JP2010004254A - Electrostatic speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reproduce bass without causing a vibrator to be brought into contact with an electrode even if a member is not interposed between the electrode and the vibrator. <P>SOLUTION: In the electrostatic speaker 1, a vibrator 10 is positioned between electrodes 20U and 20L while tension is applied thereto. A plurality of micro through-holes 21 penetrating the electrodes 20U and 20L from their front faces to their rear faces are regularly made at specified intervals in X and Y directions. In case when the vibrator 10 is displaced in the direction of the electrode 20L (electrode 20U), air between the vibrator 10 and the electrode 20L (electrode 20U) flows into the plural micro through-holes 21 provided in the electrode 20L (electrode 20U) when the vibrator 10 vibrates. However, the movement of the air is limited by the sound transmission resistance of the through-holes 21 and the displacement of the vibrator 10 is also limited, so that it is not be brought into contact with the electrode 20L (electrode 20U). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrostatic speaker.

  The electrostatic speaker is composed of two parallel flat electrodes facing each other at an interval, and a conductive sheet-like vibrating body disposed with tension applied between the two electrodes. When a predetermined bias voltage is applied to the vibrating body and the voltage applied to the electrode is changed, the electrostatic force acting on the vibrating body changes, and thereby the vibrating body is displaced. If the applied voltage is changed according to the input acoustic signal, the vibrating body repeats displacement (that is, vibrates) accordingly, and an acoustic wave corresponding to the acoustic signal is generated from the vibrating body. The generated acoustic wave passes through a hole formed in the planar electrode and is radiated to the outside (see Patent Document 1).

  Further, as the electrostatic speaker, there is an electrostatic speaker having a configuration disclosed in Non-Patent Document 1. In this electrostatic speaker, a vibrating body is sandwiched between sheet-like ester wool and supported between flat electrodes. According to this configuration, the vibrating body is supported at a fixed position between the flat electrodes. There is no contact with.

JP 7-46697 A Masanori Okazaki, 4 others, "Condenser speaker with diaphragm that vibrates piston in all bands and its application", Acoustical Society of Japan 2004 Fall Meeting Presentation, Acoustical Society of Japan, September 2004, p. 563-564

In the electrostatic speaker disclosed in Patent Document 1, since the amount of displacement of the vibrating body toward the electrode is limited by applying tension to the vibrating body, the vibrating body and the electrode come into contact with each other and are short-circuited. There is no fear of doing it. However, in order to reduce the thickness of the electrostatic speaker, it is necessary to increase the tension applied to the vibrating body to suppress the displacement amount of the vibrating body. Here, when the tension applied to the vibrating body is increased, the amplitude of the vibrating body is decreased, the minimum resonance frequency is increased, and reproduction in a low range cannot be sufficiently performed.
On the other hand, in the electrostatic speaker disclosed in Non-Patent Document 1, when the vibrating body is displaced by receiving an electrostatic force, the sheet-like ester wool is compressed and deformed. The deformed ester wool tries to return to its original shape due to elasticity, but the volume density of the ester wool fibers is not necessarily uniform depending on the position of the sheet, so the force to return to the original shape, that is, the force applied to the vibrator Variation will occur. If there is a variation in the force applied from the ester wool to the vibrator, the displacement of the vibrator will vary, and the acoustic signal will not be reproduced correctly when the acoustic signal is input.

  The present invention has been made under the background described above, and provides a technique capable of reproducing a low frequency without bringing a vibrating body into contact with an electrode without interposing a member between the electrode and the vibrating body. With the goal.

  In order to solve the above-described problems, the present invention provides a first electrode having a plate-like conductivity and having a plurality of through holes penetrating from one surface of the plate shape to the other surface, and a plate-like conductivity. A plurality of through-holes penetrating from one side of the sheet plate to the other side, the second electrode spaced apart from the first electrode, and having conductivity, the first electrode and the A tension member that is tensioned between the first electrode and the second electrode; and the first electrode and the vibration member that are displaced when the vibration member is displaced. And the movement of air between the second electrode and the vibrating body is limited by the sound transmission resistance of the through-hole, and the vibrating body is in contact with either the first electrode or the second electrode There is provided an electrostatic speaker characterized by not.

