JP4998299B2 - Electrostatic speaker - Google Patents

Description

  The present invention relates to an electrostatic speaker.

In the field of speakers, there are speakers called electrostatic speakers. The electrostatic speaker is composed of two fixed electrodes facing each other with a gap therebetween, and a conductive sheet-like vibrating body inserted between the two fixed electrodes. When the voltage applied to the fixed electrode is changed and the electrostatic force acting on the vibrating body is changed, the vibrating body is thereby displaced. If this applied voltage is changed according to the input acoustic signal, the vibrating body repeats displacement (that is, vibrates) accordingly, and a reproduction wave corresponding to the acoustic signal is generated from the vibrating body.
In such an electrostatic speaker, as described in Patent Document 1, a punching metal having a plurality of holes is employed as two fixed electrodes. In this configuration, The sound generated by the vibrating body passes through the hole in the punching metal and is radiated to the outside of the speaker.

JP-A-11-178098

By the way, when the punching metal is employed as the fixed electrode, if the diameter of the hole of the punching metal is increased, the area of the metal portion acting as the electrode on the surface of the punching metal is reduced, and the electrostatic force acting on the vibrating body is also reduced. There arises a problem that the amplitude of the vibrating body is reduced.
For this reason, in the fixed electrode of a punching metal, it is preferable to reduce the diameter of the hole and increase the area as an electrode while ensuring sound transmission by having a hole. However, punching metal punches holes in a plate-shaped metal plate with a mold, so it is easier to punch holes when the plate thickness is thinner to make small holes, but if the fixed electrode is thin, the rigidity of the fixed electrode is reduced. Another problem arises that the distance between the fixed electrode and the vibrating body becomes difficult to keep constant.

  The present invention has been made under the above-described background, and an object of the present invention is to provide a technique capable of increasing the amplitude of a vibrating body while having sound permeability and rigidity.

  In order to solve the above-described problems, the present invention provides a first electrode formed of a porous body having a three-dimensional network structure having conductivity and air permeability, and a three-dimensional network structure having conductivity and air permeability. The second electrode is formed of a porous body and spaced apart from the first electrode, and has conductivity, and the first electrode and the first electrode are interposed between the first electrode and the second electrode. An electrostatic loudspeaker having two vibrators and a vibrating body that is spaced apart is provided.

  In the present invention, in the first electrode and the second electrode, the size of the hole in the surface facing the vibrating body is on the surface opposite to the surface facing the vibrating body. You may make it smaller than the magnitude | size of a hole.

  According to the present invention, it is possible to increase the amplitude of the vibrating body while having sound permeability and rigidity.

[Mechanical Configuration of Embodiment]
FIG. 1 is a diagram schematically showing the appearance of an electrostatic speaker 1 according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the electrostatic speaker 1, and FIG. It is a disassembled perspective view.
As shown in the figure, the electrostatic speaker 1 has a vibrating body 10, an electrode 20U and an electrode 20L, a spacer 30U, and a spacer 30L facing each other with the vibrating body 10 interposed therebetween. In the present embodiment, the configuration of the electrodes 20U and 20L is the same, and the configuration of the spacers 30U and 30L is the same. Therefore, when there is no need to distinguish between the two, the description of “L” and “U” is given. Is omitted. 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. Also, in the figure, “•” in “○” means an arrow heading from the back of the drawing to the front, and “×” in “○” is the front of the drawing. It means an arrow pointing from the back to the back.

(Configuration of each part of the electrostatic speaker 1)
The vibrating body 10 is, for example, a film such as PET (polyethylene terephthalate), PP (polypropylene, polypropylene) or the like obtained by vapor-depositing a metal film or applying a conductive paint, and has a thickness of several μm to The thickness is about several tens of μm.

  The spacer 30 is formed of an insulator, and the shape thereof is a square tube as shown in FIG. In this embodiment, the length of the spacer 30 in the X direction and the Y direction is the same as the length of the electrode 20 in the X direction and the Y direction. Further, the heights of the spacer 30U and the spacer 30L in the Z direction are the same.

