Electrostatic speaker

Abstract

To provide a technique materializing improvement of flexibility of an electrostatic loudspeaker.SOLUTION: An electrostatic loudspeaker 101 includes: a first electrically conductive cloth 111 which is an electrically conductive cloth; a second electrically conductive cloth 121 and a third electrically conductive cloth 131 which are electrically conductive clothes and arranged with the first electrically conductive cloth 111 between them, and are insulated from the first electrically conductive cloth; and a first outer sheath cloth 140 and a second outer sheath cloth 150 which are arranged in such a way as to cover the first electrically conductive cloth 111, the second electrically conductive cloth 121, and the third electrically conductive cloth 131, and are constructed by the electrically insulating cloth. The first electrically conductive cloth 111, the second electrically conductive cloth 121, and the third electrically conductive cloth 131 and the first outer sheath cloth 140 and the second outer sheath cloth 150 are sewn by an electrically insulating thread.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to an electrostatic speaker.

Background Art

[0002] As a speaker that generates sound according to an electrical signal, an electrostatic speaker is known. This electrostatic speaker is composed of a pair of electrodes facing each other with a gap therebetween, and a sheet-like vibrating body having conductivity inserted between the pair of electrodes. Then, with a predetermined bias voltage applied to the vibrating body, by changing the voltage applied to the electrodes according to the electrical signal, the vibrating body is displaced according to the electrical signal and sound is generated. And in recent years, various techniques that enable bending have been proposed for such electrostatic speakers (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the electrostatic speaker proposed in Patent Document 1, since an elastic member is inserted between a pair of electrodes made of conductive cloth and the vibrating body, the flexibility of the obtained electrostatic speaker is not necessarily sufficient.

[0005] This invention has been made to solve the above-described conventional problems, and an object thereof is to provide a technique for increasing the flexibility of an electrostatic speaker.

Means for Solving the Problems

[0006] In order to achieve at least a part of the above object, the present invention can be realized in the following forms or application examples.

[0007] [Application Example 1] An electrostatic speaker, comprising: a first conductive cloth which is a conductive woven fabric; second and third conductive cloths which are conductive woven fabrics arranged so as to sandwich the first conductive cloth and are insulated from the first conductive cloth; and first and second exterior cloths which are arranged so as to cover the first to third conductive cloths and are composed of insulating woven fabrics, wherein the first to third conductive cloths and the first and second exterior cloths are sewn with insulating threads, and the first to third conductive cloths are woven fabrics woven from threads obtained by plating a metal on a raw yarn made of a flame-retardant polyamide fiber or an aramid fiber, or woven fabrics woven from a raw yarn containing fine metal wires. At the same time, the second conductive fabric and the third conductive fabric have a lower weaving density than that of the first conductive fabric. An electrostatic speaker characterized by the above.

[0008] According to this application example, since the first to third conductive cloths and the first and second exterior cloths can move in the plane direction within a range allowed by their deformation, expansion and contraction and the deflection of the sewing threads, the flexibility of the electrostatic speaker can be further increased. Also, according to this application example, since a decrease in the flexibility of the conductive fabric can be suppressed, the flexibility of the electrostatic speaker can be made higher.

[0009] [Application Example 2] The electrostatic speaker according to Application Example 1, wherein insulating films are attached to both surfaces of the first conductive cloth.

[0010] According to this application example, it is possible to make it easier to release the sound generated by the vibration of the first conductive cloth serving as a diaphragm to the outside, and to further suppress the vibration of the first conductive cloth.

[0011] [Application Example 3] The electrostatic speaker according to Application Example 2, wherein insulating films are attached to the surfaces of the second and third conductive cloths on the side of the first conductive cloth.

[0012] According to this application example, damage to the insulating film can reduce the possibility of a short circuit between the first conductive cloth and the second or third conductive cloth.

[0015] Application Example 4 Application Examples 1 to 3 A projector screen using an electrostatic speaker described in any of Application Example 4 as a projection surface.

