JP2014176006A - Electrostatic speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction of a sound pressure in the case where an object, such as a wall, which causes an air spring exists in proximity to a rear surface of an electrostatic speaker.SOLUTION: An electrostatic speaker 10 includes a vibration film 11 and fixed electrode films 12F and 12R. The fixed electrode films 12F and 12R are each a porous conductor film, which includes a large number of ventilation holes 120, and applied with a driving signal. The vibration film 11 is arranged between the fixed electrode films 12F and 12R. The vibration film 11 includes a large number of ventilation holes 110 formed in a predetermined pattern, first ventilation regions LS1, LS2, LS3, and LS4, second ventilation regions LC1, LC2, LC3, LC4, and LC5, and a plurality of vibration regions ARs partitioned by the ventilation regions.

Description

  The present invention relates to an electrostatic speaker that emits sound by vibrating a flat membrane-like vibrating membrane by applying an electric field from the outside.

  Currently, various types of flat speakers with a wide sound emitting surface and a small thickness have been devised. Among such planar speakers, there is an electrostatic speaker that uses electrostatic force, and has a structure as shown in Patent Document 1, for example.

  The electrostatic speaker described in Patent Document 1 includes a vibration film made of a thin film conductor, and fixed electrode films are arranged on both sides of the vibration film with a predetermined interval.

  Such an electrostatic speaker can be used by being placed close to a wall or mounted on a wall surface because of its shape characteristics. At this time, the sound emitting surface and the wall surface are generally parallel.

JP 2009-272861 A

  In the electrostatic speaker used in this way, the distance between the back surface of the electrostatic speaker and the wall is inevitably narrow. In this case, the electrostatic speaker having the conventional configuration has the following problems. FIG. 8 is a side view for explaining a problem caused by a conventional electrostatic speaker. FIG. 8A shows a state in which the electrostatic speaker is arranged in free space, and FIG. 8B shows a state in which the electrostatic speaker is arranged with the back face close to the wall.

  The conventional electrostatic speaker 10P includes a vibration film 11P and fixed electrode films 12F and 12R. The vibration film 11P is formed by depositing or coating a conductor such as aluminum on a flexible film. The fixed electrode films 12F and 12R are made of a conductor formed on the surface of an interference film or the like (not shown). The fixed electrode films 12F and 12R are made of aluminum or the like, for example, similarly to the vibration film 11P. The fixed electrode films 12F and 12R are porous.

  As shown in FIG. 8A, when the back surface of the electrostatic speaker 10P is free space, air waves generated on the front surface and the back surface of the electrostatic speaker 10P due to the vibration of the vibration film 11P are both free space. Propagate to. In this configuration, since air waves propagate to free space, as shown in FIG. 8A, there is no air spring, and the vibration film 11P is free to have an amplitude corresponding to the signal level of the drive signal. Vibrate. That is, the force which suppresses the vibration from the outside is not added. Therefore, a desired sound pressure can be obtained on the front side of the electrostatic speaker 10P.

  On the other hand, as shown in FIG. 8B, when the wall 900 exists in the vicinity of the back surface of the electrostatic speaker 10P, the air pushed out to the back side by the vibration of the vibration film 11P, that is, the air generated on the back side. The wave 900 is prevented from propagating in the direction perpendicular to the back surface by the wall 900. Air is pushed to the edge of the electrostatic speaker 10P along the wall surface of the wall 900, and is propagated to the outside from the edge of the electrostatic speaker 10P as indicated by the dotted thick arrow in FIG. 8B. The

  In such a case, the air that is generated by the vibration of the vibration film 11P and flows to the back side propagates to the free space only in the flow rate according to the distance between the electrostatic speaker 10P and the wall 900, and the back surface of the electrostatic speaker 10P. The air pressure on the side increases. Therefore, as shown in FIG. 8B, an air spring 910 corresponding to the air pressure is interposed between the electrostatic speaker 10P and the wall 900. When such an air spring 910 is interposed, the vibration of the vibration film 11P is suppressed and the sound pressure is reduced. Here, the air pressure rises and the stiffness of the air spring 910 increases as the distance between the electrostatic speaker 10P and the wall 900 decreases. Thereby, the vibration of the vibration film 11P is further suppressed, and the sound pressure is further reduced.

