JP2011188037A - Electroacoustic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroacoustic transducer using high-frequency discharge capable of preventing the wear of a tip in a needle-like electrode and the adhesion of discharge products even if high-frequency discharge is performed continuously, and preventing abnormal discharge. <P>SOLUTION: The electroacoustic transducer includes the needle-like electrode 23, a counter electrode 24 opposing the needle-like electrode 23, a discharge unit formed between the needle-like electrode 23 and the counter electrode 24, and a high-frequency oscillation circuit including the discharge unit and inducing high-frequency discharge at the discharge unit. The electroacoustic transducer takes out a voice signal modulated according to sound waves introduced to the discharge unit or performs discharge according to a high-frequency signal modulated by a voice signal at the discharge unit for conversion to a voice. The electroacoustic transducer includes an inert gas supply path 251 for supplying inert gas toward an outer peripheral surface of the needle-like electrode 23. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a further improvement of an electroacoustic transducer capable of eliminating a diaphragm by performing electroacoustic conversion using high-frequency discharge.

  A diaphragm is used in a general electroacoustic transducer such as a microphone or a speaker. In the case of a microphone, the vibration of a diaphragm that vibrates in response to a sound wave is detected as an electromagnetic change, a change in capacitance, an optical change, or the like, and converted into an electrical signal. In the case of a speaker, generally, an audio signal is electromagnetically converted into a vibration of a diaphragm and output as a sound wave. The diaphragms in these electroacoustic transducers are used for conversion between air vibration and electrical signals. In other words, one diaphragm is connected to three systems of an acoustic system, a mechanical vibration system, and an electric circuit system. As described above, a conventional general electroacoustic transducer, particularly a microphone, includes a diaphragm regardless of which method is used, and thus there is a limit in frequency response due to the presence of the diaphragm. Therefore, even if the mass of the diaphragm is reduced to the limit, the inertial force works as long as the mass exists, and the sound collection limit exists at the frequency.

  As an example of an electroacoustic transducer that does not have a diaphragm, Patent Document 1 discloses a method of detecting particle velocity using discharge and performing electroacoustic conversion. The invention described in Patent Document 1 includes a needle-like discharge electrode and a counter electrode that surrounds the discharge electrode with an interval, and the counter electrode is formed of a conductive material that has a spherical shape and is perforated to transmit sound waves. Thus, the discharge electrode extends toward the inside of the spherical counter electrode and reaches the vicinity of the center of the sphere. A high-frequency voltage signal is applied to the discharge electrode from a high-frequency voltage generation circuit modulated by a low-frequency signal to be converted into sound waves, and corona discharge corresponding to the high-frequency voltage signal is performed between the discharge electrode and the counter electrode. As a result, the low-frequency signal, that is, a sound wave is emitted.

  The invention described in Patent Document 1 converts an electrical sound signal into a sound wave using discharge, and is called an ion speaker. It is impossible to use the invention described in Patent Document 1 as a microphone as it is, and there is no suggestion about the possibility of using it as a microphone.

  The inventor has an acoustic tube whose cross-sectional area is unchanged in the length direction, an internal electrode disposed in the acoustic tube, an external electrode disposed on the outer periphery of the acoustic tube corresponding to the position of the internal electrode, A drive circuit that applies a high voltage signal modulated with an audio signal between an internal electrode and an external electrode to cause corona discharge with a strength corresponding to the audio signal in an acoustic tube, and an invention related to headphones, A patent application was first filed (see Patent Document 2). An acoustic tube with little change in the cross-sectional area in the length direction and a discharge type speaker are combined so that no reflected wave is generated in the acoustic tube so that the frequency response does not undulate.

JP-A-55-140400 JP 2008-236235 A

  The inventor also includes a needle-like electrode, a counter electrode facing the needle-like electrode, a discharge portion formed between the needle-like electrode and the counter electrode, and a high-frequency discharge including the discharge portion. A high-frequency oscillation circuit that generates a sound wave, a sound wave introduction unit that introduces a sound wave into the discharge unit, a modulation signal extraction unit that extracts a signal oscillated by the high-frequency oscillation circuit and modulated according to the sound wave introduced into the discharge unit, A patent application was previously filed for a microphone equipped with the above. The invention according to Japanese Patent Application No. 2009-024697 has not yet been published.

