JP2013013057A - Electrostatic type electro-acoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electrode as a fixed electrode and a vibration body from coming into contact with each other while suppressing a voltage applied to the electrode as the fixed electrode.SOLUTION: An elastic member which is non-woven fabric made of fiber with electric conductivity and through which air and sound pass is arranged between a vibration body 10 and electrodes 20U and 20L. The elastic member is provided with a first layer 31 in which the fiber of the non-woven fabric is fine and a second layer 32 in which the fiber is coarser that of the first layer 31 and which is approximately several μm in thickness. The second layer 32 is lower in density of the fiber than the first layer 31 and higher in resistance value than the first layer 31, so that two plane electrodes are positioned across an air layer of thickness (δ) of the second layer 32. As compared with a configuration including an air layer of thickness (d) between the electrodes 20U and 20L and the vibration body 10, the distance between the plane electrodes becomes small and the same sound pressure is obtained even by driving with a low voltage. Further, the electrodes 20U and 20L and the vibration body 10 never come into direct contact with each other because of the presence of the elastic member.

Description

  The present invention relates to an electrostatic electroacoustic transducer.

  The electrostatic speaker disclosed in Patent Document 1 has a configuration in which a metal wire in a lattice shape is used as a fixed pole, and a vibration film (vibrating body) is provided between a pair of fixed poles. The portion where the diaphragm and the vibrating membrane are in contact with each other is insulated. In this electrostatic speaker, a fixed distance is maintained between the portion of the fixed pole that is not in contact with the diaphragm and the diaphragm, and the portion of the diaphragm that is not in contact with the fixed pole is the fixed pole. It vibrates according to the signal supplied to it.

JP 2009-272853 A

The electrostatic force acting on the vibration membrane in the electrostatic speaker increases as the distance between the fixed pole and the vibration membrane is shorter. For this reason, in the electrostatic loudspeaker of Patent Document 1, as the thickness of the metal wire constituting the fixed pole is thinner, the distance between the fixed pole and the diaphragm becomes closer, and the force acting on the diaphragm becomes larger and the sound is increased. Pressure increases. Also, if the distance between the fixed pole and the diaphragm is shortened and the force acting on the diaphragm is increased, the voltage applied to the fixed pole can be reduced compared to the case where the distance between the fixed pole and the diaphragm is long. An electrostatic speaker can be driven. However, in the electrostatic speaker disclosed in Patent Document 1, when the metal wire is thinned, the space between the fixed pole and the vibrating membrane becomes narrow, and when the vibrating membrane vibrates, there is a possibility that the fixed pole is contacted and short-circuited. is there.
Note that the structure in which the vibration film is sandwiched between the pair of fixed poles can also be used as an electrostatic microphone. When used as a microphone, a signal corresponding to the sound reaching the vibrating body can be obtained from the fixed pole. However, in the case of using as a microphone, as in the case of a speaker, the fixed pole is vibrated. There is a risk that the vibrating membrane may come into contact with the short circuit.

  The present invention has been made under the background described above, and an object thereof is to provide a technique for preventing contact between an electrode serving as a fixed pole and a vibrating body while suppressing a voltage applied to the electrode serving as a fixed pole. To do.

  In order to achieve the above-described object, the present invention provides a first electrode, a second electrode disposed to face the first electrode, and a conductivity disposed between the first electrode and the second electrode. A first layer that has conductivity and elasticity and transmits sound; and a second layer that has conductivity and elasticity and transmits sound and has a higher resistance than the first layer. A first elastic member positioned between the first electrode and the vibrating body, the first layer being on the first electrode side, and the second layer being on the vibrating body side, and having conductivity and elasticity. A third layer through which sound is transmitted, and a fourth layer having conductivity and elasticity, through which sound is transmitted, and having a resistance value greater than that of the third layer, between the second electrode and the vibrating body And the third layer is on the second electrode side, the fourth layer is on the vibrating body side, and the vibrating body is connected via a resistor. It is connected to the bias power source, to provide an electrostatic electro-acoustic transducer, wherein the resistance value of the resistor the first layer than the resistance value of and the third layer is large.