In the present invention, the diameter of the through hole in the central part of the first electrode and the second electrode may be smaller than the diameter of the through hole in the peripheral part of the first electrode and the second electrode. .
In the present invention, the number of through holes per unit area in the central portion of the first electrode and the second electrode is equal to the number of through holes per unit area in the peripheral portion of the first electrode and the second electrode. It is good also as a structure fewer than the number of holes.
In the present invention, when the minimum resonance frequency is f, 2πf is ω, the diameter of the through hole is d, the density of air is ρ ₀ , the viscous resistance of air is μ, and the acoustic Reynolds number Rey is , Rey <2.0 may be satisfied.

前記貫通孔の前記第１電極全体での音響透過抵抗と前記貫通孔の前記第２電極全体での音響透過抵抗ｒｐを次式としたとき、

ｒｐ＞２Ｒａの条件を満たす構成としてもよい。 In the present invention, the density of air is ρ ₀ , the speed of sound is c, the wavelength of sound waves is λ, 2π / λ is K, the thicknesses of the first electrode and the second electrode are t, The aperture ratio of the second electrode is σ, the viscous resistance of air is μ, the radius of a circle having the same area as the area of the rectangular first electrode and the second electrode is a, and the first electrode and the second electrode S is the area, and the acoustic radiation resistance Ra to the atmosphere at the lowest resonance frequency of the first electrode and the second electrode is represented by the following equation:

When the acoustic transmission resistance of the entire through hole of the through hole and the acoustic transmission resistance of the entire second electrode of the through hole are represented by the following equations:

It is good also as a structure which satisfy | fills the conditions of rp> 2Ra.

  According to the present invention, it is possible to reproduce the low frequency range without bringing the vibrating body into contact with the electrode without interposing a member between the electrode and the vibrating body.

[Embodiment]
FIG. 1 is a diagram schematically showing an external appearance of an electrostatic speaker 1 according to an embodiment of the present invention, and FIG. 2 is a diagram schematically showing a cross section and an electrical configuration of the electrostatic speaker 1. 3 is an exploded perspective view of the electrostatic speaker 1.
As shown in the figure, the electrostatic speaker 1 includes a vibrating body 10, electrodes 20U and 20L, and spacers 30U and 30L. In the present embodiment, the configurations of the electrodes 20U and 20L are the same, and therefore the description of “L” and “U” is omitted unless it is particularly necessary to distinguish between them. In addition, since the configuration of the spacer 30U and the spacer 30L is the same, the description of “L” and “U” is omitted if it is not particularly necessary to distinguish between these members. In addition, the dimensions of each component such as the vibrator and electrode in the figure are different from the actual dimensions so that the shape of the component can be easily understood. "Means an arrow heading from the back of the drawing to the front.

(Structure of electrostatic speaker 1)
In the electrostatic speaker 1, the periphery of the vibrating body 10 is sandwiched between the spacer 30U and the spacer 30L in a state where tension is applied. The tension applied to the vibrating body 10 is set so that the lowest resonance frequency of the electrostatic speaker 1 becomes a desired frequency.
In the electrostatic speaker 1, the electrode 20U is fixed to the spacer 30U, the electrode 20L is fixed to the spacer 30L, and the electrodes 20U and 20L and the vibrating body 10 are parallel to vibrate with the electrodes 20U and 20L. There is a gap with the height of the spacer 30 between the body 10.

(Configuration of each part of the electrostatic speaker 1)
Next, each member constituting the electrostatic speaker 1 will be described. The vibrating body 10 is obtained by, for example, depositing a conductive metal or applying a conductive paint on a film such as PET (polyethylene terephthalate) or PP (polypropylene). A conductive metal layer is formed on the surface with a thickness of about μm to several tens of μm.