  FIG. 4 shows an example of an electroacoustic transducer that uses substantially the same high-frequency discharge as that of the invention according to Japanese Patent Application No. 2009-024697, and is configured as a microphone unit. In FIG. 4, the microphone unit 10 includes a needle electrode 3 and a counter electrode 4 for discharging between the needle electrode 3 as main constituent members. The base of the needle-like electrode 3 is covered with a cylindrical insulating cylinder 6, and the insulating cylinder 6 is further fitted into a cylindrical insulating cylinder 5, and the insulating cylinder 5 is fitted through the base 1 in the thickness direction. ing. Accordingly, the base of the needle-like electrode 3 is fixed to the base 1 through the base 1 in the thickness direction with the insulating cylinders 5 and 6 interposed therebetween. A cylindrical case 2 extends from one side of the outer periphery of the base 1, and the tip of the needle electrode 3 extends in the extending direction of the case 2, and the needle electrode 3 is substantially the central axis of the case 2. It is located on the line and in the space surrounded by the case 2.

  The counter electrode 4 is fixed to the open end of the case 2 opposite to the base 1 so as to close the open end. The counter electrode 4 is a flat electrode. For example, by using a punching metal having countless small holes or a material in which conductive wires are knitted in a net shape, a structure that allows sound waves to pass therethrough is used. ing. The surface of the counter electrode 4 is covered with an insulating material. The counter electrode 4 is opposed to the tip of the needle electrode 3 at an appropriate interval, and constitutes a discharge part between the counter electrode 4 and the needle electrode 3. This discharge part constitutes a part of a high-frequency oscillation circuit that generates high-frequency discharge, and high-frequency discharge is generated in this discharge part. This discharge is called a flame discharge, and reference numeral 7 in FIG. 4 indicates a flame generated by the discharge in the discharge portion between the counter electrode 4 and the needle electrode 3. The counter electrode 4 constitutes a sound wave introduction part that introduces sound waves into the discharge part in the case 2 as described above.

  In order to generate a high frequency discharge between the needle electrode 3 and the counter electrode 4, it is necessary to apply a high voltage. Therefore, the high frequency oscillation circuit uses a vacuum tube that can withstand the high voltage as an active element for oscillation. It is used as The discharge current of the discharge path formed between the needle electrode 3 and the counter electrode 4 is fed back to the vacuum tube, whereby a high-frequency oscillation circuit by self-excited oscillation is configured. The acicular electrode 3 and the counter electrode 4 constitute a high-frequency discharge part, and the particle velocity of the high-frequency discharge part changes depending on the particle speed of the sound wave, and the equivalent impedance of the high-frequency discharge part changes. When the equivalent impedance of the high-frequency discharge unit is changed by the sound wave, the transmission signal by the oscillation circuit is modulated by the sound wave. This modulation signal includes frequency modulation, that is, FM modulation component and amplitude modulation, that is, AM modulation component, but more FM modulation component is included. Therefore, if the FM modulated signal is taken out and input to the FM demodulation circuit, it can be converted into an audio signal corresponding to the sound wave introduced from the sound wave introducing unit.

  As an example of the electroacoustic transducer using the high frequency discharge described above, there is an ion speaker or an ion tweeter. The principle is that plasma is generated by high-frequency discharge, and when this is amplitude-modulated by an audio signal, the plasma expands and contracts, so that sound waves are generated. The invention according to Japanese Patent Application No. 2009-024697 is classified as an ion microphone.

  In any case, an electroacoustic transducer using a high-frequency discharge generates an unequal electric field with a needle-like electrode and a flat plate electrode, and forms a plasma by applying a high-frequency high voltage thereto. Since the acicular electrode has a high electric field, plasma is generated near the acicular electrode and extends toward the flat plate electrode. Since the needle-shaped electrode is in contact with the plasma and becomes hot, the tip of the needle-shaped electrode is worn out and discharge products adhere to the vicinity of the tip, thereby deteriorating the discharge situation, for example, the length and shape of the plasma. Let An abnormal discharge occurs due to deterioration of the discharge state, and an abnormal sound wave is emitted from the discharge part.