[0016] According to this application example, when winding up a projector screen including an electrostatic speaker, the radius of curvature can be made smaller, so that the size of the projector screen during storage can be made smaller, and the portability and storability of the projector screen can be improved.

[0017] Note that the present invention can be realized in various aspects. For example, it can be realized in aspects such as an electrostatic speaker, a speaker system including the electrostatic speaker and a drive unit of the electrostatic speaker, a projector screen using the electrostatic speaker, a fabric for clothing, bedding, and stuffed toys, and a sound insulation system using the electrostatic speaker or the speaker system.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0019] Hereinafter, the modes for carrying out the present invention will be described in the following order. A. Usage mode of the speaker system: B. Electrical configuration of the speaker system: ​​C. Specific Configuration of Electrostatic Speaker: D. Modification Example:

[0020] A. Usage Mode of Speaker System: FIG. 1 is an explanatory diagram showing the usage mode of a speaker system 10 as an embodiment of the present invention. As shown in FIG. 1, the speaker system 10 of this embodiment has a projector screen 100 (hereinafter also simply referred to as "screen") and a drive unit 200 connected to the screen 100.

[0021] In the usage mode shown in FIG. 1, an audio signal AS is supplied from a video disc player 900 that plays a video disc on which an image is recorded to the drive unit 200. Also, a video signal VS is supplied from the video disc player 900 to a projector (not shown). Then, by irradiating the projection surface 101 of the screen 100 with modulated light modulated by the video signal VS from the projector, a projected image PIM is displayed on the projection surface 101 of the screen 100.

[0022] On the other hand, although details will be described later, the drive unit 200 vibrates and drives the projection surface 101 of the screen 100 based on the supplied audio signal AS. As a result, sound corresponding to the audio signal AS supplied from the video disc player 900 is radiated from the projection surface 101 of the screen 100 in the direction normal to the projection surface 101.

[0023] B. Electrical Configuration of Speaker System: FIG. 2 is an explanatory diagram showing the electrical configuration of the speaker system 10 of this embodiment. As shown in FIG. 2, in the speaker system 10, a drive unit 200 is connected to the projection surface 101 of the screen 100 (FIG. 1) that radiates sound.

[0024] The projection surface 101 has a diaphragm 110 that radiates sound by vibrating, and two electrode films 120 and 130 arranged to face the diaphragm 110 with a gap therebetween. The drive unit 200 connected to the projection surface 101 of the screen 100 has an amplifier circuit 210, a transformer output circuit 220, and a high voltage generation circuit 230.

[0025] The amplifier circuit 210 is composed of a differential amplifier U1 that amplifies the input single-ended signal and outputs a differential signal obtained by combining signals of opposite polarities of + and -. The single-ended audio signal AS input to the amplifier circuit 210 is amplified by the differential amplifier U1 and supplied from the amplifier circuit 210 to the transformer output circuit 220 as a differential audio signal DAS.

[0026] In this embodiment, a differential amplifier U1 that outputs a differential signal is used in the amplifier circuit 210. However, it is also possible to use an amplifier that outputs a single-ended signal similar to the input audio signal AS. However, since the high voltage generation circuit 230 that constitutes the drive unit 200 has a chopper circuit as described later, there is a possibility of generating large noise. In order to reduce the influence of the noise generated in the high voltage generation circuit 230 in this way, it is preferable to use a differential amplifier that outputs a differential signal as the amplifier circuit 210 so as to output a differential audio signal DAS.

[0027] The transformer output circuit 220 has two transformers T1 and T2 of the same configuration. These two transformers T1 and T2 are connected in parallel on the primary side connected to the amplifier circuit 210. On the other hand, on the secondary side connected to the projection surface 101 of the screen 100, the two transformers T1 and T2 are connected in series. Also, the number of turns of the secondary side of the transformers T1 and T2 is set higher than the number of turns of the primary side. As a result, the differential audio signal DAS supplied from the amplifier circuit 210 is boosted to a voltage twice the winding ratio of the transformers T1 and T2 at both ends of the transformers T1 and T2 connected in series and transmitted to the two electrode films 120 and 130 that constitute the projection surface 101.