  Here, since the sound pressure is proportional to the particle velocity of air, the sound pressure cannot be obtained unless the displacement is larger as the frequency is lower. Therefore, if the stiffness of the air spring 910 increases, particularly low sound pressure cannot be obtained. As a specific example, in the case of 1 kHz sound emitted from the A0 size electrostatic speaker 10P, the sound is generated when the distance between the electrostatic speaker 10P and the wall 900 is 5 cm or less with reference to a state where the wall 900 is not present. When the pressure starts to decrease from 1 cm to 2 cm, the sound pressure is greatly reduced.

  Therefore, an object of the present invention is to provide an electrostatic speaker that can suppress a decrease in sound pressure when an object that generates an air spring, such as a wall, is arranged close to the back surface.

  The electrostatic speaker according to the present invention includes first and second fixed electrode films and a vibration film. The first and second fixed electrode films are porous films and are electrode films to which a drive signal is applied. The vibration film has conductivity and is disposed between the first fixed electrode film and the second fixed electrode film, and the first fixed electrode film and the second fixed electrode film vibrate due to an electrostatic field generated by a drive signal. It is a membrane. Further, the vibration membrane includes a ventilation region provided with a plurality of ventilation holes for venting in the thickness direction of the vibration membrane, and a vibration region in which no hole is formed.

  In this configuration, even if air accumulates on the back side of the electrostatic speaker due to vibration of the vibrating membrane, the accumulated air flows out to the front side by the vent hole formed in the ventilation region. Thereby, the stiffness of the air spring on the back side of the electrostatic speaker is substantially reduced, and a decrease in sound pressure can be suppressed.

  In the electrostatic speaker of the present invention, the air permeability in the ventilation region is determined by the stiffness of the air spring generated on the back surface of the electrostatic speaker.

  In this configuration, the ventilation region can be appropriately formed based on the environment related to the air flow on the back side of the electrostatic speaker.

  In the electrostatic speaker according to the present invention, the ventilation region is formed in a lattice shape, the width of the ventilation region is narrower than the width of the vibration region, and the width of the ventilation region and the width of the vibration region are determined according to the air permeability and the desired value. And the sound pressure to be determined.

  In this configuration, a more specific shape of the electrostatic speaker is shown, and a desired sound emission characteristic can be realized by using such a shape.

  In addition, the electrostatic speaker of the present invention includes a flat sound absorbing material on the surface of the second fixed electrode film opposite to the vibration film. The thickness of the sound absorbing material is approximately ½ of the width of the vibration region.

  In this configuration, since at least a part of the sound toward the second fixed electrode film side, that is, the back side is absorbed by the sound absorbing material, it is possible to further suppress a decrease in sound pressure.

  Further, the electrostatic speaker of the present invention is used so as to be disposed on the front side of the flat plate surface in a member having a flat plate surface, and the width of the vibration region is set between the back surface of the electrostatic speaker and the flat plate surface. Is approximately twice the distance.

  In this configuration, a shape example corresponding to a more specific use environment of the electrostatic speaker is shown. By adopting such a shape, a desired sound emission characteristic can be realized according to the use environment.

  According to the present invention, even when an object that generates an air spring such as a wall is arranged close to the back surface, the sound pressure is hardly lowered and a sound emission characteristic closer to sound emission in free space is obtained. be able to.

It is side surface sectional drawing of the electrostatic speaker which concerns on the 1st Embodiment of this invention. 1 is a plan view of a vibrating membrane according to a first embodiment of the present invention. It is the top view which expanded the diaphragm which concerns on the 1st Embodiment of this invention partially. 1 is a plan view of a fixed electrode film according to a first embodiment of the present invention. It is a side view which shows the suppression principle of the sound pressure fall at the time of using the electrostatic speaker which concerns on the 1st Embodiment of this invention. It is a graph which shows the sound pressure frequency characteristic of the electrostatic loudspeaker which concerns on the 1st Embodiment of this invention, and the conventional electrostatic loudspeaker (electrostatic loudspeaker which does not have a ventilation hole in a diaphragm). It is side surface sectional drawing of the electrostatic speaker which concerns on the 2nd Embodiment of this invention. It is a side view for demonstrating the problem which arises with the electrostatic speaker of a conventional structure.

