JP7709211B2 - Electrostatic Speaker - Google Patents

Description

This invention relates to an electrostatic speaker, and in particular to an electrostatic speaker with excellent flexibility.

Electrostatic speakers are known as speakers that generate sound in response to an electrical signal. Electrostatic speakers are generally composed of a pair of electrodes facing each other with a gap between them, and a sheet-like conductive vibrating body inserted between the pair of electrodes. When a predetermined bias voltage is applied to the vibrating body, the voltage applied to the electrodes is changed in response to the electrical signal, causing the vibrating body to displace in response to the electrical signal, generating sound. In recent years, various technologies have been proposed that allow such electrostatic speakers to bend (see, for example, Patent Document 1).

JP 2009-100438 A

However, in the electrostatic speaker proposed in Patent Document 1, an elastic member is inserted between the pair of electrodes made of conductive cloth and the vibrating body, so the flexibility of the resulting electrostatic speaker is not necessarily sufficient.

In addition, even if it is possible to give an electrostatic speaker a certain degree of flexibility, if wrinkles or other imperfections occur in the electrostatic speaker, it becomes difficult to use the electrostatic speaker effectively.

The present invention was made to solve the above-mentioned problems in the conventional technology, and aims to provide technology that increases the flexibility of electrostatic speakers and enables more effective use of electrostatic speakers.

In order to achieve at least part of the above objectives, the present invention can be realized in the following forms or application examples.

[Application Example 1]
1. An electrostatic speaker comprising: a first conductive cloth, which is a conductive cloth; second and third conductive cloths arranged to sandwich the first conductive cloth and insulated from the first conductive cloth; and first and second exterior cloths arranged to cover the first, second and third conductive cloths, which are thicker than the first, second and third conductive cloths and are made of insulating cloth, wherein the first, second and second exterior cloths are sewn together with insulating thread, and each end of the first, second and third conductive cloths is treated to prevent fraying, and an insulating protective cloth is attached to cover each end of the first, second and third conductive cloths .

According to this application example, the first to third conductive cloths and the first and second exterior cloths are movable in the planar direction within the range allowed by their deformation and expansion/contraction and the bending of the sewing thread, so that the flexibility of the electrostatic speaker can be increased. Furthermore, by constructing the first and second exterior cloths from fabrics thicker than the first to third conductive cloths, the occurrence of wrinkles and the like in the electrostatic speaker is suppressed, so that the electrostatic speaker can be used more effectively.
Furthermore, according to this application example, it is possible to prevent a short circuit from occurring between the first to third conductive cloths due to conductive threads frayed from the first to third conductive cloths.
Furthermore, according to this application example, even if the electrostatic speaker is repeatedly bent and frayed, the effect of the frayed conductive threads is suppressed, thereby making it possible to further increase the durability of the electrostatic speaker.

[Application Example 2]
An electrostatic speaker according to Application Example 1, wherein the electrostatic speaker is configured to be wound up with the first exterior cloth positioned more inward than the second exterior cloth, the first exterior cloth has elasticity in the winding direction in which the electrostatic speaker is wound up, and the ends of the first and second exterior cloths are sewn together such that the length of the first exterior cloth in the winding direction is its natural length when the electrostatic speaker is wound up.

According to this application example, the occurrence of wrinkles and the like on the outer surface of the electrostatic speaker is more reliably suppressed in both the rolled-up state in which it is rolled up for storage, etc., and the unrolled state in which it is unrolled for use, etc., making it easier to more effectively utilize the electrostatic speaker, whose inner and outer peripheries in the rolled-up state are predetermined.

[Application Example 3]
An electrostatic speaker according to Application Example 2, wherein the first to third conductive cloths are stretchable in the winding direction, and the ends of the first to third conductive cloths and the first and second exterior cloths are sewn together such that the lengths of the first to third conductive cloths in the winding direction are natural lengths when the electrostatic speaker is wound up.

This application example prevents wrinkles from forming in the first to third conductive cloths involved in the generation of sound, making it possible to more reliably radiate sound as a plane wave from the electrostatic speaker.

[Application Example 6]
The electrostatic speaker according to any one of the first to third aspects, wherein the first and second exterior fabrics are formed of fibers that are more positive than paper in the triboelectric series.

Generally, fibers that are more positive than paper in the triboelectric series are hygroscopic and therefore less susceptible to static electricity accumulation. Therefore, according to this application example, the application of a high-voltage DC voltage suppresses the accumulation of static electricity in the surface fabric 140 and the base fabric 150, reducing the possibility of discharge occurring between the electrostatic speaker and a user who comes into contact with the electrostatic speaker due to accumulated static electricity.

The present invention can be realized in various ways. For example, it can be realized in an electrostatic speaker, a speaker system including the electrostatic speaker and a drive unit for the electrostatic speaker, a projector screen using the electrostatic speaker, a soundproofing system using the electrostatic speaker or speaker system, etc.