  In the present invention, the first elastic member and the second elastic member are nonwoven fabrics formed of conductive fibers, and the second layer has a density of the fibers smaller than that of the first layer, The fourth layer may have a configuration in which the density of the fibers is smaller than that of the third layer.

  The present invention also includes a vibrating body having conductivity, an electrode disposed opposite to the vibrating body, a first layer having conductivity and elasticity and transmitting sound, and having conductivity and elasticity. And has a second layer that transmits sound and has a resistance value greater than that of the first layer, and is located between the electrode and the vibrating body, the first layer is on the electrode side, and the second layer And an elastic member on the vibrating body side, and the vibrating body is connected to a bias power source through a resistor, and the resistance value of the first layer is larger than the resistance value of the resistor. An electric electroacoustic transducer is provided.

  In the present invention, the elastic member may be a nonwoven fabric formed of conductive fibers, and the second layer may have a configuration in which the density of the fibers is smaller than that of the first layer.

  ADVANTAGE OF THE INVENTION According to this invention, the contact between the electrode used as a fixed pole and a vibrating body can be prevented, suppressing the voltage applied to the electrode used as a fixed pole.

1 is an external view of an electrostatic speaker according to an embodiment of the present invention. AA sectional view taken on the line AA of FIG. FIG. 3 is an exploded view of the electrostatic speaker 1. The figure which showed the electrical structure which concerns on the electrostatic speaker. The figure which showed the equivalent circuit when the elastic member 30 is seen as a resistor. The figure which showed the electrical structure which concerns on the electrostatic microphone 2. FIG.

[Embodiment]
FIG. 1 is an external view of an electrostatic speaker 1 (electrostatic electroacoustic transducer) according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the electrostatic speaker 1 taken along line AA. FIG. 3 is an exploded view of the electrostatic speaker 1, and FIG. 4 is a diagram showing an electrical configuration of the electrostatic speaker 1. In the figure, directions are indicated by orthogonal X-axis, Y-axis, and Z-axis. When the electrostatic speaker 1 is viewed from the front, the left-right direction is the X-axis direction, and the depth direction is the Y-axis direction. The height direction is the Z-axis direction. Also, in the figure, “•” in “◯” means an arrow heading from the back of the drawing to the front. Further, in the figure, “x” in “◯” means an arrow pointing backward from the front of the drawing.

  As shown in the figure, the electrostatic speaker 1 has a vibrating body 10, electrodes 20U and 20L, elastic members 30U and 30L, and protective members 60U and 60L. In the present embodiment, the configurations of the electrode 20U and the electrode 20L are the same, and the configurations of the elastic member 30U and the elastic member 30L are the same. For this reason, when it is not particularly necessary to distinguish between these members, descriptions of “L” and “U” are omitted. Further, since the protection member 60U and the protection member 60L have the same configuration, the description of “L”, “U”, and the like is omitted when it is not particularly necessary to distinguish the protection members 60U and 60L. In addition, the dimensions of the constituent elements such as the vibrating body and the electrodes in the drawing are different from the actual dimensions so that the shapes of the constituent elements can be easily understood.

(Configuration of each part of the electrostatic speaker 1)
First, each part constituting the electrostatic speaker 1 will be described. The rectangular vibrating body 10 viewed from a point on the Z-axis is made of a synthetic resin film (insulating layer) having insulating properties and flexibility such as PET (polyethylene terephthalate) or PP (polypropylene). And a sheet-like structure in which a conductive metal is deposited on one surface of the film to form a conductive film (conductive layer). In the present embodiment, the conductive film is formed on one surface of the film, but may be formed on both surfaces of the film. Moreover, the film of the vibrating body 10 is not limited to PET or PP, and may be a film made of another synthetic resin obtained by vapor-depositing a conductive metal or applying a conductive paint. Moreover, the vibrating body 10 may have a configuration of a conductive film obtained by rolling a metal having conductivity into a film shape.

