Electrostatic speaker

An electrostatic speaker is constituted of a vibrator, conductive cloths, and elastic members, which are laminated together and woven together using strings. Since all the constituent elements are restrained in positioning by strings, the overall structure thereof is not substantially changed even when the electrostatic speaker is deformed in shape by bending or curving, wherein it is possible to secure the prescribed positional relationship between the constituent elements, which are not deviated in positioning. It is possible to introduce a sheet composed of a thermoplastic resin, which holds the vibrator and elastic members therein. The conductive cloths can be replaced with film electrodes, each of which is formed such that a conductive polymer layer is formed on a base film composed of a thermoplastic resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrostatic speakers in which vibrators held between opposite electrodes vibrate in response to audio signals so as to generate sounds.

The present application claims priority on Japanese Patent Application No. 2007-251158 and Japanese Patent Application No. 2008-132235, the contents of which are incorporated herein by reference.

2. Description of the Related Art

Electrostatic speakers are constituted of opposite electrodes, which are distanced from each other with prescribed distances therebetween and which hold sheet-like vibrators (or vibrating members) having conductive properties therebetween. Due to variations of a voltage applied between opposite electrodes of an electrostatic speaker whose vibrator is supplied with a bias voltage, an electrostatic force exerted on the vibrator is varied so as to cause the displacement of the vibrator. Due to variations of the applied voltage in response to audio signals, displacements repeatedly occur in the vibrator causing vibration, thus generating reproduction waves from the vibrator in response to audio signals.

Various types of electrostatic speakers having flexibilities have been developed and disclosed in various documents such as Non-Patent Document 1 and Non-Patent Document 2.Non-Patent Document 1: Technical Report of the Institute of Electronics, Information and Communication Engineers entitled “1-bit Wave Field Recording/Reproduction System Using Electrostatic Microphone and Loudspeaker” written by Shigeto Takeoka and five members, EA, Applied Acoustics, Institute of Electronics, Information and Communication Engineers, pp. 25-30, June of 2005 Non-Patent Document 2: <A & V Festa 2006 Report: 1-bit audio> exhibition of 1-bit distribution system using IEEE 1394: [online], Sep. 21, 2006, Phile-web editorial department: [Retrieval on Aug. 23, 2007]: Internet <http://www.phileweb.com/news/d-av/200609/21/16653.html>

Non-Patent Document 1 teaches a flexible electrostatic speaker including opposite electrodes and a vibrator, which are composed of flexible materials having the capabilities to change shapes. Non-Patent Document 2 teaches an electrostatic speaker in which electrodes are composed of flexible cloth.

Both of Non-Patent Document 1 and Non-Patent Document 2 teach edgeless flexible electrostatic speakers in which electrodes and vibrators are not restrained in shapes. Since the flexible electrostatic speaker disclosed in Non-Patent Document 1 is not restrained in shape, it can be freely bent and curved and thus changed into various shapes. However, such a non-restraint property of the electrostatic speaker causes another problem in that electrodes and vibrators may be easily deviated in positioning.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrostatic speaker having flexibility, which can be easily bent or curved without causing positional deviations of electrodes and a vibrator.

An electrostatic speaker of the present invention is constituted of a first electrode corresponding to a cloth formed using conductive fibers, a second electrode corresponding to a cloth formed using conductive fibers, which is positioned opposite to the first electrode with a prescribed distance therebetween, a vibrator having a conductive property, which is positioned between the first electrode and the second electrode, a first elastic member having an insulating property, elasticity, and acoustic transmittance, which is positioned between the vibrator and the first electrode, a second elastic member having an insulating property, elasticity, and acoustic transmittance, which is positioned between the vibrator and the second electrode, and a restraint member for restraining the first electrode, the first elastic member, the vibrator, the second elastic member, and the second electrode in position.

In the above, the restraint member corresponds to a plurality of strings for weaving the first electrode, the first elastic member, the vibrator, the second elastic member, and the second electrode together. The first electrode and the second electrode can be formed by weaving conductive strings. The first electrode and the second electrode can be woven with flexibilities. The first electrode and the second electrode can be woven together while being stretched.