[0028] The high-voltage generation circuit 230 is a circuit that generates a DC voltage higher than the power supply voltage Vdd, and the generated high-voltage DC voltage is supplied to the transformer output circuit 220 connected to the high-voltage generation circuit 230. In this embodiment, as the high-voltage generation circuit 230, a boost chopper circuit that turns on and off the drain-source of the MOS field-effect transistor Q1 by a rectangular wave generated by the oscillator OSC and generates a high voltage by the back electromotive force of the choke coil L, and a Cockcroft-Walton circuit that boosts using diodes D1 to D6 and capacitors C1 to C6 are combined. However, as the high-voltage generation circuit, various boost circuits such as a boost circuit using a boost chopper circuit or a Cockcroft-Walton circuit alone, or a boost circuit using an oscillator and a flyback transformer can also be used.

[0029] The high-voltage DC voltage generated by the high-voltage generation circuit 230 is supplied between two transformers T1 and T2 connected in series in the transformer output circuit 220. Then, both ends of the transformers T1 and T2 connected in series are connected to two electrode films 120 and 130 on the projection plane 101, and the vibration film 110 is connected to the ground electrode of the transformer output circuit 220 and grounded, so that a high-voltage DC voltage is applied to the two electrode films 120 and 130 with the vibration film 110 as a reference.

[0030] On one hand, as described above, the differential audio signal DAS is boosted at both ends of the transformers T1 and T2 connected in series, and transmitted to the two electrode films 120 and 130 that constitute the projection surface 101. Therefore, voltages with opposite polarities corresponding to the differential audio signal DAS or the audio signal AS are applied to the electrode films 120 and 130 with respect to the vibrating diaphragm 110, and the voltages of the two electrode films 120 and 130 with respect to the vibrating diaphragm 110 vary in opposite directions. The vibrating diaphragm 110 vibrates as a whole in the direction facing the electrode films 120 and 130 in response to the voltage variations of these electrode films 120 and 130, and sound corresponding to the differential audio signal DAS (audio signal AS) is radiated from the vibrating diaphragm 110. Note that, as such, the projection surface 101 composed of the vibrating diaphragm 110 and the two electrode films 120 and 130 has a function of radiating sound by electrostatic action, and can also be referred to as an "electrostatic speaker".

[0031] C. Specific Configuration of Electrostatic Speaker: FIG. 3 is an explanatory diagram showing the specific configuration of the electrostatic speaker 101 (hereinafter simply referred to as "speaker 101"). As described above, as an electrical configuration, the speaker 101 has a vibrating diaphragm 110 and two electrode films 120 and 130 arranged to face the vibrating diaphragm 110 with a gap therebetween. The speaker 101 also has, in addition to these vibrating diaphragm 110 and electrode films 120 and 130, a surface layer cloth 140 on which the projection video image PIM is displayed on the screen 100 (FIG. 1), and a base cloth 150 as a base on which the speaker (projection surface) 101 is attached on the screen 100.

[0032] The vibrating diaphragm 110 is composed of a conductive cloth 111 which is a woven cloth having conductivity, and insulating films 112 and 113 adhered to both surfaces of the conductive cloth 111. The conductive cloth 111 is formed by plating a metal such as copper or aluminum on the raw yarn and weaving the plated raw yarn using a well-known weaving technique.

[0033] As the raw yarn for weaving the conductive fabric 111, chemical fibers such as polyester and acrylic, natural fibers such as cotton and wool, or blended fibers obtained by mixing multiple types of fibers can be used. However, in order to ensure flame retardancy, it is preferable to use flame-retardant polyamide fibers, aramid fibers, or various fibers subjected to flame-retardant treatment as the raw yarn.

[0034] In addition, as the conductive fabric 111, in addition to the woven fabric woven from the plated raw yarn, a woven fabric woven from a raw yarn containing fine metal wires such as copper, or a carbon fiber woven fabric woven using conductive fibers such as carbon fibers as the raw yarn can also be used. However, in terms of suppressing a decrease in the flexibility of the conductive fabric 111, it is preferable to use a woven fabric woven from the plated raw yarn as the conductive fabric 111.