FIG. 1 is an explanatory diagram showing a usage mode of a speaker system according to an embodiment of the present invention. FIG. 1 is an explanatory diagram showing an electrical configuration of a speaker system according to a first embodiment. FIG. 2 is an explanatory diagram showing a specific configuration of the speaker according to the first embodiment. FIG. 11 is an explanatory diagram showing a specific configuration of a speaker according to the second embodiment. FIG. 13 is an explanatory diagram showing a specific configuration of a speaker according to the third embodiment. 4A and 4B are explanatory diagrams showing the speaker in a rolled-up state and an unrolled state, respectively.

Hereinafter, embodiments of the present invention will be described in the following order.
A. First embodiment:
A1. How to use the speaker system:
A2. Electrical configuration of the speaker system:
A3. Specific configuration of electrostatic speaker:
B. Second embodiment:
C. Third embodiment:
D. Variations:

A. First embodiment:
A1. How to use the speaker system:
Fig. 1 is an explanatory diagram showing a usage mode of a speaker system 10 according to a first embodiment of the present invention. As shown in Fig. 1, the speaker system 10 according to the first embodiment has a pull-out type projector screen 100 (hereinafter also simply referred to as "screen") having a winding mechanism, and a drive unit 200 connected to the screen 100.

In the usage mode shown in FIG. 1, an audio signal AS is supplied to the drive unit 200 from a video disc player 900 that plays a video disc on which video is recorded. A video signal VS is also supplied from the video disc player 900 to a projector (not shown). Then, the projector irradiates modulated light modulated by the video signal VS onto the projection surface 101 of the screen 100, thereby displaying a projected image PIM on the projection surface 101 of the screen 100.

Meanwhile, as will be described in detail later, the drive unit 200 drives the projection surface 101 of the screen 100 to vibrate 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 emitted from the projection surface 101 of the screen 100 in the normal direction of the projection surface 101.

A2. Electrical configuration of the speaker system:
Fig. 2 is an explanatory diagram showing the electrical configuration of the speaker system 10 of the first embodiment. As shown in Fig. 2, in the speaker system 10, a drive unit 200 is connected to a projection surface 101 of a screen 100 (Fig. 1) that radiates sound.

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

The amplifier circuit 210 is composed of a differential amplifier U1 that amplifies the input single-ended signal and outputs a differential signal that combines signals of opposite polarity (+ and -). The single-ended audio signal AS input to the amplifier circuit 210 is amplified by the differential amplifier U1 and is supplied from the amplifier circuit 210 to the transformer output circuit 220 as a differential audio signal DAS.

In the first embodiment, the amplifier circuit 210 uses a differential amplifier U1 that outputs a differential signal, but 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 generating circuit 230 that constitutes the drive unit 200 has a chopper circuit as described below, there is a possibility that large noise will be generated. In order to reduce the influence of the noise generated in the high-voltage generating circuit 230 in this way, it is preferable to use a differential amplifier that outputs a differential signal as the amplifier circuit 210 and output the differential audio signal DAS.

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. In addition, the number of turns on the secondary side of the transformers T1 and T2 is set higher than the number of turns on 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 series-connected transformers T1 and T2, and is transmitted to the two electrode films 120 and 130 that constitute the projection surface 101.

The high voltage generating 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 generating circuit 230. In the first embodiment, the high voltage generating circuit 230 uses a boost circuit that combines a boost chopper circuit that turns on/off the drain-source of a MOS field effect transistor Q1 using a rectangular wave generated by an oscillator OSC to generate high voltage using the back electromotive force of a choke coil L, and a Cockcroft-Walton circuit that boosts the voltage using diodes D1 to D6 and capacitors C1 to C6. However, it is also possible to use various boost circuits as the high voltage generating circuit, such as a boost circuit that uses a boost chopper circuit or a Cockcroft-Walton circuit alone, or a boost circuit that uses an oscillator and a flyback transformer.

The high-voltage DC voltage generated by the high-voltage generating circuit 230 is supplied between two transformers T1, T2 connected in series in the transformer output circuit 220. Then, by connecting both ends of the series-connected transformers T1, T2 to the two electrode films 120, 130 of the projection surface 101 and connecting the diaphragm 110 to the ground electrode of the transformer output circuit 220 for grounding, a high-voltage DC voltage is applied to the two electrode films 120, 130 with the diaphragm 110 as the reference.

On the other hand, as described above, the differential audio signal DAS is boosted at both ends of the series-connected transformers T1 and T2 and transmitted to the two electrode films 120 and 130 that constitute the projection surface 101. Therefore, voltages of opposite polarities according to the differential audio signal DAS or audio signal AS are applied to the electrode films 120 and 130 with respect to the diaphragm 110 as a reference, and the voltages of the two electrode films 120 and 130 relative to the diaphragm 110 fluctuate in opposite directions. The diaphragm 110 vibrates as a whole in the opposing direction of the electrode films 120 and 130 in response to the voltage fluctuations of the electrode films 120 and 130, and sound according to the differential audio signal DAS (audio signal AS) is emitted from the diaphragm 110. In this way, the projection surface 101 consisting of the diaphragm 110 and the two electrode films 120 and 130 has the function of emitting sound by electrostatic action, so it can also be called an "electrostatic speaker".