  An electrostatic speaker according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view of an electrostatic speaker according to a first embodiment of the present invention. FIG. 2 is a plan view of the vibrating membrane according to the first embodiment of the present invention. FIG. 3 is a partially enlarged plan view of the vibrating membrane according to the first embodiment of the present invention. FIG. 4 is a plan view of the fixed electrode film according to the first embodiment of the present invention. In FIG. 1 to FIG. 4, symbols are not attached to all of the vent holes 110 and 120, but symbols are attached only to the representative vent holes 110 and 120.

  The electrostatic speaker 10 according to the present embodiment includes a vibration film 11, a fixed electrode film 12F (corresponding to a first fixed electrode film), a fixed electrode film 12R (corresponding to a second fixed electrode film), and a buffer film 13F. , 13R, gap members 14F, 14R, and protective films 15F, 15R.

  The vibration film 11 is a flat film having conductivity and has a predetermined plane area. The planar area is, for example, A0 size (841 mm × 1189 mm). The vibration film 11 is formed by depositing or applying a metal such as aluminum on a base film made of PET (polyethylene terephthalate) or PP (polypropylene), for example. The thickness of the vibration film 11 is, for example, about several μm to several tens of μm.

  The vibration film 11 includes a large number of vent holes 110 in a predetermined arrangement pattern. The vent hole 110 is a hole that vents along the thickness direction of the vibration film 11. A more specific shape of the vibration film 11 will be described later with reference to FIGS.

  The fixed electrode films 12F and 12R are formed by depositing or applying a metal such as aluminum on a base film made of PET or PP, like the vibrating film 11. The planar areas of the fixed electrode films 12F and 12R are substantially the same as the planar area of the vibration film 11. The fixed electrode films 12F and 12R include a large number of vent holes 120. As shown in FIG. 4, the vent holes 120 are formed at equal intervals over substantially the entire surface of the fixed electrode films 12F and 12R. The diameter and the number of the vent holes 120 may be determined based on the required ventilation amount and the amount of electrostatic charge generated by the electrode portions of the fixed electrode films 12F and 12R by the drive signal.

  The buffer film 13F is disposed between the vibration film 11 and the fixed electrode film 12F. The buffer film 13F is made of a material having insulating properties and air permeability. The fixed electrode film 12F is attached to the buffer film 13F. The gap material 14F is disposed on the vibration film 11 side of the buffer film 13F. The gap material 14F is made of a material having predetermined elasticity and insulation. The gap material 14F is fixed to the buffer film 13F and is not fixed to the vibration film 11. The gap material 14F has, for example, a lattice shape or a stripe shape, and is in local contact with the buffer film 13F and the vibration film 11.

  The buffer film 13R is disposed between the vibration film 11 and the fixed electrode film 12R. The buffer film 13R is made of a material having insulating properties and air permeability. The fixed electrode film 12R is attached to the buffer film 13R. The gap material 14R is disposed on the vibration film 11 side of the buffer film 13R. The gap material 14R is made of a material having predetermined elasticity and insulation. The gap material 14R is fixed to the buffer film 13R and is not fixed to the vibration film 11. The gap material 14 </ b> R has, for example, a lattice shape or a stripe shape, and is in local contact with the buffer film 13 </ b> R and the vibration film 11.

  The protective film 15F is disposed on the surface of the fixed electrode film 12F opposite to the buffer film 13F. The protective film 15R is disposed on the surface of the fixed electrode film 12R opposite to the buffer film 13R. The protective films 15F and 15R are made of a material having insulating properties and air permeability, more preferably have a property such as flame retardancy, and the sound emitting function portion including the vibration film 11 and the fixed electrode films 12F and 12R is provided in the external environment. It should be a material that protects from

  The electrostatic speaker 10 having such a configuration has a flat membrane shape as a whole, and does not take up space in the depth direction. Therefore, for example, as shown in FIG.

