JP7709192B2 - Electrostatic Speaker - Google Patents

Description

This invention relates to an electrostatic speaker.

Electrostatic speakers are known as speakers that generate sound in response to an electrical signal. These speakers are composed of a pair of electrodes that face 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.

The present invention was made to solve the above-mentioned problems in the past, and aims to provide a technology that increases the flexibility 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 fabric, which is a conductive woven fabric; second and third conductive fabrics which are conductive woven fabrics arranged so as to sandwich the first conductive fabric and are insulated from the first conductive fabric; and first and second exterior fabrics which are arranged so as to cover the first to third conductive fabrics and are made of insulating woven fabrics, wherein the first to third conductive fabrics and the first and second exterior fabrics are sewn together with insulating thread, and the first to third conductive fabrics are woven with threads plated with metal from raw yarns made of flame-retardant polyamide fiber or aramid fiber, or are woven with raw yarns including thin metal wires, and the second conductive fabric and the third conductive fabric have a lower weave density than that of the first conductive fabric .

According to this application example, the first to third conductive cloths and the first and second exterior cloths can move 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. Also, according to this application example, the decrease in the flexibility of the conductive cloths can be suppressed, so that the flexibility of the electrostatic speaker can be increased.

[Application Example 2]
The electrostatic speaker according to application example 1, wherein an insulating film is attached to both sides of the first conductive cloth.

This application example makes it easier to release to the outside the sound generated by the vibration of the first conductive cloth, which acts as a vibrating membrane, and can be configured to further suppress the suppression of the vibration of the first conductive cloth.

[Application Example 3]
The electrostatic speaker according to application example 2, wherein an insulating film is attached to the surfaces of the second and third conductive cloths facing the first conductive cloth.

This application example reduces the possibility of a short circuit occurring between the first conductive cloth and the second or third conductive cloth due to damage to the insulating film.

[ Application Example 4 ]
A projector screen that uses the electrostatic speaker according to any one of application examples 1 to 3 as a projection surface.

According to this application example, the radius of curvature when rolling up the projector screen including the electrostatic speaker can be made smaller, so the size of the projector screen when stored can be made smaller, and the portability and storability of the projector screen can be improved.

The present invention can be realized in various ways. For example, it can be realized in the form of 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, fabric for clothing, bedding, and stuffed toys, a soundproofing system using the electrostatic speaker or speaker system, etc.

1 is an explanatory diagram showing a usage mode of a speaker system 10 according to an embodiment of the present invention; FIG. 1 is an explanatory diagram showing a configuration of a speaker system according to a first embodiment. FIG. 1 is an explanatory diagram showing a specific configuration of an electrostatic speaker.

Hereinafter, embodiments of the present invention will be described in the following order.
A. Speaker system usage:
B. Speaker system electrical configuration:
C. Specific configuration of electrostatic speaker:
D. Variations:

A. Speaker system usage:
1 is an explanatory diagram showing a usage mode of a speaker system 10 according to 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 a "screen") 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.

B. Speaker system electrical configuration:
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 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 this 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 generation 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 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 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 this 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".

C. Specific configuration of electrostatic speaker:
3 is an explanatory diagram showing a specific configuration of an electrostatic speaker 101 (hereinafter, simply referred to as "speaker 101"). 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 a woven cloth made of plated yarn, the conductive cloth 111 may be a woven cloth made of yarn containing fine metal wires such as copper, or a carbon fiber woven cloth made of conductive fibers such as carbon fiber. However, it is preferable to use a woven cloth made of plated yarn as the conductive cloth 111, since this can prevent a decrease in the flexibility of the conductive cloth 111.

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 fabrics appropriately selected based on mechanical properties such as strength and other properties so that the screen 100 (FIG. 1) can function. In order to function as the screen 100, for example, the outer surface of the surface cloth 140, i.e., the surface opposite the electrode film 120, is subjected to various processing steps to effectively reflect the irradiated light. Note that, although various fibers can be used for the surface cloth 140 and the base cloth 150, it is preferable to use fibers with low moisture absorption such as acrylic fibers or polyamide fibers in order to ensure insulation between the electrode films 120 and 130 to which high-voltage DC voltage is applied and the outside. In addition, since the surface cloth 140 and the base cloth 150 are woven fabrics provided on the outside of the diaphragm 110 and the electrode films 120 and 130 so as to cover them, they can also be called "exterior cloths".