A3. Specific configuration of electrostatic speaker:
3 is an explanatory diagram showing a specific configuration of the electrostatic speaker 101 (hereinafter simply referred to as "speaker 101") of the first embodiment. As described above, the speaker 101 has, as an electrical configuration, a diaphragm 110 and two electrode films 120 and 130 arranged to face the diaphragm 110 with a gap therebetween. In addition to the diaphragm 110 and the electrode films 120 and 130, the speaker 101 also has a surface cloth 140 on which the projected 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.

The diaphragm 110 is composed of conductive cloth 111, which is a woven cloth having electrical conductivity, and insulating films 112, 113 adhered to both sides of the conductive cloth 111. The conductive cloth 111 is formed by plating raw threads with a metal such as copper or aluminum, and weaving the plated raw threads using well-known weaving techniques.

The raw yarn for weaving the conductive cloth 111 can be chemical fibers such as polyester or acrylic, natural fibers such as cotton or wool, or a blended fiber made by mixing multiple types of fibers. However, to ensure flame retardancy, it is preferable to use flame-retardant polyamide fibers or aramid fibers, or various fibers that have been treated to make them flame-retardant, as the raw yarn.

In addition to woven cloth made of plated raw yarn, the conductive cloth 111 may be woven cloth made of thin metal wires or metal threads such as copper, a mesh made of metal such as copper, woven cloth made of raw yarns containing thin metal wires such as copper, or carbon fiber woven cloth made of conductive fibers such as carbon fiber. However, it is preferable to use woven cloth made of plated raw yarns as the conductive cloth 111, since it is possible to suppress a decrease in the flexibility of the conductive cloth 111. In addition, since plated raw yarns, raw yarns containing thin metal wires, and raw yarns made of conductive fibers such as carbon fiber are all conductive, they can also be called "conductive raw yarns".

The insulating films 112, 113 that are adhered to the conductive cloth 111 can be films made of various resins, such as polyesters such as polyethylene terephthalate (PET), epoxy, polyimide, or aramid. Since these insulating films 112, 113 are adhered to the conductive cloth 111, they do not need to ensure their own strength. Therefore, it is preferable to use thinner films as long as they have sufficient voltage resistance to the high-voltage DC voltage applied to the electrode films 120, 130.

The electrode films 120 and 130 are each composed of conductive cloth 121 and 131, which is a woven cloth having electrical conductivity, and insulating films 122 and 132, which are adhered to the vibration membrane 110 side. The conductive cloth 121 and 131 are formed in the same manner as the conductive cloth 111 that constitutes the vibration membrane 110. The insulating films 122 and 132 are also formed in the same manner as the insulating films 112 and 113 that constitute the vibration membrane 110.

The conductive cloths 121, 131 facilitate the release of sound generated by the vibration of the diaphragm 110 to the outside through the electrode film 120, and also prevent the vibration of the diaphragm 110 from being suppressed by the back pressure between the diaphragm 110 and the electrode film 130. Therefore, it is preferable to set the weave density of the conductive cloths 121, 131 lower than the weave density of the conductive cloth 111 of the diaphragm 110.

The surface cloth 140 and the base cloth 150 are insulating woven cloths that are appropriately selected based on mechanical properties such as strength and other properties so that they can function as the screen 100 (Figure 1). The surface cloth 140 and base cloth 150 are woven cloths that are provided on the outside of the vibration membrane 110 and the electrode membranes 120 and 130 so as to cover them, and therefore can also be called "exterior cloths."

For both the surface cloth 140 and the base cloth 150, a thicker woven cloth is used than the conductive cloths 111, 121, and 131. Here, a thick woven cloth refers to a woven cloth that is thick and taut. Examples of such thick woven cloth include denim and canvas. To give the surface cloth 140 and base cloth 150 thickness, the surface cloth 140 and base cloth 150 may be formed by weaving thick raw yarn of, for example, 7.5 or 10 count, or may be formed by multiple weaving such as double weaving or triple weaving.

Although various fibers can be used as the raw yarns for weaving the surface fabric 140 and the base fabric 150, it is preferable to use fibers that are easily positively charged, that is, fibers that are more positive than paper in the triboelectric series. It is also possible to form the surface fabric 140 and the base fabric 150 by weaving raw yarns that are a blend of multiple types of fibers that are easily positively charged. Examples of fibers that are easily positively charged include natural fibers such as hemp, cotton, and wool, and polyamide fibers such as acetate fibers and nylon.

Generally, fibers that are easily positively charged have hygroscopic properties and are therefore less likely to accumulate static electricity. Therefore, by forming the surface cloth 140 and the base cloth 150 using fibers that are easily positively charged, the accumulation of static electricity in the surface cloth 140 and the base cloth 150 due to the application of a high-voltage DC voltage to the electrode films 120, 130 (conductive cloths 121, 131) is suppressed, thereby reducing the possibility of discharge occurring between the user who comes into contact with the speaker 101 due to accumulated static electricity.