  When a direct current bias is applied to the vibration film 11 of the electrostatic speaker 10 having such a configuration and a drive signal is applied to the fixed electrode films 12F and 12R, the static electricity between the fixed electrode films 12F and 12R generated by the drive signal is applied. Due to the change in the electric field, the vibration film 11 is displaced so as to approach either the fixed electrode film 12F or the fixed electrode film 12R. In other words, the vibration film 11 vibrates with the direction orthogonal to the flat film surface (front and back) of the electrostatic speaker 10 as the vibration direction. This vibration causes air to vibrate and emit sound in the front direction (see Sound in FIG. 1).

  At this time, sound propagates also in the back direction, in other words, air waves propagate, but with the configuration of this embodiment, the sound emission characteristics are deteriorated due to the flow of air to the back side. Can be suppressed. Specifically, deterioration of sound emission characteristics can be suppressed by the following configuration and principle.

  As shown in FIGS. 2 and 3, the vibrating membrane 11 has a large number of vent holes 110 formed in a predetermined pattern. More specifically, the large number of ventilation holes 110 are formed only in the first ventilation regions LS1, LS2, LS3, and LS4 and the second ventilation regions LC1, LC2, LC3, LC4, and LC5. It is not formed except for the first and second ventilation regions.

  The first ventilation regions LS1, LS2, LS3, and LS4 are regions that are long in the vertical direction of the diaphragm 11 and have a width W along the horizontal direction. The first ventilation region LS1 is formed in the vicinity of one end of the vibration film 11 in the lateral direction. The first ventilation regions LS1 and LS2 are arranged at an interval P1s along the lateral direction of the vibration film 11. The first ventilation regions LS2 and LS3 are arranged at an interval P2s along the lateral direction of the vibration film 11. The first ventilation regions LS3, LS4 are arranged with a spacing P3s along the lateral direction of the vibration film 11. The first ventilation region LS4 is formed in the vicinity of the other end of the vibration film 11 in the lateral direction. The intervals P1s, P2s, and P3s have the same value.

  The second ventilation regions LC1, LC2, LC3, LC4, and LC5 are regions that are long in the horizontal direction of the vibration film 11 and have a width W along the vertical direction. The second ventilation region LC1 is formed in the vicinity of one end of the vibration film 11 in the vertical direction. The second ventilation regions LC <b> 1 and LC <b> 2 are arranged along the longitudinal direction of the vibration film 11 with a space P <b> 1 c. The second ventilation regions LC <b> 2 and LC <b> 3 are arranged along the longitudinal direction of the vibration film 11 with a space P <b> 2 c. The second ventilation regions LC3 and LC4 are arranged along the longitudinal direction of the vibration film 11 with a space P3c. The second ventilation regions LC4 and LC5 are arranged along the longitudinal direction of the vibration film 11 with a space P4c. The second ventilation region LC5 is formed in the vicinity of the other end of the vibration film 11 in the vertical direction. The intervals P1c, P2c, P3c, and P4c are the same value. The intervals P1c, P2c, P3c, and P4c may be the same as or different from the intervals P1s, P2s, and P3s. However, it is preferable to be as close to the same value as possible. These intervals P1c, P2c, P3c, P4c, P1s, P2s, and P3s are preferably shorter than the width W. Thereby, it is easy to ensure a vibration region described later as wide as possible.

  By configuring the first ventilation regions LS1, LS2, LS3, and LS4 and the second ventilation regions LC1, LC2, LC3, LC4, and LC5 in such a configuration, the ventilation regions are formed in a lattice pattern on the plane of the vibration film 11. Is done. With this configuration, the vibration film 11 is formed with the vent holes 110 partitioned by the first vent areas LS1, LS2, LS3, LS4 and the second vent areas LC1, LC2, LC3, LC4, LC5. No rectangular vibration area ARs is formed. Accordingly, the above-described intervals P1s, P2s, P3s and intervals P1c, P2c, P3c, P4c correspond to the width of the vibration region of the present invention.

  By providing the vibration region ARs having such a continuous conductive film having a predetermined area, the vibration film 110 can be vibrated by an electrostatic field even if the vent hole 110 that does not contribute to the generation of vibration is provided.

  With such a configuration, it is possible to form the vibration film 11 that can vibrate even when the vent hole 110 is formed.