  In this embodiment, the elastic member 30 is a non-woven fabric formed of conductive fibers, and allows air and sound to pass through. The shape of the elastic member 30 is rectangular when viewed from a point on the Z axis. Yes. The elastic member 30 has elasticity, and is deformed when a force is applied from the outside, and returns to its original shape when the force applied from the outside is removed. In this embodiment, the length of the elastic member 30 in the X-axis direction is longer than the length of the vibrating body 10 in the X-axis direction, and the length of the elastic member 30 in the Y-axis direction is the length of the vibrating body 10 in the Y-axis direction. It is longer than the length.

  The electrode 20 is made of an insulating synthetic resin film (insulating layer) such as PET or PP as a base material, and a conductive metal is deposited on one surface of the film to form a conductive film (conductive layer). It has a configuration. The electrode 20 has a rectangular shape when viewed from a point on the Z-axis, and has a plurality of holes penetrating from the front surface to the back surface, so that air and sound can pass therethrough. In addition, illustration of this hole is abbreviate | omitted in drawing. In the present embodiment, the length in the X-axis direction and the length in the Y-axis direction of the electrode 20 are the same as those of the elastic member 30. Further, the electrode 20 may have a conductive film configuration in which a conductive metal is rolled into a film shape.

  The protection member 60 is an insulating cloth. The protection member 60 has a rectangular shape when viewed from a point on the Z axis, and allows passage of air and sound. In the present embodiment, the length in the X-axis direction and the length in the Y-axis direction of the protection member 60 are the same as those of the elastic member 30.

(Structure of electrostatic speaker 1)
Next, the structure of the electrostatic speaker 1 will be described. In the electrostatic speaker 1, the vibrating body 10 is disposed between the lower surface of the elastic member 30U and the upper surface of the elastic member 30L. The vibrating body 10 is coated with an adhesive with a width of several mm inward from the left and right edges and the depth edge, and is bonded to the elastic member 30U and the elastic member 30L. Is not fixed to the elastic member 30U and the elastic member 30L.

  The electrode 20U is bonded to the upper surface of the elastic member 30U. The electrode 20L is bonded to the lower surface of the elastic member 30L. The electrode 20U is bonded to the elastic member 30U by applying an adhesive with a width of several millimeters inward from the left and right edges and the depth edge, and the electrode 20L is bonded to the left and right edges and the depth direction. An adhesive is applied with a width of several millimeters from the edge to the inside and is adhered to the elastic member 30L. The electrode 20 is not fixed to the elastic member 30 on the inner side of the portion where the adhesive is applied. The electrode 20U is in contact with the elastic member 30U on the side with the conductive film, and the electrode 20L is in contact with the elastic member 30L on the side with the conductive film.

  The protective member 60U is bonded to the upper surface of the electrode 20U. The protective member 60L is bonded to the lower surface of the electrode 20L. The protective member 60U is coated with an adhesive with a width of several millimeters inward from the left and right edges and the depth direction edge and adhered to the electrode 20U, and the protective member 60L has the left and right edges and the depth direction. An adhesive is applied with a width of several mm inward from the edge of the electrode and adhered to the electrode 20L. The protective member 60 is not fixed to the electrode 20 on the inner side of the portion where the adhesive is applied.

  When the elastic member 30 and the vibrating body 10 are bonded, the lower surface of the elastic member 30U and the upper surface of the elastic member 30L are bonded to the vibrating body 10 in a state in which nonwoven fabric fibers are fluffed. Further, when the elastic member 30 is bonded to the electrode 20, the upper surface of the elastic member 30U and the lower surface of the elastic member 30L are bonded in a state where the fibers of the nonwoven fabric are leveled without fluffing. When the surface of the elastic member 30 is fluffed and adhered to the vibrating body 10 in this way, in the elastic member 30, the portion where the fibers become rough due to the fluff comes into contact with the vibrating body 10, and the electrode 20 and the vibrating body 10 are touched. In the meantime, as shown in an enlarged view in FIG. 2, a first layer 31 in which the fibers of the nonwoven fabric are dense and a second layer 32 in which the fibers are coarse due to fluffing are generated. In addition, it is preferable that the thickness of the 2nd layer 32 is about several micrometers.