The above description shows an example of the use of the speaker 101 of the first embodiment in which the speaker 101 is applied to the projector screen 100. In this way, when the speaker 101 is applied to the projector screen 100, in order to realize the function of the screen 100 in the speaker 101, for example, various types of processing are applied as necessary to the outer surface of the surface fabric 140, i.e., the surface opposite the electrode film 120, in order to effectively reflect the irradiated light.

The diaphragm 110, electrode films 120, 130, surface cloth 140, and base cloth 150 that make up the speaker 101 are sewn together with insulating thread in the stacking direction (the up-down direction on the paper surface of FIG. 3). This forms the speaker 101 in which the diaphragm 110, electrode films 120, 130, surface cloth 140, and base cloth 150 are integrated.

The connection between the speaker 101 thus formed and the drive unit 200 is made by sewing the wires 119, 129, 139 extending from the ground electrode of the transformer output circuit 220 (FIG. 2) and both ends of the series-connected transformers T1, T2 to the diaphragm 110 and the electrode films 120, 130, respectively. Note that in the example of FIG. 3, the wires 119, 129, 139 are sewn to the ends of the diaphragm 110 and the electrode films 120, 130, but the locations where the wires are sewn can be changed as appropriate.

In the first embodiment, the wiring 119, 129, 139 extending from the transformer output circuit 220 is sewn to the diaphragm 110 and the electrode films 120, 130, respectively, but it is also possible to connect the speaker 101 and the drive unit 200 by other methods. For example, the wiring 119, 129, 139 extending from the transformer output circuit 220 may be attached to the diaphragm 110 and the electrode films 120, 130 using a conductive paste or the like to connect the speaker 101 and the drive unit 200. However, it is preferable to sew the wiring 119, 129, 139 to the diaphragm 110 and the electrode films 120, 130, in order to make the connection between the wiring 119, 129, 139 and the diaphragm 110 and the electrode films 120, 130 more reliable and to increase the strength of the connection portion.

In the speaker 101 of the first embodiment configured in this manner, the diaphragm 110, the electrode films 120, 130, the surface cloth 140, and the base cloth 150 are sewn together. Therefore, the diaphragm 110, the electrode films 120, 130, the surface cloth 140, and the base cloth 150 are movable in the surface direction, i.e., in the direction perpendicular to the stacking direction, within the range permitted by their deformation and expansion/contraction and the bending of the sewing thread. Since the diaphragm 110, the electrode films 120, 130, the surface cloth 140, and the base cloth 150 are movable in the surface direction in this manner, the flexibility of the speaker 101 is increased, and the radius of curvature when the cloth portion of the screen including the speaker 101 is rolled up can be made smaller. Therefore, the size of the screen 100 when stored can be made smaller, and the portability and storability of the screen 100 can be improved.

Furthermore, in the speaker 101 of the first embodiment, the surface cloth 140 and the base cloth 150 are made of a thick woven cloth that is thicker and firmer than the conductive cloths 111, 121, and 131. This prevents wrinkles from forming on the projection surface (speaker) 101 when the projector screen 100 is in use (Figure 1), making it possible to more appropriately display the projected image PIM.

In addition, by making the surface cloth 140 and the base cloth 150 out of thick woven fabric, the insulation between the conductive cloths 121, 131 to which the high-voltage DC voltage is applied and the outer surface of the speaker 101 is increased. This reduces the risk of the high-voltage DC voltage applied to the conductive cloths 121, 131 leaking to the outside.

In addition, by using the speaker 101 of the first embodiment, as shown in FIG. 1, a projected image PIM corresponding to a video signal VS supplied from a video disc player 900 is displayed on the projection surface 101 of the screen 100, and sound corresponding to an audio signal AS supplied from the video disc player 900 is emitted from the projection surface (speaker) 101. Therefore, it is possible to broadcast a presentation video or hold a remote conference without preparing a speaker separate from the screen 100.

In the speaker 101 of the first embodiment, sound is emitted by vibrating the entire diaphragm 110, so sound is emitted as a plane wave in the stacking direction of the diaphragm 110 and the electrode films 120, 130, i.e., in the normal direction of the speaker 101. As a result, sound is emitted intensively in the normal direction of the speaker 101, so the speaker 101 of the first embodiment makes it possible to limit the target audience when broadcasting a presentation video, etc.

Furthermore, the sound corresponding to the audio signal AS is emitted from the projection surface (speaker) 101 on which the projected image PIM is displayed, so if the projected image PIM contains an image of a speaker, etc., as shown in FIG. 1, the viewer of the projected image PIM can feel as if the speaker is actually making the sound. This can enhance the sense of realism of presentation videos and remote conferences.

In the first embodiment shown in FIG. 1, a portable screen 100 is used for presentations and remote conferences, but the present invention can also be applied to a stationary screen used in a home theater or the like. Even in this case, the sense of realism is enhanced by the sound being emitted from the screen on which the video is displayed, so that the viewer of the video can feel a good sense of immersion.

In addition, when a screen (speaker) to which this invention is applied is used in a home theater or the like that reproduces sound in surround sound, the screen itself can be used as a center speaker placed on the screen side. In this case, the placement of a separate center speaker can be omitted, allowing for greater freedom in screen placement.