  Furthermore, by providing the vent hole 110, it is possible to suppress a decrease in sound pressure by the principle as shown in FIG. FIG. 5 is a side view showing the principle of suppressing the decrease in sound pressure when the electrostatic speaker 10 according to the first embodiment of the present invention is used.

  When the vibration film 11 of the electrostatic speaker 10 vibrates and is displaced toward the fixed electrode film 12R side, that is, when the vibration film 11 is displaced toward the back surface side of the electrostatic speaker 10, air is pushed away to the back surface side of the vibration film 11. Here, as shown in the above-described problem, if the wall 900 near the back surface of the electrostatic speaker 10 exists, the air pressure on the back surface side of the electrostatic speaker 10 increases according to this distance.

  However, since the electrostatic speaker 10 having the configuration of the present embodiment has a large number of air holes 110 formed in the vibration film 11, the air swept away from the back side is separated from the electrostatic speaker 10 and the wall 900. In addition to propagating from the position of the edge of the electrostatic speaker 10 in the gap to the outside, through the vent hole 120 of the fixed electrode film 12R, the vent hole 110 of the vibration film 11, and the vent hole 120 of the fixed electrode film 12F. The electrostatic speaker 10 is also swept away from the front side.

  As a result, the air pressure on the back side of the electrostatic speaker 10 decreases, and the stiffness of the air spring 911 decreases. Therefore, the vibration of the vibration film 11 is not suppressed, and a sound pressure that emits sound in the front direction can be obtained.

  As described above, with the configuration of the present embodiment, even when an object that generates an air spring, such as a wall, is disposed close to the back surface, the sound pressure does not decrease much and is released in free space. Sound emission characteristics close to sound can be obtained.

  The width of the vibration region, that is, the intervals P1s, P2s, P3s and the intervals P1c, P2c, P3c, P4c may be set as follows. Here, in order to simplify the description, a case where the intervals P1s, P2s, P3s and the intervals P1c, P2c, P3c, P4c have the same length is shown. An example in which the vibration film 11 is A0 size is shown.

  The interval P1s may be approximately ½ of the distance DIS between the back surface of the electrostatic speaker 10 and the wall surface of the wall 900. Further, the aperture ratio of the ventilation region, that is, the area of the entire ventilation hole 110 with respect to the entire area of the vibration film 11 is preferably about 30%.

  By adopting such a configuration, it is easy to ensure a desired sound pressure even when the electrostatic speaker 10 is brought close to about 10 mm to 20 mm with respect to the wall 900.

  FIG. 6 is a graph showing sound pressure frequency characteristics of the electrostatic speaker according to the first embodiment of the present invention and a conventional electrostatic speaker (an electrostatic speaker having no vibration hole in the vibration membrane).

  As shown in FIG. 6, the electrostatic loudspeaker having the conventional configuration has a characteristic that the sound pressure of the frequency component of 400 Hz is reduced by 10 dB with respect to the sound pressure of the high frequency component in the free space (FIG. 6). See dotted line). And, when the electrostatic speaker having the conventional configuration is arranged in the vicinity of the wall, the frequency at which the 10 dB sound pressure decreases increases to 2 kHz, and the frequency component at 400 Hz further decreases the sound pressure. (See broken line in FIG. 6).

  However, by using the configuration of the present embodiment, even when arranged near the wall, the amount of decrease in the sound pressure of the frequency component from 400 Hz to 2 kHz is small, and a conventional electrostatic speaker is arranged near the wall. As a result, it is possible to obtain a sound pressure of a frequency component from 400 Hz to 2 kHz, and to obtain a sound pressure characteristic close to that when a conventional electrostatic speaker is arranged in a free space.

  Specifically, when the aperture ratio is 30% as described above, the sound pressure is reduced by about 3 dB with respect to the sound pressure when the conventional electrostatic speaker is disposed in free space. Thereby, it is possible to emit sound having characteristics very close to the desired sound emission characteristics. Further, in this case, if the drive signal voltage is increased to some extent, it is easy to raise the sound pressure of 3 dB. Therefore, a desired sound emission characteristic can be reliably realized with only a slight increase in the drive signal voltage.

