JP5201247B2 - Electrostatic speaker - Google Patents

Description

  The present invention relates to a structure of an electrostatic speaker.

  A speaker called an electrostatic speaker (condenser speaker) is known. Since the structure of the electrostatic speaker is relatively simple, it has been attracting attention because it can be designed to be lightweight and compact, and the theoretical handling is also simple. An electrostatic loudspeaker typically includes two parallel flat electrodes facing each other across a gap, and a conductive sheet-like member (hereinafter referred to as “inserted between the electrodes” supported by a housing or the like). , Called a diaphragm or diaphragm) (so-called push-pull type). When a predetermined bias voltage is applied to the vibrating membrane and the voltage applied to the electrode is changed, the electrostatic force acting on the vibrating membrane changes, and thereby the vibrating membrane is displaced. If this applied voltage is changed according to the input musical sound signal, the vibrating membrane repeats displacement (that is, vibrates) accordingly, and an acoustic wave corresponding to the input musical sound signal is generated from the vibrating membrane. The generated musical sound is emitted to the outside through, for example, a hole or other porous layer formed in the metal plate electrode (see Patent Document 1).

Japanese translation of PCT publication No. 2002-513263 (FIG. 1 etc.)

  However, as an electrode, for example, when a large number of through holes are formed in a metal plate (so-called punching metal) or a porous material is used, it contributes to the electric field generated between the electrode plates compared to the case where there is no hole at all. The effective area (effective electrode area) decreases, and as a result, the capacitance between the electrodes decreases, and the force (driving force) that acts on the diaphragm even when the applied voltage is the same (hereinafter referred to as effective) The size of the electrode area is called the electrostatic capacity performance of the electrostatic speaker). If the distance between the electrode and the diaphragm is increased, the effect of the hole is relatively reduced, but the size of the speaker must be increased, and if the distance between the diaphragm and the electrode is increased, the effect on the diaphragm is increased. Since the amount of static electricity is small, there is a demerit such that it is necessary to increase the applied voltage in order to maintain the sound pressure. Although the influence of the holes can be reduced by reducing the size and number of the holes, the sound transmission performance is deteriorated in this case.

  Thus, it has been difficult for conventional electrostatic speakers to achieve both sound transmission performance and capacitance performance. Accordingly, an object of the present invention is to provide an acoustic element and an electrostatic speaker that simultaneously satisfy a certain standard for acoustic transmittance and effective electrode area.

In one aspect, the present invention provides a vibrating membrane that can be displaced by an electrostatic force, an electrode that is provided opposite to the vibrating membrane and has a network structure, and a buffer member that is provided between the vibrating membrane and the electrode. And a support portion that supports the planar electrode in the vibration direction of the vibrating membrane, wherein the support portion has a curved contact surface with the electrode.

In a preferred aspect, the electrodes are planar electrodes provided on both sides of the vibrating membrane, respectively, and have substantially the same capacitance as when the electrodes are made of metal.

  According to the electrostatic speaker according to the present invention, a certain standard is satisfied with respect to both sound transmission performance and capacitance performance.

1 is an external perspective view of an electrostatic speaker 1. FIG. 1 is a cross-sectional view of an electrostatic speaker 1. FIG. It is an experimental data about an electrostatic capacitance characteristic. It is an experimental data about a sound transmission characteristic. 3 is a cross-sectional view of the electrostatic speaker 2. FIG. 3 is a detailed view of a wire mesh electrode 40. FIG. It is an experimental data about an electrostatic capacitance characteristic. 3 is a cross-sectional view of the electrostatic speaker 3. FIG. 4 is a diagram for explaining an example of a structure of a support member 50. FIG. It is a figure for demonstrating the other example of the structure of the supporting member 50. FIG.

<Example 1>
FIG. 1 is a perspective view of a schematic structure of an electrostatic speaker 1 according to an embodiment of the present invention. As shown in the figure, the electrostatic speaker 1 includes a vibrating membrane 10, two parallel flat electrodes (hereinafter simply referred to as electrodes) 20L and 20R facing the vibrating membrane 10, and the vibrating membrane 10 and the electrodes 20L and 20R. It is generally composed of cushion materials 30L and 30R provided between them. In the drawing, the electrode surfaces of the electrodes 20L and 20R are fixed in the X direction and the Y direction, and an example of an arrangement in which the vibrating membrane 10 can vibrate in the Z direction perpendicular to the electrode surfaces is shown. Hereinafter, since the electrodes 20L and 20R have the same structure, “L” and “R” are omitted unless it is particularly necessary to distinguish between them. The omitted “L” and “R” are the same for the other components.