  The electrode 20 is formed by processing a metal porous body having a three-dimensional three-dimensional network structure, such as a sponge, into a rectangular plate having a predetermined thickness. In the present embodiment, the length of the electrode 20 in the X direction and the Y direction is the same as the length of the vibrating body 10 in the X direction and the Y direction. Further, the metal porous body that forms the electrode 20 has electrical conductivity and air permeability (acoustic transmission), and the size of the hole on the back surface facing the vibrating body 10 faces the opposite side of the vibrating body 10. It is smaller than the size of the hole on the surface side.

  Here, an example of the manufacturing method of this metal porous body is demonstrated. First, a metal powder, a binder (bonding agent), and water are kneaded to create a slurry. Next, the prepared slurry is impregnated into plate-like foamed urethane having a three-dimensional three-dimensional network structure with a predetermined thickness to form a slurry film on the branch surface of the foamed urethane network structure. Here, by adjusting the amount of binder and water for the slurry and adjusting the viscosity and time to cure, the impregnated slurry is cured while moving from the front side to the back side of the urethane foam. The film thickness of the slurry attached to the branch is different between the front surface side and the back surface side. In addition, as a method of changing the film thickness of the slurry between the front side and the back side, after the slurry is infiltrated into the entire urethane foam and dried, the slurry is again infiltrated from the center to the back side, and the back side from the center. The thickness of the slurry on the back surface side may be increased by overlapping the slurry layers.

Then, after the slurry is dried, the foamed urethane formed in the slurry film is fired to remove the foamed urethane and the binder, and the metal contained in the slurry is sintered into the form of the urethane foam.
In the metal porous body manufactured in this way, the thickness of the slurry is thicker on the back side than on the front side, so that the branches forming the network structure of the metal porous body become thicker from the center side toward the back side. It becomes thinner from the center side toward the surface. And since the branch is thick on the back side, the pore size of the porous body is small. On the front side, the branch is narrower than the back side, so the hole of the porous body is larger than the back side.

(Overall configuration of electrostatic speaker 1)
When the electrostatic speaker 1 is assembled, the spacer 30L is fixed to the peripheral portion of the electrode 20L, and the peripheral portion of the vibrating body 10 is fixed to the spacer 30L. The vibrating body 10 is fixed to the spacer 30L in a state where tension is applied. Then, the spacer 30U is fixed on the peripheral portion of the vibrating body 10, and the peripheral portion of the electrode 20U is fixed on the spacer 30U.
In this configuration, the electrodes 20U and 20L are fixed to the spacers 30U and 30L so as to face each other with the vibrating body 10 therebetween, and the vibrating body 10 is perpendicular to the electrode 20 in the space between the electrode 20U and the electrode 20L. It is supported so that it can vibrate in the Z direction.

[Electrical Configuration of Embodiment]
Next, the electrical configuration of the electrostatic speaker 1 will be described. As shown in FIG. 2, the electrostatic speaker 1 includes a transformer 50, an input unit 60 to which an acoustic signal is input from the outside, and a bias power source 70 that applies a DC bias to the vibrating body 10. The bias power source 70 is connected to the vibrating body 10 and the midpoint of the output side of the transformer 50, the electrode 20U is connected to the output side terminal of the transformer 50, and the electrode 20L is the output side of the transformer 50. Is connected to the other terminal. In this configuration, when an acoustic signal is input to the input unit 60, a voltage corresponding to the input acoustic signal is applied to the electrode 20 and the vibrating body 10.

  When a potential difference is generated between the electrode 20U and the electrode 20L due to the applied voltage, an electrostatic force that is attracted to one of the electrodes 20 acts on the vibrating body 10. That is, the vibrating body 10 is displaced (bends) in the Z direction of the figure in accordance with the acoustic signal, and the vibration is generated by sequentially changing the displacement direction, and a sound corresponding to the vibration state (frequency, amplitude, phase) is generated. Generated from the vibrating body 10. The generated sound passes through the electrodes 20U and 20L and is radiated to the outside of the electrostatic speaker 1.