(Electrical configuration of the electrostatic speaker 1)
Next, an electrical configuration relating to the electrostatic speaker 1 will be described. As shown in FIG. 4, the electrostatic speaker 1 is provided with an amplifier unit 130 to which an acoustic signal representing sound is input, a transformer 110, and a drive having a bias power source 120 that applies a DC bias to the vibrating body 10. A circuit 100 is connected.
The electrode 20U is connected to the terminal T1 on the secondary side of the transformer 110, and the electrode 20L is connected to the other terminal T2 on the secondary side of the transformer 110. In addition, the vibrating body 10 is connected to the bias power source 120 via the resistor R1. The middle point terminal T3 of the transformer 110 is connected to the ground GND, which is the reference potential of the drive circuit 100, via the resistor R2.
An acoustic signal is input to the amplifier unit 130. The amplifier unit 130 amplifies the input acoustic signal and outputs the amplified acoustic signal. The amplifier unit 130 includes terminals TA1 and TA2 that output acoustic signals. The terminal TA1 is connected to the primary terminal T4 of the transformer 110 via the resistor R3, and the terminal TA2 is connected to the resistor R4. Is connected to the other terminal T5 on the primary side of the transformer.

(Operation of electrostatic speaker 1)
Next, the operation of the electrostatic speaker 1 will be described. When an AC acoustic signal is input to the amplifier unit 130, the input acoustic signal is amplified and supplied to the primary side of the transformer 110. When the acoustic signal boosted by the transformer 110 is supplied to the electrode 20 and a potential difference is generated between the electrode 20U and the electrode 20L, the vibrating body 10 between the electrode 20U and the electrode 20L has the electrode 20U. An electrostatic force that is attracted to either side of the electrode 20L works.

  Specifically, the polarity of the acoustic signal output from the terminal T2 is opposite to that of the acoustic signal output from the terminal T1. When a positive acoustic signal is output from the terminal T1 and a negative acoustic signal is output from the terminal T2, a positive voltage is applied to the electrode 20U, and a negative voltage is applied to the electrode 20L. Since a positive voltage is applied to the vibrating body 10 by the bias power source 120, the vibrating body 10 is weakened in electrostatic attraction with the electrode 20U to which the positive voltage is applied, while a negative voltage is applied. The electrostatic attractive force between the electrode 20L and the electrode 20L is increased. The vibrating body 10 is displaced toward the electrode 20L (in the negative direction of the Z-axis) due to an attractive force acting on the electrode 20L according to the difference in electrostatic attraction applied to the vibrating body 10.

  When a negative acoustic signal is output from the terminal T1 and a positive acoustic signal is output from the terminal T2, a negative voltage is applied to the electrode 20U and a positive voltage is applied to the electrode 20L. Since a positive voltage is applied to the vibrating body 10 by the bias power source 120, the vibrating body 10 is weakened in electrostatic attraction between the electrode 20L to which the positive voltage is applied, while a negative voltage is applied. The electrostatic attractive force between the electrode 20U and the electrode 20U is increased. The vibrating body 10 is displaced toward the electrode 20U (in the positive direction of the Z axis) due to an attractive force acting on the electrode 20U according to the difference in electrostatic attraction applied to the vibrating body 10.

  In this way, the vibrating body 10 is displaced in the positive direction of the Z-axis and the negative direction of the Z-axis in accordance with the acoustic signal (deflection), and vibration is generated by sequentially changing the displacement direction. Sound waves corresponding to the frequency, amplitude, and phase are generated from the vibrating body 10. The generated sound wave is radiated as sound to the outside of the electrostatic speaker 1 through the elastic member 30 having acoustic transparency, the electrode 20 and the protective member 60.