  Further, in the electrostatic speaker 1, a desired voltage is applied to each electrode 20 from a power source (not shown), and a bias voltage is applied to the vibrating membrane 10. Since a conventional technique can be adopted as a method for supplying power to the electrode 20, illustration of components related to power supply is omitted. The electrostatic speaker 1 further includes an input unit for inputting a sound signal from the outside, and causes the vibration film 10 to vibrate according to the sound signal by changing the value of the applied voltage according to the sound signal. Can be done. The sound wave generated by the vibration of the vibration film 10 passes through at least one electrode 20 and is emitted to the outside of the speaker. In order to prevent the drawing from becoming complicated, illustration of components that generate and supply audio signals is also omitted.

  The vibration film 10 is obtained by depositing a metal film or applying a conductive paint on a film such as PET (polyethylene terephthalate) or PP (polypropylene), and has a thickness of several microns to several tens of microns, for example. It is a conductive plate-like (film-like) member of about a micron. Or what laminated | stacked the metal thin film and what polarized by applying a high voltage to the insulating film may be used. Further, the vibration film 10 is in a state where a predetermined tension is applied to the vibration film 10 in a fixing means (not shown) formed of an insulating material such as vinyl chloride, acrylic (methyl methacrylate), or rubber. For example, one side of the edge may be supported by a casing (not shown) of the electrostatic speaker 1, or such a support portion is not provided, and is supported by the action of the cushion materials 30L and 30R. It may be a configuration.

  The electrode 20 has a square electrode surface and is fixed to a housing (not shown) of the electrostatic speaker 1. At this time, the distance d (for example, about 0.1 to 10 mm) from the vibrating membrane 10 to both the electrodes 20L and 20R is arranged to be equal. In other words, the position just in the middle of the opposing electrodes is the fixed position of the vibration film 10 (more precisely, the vibration film 10 in the non-displacement state, which is the state when no signal is input). The shape of the electrode surface is not limited to a square, and may be, for example, a rectangle or a circle.

  FIG. 2 is a cross-sectional view in a direction perpendicular to the electrode surface of the electrostatic speaker 1, and the detailed structure of the electrode 20 will be described with reference to this drawing. The electrode 20 includes a nonwoven fabric layer 201 and a conductive layer 202. The conductive layer 202 is formed over the entire surface of the nonwoven fabric layer 201 and is generated, for example, by sputtering a metal such as aluminum on the nonwoven fabric layer 201. Alternatively, metal printing may be performed on the nonwoven fabric layer 201. Alternatively, a conductive paint may be applied to the nonwoven fabric layer 201.

  Here, the nonwoven fabric is a fiber having a porous (porous) structural fiber, and has a sheet-like shape. For example, it is produced by collecting in a certain direction or randomly, chemically bonding with an adhesive resin, mechanically entangled, entangled with a water stream under pressure, or bonded with a matured fused fiber. In the present invention, punching metal (hereinafter referred to as PM) is used so that the capacitance is substantially the same as in the case of using a flat electrode without holes and the air permeability (that is, the sound transmission performance). The nonwoven fabric which has a high structure compared with the case where an electrode is comprised using is used. For example, those having a basis weight of 40 g / m ^ 2, a thickness of 0.1 mm, and a fiber diameter of 2 denier are suitable. However, the nonwoven fabric which concerns on a present Example is not limited to the thing which has a structure specified by said value, The thing of the structure which has a value other than this can be used. Hereinafter, the structure of a suitable nonwoven fabric is further demonstrated from each viewpoint of electrostatic capacity performance and sound transmission performance.

  The cushion material 30 is made of an insulating material, and is, for example, a sponge, a sheet-like cotton, or an insulating nonwoven fabric. By inserting the cushion material 30, it is possible to support the vibration film 10 with respect to the casing or to apply an appropriate elastic stress to the vibration film 10. Although the mechanical property etc. are not specifically limited, It has air permeability larger than the air permeability of the electrode 20, Comprising: For example, 95% or more of air permeability is preferable.