In the present embodiment, a metal porous body is adopted as the electrode 20 for vibrating the vibrating body 10, and the size of the hole for ensuring sound transmission is small on the electrode surface, and the area as the electrode is widened. Yes.
In addition, since the holes of the electrode 20 are distributed throughout the electrode 20, the electrode 20 has high air permeability and good sound transmission.
In the electrode 20, the area of the metal part on the back surface affects the electrostatic force that drives the vibrating body 10, and the amplitude of the vibrating body decreases as the size of the hole increases. Has a large number of holes, but on the back side, the network structure is thick and the size of the holes is smaller than the size of the holes on the front side. While having transparency, the amplitude of the vibrator 10 is not reduced.
Moreover, in this embodiment, in the electrode 20 which is a porous body, the thickness of the branch which forms a porous body is thinner on the front surface side, and the size of the hole is larger than that on the back surface side.
Thus, in this embodiment, the thickness of the branch on the front surface side is thin, and compared with the case where the thickness of the hole on the back side is reduced by making the thickness of the branch of the porous body the same overall, the porous body is formed. Since the amount of metal to be reduced is reduced, the mass of the electrostatic speaker 1 can be reduced.
Further, in the present embodiment, when forming a small hole in the electrode 20, it is not necessary to reduce the thickness of the electrode 20 unlike punching metal, so that the rigidity of the electrode can be increased, and the fixed electrode and the vibrating body The distance between can be kept constant.

[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 the electrode 20 of the above-described embodiment, the size of the hole of the metal porous body is different on the back surface side and the front surface side, but the size of the hole may be the same on the front surface side and the back surface side.

  When forming the electrode 20, the size of the hole on the surface of the electrode 20, the thickness in the Z direction, the shape, and the like may be adjusted by pressing the metal porous body in the X direction, the Y direction, or the Z direction. Since the electrode 20 is a three-dimensional three-dimensional metallic porous metal body and has a large space, it can be easily pressed as compared with a simple plate metal. In addition, when processing the shape of the electrode 20, it is not limited to the shape of the said embodiment, You may press-work into various shapes from a design viewpoint.

  In the electrostatic speaker 1, the periphery of the vibrating body 10 is fixed by being sandwiched between the spacers 30, and the amplitude of the vibrating body 10 is larger at the center portion farther from the spacer 30, and becomes smaller as the spacer 30 is approached. If the amplitude of the vibrating body 10 is different between the central portion and the peripheral portion, the radiation characteristic (directivity characteristic) of the sound output from the electrostatic speaker 1 is affected.

In order to control the radiation characteristics of the output sound, the distance from the electrode 20 to the vibrating body 10 is made different between the central portion and the peripheral portion, and the magnitude of the electrostatic force acting on the vibrating body 10 is changed between the central portion and the peripheral portion. There is a method of controlling the radiation characteristics by controlling the amplitude of the vibrating body 10 in different ways.
When this method is adopted, the back surface side of the electrode 20 may be processed into a curved surface by press working so that the thickness of the electrode 20 changes from the central portion toward the periphery. When the electrode 20 having this configuration is used, the distance from the electrode 20 to the vibrating body 10 is different between the central portion and the peripheral portion. Then, compared with the case where the thickness of the electrode 20 is uniform, the magnitude of the electrostatic force acting on the peripheral portion of the vibrating body 10 and the amplitude of the vibrating body 10 are different and are output from the electrostatic speaker 1. The sound radiation characteristics are different from the case where the thickness of the electrode 20 is uniform.
In addition, as a shape of the electrode 20 of this configuration, there is a shape in which the back side is processed into a convex lens-like curved surface, and the central portion is thick and the thickness is reduced toward the peripheral portion.

1 is a schematic diagram of an electrostatic speaker 1 according to an embodiment of the present invention. It is the figure which showed the cross section and electrical structure of the electrostatic speaker. 1 is an exploded perspective view of an electrostatic speaker 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrostatic type speaker, 10 ... Vibrating body, 20, 20U, 20L ... Electrode, 30, 30U, 30L ... Spacer, 50 ... Transformer, 60 ... Input part, 70 ... Bias power supply

Claims (2)

A first electrode formed of a porous body having a three-dimensional network structure having conductivity and air permeability;
A second electrode formed of a porous body having a three-dimensional network structure having electrical conductivity and air permeability, and spaced apart from the first electrode;
An electrostatic speaker having conductivity and a vibrating body disposed between the first electrode and the second electrode and spaced apart from the first electrode and the second electrode. In the first electrode and the second electrode, the size of the hole on the surface facing the vibrating body is smaller than the size of the hole on the surface opposite to the surface facing the vibrating body. The electrostatic speaker according to claim 1.

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