FIG. 5 is an equivalent circuit in which the first layer 31 of the elastic member 30 is represented by a resistor having a resistance value Rc, and the second layer 32 of the elastic member 30 is represented by a resistor having a resistance value Ra. Although the first layer 31 and the second layer 32 are conductive fiber layers, the first layer 31 is dense with respect to the second layer 32 in terms of the density of the nonwoven fabric fibers. In the second layer 32, the fibers are coarser than the first layer 31, and the ratio of air to the fluffy fibers is large. Therefore, when the resistance values of the first layer 31 and the second layer 32 are compared, Rc << Ra, and when the resistivity (volume resistivity) is compared, the resistivity ρ1 of the first layer 31 << the resistivity ρ2 of the second layer 32.
As described above, since the resistance value of the first layer 31 is lower than that of the second layer 32, the voltage applied from the bias power supply 120 to the vibrating body 10 greatly drops in the second layer 32 in terms of DC. At the boundary between the first layer 31 and the second layer 32, the voltage is almost 0V. In other words, in the present embodiment, the distance between the electrode 20U (electrode 20L) and the vibrating body 10 is a distance (d) corresponding to the thickness of the elastic member 30, but the two plate electrodes are the vibrating body 10. It can be seen that the air layer having the thickness (δ) of the second layer 32 is positioned between the two.
For example, by setting R1 << Rc << Ra (R1 = about 10 MΩ, Rc = 100 M or more, Ra = 1 GΩ or more), the voltage drop at R1 can be suppressed, and the voltage applied to the vibrating body 10 decreases. And a sufficient bias voltage can be applied between the vibrating body 10 and the second layer 32. The resistance values of R1, Rc, and Ra are not limited to the above values as long as the respective resistance values have a relationship of R1 << Rc << Ra, and may be different values.

  Here, the electrostatic attraction acting between the electrode 20U (electrode 20L) and the vibrating body 10 will be considered. The electrostatic attractive force acting between the two plate electrodes is determined by the voltage applied between the plate electrodes, the area of the plate, the distance between the plates, the dielectric constant of the medium between the plates, and is inversely proportional to the square of the distance. Here, for comparison with the present embodiment, considering a configuration in which an air layer is provided between the vibrating body 10 and the electrode 20 as in the electrostatic speaker of Patent Document 1, the configuration of the comparison is 2 It can be seen that the plate electrodes are located with the air layer having the thickness (d) of the first layer 31. On the other hand, in the present embodiment, the distance between the electrode 20 and the vibrating body 10 is d by the amount of the elastic member 30, but as described above, the two flat plate electrodes are formed of the second layer 32. It can be seen that the air layer of thickness (δ) is positioned.

  Assuming that the configuration of the drive circuit 100 is the same between the configuration in which the air layer is between the vibrating body 10 and the electrode 20 and the present embodiment, the electrostatic attraction is inversely proportional to the square of the distance between the plate electrodes, Since δ is shorter than d, even if the distance from the electrode 20 to the vibrating body 10 is the same, this embodiment can obtain a larger electrostatic attraction. The fact that a large electrostatic attractive force can be obtained means that the amount of displacement of the vibrating body 10 also increases. Therefore, compared with the comparative configuration, this embodiment can obtain a larger sound pressure even when the same voltage is applied. it can.

  Since the electrostatic attractive force is proportional to the square of the voltage applied between the flat plate electrodes, the voltage applied to the electrode 20 may be lowered in order to obtain the same electrostatic attractive force as the comparative configuration. Even if the voltage is lowered to the electrode 20, the same sound pressure as that of the electrostatic speaker having the conventional configuration can be obtained, so that power consumption can be suppressed. In addition, since the voltage applied to the electrode 20 can be lowered while ensuring sound pressure as compared with an electrostatic speaker having a conventional configuration, the possibility of electric shock when a human body touches the electrode 20 can be reduced. it can.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with another various form. For example, the present invention may be implemented by modifying the above-described embodiment as follows. In addition, you may combine each of embodiment mentioned above and the following modifications.

In the embodiment described above, the electrostatic speaker 1 includes the protection member 60, but the electrostatic speaker 1 may not include the protection member 60.
In the above-described embodiment, each member is bonded to other members by applying an adhesive to the edge portion, but the portion to which the adhesive is applied is not limited to the edge portion of the member. For example, an adhesive may be applied to each member in a lattice shape and bonded to other members. Alternatively, a region where the adhesive is applied in the form of dots may be regularly provided on each member, such as a matrix, to adhere to other members.
Moreover, the method of preventing members from shifting in the electrostatic speaker 1 is not limited to the method of fixing with an adhesive, and for example, the members may be formed with double-sided tape.