  The spacer 30 is made of an insulator and has a rectangular frame shape as shown in FIG. In the present 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 of a conductive metal in the shape of a rectangular plate. In this embodiment, the length of the electrode 20 in the X direction and the Y direction and the length of the vibrating body 10 in the X direction and the Y direction are used. It is the same.
Further, in the electrode 20, a plurality of fine through holes 21 penetrating from the front surface to the back surface of the electrode 20 are regularly provided at predetermined intervals in the X direction and the Y direction. Note that f = the minimum resonance frequency of the electrostatic speaker 1, ω = 2πf, d = diameter of the through hole 21, ρ ₀ = air density, and μ = air viscosity resistance. The diameter of the through hole 21 is determined so that the acoustic Reynolds number Rey represented by the following formula becomes Rey <2.0.

  For example, when the minimum resonance frequency f is 125 [Hz] and the Reynolds number Rey is 2.0, the diameter d = 0.55 [mm] of the through-hole 21 is obtained from the equation (1), so the Reynolds number Rey is 2.0. In order to make it less than this, the diameter d should be less than 0.55 [mm]. In the present invention, the diameter of the through hole 21 preferably does not exceed 1 [mm].

Ρ ₀ = density of air, c = velocity of sound, K = wave number (2π / λ: λ = wavelength of sound wave), a = equivalent radius (radius of a circle having the same area as the rectangular area), πa ² = electrode 20 Where S = t, thickness of electrode 20, d = diameter of through-hole 21, σ = opening ratio of electrode 20, μ = viscosity resistance of air, electrode 20 at the lowest resonance frequency into the atmosphere The acoustic radiation resistance Ra is expressed by the following equation (5), and the acoustic transmission resistance rp of the entire electrode 20 of the through hole 21 (resistance when sound passes through the through hole 21) is expressed by the following equation (6). .

Here, when the plate thickness t of the electrode 20, the diameter d of the through-hole 21, and the aperture ratio σ of the electrode 20 are set so that rp> 2Ra, the gap between the vibrating body 10 and the electrode 20 when the vibrating body 10 vibrates is set. However, the movement of air is limited by the acoustic resistance of the through-hole 21 (resistance when sound passes through the through-hole 21: hereinafter referred to as acoustic transmission resistance). If it does, the displacement of the vibrating body 10 will also be restrict | limited and will not contact the electrode 20. FIG.
For example, when the size and thickness of the electrode 20 and the diameter of the through hole 21 are determined in advance to determine the aperture ratio of the electrode 20, first, the size of the electrode 20 in the X direction and the Y direction is set to 30 [cm] × 30 [cm]. Then, the equivalent radius a≈17 [cm]. Further, when the thickness t of the electrode 20 is 1 [mm], the diameter d of the through hole 21 is 0.5 [mm], and the minimum resonance frequency f is set to 125 [Hz], first, Ka in Equation 2 is obtained. Since K = 2π / λ, Ka≈ (2π / 272) · 17≈0.4. When there is no baffle as in the present embodiment, the acoustic radiation resistance Rp is 0.002 times ρ ₀ c when Ka = 0.4, and the acoustic radiation resistance Ra is 1.2 when the temperature is 20 ° C. 2 [kg / m ³ ] × 343.7 [m / s] × 0.002 = 0.82. Therefore, when rp is set to 1.7 or more so as to satisfy rp> 2Ra, the aperture ratio σ of the electrode 20 is 0.59% from the equation (3).

(Electrical configuration of the electrostatic speaker 1)
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 conductive metal layer formed on the surface of the vibrating body 10 and the midpoint of the output side of the transformer 50. The electrodes 20U and 20L are respectively connected to the output side of the transformer 50. Are connected to one end and the other end. 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.

(Operation of electrostatic speaker 1)
Next, the operation of the electrostatic speaker 1 will be described.
When the acoustic signal input to the input unit 60 is supplied to the transformer 50 and a potential difference is generated between the opposing electrode 20U and the electrode 20L due to the voltage applied from the transformer 50, the vibrating body 10 is moved to Z in the figure. An electrostatic force attracting toward the direction side or the direction side opposite to the Z direction acts on the vibrating body 10.