FIGS. 5 and 8 show a state in which the discharge product adheres to the needle electrode. 2 and 6 show a pointed portion of the needle-like electrode 3 before discharging. The tip of the needle-like electrode 3 is sharply pointed before discharge as shown in FIGS. 2 and 6. However, if high-frequency discharge is continued for about 1 hour, the tip is worn as described above, and discharge occurs near the tip. Product adheres. FIG. 5 shows this state. Reference numeral 31 indicates a worn tip of the needle electrode 3, and reference 32 indicates a discharge product adhering to the vicinity of the tip of the needle electrode 3. FIG. 8 is a photographic image of the tip portion of the needle electrode corresponding to FIG. The tip portion of the needle-like electrode 3 is blown away by about 0.4 mm due to electric discharge, and wear is caused. When the discharge product 32 adheres to the tip of the needle-like electrode 3, the discharge state deteriorates and abnormal discharge occurs.
As a result of investigating the cause of the discharge product adhering to the vicinity of the tip of the needle electrode, the present inventor was able to infer that the causative substance of the discharge product is in the air.

  The present invention eliminates the problems of the conventional electroacoustic transducer using the high frequency discharge described above, that is, the wear of the tip portion of the needle electrode and the discharge product even if the high frequency discharge is continuously performed. It is an object of the present invention to provide an electroacoustic transducer using high frequency discharge that does not adhere and does not cause abnormal discharge.

  The present invention includes a needle electrode, a counter electrode facing the needle electrode, a discharge part formed between the needle electrode and the counter electrode, and the discharge part. A high-frequency oscillation circuit that extracts the audio signal modulated according to the sound wave introduced into the discharge unit, or causes the discharge unit to discharge according to the high-frequency signal modulated with the audio signal. It is an electroacoustic transducer for converting to sound, and is characterized by having an inert gas supply path for supplying an inert gas toward the outer peripheral surface of the needle electrode.

The inert gas supply path may be configured by a supply path directed to the electroacoustic transducer and an inert gas guide path for flowing an inert gas along the outer peripheral surface of the needle electrode in the electroacoustic transducer. .
The inert gas guide path includes a gas outlet that surrounds the outer periphery of the needle electrode with a space between the outer periphery of the needle electrode and allows the inert gas to flow along the peripheral surface of the tip of the needle electrode. It is good to have.

  Contact between the surface of the needle-shaped electrode and air by supplying an inert gas from the inert gas supply path toward the outer peripheral surface of the needle-shaped electrode when discharge is performed between the needle-shaped electrode and the counter electrode Is blocked, and the discharge product causative substance in the air can be prevented from adhering to the needle electrode. Therefore, an abnormal discharge caused by the adhesion of discharge products can be prevented, and an electroacoustic transducer using high-frequency discharge with stable operation can be provided.

It is a longitudinal cross-sectional view which shows the Example of the electroacoustic transducer which concerns on this invention. It is a side view which expands and shows the front-end | tip part before use of the acicular electrode in the said electroacoustic transducer. It is a side view which expands and shows the front-end | tip part of the acicular electrode after operating the Example of the electroacoustic transducer based on this invention for the predetermined time. It is a longitudinal cross-sectional view which shows the example of the electroacoustic transducer by the conventional high frequency discharge. It is a side view which expands and shows the front-end | tip part of the acicular electrode after operating the said conventional electroacoustic transducer for the predetermined time. It is a side view by the photograph image of the acicular electrode corresponding to FIG. It is a side view by the photograph image of the acicular electrode corresponding to FIG. It is a side view by the photograph image of the acicular electrode corresponding to FIG.

Embodiments of an electroacoustic transducer according to the present invention will be described below with reference to the drawings.
In FIG. 1, the microphone unit 20 has a needle electrode 23 and a counter electrode 24 for discharging between the needle electrode 23. The base of the needle-like electrode 23 is formed in a cylindrical shape and is covered with a cylindrical insulating cylinder 26. The insulating cylinder 26 is further fitted into a cylindrical insulating cylinder 25, and the insulating cylinder 25 extends the base 21 in the thickness direction. Is fitted through. In other words, the base of the needle-like electrode 23 passes through the base 21 in the thickness direction with the insulating cylinders 25 and 26 interposed therebetween, and is fixed to the base 21. A cylindrical case 22 extends integrally from one side of the outer periphery of the base 21, and the tip of the needle electrode 23 extends in the extending direction of the case 22, and the needle electrode 23 is substantially the same as the case 22. It is located on the central axis and in a space surrounded by the case 22. As a material for the needle-like electrode 23, for example, tungsten having a tip curvature of 50 μm can be used.