In the above-described embodiment, the electrode 20 has a configuration in which a conductive film is formed on the surface of the film, but the configuration of the electrode 20 is not limited to this configuration. For example, a metal plate having conductivity may be used as the electrode 20. Alternatively, a cloth woven with conductive threads may be formed into a rectangular shape, and the cloth formed into a rectangular shape may be used as the electrode 20. Alternatively, the electrode 20 may be formed by forming a conductive film over a substrate in which an insulating material (for example, glass or phenol resin) is formed in a plate shape.
In the above-described embodiment, the electrode 20 has the conductive film side facing the elastic member 30, but the electrode 20 may be arranged so that the conductive film side faces the protective member 60 side. Good.

  In the embodiment described above, the electrode 20 is rectangular when viewed from a point on the Z axis, but the shape of the electrode 20 is not limited to a rectangle. For example, other shapes such as a circle, an ellipse, or a polygon may be used. In addition, the shape of the vibrating body 10 viewed from a point on the Z axis is not limited to a rectangle, and may be another shape such as a circle, an ellipse, or a polygon. Also, the shape of the electrostatic speaker 1 is not limited to a rectangle as viewed from a point on the Z axis, and may be another shape such as a circle, an ellipse, or a polygon. .

  In the embodiment described above, the electrostatic speaker 1 is a push-pull type, but is not limited to the push-pull type. In the electrostatic speaker 1, an elastic member 30 is sandwiched between one electrode 20 and the vibrating body 10 so that the first layer 31 is in contact with the electrode 20 and the second layer 32 is in contact with the vibrating body 10. May be a single-type electrostatic speaker that vibrates the vibrating body 10.

  In the embodiment described above, the elastic member 30 is a nonwoven fabric, but is not limited to a nonwoven fabric. For example, the elastic member 30 is obtained by electrostatically flocking a conductive fiber on one surface of a sheet-like (or film-like) base material having conductivity and elasticity and having a plurality of through holes. It is good also as a structure which makes the vibrating body 10 the side by which hair was planted. Also in this configuration, a layer of a base material that has conductivity and allows air and sound to pass through, and a layer that is formed of a flocked fiber and has a higher resistance value than the base material are between the electrode 20 and the vibrating body 10. Therefore, the same actions and effects as those of the above-described embodiment can be obtained.

In the above-described embodiment, the configuration in which the electrode, the vibrating body, and the elastic member are stacked is a speaker that converts an acoustic signal into sound. This configuration is a microphone (electrostatic electroacoustic that converts sound into an acoustic signal). Converter).
FIG. 6 is a diagram illustrating a configuration of the electrostatic microphone 2 according to the present modification and an acoustic signal generation circuit 200 that generates an acoustic signal representing sound collected by the electrostatic microphone 2. In this modification, the electrostatic microphone 2 includes the same members as those of the electrostatic speaker 1 described above. Therefore, the members constituting the electrostatic microphone 2 include the members of the electrostatic speaker 1 and The same reference numerals are given and description thereof is omitted. The configuration of the acoustic signal generation circuit 200 is the same as that of the drive circuit 100 except that the direction in which the signal flows is different from that of the drive circuit 100. Therefore, the components included in the acoustic signal generation circuit 200 are the same as the components included in the drive circuit 100. The same reference numerals are given and description of each component is omitted. In addition, the transformation ratio of the transformer 110 and the resistance value of each resistor are adjusted as appropriate.

In the electrostatic microphone 2, the electrode 20 as a conductor and the vibrating body 10 as a conductor face each other at a distance, and the electrode 20 and the vibrating body 10 function as a capacitor composed of parallel plate conductors. Yes. Since a bias voltage is applied to the vibrating body 10, when no sound reaches the electrostatic microphone 2, a constant charge is accumulated in the capacitor.
When sound reaches the electrostatic microphone 2, the vibrating body 10 vibrates by the reached sound. When the vibrating body 10 vibrates, the distance between the vibrating body 10 and the electrodes 20U and 20L changes, so that the capacitance between the vibrating body 10 and the electrode 20 changes.