In addition, the area of the first electrode is larger than the area of the vibrator, and the area of the second electrode is larger than the area of the vibrator.

The restraint member corresponds to a plurality of tag-pins which run through the first electrode, the first elastic member, the vibrator, the second elastic member, and the second electrode.

The restraint member is a sheet composed of a thermoplastic resin, which is positioned between the first electrode and the vibrator and between the vibrator and the second electrode, and wherein when the sheet is melted, the first electrode and the vibrator are adhered together, while the vibrator and the second electrode are adhered together.

It is possible to further introduce a first quilting member which is positioned opposite to the first elastic member in view of the first electrode and a second quilting member which is positioned opposite to the second elastic member in view of the second electrode, wherein both the first quilting member and the second quilting member are restrained by the restraint member.

As described above, the electrostatic speaker can be freely bent or curved in shape, wherein all the constituent elements are not deviated in positioning without causing substantial variations of the distance between the electrodes (e.g., conductive cloths). Even when the electrostatic speaker is bent, it is possible to maintain substantially the constant distance between the electrodes (and the constant distances between the vibrator and the electrodes, whereby it is possible to set the uniform electrostatic force exerted on the vibrator at any positions, thus achieving desired acoustic characteristics.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in further detail by way of examples with reference to the accompanying drawings.

FIG. 1diagrammatically shows the exterior appearance of an electrostatic speaker1in accordance with a preferred embodiment of the present invention.FIG. 2shows the electronic configuration and sectional configuration of the electrostatic speaker1.

The electrostatic speaker1is constituted of a vibrator10, conductive cloths20U and20L, elastic members30U and30L, and strings40. In the present embodiment, both the conductive cloths20U and20L have the same constitution, and both the elastic members30U and30L have the same constitution. For the sake of convenience, both the reference numerals20U and20L are designated by the same reference numeral “20”, and both the reference numerals30U and30L are designated by the same reference numeral “30”. To simplify the illustrations in a visually easy-to-grasp manner, the aforementioned constituent elements are not precisely illustrated in the drawings in terms of the shapes and dimensions; hence, they may differ from the actually produced elements for use in products. In this connection,FIG. 1is a three-dimensionally illustrated drawing along with X, Y, and Z axes, whileFIG. 2is a drawing along with X and Z axes in view of the Y-axis (which is designated by a circle having a dot indicating that the Y-axis is directed from the backside of the sheet).

Next, the constitution of the electrostatic speaker1will be described in detail. The vibrator10is formed using a film (or films) composed of PET (Polyethylene Terephthalate) or PP (Polypropylene), which is deposited with metal films or which is applied with conductive materials, wherein the thickness thereof substantially ranges from several micro-meters to several tens of micro-meters (μm).

The elastic member30having elasticity is formed in a rectangular shape in plan view by heating and compressing soft cotton so as to allow air to transmit therethrough. The elastic member30is deformable due to an external force applied thereto and is restored in shape by eliminating the external force. In the present embodiment, the lengths of the elastic member30are longer than the lengths of the conductive cloth20(having a rectangular shape) in the X-axis and Y-axis directions. In addition, the lengths of the elastic member30are longer than the lengths of the vibrator10in the X-axis and Y-axis directions. Both the elastic members30U and30L have the same height in the Z-axis direction.

The conductive cloths20each formed in a rectangular shape in plan view are plain woven cloths woven using longitudinal strings and latitudinal strings having conductive properties. The plain woven cloths transmit air therethrough, thus securing acoustic transmittances.

The vibrator10, the conductive cloths20, and the elastic members30are woven together using the strings40, which are composed of non-conductive cotton.

Next, the assembling of the electrostatic speaker1will be described in detail. In the assembling of the electrostatic speaker1, the elastic member30L is mounted on the conductive cloth20L in such a way that all the side portions of the elastic member30L are positioned outside of all the side portions of the conductive cloth20L.

Next, the vibrator10is mounted on the elastic member30L in such a way that all the side portions of the vibrator10are positioned inwardly of all the side portions of the elastic member30L.