(1) Capacitance performance FIG. 3 shows a case where one electrode is measured when the capacitance measured with a pair of parallel plane electrodes made of metal (having no holes) is 1 (100%). The capacitance value measured by replacing the electrode using the nonwoven fabric with the structure of the above exemplified value of the same area (hereinafter referred to as the nonwoven fabric electrode), and PM having several pore diameters and aperture ratios. The capacitance value measured by replacement is shown together with the electrode spacing. In the figure, A shows the data when replaced with a non-woven fabric electrode, and E to I have pore diameters and aperture ratios of {2 mm, 20%}, {2 mm, 40%}, {3 mm, 40%}, {6 mm, respectively. , 40%} and {8 mm, 40%}. As can be seen from the figure, when PM is used, the capacitance is remarkably reduced as the distance between the electrodes is reduced. This is because, as described above, the influence of the holes increases as the distance between the electrodes decreases. On the other hand, when the nonwoven fabric electrode according to the present example is used, the capacitance does not drop even when the distance between the electrodes is reduced, and takes a substantially constant value (about 100%). It can be said that it has substantially the same electrostatic capacity performance as the case of the planar electrode formed.

(2) Sound transmission performance FIG. 4 shows a general speaker and a measuring device for analyzing the frequency characteristics of the sound emitted from the speaker at a predetermined distance from the speaker. Compare the frequency characteristics deviation (acoustic wave distortion) obtained with the measuring instrument when the measurement was performed with the PM placed between the measurement and the nonwoven fabric electrode according to this example. It is a thing. In the figure, PM (1) to (3) are data when PM having a hole diameter of 8 mm, 2 mm, and 2.5 mm is placed, and NW is data when a nonwoven fabric electrode is placed. If there is no shielding object between the speaker and the measuring instrument, the sound emitted from the speaker and the frequency characteristic of the measuring instrument substantially coincide with each other, so that the obtained data becomes zero regardless of the frequency. That is, it can be said that the smaller the deviation from zero, the better the sound transmission performance. When PM is used as the shielding object, it can be seen that the acoustic wave is distorted by the frequency band before reaching the measuring instrument due to the influence of the sound wave passing through the PM. On the other hand, when a nonwoven fabric electrode is used as the shield, some distortion is measured, but compared to the case of PM, the sound pressure level is generally about 1/3 to 1/4. Thus, it can be said that the electrode 20 comprised with the nonwoven fabric which concerns on a present Example is excellent in the point of the sound transmission performance compared with general PM.

<Example 2>
FIG. 5 is a cross-sectional view of an electrostatic speaker 2 according to another embodiment of the present invention. The electrostatic speaker 2 is different from the electrostatic speaker 1 in that the electrodes 40R and 40L are used instead of the electrodes 20R and 20L.
FIG. 6 shows details of the structure of the electrode 40. As shown in the figure, the electrode 40 is a lattice formed of a conductive material such as metal. For example, woven wire meshes of JIS standards G3555 and 3556, etc., and those having meshes # 20 to # 500 can be used. Here, the mesh refers to the number of eyes between 25.4 mm on one side.
FIG. 7 shows a wire mesh having the above-mentioned exemplified value of the same area when one of the electrodes has an electrostatic capacity measured by a pair of parallel flat metal electrodes (having no holes) of 1 (100%). Capacitance value measured by replacing the electrode with a non-woven fabric electrode (referred to as a wire mesh electrode) (referred to as effective capacitance) and PM measured with several pore sizes and aperture ratios. Is shown together with the electrode spacing. In the figure, B to D show data when replaced with wire mesh electrodes, respectively, and E to I are the same as the PM data shown in FIG. As can be seen from the figure, when the metal electrode according to the present embodiment is used, even if the distance between the electrodes is reduced, the drop in the capacitance is small compared to the case where PM is used. For example, an effective capacitance of 95% or more can be obtained even when the electrode spacing is 1 mm.
For example, when a plain weave wire mesh having a mesh # 40 and a wire diameter of 0.16 mm is used, the space ratio affecting the sound transmission performance (corresponding to the aperture ratio in PM) is about 40%. That is, if the electrode 40 according to the present embodiment is used, a capacitance performance higher than that of a PM having the same degree of aperture ratio can be obtained while realizing a sound transmission performance equivalent to that of PM.
The wire mesh used for the electrode 40 is, for example, a weaving method, a wire diameter, and a mesh size so long as the space ratio (for example, 20 to 50%) does not substantially deteriorate the sound transmission performance when used as an audio speaker. Any material can be used.