  For example, when the vibrating body 10 is displaced toward the electrode 20U, the distance between the electrode 20U and the vibrating body 10 is shortened, and the capacitance between the electrode 20U and the vibrating body 10 is increased. In addition, the distance between the electrode 20L and the vibrating body 10 is increased, and the capacitance between the electrode 20L and the vibrating body 10 is decreased. When the capacitance changes in this way, the potential of the electrode 20U changes so that the potential difference between the electrode 20U and the vibrating body 10 decreases, and the potential of the electrode 20L increases so that the potential difference between the electrode 20L and the vibrating body 10 increases. Changes. Here, since a potential difference is generated between the electrode 20U and the electrode 20L, a current flows through the secondary coil of the transformer 110.

  Further, when the vibrating body 10 is displaced to the electrode 20L side, the distance between the electrode 20L and the vibrating body 10 is shortened, and the capacitance between the electrode 20L and the vibrating body 10 is increased. In addition, the distance between the electrode 20U and the vibrating body 10 is increased, and the capacitance between the electrode 20U and the vibrating body 10 is decreased. Then, the potential of the electrode 20L changes so that the potential difference between the electrode 20L and the vibrating body 10 becomes small, and the potential of the electrode 20U changes so that the potential difference between the electrode 20U and the vibrating body 10 becomes large. Here, a potential difference is generated between the electrode 20U and the electrode 20L, and a current flows through the secondary coil of the transformer 110 in a direction opposite to that when the vibrating body 10 is displaced in the direction of the electrode 20U.

  When a current flows through the secondary coil of the transformer 110, a current also flows through the primary coil of the transformer 110 corresponding to this current. The signal that has flowed through the primary coil is amplified by the amplifier unit 130, and the amplified signal is output from the amplifier unit 130 as an acoustic signal representing the sound collected by the electrostatic microphone 2.

  In this modification, when the impedance of the transformer 110 is low, the frequency characteristics at a low frequency may be deteriorated due to the influence of the load capacity of the electrostatic microphone 2. In this case, an amplifier having a high impedance may be connected to the electrodes 20U and 20L instead of the transformer 110 to suppress a decrease in frequency characteristics.

DESCRIPTION OF SYMBOLS 1 ... Electrostatic speaker, 2 ... Electrostatic microphone, 10 ... Vibrating body, 20, 20U, 20L ... Electrode, 30, 30U, 30L ... Elastic member, 31 ... First layer, 32 ... Second layer, 60, 60U, 60L ... Protective member, 100 ... Drive circuit, 110 ... Transformer, 120 ... Bias power supply, 130 ... Amplifier unit, 200 ... Acoustic signal generation circuit

Claims (4)

A first electrode;
A second electrode disposed opposite the first electrode;
A vibrating body disposed between the first electrode and the second electrode and having conductivity;
A first layer having conductivity and elasticity to transmit sound; and a second layer having conductivity and elasticity to transmit sound and having a resistance value larger than that of the first layer, the first electrode And the first elastic member located between the vibrating body and the first layer on the first electrode side, and the second layer on the vibrating body side,
A second layer having conductivity and elasticity to transmit sound; and a fourth layer having conductivity and elasticity to transmit sound and having a resistance value larger than that of the third layer, and the second electrode. And the second elastic member located between the vibrating body and the third layer on the second electrode side, and the fourth layer on the vibrating body side,
The vibrator is connected to a bias power source via a resistor, and the resistance values of the first layer and the third layer are larger than the resistance value of the resistor. The first elastic member and the second elastic member are nonwoven fabrics formed of conductive fibers,
2. The electrostatic electricity according to claim 1, wherein the second layer has a lower density of the fibers than the first layer, and the fourth layer has a lower density of the fibers than the third layer. Acoustic transducer. A vibrating body having electrical conductivity;
An electrode disposed opposite to the vibrating body;
A first layer having conductivity and elasticity to transmit sound; a second layer having conductivity and elasticity to transmit sound; and having a resistance value greater than that of the first layer; An elastic member located between the vibrating bodies, wherein the first layer is on the electrode side, and the second layer is on the vibrating body side,
The vibrator is connected to a bias power source through a resistor, and the resistance value of the first layer is larger than the resistance value of the resistor. The elastic member is a non-woven fabric formed of conductive fibers,
The electrostatic electroacoustic transducer according to claim 3, wherein the second layer has a density of the fibers smaller than that of the first layer.

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