  The counter electrode 24 is fixed to the open end of the case 22 opposite to the base 21 so as to close the open end. The counter electrode 24 is a plate-like electrode. For example, a structure that allows a sound wave to pass therethrough by using a punching metal having innumerable small holes or using a material in which conductive wires are knitted in a net shape. It has become. The surface of the counter electrode 24 is covered with an insulating material. As the counter electrode 24, for example, a stainless steel plate provided with a large number of openings for passing sound waves can be coated with a ceramic (silica) having a thickness of 0.1 mm. The counter electrode 24 is opposed to the tip of the needle electrode 23 at an appropriate interval, and constitutes a discharge part between the counter electrode 24 and the needle electrode 23. This discharge part constitutes a part of a high-frequency oscillation circuit that generates high-frequency discharge, and high-frequency discharge is generated in this discharge part. This discharge is called a flame discharge, and reference numeral 27 in FIG. 1 indicates a flame generated by the discharge at the discharge portion between the counter electrode 24 and the needle electrode 23. The counter electrode 24 constitutes a sound wave introduction part that introduces sound waves into the discharge part in the case 22 as described above. Further, a hole as a sound wave introduction part for introducing sound waves into the discharge part in the case 22 may be formed in the peripheral wall of the case 22.

  In order to generate a high frequency discharge between the needle electrode 23 and the counter electrode 24, it is necessary to apply a high voltage. Therefore, the high frequency oscillation circuit uses a vacuum tube that can withstand the high voltage as an active element for oscillation. It is used as By configuring the circuit so that the discharge current of the discharge path formed between the needle electrode 23 and the counter electrode 24 is fed back to the vacuum tube, a high-frequency oscillation circuit by self-excited oscillation is configured. The acicular electrode 23 and the counter electrode 24 constitute a high-frequency discharge portion, and the particle velocity of the high-frequency discharge portion changes depending on the particle velocity of the sound wave, and the equivalent impedance of the high-frequency discharge portion changes. When the equivalent impedance of the high-frequency discharge unit is changed by the sound wave, the transmission signal by the oscillation circuit is modulated by the sound wave. This modulation signal includes frequency modulation, that is, FM modulation component and amplitude modulation, that is, AM modulation component, but more FM modulation component is included. Therefore, if the FM modulated signal is taken out and input to the FM demodulation circuit, it can be converted into an audio signal corresponding to the sound wave introduced from the sound wave introducing unit.

  The configuration described so far is substantially the same as the configuration of the invention according to the previous application described with reference to FIG. 4, but the embodiment of the electroacoustic transducer according to the present invention provides an inert gas supply described below. It is characterized by the addition of roads. In FIG. 1, the outer periphery of the needle electrode 23 is surrounded by an inert gas guide path 251 to the vicinity of the tip. The inert gas guide path 251 is provided for flowing an inert gas along the outer peripheral surface of the needle electrode in the electroacoustic transducer, and the insulating cylinder holding the outer periphery of the needle electrode 23. 25, so that it is formed in a cylindrical shape with an insulating material. The inert gas guide path 251 surrounds the outer periphery of the needle electrode 23 with a space between the outer periphery of the needle electrode 23 and allows the inert gas to flow along the peripheral surface of the tip of the needle electrode 23. An outlet 252 is provided. The tip portion of the needle electrode 23 protrudes outward from the gas outlet 252 and has a shape that does not hinder the discharge with the counter electrode 24.

  A pipe 42 communicates with the inert gas guide path 251. The pipe 42 is fixed through the cylindrical case 22 in the radial direction, and the tip portion is fitted into the inert gas guide path 251, so that the internal space of the pipe 42 is connected to the inert gas guide path 251. It is connected to an inert gas guide path 251 in communication with the internal space. The other end of the pipe 42 protruding from the outer periphery of the case 22 is connected to another pipe 40 via a coupling 41. The pipe 40, the coupling 41, and the pipe 42 constitute an inert gas supply path from a gas cylinder (not shown) to the microphone unit 20, that is, the electroacoustic transducer, and the inert gas along with the inert gas guide path 251. A supply path is configured. Examples of the inert gas used include helium gas or nitrogen gas.