<Other examples>
FIG. 8 is a sectional view of the electrostatic speaker 3 according to the present invention. As shown in the figure, the electrostatic speaker 3 is configured by providing support members 50L and 50R outside the electrodes 20L and 20R of the electrostatic speaker 1, respectively. The support member 50 is made of, for example, a metal material, and is preferably a so-called flexible tube that has a bent shape and is excellent in bending durability, and is formed by winding a wire having a triangular shape around a spiral spring. It is done. In addition, the support member 50 may be fixed to the housing or may be fixed to the electrode 20. However, when the support member 50 is fixed to the electrode 20, a predetermined insulating process is performed on the fixing portion.
FIG. 9 is a view for explaining the structure of the support member 50. As shown in the figure, the support member 50 has a lattice shape so as not to substantially impair the sound transmission performance. This shape can be obtained, for example, by braiding the flexible tube.
When the non-woven fabric constituting the electrode 20 has a certain flexibility (for example, a sheet-like one), depending on conditions such as an applied voltage and an installation condition of the electrode 20, the electrode 20 It may bend. Even if the force is applied to the inside of the electrode 20, the bending can be suppressed to some extent because of the cushion material 30, but when the force is applied to the outside, the electrode 20 is bent. However, according to the present embodiment, by using the support member 50 outside the electrode 20, it is possible to prevent the bending thereof.

  Furthermore, as shown in FIG. 10, it is also possible to fix the support member 50 in a state where it is bent in the z direction in the same figure. In the example shown in FIG. 10, the center of the support member is most bent, and the bending becomes gentler toward the periphery. In this case, the bending state of the electrode 20 can be forced to a predetermined shape (for example, a parabolic shape as shown in FIG. 10). By adjusting the degree of bending, the directivity characteristic of the acoustic wave emitted from the electrode 20 can be controlled.

  In the above embodiment, the cushion material 30 is provided between the electrode 20 and the vibration film 10, but the cushion material 30 may be omitted. In this case, in order to prevent contact between the vibrating membrane 10 and the electrode, for example, it is preferable to provide spacers at four corners of the vibrating membrane.

  Further, the cushioning material 30 may be formed of the insulating nonwoven fabric having the above-described structure used for the electrode 20, and a conductive layer may be provided on the outer surface (that is, the electrode side) of the cushioning material 30. In this case, the electrode 20 is not provided, and the cushion material 30 can also function as the electrode 20.

  Moreover, in Example 1, although the example of the electrode 20 in which the conductive layer was formed on the surface of the nonwoven fabric was shown, the thickness of this layer is arbitrary. In short, the non-woven fabric constituting the electrode according to the present invention may be of any structure as long as it exhibits the above-described sound transmission performance and capacitance performance, and does not necessarily have a layer structure. For example, each fiber may have conductivity, and may have conductivity at an arbitrary location inside the nonwoven fabric.

  The place where the support member 50 is provided is not limited to the outside of the electrode 20 or 40, but may be provided inside (that is, between the vibrating membrane 10 (or the cushion material 30) and the electrode 20 or 40), or both inside and outside It may be.

  In the embodiments described above, only specific combinations of the vibration membrane 10, the electrode 20 or 40, the cushion material 30, and the support member 50 are illustrated as constituent elements of the electrostatic speaker. For this reason, for example, any combination other than those described above can be employed for the presence or absence of the cushion material 30 and the presence or absence of the support member 50.

  In the embodiment described above, an example of a push-pull type electrostatic speaker using a pair of opposing electrodes 20 or 40 has been shown. However, the present invention is not limited to this, and only one electrode according to the present invention is provided. It is also possible to configure a push-type electrostatic speaker by using it.

1, 2, 3 ... electrostatic speaker, 10 ... vibrating membrane, 20, 20L, 20R, 40L, 40R ... electrode, non-woven fabric electrode, 30L, 30R ... cushion material, 50L , 50R ... support member, 201L, 201R ... non-woven fabric layer, 202L, 202R ... conductive layer

Claims (2)

A diaphragm that can be displaced by an electrostatic force;
An electrode provided opposite to the vibrating membrane and having a network structure;
A buffer member provided between the vibrating membrane and the electrode ;
A support portion for supporting the planar electrode in the vibration direction of the vibrating membrane;
Have
The support portion has a curved contact surface with the electrode.
An electrostatic speaker characterized by that. The electrodes are electrodes provided on both sides of the vibrating membrane,
The electrostatic speaker according to claim 1, wherein the electrostatic capacity is substantially the same as when the electrode is made of metal.

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