Furthermore, by appropriately adjusting the weave density of the conductive fabrics 111, 121, 131 constituting the diaphragm 110 and the electrode films 120, 130, and the surface fabric 140 and base fabric 150, it is possible to transmit sound well from the base fabric 150 side to the surface fabric 140 side. In this way, the speaker can be placed behind the screen, further increasing the freedom of screen placement.

B. Second embodiment:
4 is an explanatory diagram showing a specific configuration of the speaker 101a in the second embodiment. The second embodiment differs from the first embodiment in that the configuration of the speaker 101a is different. The other configurations are the same as those in the first embodiment, so the description thereof will be omitted here.

Specifically, the speaker 101a of the second embodiment differs from the speaker 101 of the first embodiment shown in FIG. 3 in that protective cloths 114a, 124a, and 134a, which are insulating woven cloths, are attached to the ends of the diaphragm 110a and the electrode films 120a and 130a, respectively. Note that, for convenience, FIG. 4 omits the attachment portions of the wiring 119, 129, and 139 (FIG. 3) to the diaphragm 110a and the electrode films 120a and 130a.

As shown in FIG. 4, the protective cloths 114a, 124a, and 134a are attached so as to wrap the ends of the vibration membrane 110a and the electrode membranes 120a and 130a. The protective cloths 114a, 124a, and 134a are attached to the ends of the vibration membrane 110a and the electrode membranes 120a and 130a by, for example, sewing them with insulating thread.

The protective cloths 114a, 124a, and 134a are formed by weaving raw yarns made of chemical fibers such as polyester and acrylic, natural fibers such as cotton and wool, or blended fibers made by mixing multiple types of fibers. However, to ensure flame retardancy, it is preferable to use flame-retardant polyamide fibers or aramid fibers, or various fibers that have been treated to make them flame-retardant, as the raw yarns.

When the speaker 101a is used, the ends of the conductive cloths 111, 121, and 131 that constitute the diaphragm 110a and the electrode films 120a and 130a may fray. However, in the second embodiment, as shown in FIG. 4, the protective cloths 114a, 124a, and 134a prevent the exposure of frayed conductive threads from the conductive cloths 111, 121, and 131. This prevents short circuits between the conductive cloths 111, 121, and 131 through the frayed threads. In addition, by preventing the exposure of frayed threads, the risk of the high voltage DC voltage applied to the conductive cloths 121 and 131 leaking to the outside can be reduced.

In the example of FIG. 4, the protective cloths 114a, 124a, and 134a are used to cover the ends of the conductive cloths 111, 121, and 131 (the vibration membrane 110a and the electrode membranes 120a and 130a), thereby preventing exposure of frayed threads from the conductive cloths 111, 121, and 131, preventing short circuits between the conductive cloths 111, 121, and 131, and preventing leakage of high-voltage DC voltage applied to the conductive cloths 121 and 131 to the outside. This reduces the effect of frayed threads from the conductive cloths 111, 121, and 131, so the speaker 101a of the second embodiment can be considered to have been subjected to a fraying prevention process that prevents fraying of the conductive cloths 111, 121, and 131.

In this way, from the viewpoint of preventing fraying of the conductive cloths 111, 121, and 131, it is possible to realize anti-fraying processing by using a configuration other than the configuration in which the ends of the conductive cloths 111, 121, and 131 are wrapped with protective cloths 114a, 124a, and 134a shown in the example of Figure 4.

For example, fraying of the conductive cloths 111, 121, and 131 can be suppressed by applying an anti-fraying liquid to the ends of the conductive cloths 111, 121, and 131. For example, a commercially available anti-fraying liquid in which nylon is dissolved in ethanol can be used as the anti-fraying liquid to be applied. In addition, if the raw yarns used to weave the conductive cloths 111, 121, and 131 are fibers having thermoplastic properties, fraying of the conductive cloths 111, 121, and 131 can also be suppressed by heating the ends of the conductive cloths 111, 121, and 131 to weld the raw yarns at the ends.

However, if anti-fraying liquid is applied to the ends of the conductive cloths 111, 121, and 131, or if the raw threads at the ends of the conductive cloths 111, 121, and 131 are welded, the number of times the speaker is bent may increase, which may reduce the effect of preventing fraying. For this reason, it is preferable to perform the anti-fraying process by attaching protective cloths 114a, 124a, and 134a to the conductive cloths 111, 121, and 131 so as to wrap the ends of the conductive cloths 111, 121, and 131, as in the second embodiment. In this way, even if the speaker is repeatedly bent and fraying occurs, the effect of the frayed conductive threads is suppressed, making it possible to increase the durability of the speaker 101a.

C. Third embodiment:
Fig. 5 is an explanatory diagram showing a specific configuration of a speaker 101b in the third embodiment. The speaker 101b in the third embodiment differs from the speaker 101 in the first embodiment in that the configurations of the diaphragm 110b, the electrode films 120b, 130b, and the surface cloth 140b are different. The other configurations are the same as those in the first embodiment, so the description thereof will be omitted here. Also, in Fig. 5, for convenience, the attachment portions of the wirings 119, 129, 139 (Fig. 3) to the diaphragm 110b and the electrode films 120b, 130b are omitted from the illustration.