Then, the elastic member30U is mounted on the vibrator10in such a way that all the side portions of the elastic member30U are positioned outside of all the side portions of the vibrator10while the four corners of the elastic member30U vertically match the four corners of the elastic member30L in positioning in view of the Z-axis direction. Since the lengths of the elastic members30U and30L are longer than the lengths of the vibrator10in the X-axis and Y-axis directions, the vibrator10is entirely held between the elastic members30U and30L in such a way that all the side portions of the vibrator10are not positioned outside of the elastic members30U and30L.

Next, the conductive cloth20U is mounted on the elastic member30U in such a way that all the side portions of the conductive cloth20U are positioned inwardly of all the side portions of the elastic member30U while four corners of the conductive cloth20U vertically match four corners of the conductive cloth20L in positioning in view of the Z-axis direction.

After combining the vibrator10, the conductive cloths20, and the elastic members30together, they are woven together using the non-conductive strings40. Since all the constituent elements10,20, and30are restrained in positioning since they are woven together using the strings40(which run through the constituent elements10,20, and30), it is possible to prevent the vibrator10, the conductive cloths20, and the elastic members30from being deviated in positioning even when the electrostatic speaker10is deformed in shape.

Since the areas of the elastic members30having insulating properties are larger than the area of the vibrator10and the areas of the conductive clothes20, the side portions of the elastic members30are positioned outside of the side portions of the vibrator10and the side portions of the conductive clothes20; hence, it is possible to prevent the conductive cloths20from unexpectedly coming in contact with and short-circuiting with the vibrator10.

Next, the electronic constitution of the electrostatic speaker1will be described in detail.FIG. 2shows an equivalent circuit in which the electrostatic speaker1is connected with a transformer50, an input unit60(for inputting audio signals from an external device, not shown), and a bias voltage source70(for applying a DC bias voltage to the vibrator10). The bias voltage source70is connected between the vibrator10and a midpoint of the transformer50, wherein the conductive cloths20U and20L are connected to the opposite ends of the transformer50. In this constitution, a predetermined voltage is applied to the conductive clothes20U and20L in response to audio signals applied to the input unit60.

The applied voltage causes a potential difference between the conductive cloths20U and20L, by which an electrostatic force is exerted on the vibrator10, which is thus attracted to one of the conductive cloths20U and20L (serving as electrodes). That is, the vibrator10is displaced (or deflected) in the Z-axis direction in response to audio signals, wherein the displacement direction of the vibrator10is successively varied so as to cause vibration (having a certain frequency, amplitude, and phase). This makes it possible for the electrostatic speaker1to generate sound due to the vibration of the vibrator10. At least one of the conductive cloths20U and20L propagate the generated sound, which is thus emitted to the external space of the electrostatic speaker1.

The present embodiment is characterized in that all the constituent elements of the electrostatic speaker1, i.e. the vibrator10, the conductive cloths20, and the elastic members30, are restrained in positioning due to the strings40; hence, even when the electrostatic speaker1is deformed in shape, the original structure and constitution are not affected so that the vibrator10, the conductive cloths20, and the elastic members30are not deviated in positioning.

Since all of the vibrator10, the conductive cloths20, and the elastic members30have flexibilities, they can be easily and freely deformed along with curved surfaces. Thus, it is possible to freely attach the electrostatic speaker1to clothing.

Due to the flexibilities of the constituent elements of the electrostatic speaker1, the electrostatic speaker1may not damage the human body irrespective of a collision with the human body. For this reason, it is possible to easily attach the electrostatic speaker1to a head rest or the inside of a full-face helmet without damaging the human body in generating sound towards human ears.

The present embodiment can be modified in a variety of ways; hence, variations will be described below.

As shown inFIG. 2, the electrostatic speaker1of a first variation is constituted of the vibrator10, the conductive cloths20, the elastic members30, and the strings40as well as the transformer50, the input unit60, and the bias voltage source70.