[0035] As the insulating films 112 and 113 adhered to the conductive fabric 111, films made of various resins such as polyester, epoxy, polyimide, or aramid such as polyethylene terephthalate (PET) can be used. Since these insulating films 112 and 113 are adhered to the conductive fabric 111, it is not necessary for them to have strength by themselves. Therefore, if they have sufficient withstand voltage against the high-voltage DC voltage applied to the electrode films 120 and 130, it is preferable to use thinner ones.

[0036] The electrode films 120 and 130 are each composed of a conductive woven fabric, the conductive fabrics 121 and 131, and insulating films 122 and 132 adhered to the diaphragm 110 side. The conductive fabrics 121 and 131 are formed in the same manner as the conductive fabric 111 constituting the diaphragm 110. Also, the insulating films 122 and 132 are formed in the same manner as the insulating films 112 and 113 constituting the diaphragm 110.

[0037] Note that the conductive fabrics 121 and 131 facilitate the external emission of the sound generated by the vibration of the diaphragm 110 through the electrode film 120, and also suppress the suppression of the vibration in the diaphragm 110 by the back pressure between the diaphragm 110 and the electrode film 130. Therefore, it is preferable to set the weaving density of the conductive fabrics 121 and 131 lower than the weaving density of the conductive fabric 111 of the diaphragm 110.

[0038] The surface layer fabric 140 and the base fabric 150 are insulating woven fabrics appropriately selected based on mechanical properties such as strength and other properties so that the function as the screen 100 (FIG. 1) can be realized. To realize the function as the screen 100, for example, the surface layer fabric 140 is subjected to various processes for favorably reflecting the irradiated light on its outer surface, that is, the surface opposite to the electrode film 120. Note that various fibers can be used as the surface layer fabric 140 and the base fabric 150, but in order to ensure the insulation between the electrode films 120 and 130 to which a high-voltage DC voltage is applied and the outside, it is preferable to use fibers with low hygroscopicity such as acrylic fibers and polyamide fibers. Further, since these surface layer fabric 140 and base fabric 150 are woven fabrics provided outside the diaphragm 110 and the electrode films 120 and 130 so as to cover them, they can also be called "outer covering fabrics".

[0039] In this way, the diaphragm 110, the electrode films 120 and 130, the surface layer fabric 140, and the base fabric 150 constituting the speaker 101 are sewn with insulating threads in their stacking direction (the vertical direction in the plane of FIG. 3). Thereby, the speaker 101 in which the diaphragm 110, the electrode films 120 and 130, the surface layer fabric 140, and the base fabric 150 are integrated is formed.

[0040] The connection between the speaker 101 formed in this way and the drive unit 200 is made by sewing the wirings 119, 129, and 139 extending from the ground electrode of the transformer output circuit 220 (Fig. 2) and both ends of the transformers T1 and T2 connected in series to the diaphragm 110 and the electrode films 120 and 130, respectively. In the example of Fig. 3, the wirings 119, 129, and 139 are sewn to the ends of the diaphragm 110 and the electrode films 120 and 130, but the location where the wirings are sewn can be changed as appropriate.

[0041] Also, in this embodiment, the wirings 119, 129, and 139 extending from the transformer output circuit 220 are sewn to the diaphragm 110 and the electrode films 120 and 130, respectively, but it is also possible to connect the speaker 101 and the drive unit 200 by other methods. For example, the wirings 119, 129, and 139 extending from the transformer output circuit 220 may be attached to the diaphragm 110 and the electrode films 120 and 130 using a conductive paste or the like to connect the speaker 101 and the drive unit 200. However, in terms of making the connection between the wirings 119, 129, and 139 and the diaphragm 110 and the electrode films 120 and 130 more reliable and increasing the strength of the connection portion, it is preferable to sew the wirings 119, 129, and 139 to the diaphragm 110 and the electrode films 120 and 130.