  Although not specifically described, it is preferable that the diameter of the vent hole 110 be as small as possible, and it is preferable to realize a desired air permeability by the number of the vent holes 110 formed. In addition, since the ventilation region hardly contributes to the generation of vibration, the aperture ratio in the ventilation region is a desired speaker output (sound pressure) in a frequency band of 2 kHz or more based on the required strength, conductivity, etc. of the vibration film 11. It is better to increase the aperture ratio as much as possible within the range where the

  Moreover, although the example which forms a ventilation area | region in the grid | lattice form was shown in the above-mentioned description, stripe shape may be sufficient and the space | interval of a 1st ventilation area and a 2nd ventilation area may not be constant. Furthermore, the vibration area may not be rectangular, but may be polygonal, circular, or the like.

  Further, the air permeability may be appropriately set according to a desired sound emission characteristic, and the diameter and the number of the air holes 110 may be set based on the air permeability and the sound emission characteristic (sound pressure).

  Next, an electrostatic speaker according to a second embodiment will be described with reference to the drawings. FIG. 7 is a side sectional view of an electrostatic speaker according to the second embodiment of the present invention. The electrostatic speaker 10A of the present embodiment is obtained by adding a sound absorbing material 16 to the electrostatic speaker 10 shown in the first embodiment. Accordingly, only the portions different from the electrostatic speaker 10 shown in the first embodiment will be specifically described.

  The electrostatic speaker 10 </ b> A includes the configuration of the electrostatic speaker 10 described above and a flat sound absorbing material 16. The sound absorbing material 16 is disposed on the surface of the protective film 15R opposite to the fixed electrode film 12R. The sound absorbing material 16 absorbs sound propagated to the back side of the electrostatic speaker 10. That is, the air wave propagated to the back side is attenuated.

  Even in such a configuration, a decrease in sound pressure can be suppressed by the vent hole 110 of the vibration film 11 as in the first embodiment. Furthermore, in the configuration of the present embodiment, since the sound absorbing material 16 absorbs sound, the air wave propagated to the back side does not enter the front side, and the sound pressure characteristics can be further improved.

  At this time, the thickness Dep of the sound absorbing material 16 is set to be equal to or larger than the distance DIS between the protective layer 15R on the back surface side and the wall 900, and preferably coincides with the distance DIS. Thereby, the electrostatic speaker 10 </ b> A can be used in contact with the wall surface of the wall 900. Even when the electrostatic speaker 10 </ b> A is brought into contact with the wall surface of the wall 900 as described above, desired sound emission characteristics can be obtained.

10, 10A, 10P: electrostatic speaker,
11, 11P: vibrating membrane,
12F, 12R: fixed electrode membrane,
13F, 13R: buffer membrane,
14F, 14R: Gap material 15F, 15R: Protective film,
16: Sound absorbing material,
110, 120: vent holes,
900: wall,
910, 911: Air spring

Claims (5)

A porous first fixed electrode film and a second fixed electrode film to which a drive signal is applied;
A conductive vibration film disposed between the first fixed electrode film and the second fixed electrode film, wherein the first fixed electrode film and the second fixed electrode film are vibrated by an electrostatic field generated by the drive signal. And comprising
The vibration membrane is an electrostatic loudspeaker including a ventilation region provided with a plurality of ventilation holes for venting in the thickness direction of the vibration membrane, and a vibration region in which the ventilation holes are not formed.   The electrostatic speaker according to claim 1, wherein the air permeability in the ventilation region is determined by a stiffness of an air spring generated on a back surface of the electrostatic speaker. The ventilation region is formed in a lattice shape,
The width of the ventilation region is narrower than the width of the vibration region,
The electrostatic speaker according to claim 2, wherein the width of the ventilation region and the width of the vibration region are determined based on the air permeability and a desired sound pressure. A flat sound absorbing material is provided on the surface of the second fixed electrode film opposite to the vibration film,
The electrostatic speaker according to any one of claims 1 to 3, wherein a thickness of the sound absorbing material is substantially ½ of a width of the vibration region. An electrostatic speaker having the configuration of claim 3 or 4 used to be disposed on the front side of the flat plate surface in a member having a flat plate surface,
The electrostatic speaker, wherein the width of the vibration region is approximately twice the distance between the back surface of the electrostatic speaker and the flat plate surface.

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