The first variation is characterized in that the conductive cloths20U and20L are not plain-woven cloth (woven using conductive strings) but knitted fabrics (knitted using conductive strings) as shown inFIG. 3A. The conductive cloths20corresponding to knitted fabrics have flexibilities in both the X-axis and Y-axis directions. The conductive cloths20are not necessarily limited to knitted fabrics as long as they have flexibilities in both the X-axis and Y-axis directions. For example, they can be formed by rib knitting as shown inFIG. 3B, or they can be formed by pearl knitting as shown inFIG. 3C.

The first variation of the electrostatic speaker1is assembled by sequentially laminating the conductive cloth20L, the elastic member30L, the vibrator10, the elastic member30U, and the conductive cloth20U, which are then woven together using the strings40. In the first variation, the conductive cloths20U and20L are woven together in the condition where they are slightly expanded (or stretched) in the X-axis and Y-axis directions.

Compared with knitted fabrics, plain woven cloth has low flexibility; therefore, when the electrostatic speaker1, in which plain woven cloth is used as the conductive cloths20and is woven together without being expanded (or stretched), is deformed in a circular manner, for example, the inner portions (which are not woven using the strings40) of the conductive cloths20may become partially loosened as shown inFIG. 4A, and it is difficult to maintain a constant distance between the conductive cloths20.

In the first variation, the conductive cloths20are woven together while they are stretched in the X-axis and Y-axis directions; hence, even when the electrostatic speaker1is deformed in a circular manner, the inner portions of the conductive cloths20(which are stretched in weaving) may be contracted so that they do not become loosened, while the external portions of the conductive cloths20(corresponding to knitted fabrics) having flexibilities may be expanded so as to maintain the constant distance between the conductive cloths20.

In the first variation, the conductive cloths20corresponding to knitted fabrics have flexibilities due to gaps intentionally formed between longitudinal strings and latitudinal strings; hence, compared with plain woven cloth, it is possible to improve air transmittance and acoustic transmittance.

FIG. 5shows a second variation of the electrostatic speaker1in which stitches are not aligned along rectangular lines but are aligned along diagonal lines.

The elastic members30are not necessarily composed of soft cotton but can be composed of other materials having insulating properties and deformable properties, in which they are deformed under an external force applied thereto but are restored in shape by eliminating the external force.

The constituent elements of the electrostatic speaker1such as the vibrator10, the conductive cloths20, and the elastic members30are not necessarily formed in rectangular shapes but can be formed in other shapes such as polygonal shapes, circular shapes, and elliptical shapes.

In order to avoid the occurrence of electric shock and short-circuiting, it is possible to entirely cover the electrostatic speaker1with non-conductive cloth having acoustic transmittance.

The conductive cloths20can be formed using longitudinal strings and latitudinal strings, at least one of which has the conductive property.

All of longitudinal strings and latitudinal strings do not necessarily have conductive properties; that is, the conductive cloths20may include every other string(s) having conductive property.

Alternatively, non-conductive strings are knitted so as to form knitted cloth, which is then plated with metals having conductive properties, thus forming the conductive cloths20.

Alternatively, strings plated with metals having conductive properties are woven together so as to form the conductive cloths20.

The conductive cloths20can be formed by weaving conductive filaments therein.

It is possible to use strings whose cores are wound by copper foils plated with tin, which are woven together so as to form the conductive cloths20.

The conductive cloths20can be replaced with non-woven fabrics having conductive properties.

Knitted cloth, which is formed by way of knitted weaving using strings having insulating properties, is bonded together with mesh cloth, which is formed by way of mesh weaving using strings having conductive properties, via bonding agents, thus forming the conductive cloths20. Herein, the mesh cloth of the conductive cloths20is laminated with the elastic members30; then, they are woven together using the strings40so as to form the electrostatic speaker1.

Alternatively, the knitted cloths are directed outwardly so that the mesh clothes are positioned between the knitted cloths and the elastic members30; then, they are woven together so as to form the electrostatic speaker1.

In the structure in which the knitted cloths are not bonded with the mesh cloths, all the constituent elements of the electrostatic speaker1are woven together using the strings40in the condition where the knitted cloths are stretched.