For example, when an acoustic signal is input to the input unit 60, a positive voltage is applied to the electrode 20U, and a negative voltage is applied to the electrode 20L, a positive voltage is applied to the vibrating body 10 by the bias power source 70. Therefore, the portion of the vibrating body 10 between the electrode 20U and the electrode 20L repels the electrode 20U to which a positive voltage is applied, while being attracted to the electrode 20L to which a negative voltage is applied. Displaces to the 20L side.
Next, when an acoustic signal is input to the input unit 60, a negative voltage is applied to the electrode 20U, and a positive voltage is applied to the electrode 20L, the vibrating body 10 repels the electrode 20L to which a positive voltage is applied. On the other hand, it is attracted to the electrode 20U to which a negative voltage is applied and displaced toward the electrode 20U.

  Thus, in the electrostatic loudspeaker 1 of the present embodiment, the vibrating body 10 is displaced (flexed) in response to the acoustic signal, and vibration is generated by sequentially changing the displacement direction, and the vibration state (frequency and amplitude). , A phase) is generated from the vibrating body 10. The generated sound passes through at least one of the electrode 20U side and the electrode 20L side and is radiated to the outside of the electrostatic speaker 1.

In this embodiment, when the vibrating body 10 is displaced in the direction of the electrode 20L, the air between the vibrating body 10 and the electrode 20L is directed to the plurality of fine through holes 21 provided in the electrode 20L. The movement of the air is restricted by the sound transmission resistance of the through hole 21, and when the movement of the air is restricted, the displacement of the vibrating body 10 is also restricted and does not come into contact with the electrode 20L.
Further, when the vibrating body 10 is displaced in the direction of the electrode 20U, the air between the vibrating body 10 and the electrode 20U is directed to a plurality of fine through holes 21 provided in the electrode 20U. The movement of the air is restricted by the sound transmission resistance of this, and when the movement of the air is restricted, the displacement of the vibrating body 10 is also restricted and does not contact the electrode 20U.

Further, in the present embodiment, there is no member between the vibrating body 10 and the electrodes 20U and 20L, and tension is applied to the vibrating body 10, so that the vibrating body 10 is sandwiched between ester wool and In comparison, the displacement of the vibrating body 10 does not vary, and the sound signal is correctly reproduced when the sound signal is input.
In the present embodiment, since the vibrating body 10 does not contact the electrodes 20U and 20L due to the action of the fine through-hole 21, the vibrating body 10 can be connected to the electrodes 20U and 20L even if the tension applied to the vibrating body 10 is reduced. There is no contact with 20L. In addition, since the tension applied to the vibrating body 10 can be reduced, the minimum resonance frequency can be reduced, and low-frequency reproduction can be sufficiently performed.
In general, when the tension of the vibrating body 10 is reduced, the Q0 value representing the degree of resonance at the lowest resonance frequency is also increased, and the frequency characteristics of the speaker are not smooth. However, in this embodiment, the Q0 value is the through hole 21. Therefore, the frequency characteristic of the electrostatic speaker 1 becomes smooth.

[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 embodiment described above, the sound transmission resistance of the electrode 20 is flat in the plane of the electrode 20 as shown in FIG. 4, and the vibrating body 10 is centered as shown by a two-dot chain line in FIG. The part is displaced the most. 4 shows the distribution of the sound transmission resistance in the X direction, the sound transmission resistance in the Y direction (not shown) is flat in the plane of the electrode 20, and the central portion is The largest displacement.
On the other hand, as shown in FIG. 5, in the electrode 20, the diameter of the through hole 21 in the central portion of the electrode 20 is smaller than the diameter of the through hole 21 in the peripheral portion so that the sound transmission resistance in the central portion is larger than that in the peripheral portion. Alternatively, the number of the through holes 21 per unit area in the central part of the electrode 20 may be made smaller than the number of the through holes 21 per unit area in the peripheral part while making all the through holes 21 have the same diameter. .
According to this configuration, since the sound transmission resistance at the center portion of the electrode 20 is larger than that of the periphery as shown in FIG. 5, the displacement amount of the center portion of the vibrating body 10 is set as shown by the two-dot chain line in FIG. Can be suppressed.
The diameter and arrangement of the through holes 21 may be set so that the distribution of the sound transmission resistance is a result of adding a predetermined sound transmission resistance and a Bessel function.