[0042] In the speaker 101 of this embodiment configured as described above, the diaphragm 110, the electrode films 120 and 130, the surface layer cloth 140, and the base cloth 150 are in a state of being sewn to each other. Therefore, the diaphragm 110, the electrode films 120 and 130, the surface layer cloth 140, and the base cloth 150 can move in the plane direction, that is, in the direction orthogonal to the stacking direction, within the range allowed by their deformation, expansion and contraction, and the deflection of the sewing thread. Since the diaphragm 110, the electrode films 120 and 130, the surface layer cloth 140, and the base cloth 150 can move in the plane direction in this way, the flexibility of the speaker 101 is increased, so that the radius of curvature when winding up the cloth portion of the screen including the speaker 101 can be made smaller. Therefore, the size of the screen 100 at the time of storage can be made smaller, and the portability and storability of the screen 100 can be made higher.

[0043] Further, by using the speaker 101 of this embodiment, as shown in FIG. 1, on the projection surface 101 of the screen 100, a projection video PIM corresponding to the video signal VS supplied from the video disc player 900 is displayed, and at the same time, sound corresponding to the audio signal AS supplied from the video disc player 900 is radiated from the projection surface (speaker) 101. Therefore, it is possible to conduct a presentation video screening or a remote conference without preparing a speaker separate from the screen 100.

[0044] And in the speaker 101 of this embodiment, since sound is radiated by the entire diaphragm 110 vibrating, the sound is radiated as a plane wave in the stacking direction of the diaphragm 110 and the electrode films 120 and 130, that is, in the normal direction of the speaker 101. As a result, since the sound is intensively radiated in the normal direction of the speaker 101, according to the speaker 101 of this embodiment, it is possible to limit the target viewers when screening a presentation video or the like.

[0045] Furthermore, since the sound corresponding to the audio signal AS is emitted from the projection surface (speaker) 101 on which the projection video PIM is displayed, when the projection video PIM includes an image of a speaker or the like as shown in FIG. 1, the viewer of the projection video PIM can feel as if the speaker is emitting the sound. Therefore, the sense of presence of a presentation video or a remote conference can be enhanced more.

[0046] Note that in the present embodiment shown in FIG. 1, the portable screen 100 used for presentations and remote conferences is employed, but the present invention can also be applied to a stationary screen used in a home theater or the like. Even in this case, since the sound is radiated from the screen on which the video is displayed, the sense of presence is enhanced, so that a good sense of immersion can be given to the viewer of the video.

[0047] In addition, when the screen (speaker) to which the present invention is applied is used in a home theater or the like that performs audio reproduction in a surround system, the screen itself can be used as a center speaker disposed on the screen side. In this case, the arrangement of a separate center speaker can be omitted, so that the degree of freedom in arranging the screen can be increased more.

[0048] Furthermore, by appropriately adjusting the weaving density of the conductive cloths 111, 121, 131 constituting the diaphragm 110 and the electrode films 120, 130, and the surface cloth 140 and the base cloth 150, it becomes possible to allow the sound to pass well from the base cloth 150 side to the surface cloth 140 side. In this way, the center high speaker disposed above the screen side can be disposed behind the screen, so that the degree of freedom in arranging the screen can be further increased.

[0049] D. Modification Example: The present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

[0050] D1. Modification Example 1: In the above embodiment, the insulating films 122 and 132 are provided on each of the electrode films 120 and 130, but these insulating films 122 and 132 can be omitted. In this case, the emission of the sound generated by the vibration of the diaphragm 110 to the outside becomes easier, and the suppression of the vibration of the diaphragm 110 is more suppressed.

[0051] Also, the insulating films 112 and 113 provided on the diaphragm 110 may be omitted, and insulating films 122 and 132 may be provided on each of the electrode films 120 and 130. Generally, it is only necessary that the space between the diaphragm 110 and the electrode films 120 and 130 can be insulated, and the insulating films may be provided on at least one of the diaphragm 110 and one of the electrode films 120, and at least one of the diaphragm 110 and the other electrode film 120, respectively.