Specifically, the speaker 101b of the third embodiment differs from the speaker 101 of the first embodiment in that the conductive fabrics 111b, 121b, 131b constituting the diaphragm 110b and the electrode films 120b, 130b, and the surface fabric 140b are made of stretchable knitted fabrics (knits).

The conductive cloths 111b, 121b, and 131b are formed by knitting conductive yarns selected in the same manner as in the first embodiment using known knitting techniques. The surface cloth 140b is formed by knitting insulating yarns selected in the same manner as in the first embodiment.

The conductive cloths 111b, 121b, 131b and the surface cloth 140b are formed so that the direction in which they have high elasticity coincides with the winding direction when the speaker 101b is wound up, i.e., they are formed so that they have elasticity in the winding direction.

The insulating films 112b, 113b, 122b, 132b that are adhered to the conductive cloths 111b, 121b, 131b are made of a resin that is easily stretchable, such as polyurethane, polyurea, polyurethane urea, polybutadiene, or silicone, so that the elasticity of the conductive cloths 111b, 121b, 131b is not hindered and the vibration membrane 110b and the electrode membranes 120b, 130b have elasticity. As a result, in the speaker 101b of the third embodiment, the vibration membrane 110b, the electrode membranes 120b, 130b, and the surface cloth 140b that constitute the speaker 101b have elasticity in the winding direction.

6 is an explanatory diagram showing the state of the speaker 101b in each of the wound state and the deployed state. FIG. 6(a) shows the state of the speaker 101b in the wound state, i.e., the state in which the speaker 101b is wound for storage, etc., and FIG. 6(b) shows the state of the speaker 101b in the deployed state, i.e., the state in which the speaker 101b is pulled out for use, etc. Specifically, FIG. 6(a) and FIG. 6(b) show the state of the diaphragm 110b, the electrode films 120b, 130b, and the surface cloth 140b at the end surrounded by the dashed line and the middle portion surrounded by the dashed line in the wound state and the deployed state, respectively. As can be seen from FIG. 6, in the third embodiment, the speaker 101b is wound so that the surface cloth 140b is on the inner periphery side and the base cloth 150 is on the outer periphery side.

In the wound state shown in FIG. 6(a), the vibration membrane 110b, the electrode films 120b, 130b, the surface cloth 140b, and the base cloth 150 are sewn at the ends so that the stretchable vibration membrane 110b, the electrode films 120b, 130b, and the surface cloth 140b have their natural lengths in the winding direction. Therefore, in the wound state, the vibration membrane 110b, the electrode films 120b, 130b, the surface cloth 140b, and the base cloth 150 that constitute the speaker 101b all have their natural lengths in the winding direction. This prevents the inner surface cloth 140b and the electrode film 120b from bending when the speaker 101b is wound up, and prevents wrinkles from occurring in the speaker 101b.

On the other hand, when the rolled up speaker 101b is pulled out and deployed, the vibration membrane 110b, the electrode films 120b, 130b, and the surface cloth 140b are stretchable, so the vibration membrane 110b, the electrode films 120b, 130b, and the surface cloth 140b stretch in the winding direction due to the difference in circumference with the base cloth 150. Therefore, the difference in circumference causes the outer peripheral base cloth 150 and the electrode film 130b to bend, preventing the speaker 101b from wrinkling.

In this way, in the third embodiment, the exterior cloth (i.e., the surface cloth 140b) located on the inner periphery in the rolled-up state, the vibration membrane 110b, and the electrode membranes 120b and 130b have elasticity in the rolled-up direction, so that the occurrence of wrinkles in the speaker 101b is suppressed in both the rolled-up and unrolled states.

In the third embodiment, the speaker 101b is wound up so that the surface fabric 140b is on the inner periphery, so the surface fabric 140b is made of a stretchable knitted fabric. However, if the speaker 101b is wound up so that the base fabric is on the inner periphery, the base fabric is made of a stretchable knitted fabric.

In the third embodiment, the speaker 101b is applied to a pull-out type projector screen 100 (FIG. 1) that has a winding mechanism, so the inner and outer peripheries in the rolled up state are predetermined. However, when applied to a projector screen that does not have a winding mechanism, such as a hanging curtain type or a hanging picture type projector screen, the inner and outer peripheries in the rolled up state are not determined. In such a case, if both the surface cloth and the base cloth are made of stretchable knitted cloth, the occurrence of wrinkles in the speaker is suppressed in both the rolled up state and the unfolded state. In this case, the diaphragm, the two electrode films, the surface cloth, and the base cloth are all sewn at their ends so that the length in the rolled up direction is the natural length when the speaker is unfolded.

In addition, in the third embodiment, in addition to the surface cloth 140b, the vibration membrane 110b (conductive cloth 111b) and the electrode membranes 120b, 130b (conductive cloths 121b, 131b) are made elastic, but it is also possible to make only the surface cloth 140b elastic. Even in this way, the occurrence of wrinkles on the outer surface of the speaker is suppressed, making it possible to more appropriately display the projected image PIM (Figure 1).