  In the present invention, the shape of the electrode 20, the vibrating body 10, and the spacer 30 is not limited to a rectangle, and may be other shapes such as a polygon, a circle, and an ellipse.

  In the present invention, the electrode 20 may be formed by forming a transparent conductive film such as indium tin oxide on the surface of a transparent resin sheet such as PET, and this conductive film may be connected to the transformer 50. Further, regarding the vibrating body 10, a transparent conductive film such as indium tin oxide is formed on the front and back surfaces of a transparent resin sheet such as PET, and this conductive film is connected to the bias power source 70. Good. The spacer 30 may also be formed of a transparent synthetic resin. According to this configuration, since each member constituting the electrostatic speaker 1 is transparent, a transparent speaker can be obtained.

1 is an external view of an electrostatic speaker 1 according to an embodiment of the present invention. 1 is a schematic diagram of a cross section and an electrical configuration of an electrostatic speaker 1. FIG. 1 is an exploded perspective view of an electrostatic speaker 1. FIG. FIG. 4 is a diagram showing the distribution of acoustic radiation resistance of the electrostatic speaker 1 and the displacement of the vibrating body 10. It is the figure which showed distribution of the acoustic radiation resistance of the electrostatic speaker which concerns on the modification of this invention, and the displacement of the vibrating body.

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 (5)

A plate-like first electrode having a plurality of through holes penetrating from one surface of the plate-like surface to the other;
A plate-like second electrode having conductivity and having a plurality of through-holes penetrating from one surface of the plate-like surface to the other, and spaced apart from the first electrode;
A vibrating body having electrical conductivity, tensioned between the first electrode and the second electrode, and disposed separately from the first electrode and the second electrode;
When the vibrating body is displaced, movement of air between the first electrode and the vibrating body and between the second electrode and the vibrating body is limited by an acoustic transmission resistance of the through hole, and the vibrating body Is not in contact with either the first electrode or the second electrode.   The diameter of the through hole in the central portion of the first electrode and the second electrode is smaller than the diameter of the through hole in the peripheral portion of the first electrode and the second electrode. The electrostatic speaker described.   The number of the through holes per unit area in the central part of the first electrode and the second electrode is less than the number of the through holes per unit area in the peripheral part of the first electrode and the second electrode. The electrostatic speaker according to claim 1, wherein the electrostatic speaker is characterized by the following. When the minimum resonance frequency is f, 2πf is ω, the diameter of the through hole is d, the density of air is ρ ₀ , the viscous resistance of air is μ, and the acoustic Reynolds number Rey is The electrostatic speaker according to claim 1, wherein a condition is satisfied.

The density of air is ρ ₀ , the speed of sound is c, the wavelength of sound waves is λ, 2π / λ is K, the thicknesses of the first electrode and the second electrode are t, the aperture ratio of the first electrode and the second electrode Σ, the viscous resistance of air μ, the radius of a circle having the same area as the rectangular first electrode and the second electrode a, the area of the first electrode and the second electrode S, the first The acoustic radiation resistance Ra to the atmosphere at the lowest resonance frequency of the electrode and the second electrode is represented by the following equation:

When the acoustic transmission resistance of the entire through hole of the through hole and the acoustic transmission resistance of the entire second electrode of the through hole are represented by the following equations:

5. The electrostatic speaker according to claim 1, wherein a condition of rp> 2Ra is satisfied.

Images