[0052] However, by providing the insulating films 112 and 113 on both sides of the diaphragm 110 and providing the insulating films 122 and 132 on each of the electrode films 120 and 130, the possibility of a short circuit between the diaphragm 110 and the electrode films 120 and 130 due to damage to these insulating films 112, 113, 122, and 132 can be reduced. Therefore, as in the above embodiment, it is preferable to provide the insulating films 112 and 113 on both sides of the diaphragm 110 and provide the insulating films 122 and 132 on each of the electrode films 120 and 130.

[0053] D2. Modification Example 2: In the above embodiment, since the present invention is applied to the screen 100, the surface layer cloth 140 subjected to various processes for reflecting the irradiated light well is arranged outside the electrode film 120 side, and the base cloth 150 serving as the base of the screen 100 is arranged outside the electrode film 130 side. However, the function as a speaker according to the present invention is not necessarily applied only to the projector screen.

[0054] For example, the speaker according to the present invention can also be attached to clothing. In this case, instead of a headset, the clothing itself can be used for hands-free calls. Further, in a pillow, a stuffed toy, etc., at least a part of the outer skin can be made of the speaker according to the present invention to generate sound. When used in a pillow, a stuffed toy, etc., it is difficult to reduce the size of a general speaker, and since the speaker itself is hard, the usability of a pillow, a stuffed toy, etc. deteriorates. However, since the speaker according to the present invention is mainly composed of a woven fabric, it is possible to suppress a decrease in usability due to attaching the speaker.

[0055] Furthermore, the speaker according to the present invention can also be used as wallpaper for a building. In this case, since it is possible to generate sound throughout the wallpaper, if sound is generated so as to cancel out noise from an adjacent room in an apartment house, it is possible to construct a soundproofing system that can satisfactorily remove noise from the adjacent room. Also in this case, according to the speaker according to the present invention mainly composed of a woven fabric, it is easy to construct according to the unevenness of the wall surface and it can be used more appropriately as wallpaper.

Description of Reference Numerals

[0056] 10…Speaker system 100…Screen (projector screen) 101…Speaker (projection surface) 110…Diaphragm 111…Conductive cloth 112, 113…Insulating film 119…Wiring 120, 130…Electrode film 121, 131…Conductive cloth 122, 132…Insulating film 129, 139…Wiring 140…Surface layer cloth 150…Base cloth 200…Drive unit 210…Amplification circuit 220…Transformer output circuit 230…High voltage generation circuit 900…Video Disc Player AS…Audio Signal C1~C6…Capacitor D1~D6…Diode DAS…Differential Audio Signal L…Choke Coil OSC…Oscillator PIM…Projection Image Q1…MOS Field-Effect Transistor T1,T2…Transformer U1…Differential Amplifier VS…Video Signal

Claims

1. An electrostatic speaker, comprising: a first conductive cloth which is a conductive woven fabric; second and third conductive cloths which are conductive woven fabrics arranged so as to sandwich the first conductive cloth and are insulated from the first conductive cloth; first and second exterior cloths which are arranged so as to cover the first to third conductive cloths and are composed of insulating woven fabrics; wherein the first to third conductive cloths and the first and second exterior cloths are sewn together with insulating threads, and the first to third conductive cloths are woven fabrics woven from threads obtained by plating a metal on a raw yarn made of a flame-retardant polyamide fiber or an aramid fiber, or woven fabrics woven from a raw yarn containing fine metal wires, and the second and third conductive cloths have a lower weaving density than that of the first conductive cloth.

2. The electrostatic speaker according to Claim 1, wherein insulating films are attached to both surfaces of the first conductive cloth.

3. The electrostatic speaker according to Claim 2, wherein insulating films are attached to the surfaces of the second and third conductive cloths on the side of the first conductive cloth.

4. A projector screen using the electrostatic speaker according to any one of Claims 1 to 3 as a projection surface.

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