However, by making the diaphragm 110b (conductive cloth 111b) and the electrode films 120b, 130b (conductive cloth 121b, 131b) elastic, the occurrence of wrinkles in the diaphragm 110b and the electrode films 120b, 130b involved in the generation of sound is suppressed, and sound can be more reliably radiated as a plane wave from the speaker 101b. Therefore, it is preferable to make the diaphragm 110b (conductive cloth 111b) and the electrode films 120b, 130b (conductive cloth 121b, 131b) elastic.

In the third embodiment, the conductive fabrics 111b, 121b, 131b and the surface fabric 140b are made of stretchable knitted fabrics to give them stretchability. However, if the fabrics are stretchable, it is also possible to make at least a portion of the fabrics 111b, 121b, 131b, 140b woven. When a portion of a stretchable fabric is made of woven fabric, it is preferable to make the surface fabric (or the base fabric, if the base fabric is made stretchable) woven. In this way, the outer surface of the speaker becomes a woven fabric that is resistant to scratches, thereby increasing the durability of the speaker.

In the speaker 101b of the third embodiment, the ends of the conductive cloths 111b, 121b, and 131b are not fray-proofed, but it is possible to apply fray-proofing to the ends of the conductive cloths 111b, 121b, and 131b, as in the speaker 101a of the second embodiment. When attaching an insulating protective cloth to wrap the ends of the conductive cloths 111b, 121b, and 131b, which are knitted cloths, as the fray-proofing, it is preferable to use a knitted cloth as the protective cloth, as in the case of the conductive cloths 111b, 121b, and 131b.

D. Variations:
The present invention is not limited to the above-described embodiments, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

D1. Variation 1:
In the above-described embodiments, the insulating films 122, 122b, 132, and 132b are provided on the electrode films 120, 120a, 120b, 130, 130a, and 130b, respectively, but it is also possible to omit these insulating films 122, 122b, 132, and 132b. In this case, sound generated by the vibration of the diaphragms 110, 110a, and 110b is more easily released to the outside, and the suppression of the vibration of the diaphragms 110, 110a, and 110b is more effectively suppressed.

In addition, the insulating films 112, 112b, 113, 113b provided on the vibration membranes 110, 110a, 110b may be omitted, and the insulating films 122, 122b, 132, 132b may be provided only on the electrode membranes 120, 120a, 120b, 130, 130a, 130b. In general, it is sufficient that the vibration membranes 110, 110a, 110b and the electrode membranes 120, 120a, 120b, 130, 130a, 130b are insulated from each other, and the insulating film may be provided on at least one of the vibration membranes 110, 110a, 110b and one of the electrode membranes 120, 120a, 120b, and on at least one of the vibration membranes 110, 110a, 110b and the other electrode membrane 130, 130a, 130b.

However, by providing insulating films 112, 112b, 113, 113b on both sides of the vibration membranes 110, 110a, 110b, and providing insulating films 122, 122b, 132, 132b on the electrode films 120, 120a, 120b, 130, 130a, 130b, respectively, damage to a portion of these insulating films 112, 112b, 113, 113b, 122, 122b, 132, 132b may cause the vibration membranes 110, 11 In order to reduce the possibility of short-circuiting between the vibration membranes 110a, 110b and the electrode films 120, 120a, 120b, 130, 130a, 130b, it is preferable to provide insulating films 112, 112b, 113, 113b on both sides of the vibration membranes 110, 110a, 110b, as in the above embodiments, and to provide insulating films 122, 122b, 132, 132b on the electrode films 120, 120a, 120b, 130, 130a, 130b, respectively.

D2. Variation 2:
In addition, in order to insulate the conductive cloth 111, 111b that constitutes the vibration membranes 110, 110a, 110b from the conductive cloth 121, 121b, 131, 131b that constitutes the electrode films 120, 120a, 120b, 130, 130a, 130b, insulating films 122, 122b, 132, 132b are provided on the electrode films 120, 120a, 120b, 130, 130a, 130b, respectively, but it is also possible to insulate the conductive cloth 111, 111b from the conductive cloth 121, 121b, 131, 131b by other means.

For example, as such an insulating means, it is possible to attach an insulating fabric to the conductive cloth 111, 111b, 121, 121b, 131, 131b instead of the insulating film 112, 112b, 113, 113b, 122, 122b, 132, 132b. The insulating fabric can be attached to the conductive cloth 111, 111b, 121, 121b, 131, 131b by gluing, sewing, or by using a multi-layer weaving technique.

D3. Variation 3:
In the above embodiments, the speakers 101, 101a, and 101b according to the present invention are applied to the screen 100, but the speakers according to the present invention are not necessarily applied only to projector screens. The speakers according to the present invention can also be applied to, for example, a soundproofing system.

