 20, a high-frequency current due to the electromagnetic wave enters the microphone casing 11 via the connectors 15 and 21, and the FET or circuit board 14 in the condenser microphone unit 12. May be detected by a semiconductor element of a sound output circuit mounted on the microphone and output from a microphone as noise of an audible frequency.

  In recent years, cellular phones have rapidly spread. However, cellular phones radiate electromagnetic waves having a high frequency (about several GHz) at the time of transmission, and the radiation electric field strength is large. Therefore, as shown in FIG. When the mobile phone 40 is used, noise is likely to occur due to the strong electromagnetic waves.

  As one of the methods for preventing this, there is known a method of reducing the impedance of the connection part by interposing a conductive member such as a leaf spring in the connection part of the connector, but because it is a mechanical contact, Even if the impedance is reduced, there is a limit and it may not always be effective.

  Accordingly, an object of the present invention is to provide a condenser microphone that reduces (suppresses) unpleasant noise by reducing sound output when electromagnetic waves are detected.

  In order to solve the above-described problems, the present invention provides a high-frequency detection means and a capacitor microphone unit for use in a condenser microphone that is used by connecting the condenser microphone unit to an external device such as a power supply circuit or a mixer circuit via an audio output circuit and a microphone cable. A receiving antenna having a light emitting means for emitting light by high frequency detection output, and connected in parallel between a hot side and a cold side of an audio signal output line from the audio output circuit to the external device, and emitted from the light emitting means. And a photoconductive element whose resistance value is reduced by receiving light.

  In the present invention, the receiving antenna is preferably a loop coil formed by connecting the high-frequency detection means and the light-emitting means in series. The high-frequency detection means is a Schottky diode, and a light-emitting diode that emits visible light is preferably employed as the light-emitting means.

  The photoconductive element may be a CdS (cadmium sulfide) element or a phototransistor. The photoconductive element may be connected in parallel between the output terminals of the audio output circuit. However, in order to be applicable to an existing microphone, the photoconductive element is connected in parallel between the hot side and the cold side of the microphone cable. It is preferable to be connected to.

  According to the present invention, when electromagnetic waves are detected by the receiving antenna, the light emitting means emits light, and the resistance value of the photoconductive element is reduced by the light, so that the hot side and the cold side of the audio signal output line are short-circuited ( Therefore, even if noise due to electromagnetic waves occurs, the noise is narrowed down as the audio output becomes smaller. Therefore, discomfort due to annoying noise can be eliminated.

  Next, an embodiment of the present invention will be described with reference to FIG. 1, but the present invention is not limited to this. FIG. 1 is a schematic diagram showing a main part of the present invention. For the overall configuration of the condenser microphone, the microphone cable, and the like, refer to FIG. 2 described above as an example.

  The condenser microphone of the present invention includes a receiving antenna 100 that receives electromagnetic waves, and a photoconductive element 210 that is connected in parallel between the hot-side line H and the cold-side line C of the audio signal output line 200. .

  The receiving antenna 100 is preferably a loop coil having the simplest configuration. The loop coil includes a high-frequency detection means 110 and a light-emitting means 120 that emits light based on the detection output in series.

  In this example, a Schottky diode 111 having excellent high frequency detection capability is used for the high frequency detection means 110, and a light emitting diode 121 is used for the light emitting means 120.

  The photoconductive element 210 is a visible light conductive element that receives light from the light-emitting diode 121 and has a resistance value that decreases depending on the intensity of the light. For example, a CdS (cadmium sulfide) element or a photodiode can be used.

  The connection point of the photoconductive element 210 to the audio signal output line 200 may be arbitrarily selected as long as it extends from the condenser microphone unit 12 to the external device 30 shown in FIG. 2, for example, mounted on the circuit board 14. Between the output terminals of the audio output circuit (not shown) (between the 2nd and 3rd pins of the output connector 15), but considering the application to an existing microphone, the hot side line H of the microphone cable 20 It is preferable to be between the cold side line C.

  The receiving antenna 100 may be attached to a predetermined location of the microphone casing 11 with an appropriate attachment such as a belt or a planar fastener, for example. As described above, when the receiving antenna 100 is attached to the microphone casing 11, the photoconductive element 210 is disposed so as to be optically coupled to the vicinity of the light emitting diode 121 by routing the wiring. Note that the photoconductive element 210 and the light emitting diode 121 may be coupled using an optical fiber.

  According to the present invention, for example, when a strong electromagnetic wave is applied to the receiving antenna 100 from a mobile phone, the electromagnetic wave is detected by the high frequency detection means 110 (Schottky diode 111 in this example), and the light emission means 120 (this In the example, the light emitting diode 121) emits light.

  When this light is received by the photoconductive element 210, the resistance value of the photoconductive element 210 decreases in proportion to the amount of light received. As a result, the hot-side line H and the cold-side line C of the audio signal output line 200 are brought into conduction, and one type of mute is performed in which the audio output is reduced. Therefore, even if noise due to electromagnetic waves occurs, the noise is narrowed as the audio output is reduced, so that discomfort due to annoying noise can be eliminated.

The schematic diagram which shows the principal part of this invention. The schematic diagram which shows the general use condition of a condenser microphone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Condenser microphone 11 Microphone housing 12 Condenser microphone unit 14 Circuit board 15 Output connector 20 Microphone cable 30 External device 40 Cellular phone 100 Receiving antenna 110 High frequency detection means 111 Schottky diode 120 Light emitting means 121 Light emitting diode 200 Audio signal output line 210 Light Conductive element H Hot-side line C Cold-side line

Claims (5)

In a condenser microphone that is used by connecting a condenser microphone unit to an external device such as a power supply circuit or a mixer circuit via an audio output circuit and a microphone cable.
A receiving antenna having a high-frequency detection means and a light-emitting means that emits light by the high-frequency detection output, and connected in parallel between a hot side and a cold side of an audio signal output line from the audio output circuit to the external device, A condenser microphone, comprising: a photoconductive element that receives light emitted from the light emitting means and decreases a resistance value.   2. The condenser microphone according to claim 1, wherein the receiving antenna includes a loop coil formed by connecting the high-frequency detection means and the light-emitting means in series.   3. The condenser microphone according to claim 1, wherein the high-frequency detection means is a Schottky diode, and the light-emitting means is a light-emitting diode that emits visible light.   4. The condenser microphone according to claim 1, wherein the photoconductive element comprises a CdS (cadmium sulfide) element or a phototransistor.   5. The condenser microphone according to claim 1, wherein the photoconductive element is connected in parallel between a hot side and a cold side of the microphone cable. 6.

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