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 addition, in this 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 parts.

In the speaker 101 of this embodiment configured in this way, 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, that is, in the direction perpendicular to the stacking direction, within the range allowed 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 way, the flexibility of the speaker 101 is increased, and the radius of curvature when rolling up the cloth part of the screen including the speaker 101 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.

In addition, by using the speaker 101 of this 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 this 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 with the speaker 101 of this embodiment, it is 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 present 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 center high speaker located above the screen side can be placed behind the screen, further increasing the freedom of screen placement.

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 present invention. For example, the following modifications are also possible.

D1. Variation 1:
In the above embodiment, the insulating films 122, 132 are provided on the electrode films 120, 130, respectively, but it is also possible to omit these insulating films 122, 132. In this case, it becomes easier to release sound generated by the vibration of the diaphragm 110 to the outside, and suppression of the vibration of the diaphragm 110 is further suppressed.

Also, the insulating films 112, 113 provided on the diaphragm 110 may be omitted, and insulating films 122, 132 may be provided on the electrode films 120, 130, respectively. In general, it is sufficient that the diaphragm 110 and the electrode films 120, 130 are insulated from each other, and an insulating film 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.

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

D2. Variation 2:
In the above embodiment, the present invention is applied to the screen 100, so the surface cloth 140, which has been subjected to various processes for favorably reflecting irradiated light, is disposed on the outer side of the electrode film 120, and the base cloth 150, which serves as the base of the screen 100, is disposed on the outer side of the electrode film 130. However, the speaker function according to the present invention is not necessarily applicable only to projector screens.

For example, the speaker of the present invention can be attached to clothing. In this case, the clothing itself can be used for hands-free calling instead of a headset. Also, at least a part of the outer skin of a pillow, stuffed animal, etc. can be made into a speaker of the present invention to generate sound. When used in pillows, stuffed animals, etc., it is difficult to make the shape of a typical speaker small, and the speaker itself is hard, which reduces the comfort of using the pillow or stuffed animal, but the speaker of the present invention is mainly made of woven fabric, so the deterioration of the comfort caused by attaching the speaker can be suppressed.

Furthermore, the speaker of the present invention can also be used as wallpaper for buildings. In this case, it is possible to generate sound from the entire wallpaper, so if sound is generated to cancel out noise from neighboring units in an apartment building, a soundproofing system that effectively eliminates noise from neighboring units can be constructed. Even in this case, the speaker of the present invention, which is mainly made of woven fabric, can be easily installed to match the unevenness of the wall surface, making it more suitable for use as wallpaper.

10...Speaker system 100...Screen (projector screen)
101…Speaker (projection surface)
110...Vibration membrane 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 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 to C6...Capacitors D1 to D6...Diodes DAS...Differential audio signal L...Choke coil OSC...Oscillator PIM...Projected image Q1...MOS field effect transistor T1, T2...Transformer U1...Differential amplifier VS...Video signal

Claims (4)

An electrostatic speaker,
A first conductive cloth which is a conductive woven cloth;
second and third conductive cloths, which are conductive woven cloths arranged so as to sandwich the first conductive cloth and are insulated from the first conductive cloth;
a first exterior cloth and a second exterior cloth, the first exterior cloth and the second exterior cloth being made of an insulating woven fabric and arranged so as to cover the first conductive cloth and the third conductive cloth;
Equipped with
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 made of flame-retardant polyamide fiber or aramid fiber and metal-plated yarn, or woven fabrics made of yarns containing thin metal wires ,
13. An electrostatic speaker, comprising : said second conductive cloth and said third conductive cloth each having a lower weave density than said first conductive cloth . An electrostatic speaker as described in claim 1, in which insulating films are attached to both sides of the first conductive cloth. An electrostatic speaker as described in claim 2, in which an insulating film is attached to the surfaces of the second and third conductive cloths facing the first conductive cloth. A projector screen that uses the electrostatic speaker according to any one of claims 1 to 3 as a projection surface.