In one embodiment of the application of the speaker of the present invention to a soundproofing system, the speaker of the present invention is used as wallpaper for a building. In this case, it is possible to generate sound using the entire wallpaper, so by generating sound to cancel out sounds such as conversations in a conference room or noise from neighboring units in an apartment building, it is possible to build a soundproofing system that suppresses the leakage of conversations in a conference room to the outside or effectively eliminates noise from neighboring units. Even in this case, the speaker of the present invention, which is mainly made of fabric, can be easily installed to match the unevenness of the wall surface, making it more suitable for use as wallpaper.

In another embodiment in which the speaker according to the present invention is applied to a soundproofing system, the speaker according to the present invention is used as a covering for a partition or a room divider, or as a tapestry attached to a partition or a room divider. In this case, too, if sound is generated to cancel out the sound of conversations, etc. in the area separated by the partition or a room divider, it is possible to prevent the sound of conversations, etc. in that area from leaking out to the outside.

<Applications of electrostatic speakers>
Since the electrostatic speaker of the present invention has good sound quality, high directionality and flexibility as described above, it can be used for a variety of applications including screens for projectors and the like, partitions, partitions, folding screens, floors, ceilings, walls, wallpaper, curtains, desks, desk mats, doors, doors, stairs, toilets, office supplies, book covers, schedule boards, exhibition panels and sheets, explanatory signs and boards, whiteboards, furniture, chairs, chair covers, seat headrests, chairs, bench seats, lockers, pillars, window glass, lighting fixture umbrellas, mailboxes, pillows, cushions, futons, blankets, mattresses, rugs, cushions, bedding such as beds, tablecloths, chests of drawers, hangers, cupboards, bookshelves, or the like. can be suitably used for bookshelves, magazine racks, various display shelves, benches, standing signs (made of wood or synthetic resin), awnings, stage curtains, funeral equipment, cradles, mannequins, bags, purses, shoes, clothing, miscellaneous goods, hats, helmets, umbrellas, fans, folding fans, walking sticks, tapestries, hanging scrolls, wall hangings, pictures, picture frames, sculptures, bronze statues, pedestals, Buddhist altars, calendars, posters, pet clothing, pet beds, pet huts, umbrella stands, shoe cabinets, beds, toys, play equipment, exercise equipment, electronic devices such as computers, mobile phones, and other items for business, home, interior, exterior, vehicles, ships, aircraft, medical care, nursing care, leisure, and outdoor use. By incorporating it into or attaching it to such items, it can function as a speaker that emits sounds (such as voice or music) that can only be heard by specific people (for example, a speaker that emits sound from the ceiling or headrest above a specific seat in a vehicle, but that cannot be heard by occupants of other seats).

10...Speaker system 100...Screen (projector screen)
101, 101a, 101b...Speakers (projection surface)
110, 110a, 110b... Vibration membrane 111, 111b... Conductive cloth 112, 112b, 113, 113b... Insulating film 114a, 124a, 134a... Protective cloth 119... Wiring 120, 120a, 120b, 130, 130a, 130b... Electrode film 121, 121b, 131, 131b... Conductive cloth 122, 122b, 132, 132b... Insulating film 129, 139... Wiring 140, 140b... Surface cloth 150... Base cloth 200... Drive unit 210... Amplification circuit 220... Transformer output circuit 230... High voltage generating circuit 900... Video disc player AS... Audio signal C1 to C6... Capacitor D1 to D6... Diode DAS...Differential audio signal L...Choke coil OSC...Oscillator PIM...Projected image Q1...MOS type field effect transistor T1, T2...Transformer U1...Differential amplifier VS...Video signal

Claims (4)

An electrostatic speaker,
A first conductive cloth that is a conductive cloth;
A second and a third conductive cloth are disposed so as to sandwich the first conductive cloth and are insulated from the first conductive cloth;
A first and a second exterior cloth are arranged to cover the first to third conductive cloths, are thicker than the first to third conductive cloths, and are made of insulating cloth;
Equipped with
the first to third conductive cloths and the first and second exterior cloths are sewn together with insulating threads; and
An electrostatic speaker, characterized in that the ends of each of the first to third conductive cloths are treated to prevent fraying, and insulating protective cloths are attached to wrap around the ends of each of the first to third conductive cloths . 2. An electrostatic loudspeaker according to claim 1,
the electrostatic speaker is configured to be wound up in a state in which the first exterior cloth is located on an inner circumferential side relative to the second exterior cloth,
the first exterior cloth has elasticity in a winding direction in which the electrostatic speaker is wound up,
end portions of the first and second exterior cloths are sewn together such that, when the electrostatic speaker is wound up, the length of the first exterior cloth in the winding direction becomes a natural length;
Electrostatic speaker. 3. An electrostatic loudspeaker according to claim 2,
the first to third conductive cloths have elasticity in the winding direction,
end portions of the first to third conductive cloths and the first and second exterior cloths are sewn together such that, when the electrostatic speaker is wound up, the lengths of the first to third conductive cloths in the winding direction are natural lengths;
Electrostatic speaker. An electrostatic speaker according to any one of claims 1 to 3, wherein the first and second exterior fabrics are made of fibers that are more positive than paper in the electrostatic series.