  While supplying an inert gas from the inert gas supply path, high-frequency discharge is performed between the needle electrode 23 and the counter electrode 24 to perform an electroacoustic conversion operation. The inert gas guided to the inert gas guide path 251 through the supply path composed of the pipe 40, the coupling 41, and the pipe 42 is guided to the internal space of the inert gas guide path 251 toward the gas outlet 252. Flowing. The inert gas is squeezed at the gas outlet 252 to flow along the outer periphery of the distal end portion of the needle electrode 23 and the contact between the outer peripheral surface of the distal end portion of the needle electrode 23 and the air is blocked. Therefore, the discharge product causative substance in the air can be prevented from adhering to the needle-like electrode 23, and abnormal discharge caused by the adherence of the discharge product can be prevented, and high-frequency discharge with stable operation can be used. An electroacoustic transducer can be obtained. In addition, it is possible to prevent the wear of the tip of the needle electrode, which has conventionally been caused by the air flow.

  As shown in FIGS. 2 and 6, the needle electrode 23 sharply sharpened is used, and while supplying nitrogen gas as an inert gas along the tip of the needle electrode 23, the needle electrode 23 and the counter electrode 24 are provided. For 1 hour. 3 and 7 show the tip of the needle electrode 23 after discharge. Since the texture and color cannot be expressed only by the diagram shown in FIG. 3, only the shape is shown in FIG. 3, and the corresponding photographic image is shown in FIG. Since the needle electrode 23 is heated to a high temperature due to the discharge, the needle electrode 23 has a burnt color, but the shape is the same as before the discharge, the tip is worn out, or the discharge product is attached near the tip. There were no problems such as. Therefore, according to the illustrated embodiment, it is possible to prevent abnormal discharge caused by the discharge product, and to obtain an electroacoustic transducer using high-frequency discharge with stable operation.

  In the illustrated embodiment, the microphone has been described as using a high-frequency discharge. However, a high-frequency signal oscillated by a high-frequency oscillation circuit is modulated with an audio signal, and a discharge is generated between the needle electrode 23 and the counter electrode 24 using this modulation signal. Thus, the speaker can be operated according to the principle of the ion speaker. Therefore, the electroacoustic transducer according to the present invention can be used both as a microphone and a speaker.

20 Microphone unit 21 Base 23 Needle electrode 24 Counter electrode 25 Insulating cylinder 42 Pipe as inert gas supply path 251 Inert gas guide path 252 Gas outlet

Claims (7)

A high-frequency oscillation circuit including a needle-like electrode, a counter electrode facing the needle-like electrode, a discharge part formed between the needle-like electrode and the counter electrode, and a high-frequency discharge including the discharge part And taking out an audio signal modulated according to the sound wave introduced into the discharge unit, or converting the sound signal into sound by causing the discharge unit to discharge according to the high-frequency signal modulated with the audio signal. An electroacoustic transducer,
An electroacoustic transducer comprising an inert gas supply path for supplying an inert gas toward the outer peripheral surface of the needle electrode.   The inert gas supply path includes a supply path directed to the electroacoustic transducer and an inert gas guide path for flowing an inert gas along the outer peripheral surface of the needle electrode in the electroacoustic transducer. The electroacoustic transducer according to claim 1.   The inert gas guide path includes a gas outlet that surrounds the outer periphery of the needle electrode with a space between the outer periphery of the needle electrode and allows the inert gas to flow along the peripheral surface of the tip of the needle electrode. The electroacoustic transducer according to claim 2.   The electroacoustic transducer according to claim 2 or 3, wherein the inert gas guide path is made of an insulating material.   The electroacoustic transducer according to claim 4, wherein the inert gas guide path is formed integrally with an insulating material that holds an outer periphery of the needle-like electrode.   The electroacoustic transducer according to any one of claims 1 to 5, wherein the inert gas is helium gas.   The electroacoustic transducer according to any one of claims 1 to 5, wherein the inert gas is nitrogen gas.

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