In order to secure adequate strengths of the constituent elements woven together by the strings40, it is possible to introduce a non-woven fabric member80having a mesh-like shape and a plurality of holes81as shown inFIG. 6. The non-woven fabric member80is inserted between the conductive cloths20and the elastic member30; then, the rectangular portions (corresponding to meshes) of the non-woven fabric member80are woven together with the conductive cloths20and the elastic member30by use of the strings40.

In the foregoing embodiment, the vibrator10, the conductive cloths20, and the elastic members30are woven together using the strings40, which can be replaced with tag-pins (composed of a synthetic resin), by which the constituent element10-30are restrained in positioning. When the constituent elements10-30are restrained in position by use of multiple tag-pins, it is possible to prevent the constituent elements10-30from being shifted in position even when the constituent elements10-30are deformed in shape. That is, the adhesion using the sheets90demonstrates an outstanding effect as similar to the weaving using the strings40.

It is possible to additionally introduce a plurality of sheets90each composed of a thermoplastic resin and having a rectangular shape in plan view as shown inFIG. 7Abetween the constituent elements10-30. The sheets90are pressed and heated and then cooled so as to restrain the constituent elements10-30in position.

Specifically, the sheet90is inserted between the conductive cloth20U and the elastic member30U; the sheet90is inserted between the elastic member30U and the vibrator10; the sheet90is inserted between the vibrator10and the elastic member30L; and the sheet90is inserted between the elastic member30L and the conductive cloth20L. Then, the prescribed portions of the constituent elements10-30accompanied with the sheets90are pressed and heated, whereby the sheets90each composed of a thermoplastic resin are melted so as to adhere the constituent elements10-30together.

Since the constituent elements10-30are adhered together by way of melting of the sheets90, it is possible to prevent them from being shifted in position. That is, the adhesion using the sheets90demonstrates an outstanding effect as similar to the weaving using the strings40.

The sheet90is not necessarily formed in a rectangular frame-like shape; hence, it is possible to introduce a lattice sheet90A shown inFIG. 7B.

In the above, it is possible to appropriately determine the shapes and dimensions of the vibrator10and the elastic members30, which can be held inside of the rectangular frame of the sheet90. Specifically, the sheet90is mounted on the conductive cloth20L; then, a set of the vibrator10and the elastic members30L and30U is held inside of the rectangular frame of the sheet90; thereafter, the conductive cloth20U is mounted on the elastic member30U and the sheet90. Thereafter, the sheet90is pressed and heated so as to adhere the conductive cloths20U and20L together via the sheet90. In this structure, the vibrator10and the elastic members30are held inwardly of the conductive cloths20and the sheet90; thus, it is possible to prevent the vibrator10and the elastic members30from being exposed externally.

It is possible to replace the conductive cloths20with film electrodes (not shown), each of which is composed of a thermoplastic resin and is formed in such a way that a conductive polymer is applied to the internal area internally of the edges of the thermoplastic resin.

FIG. 8shows a film electrode25having a rectangular shape. The film electrode25is formed in such a way that a conductive polymer layer25B is formed on the surface of a base film25A composed of a thermoplastic resin.

FIG. 9shows another variation of the electrostatic speaker1which uses a pair of film electrodes25L and25U instead of the conductive cloths20L and20U. First, the film electrode25L is arranged such that the conductive polymer layer25B thereof is directed upwardly. Next, the sheet90is mounted on the film electrode25L so as to hold a set of the vibrator10and the elastic members30L and30U inside of the rectangular frame thereof; then, the film electrode25U is mounted on the sheet90and the elastic member30U such that the conductive polymer layer25B thereof is directed downwardly. Thereafter, the sheet90is pressed and heated so as to adhere the film electrodes25U and25L together via the sheet90.

In the aforementioned structure, it is possible to prevent the constituent elements10,25, and30from being separated and shifted in position; and it is possible to prevent the vibrator10and the elastic members30from being exposed externally. In addition, it is possible to appropriately set the distance between the film electrodes25by adjusting the thickness of the sheet90. Furthermore, it is possible to manufacture the electrostatic speaker1with each because all the constituent elements are restrained in position by simply pressing and heating the sheet90.

It is possible to replace the sheet90with the adhesive agent, which is applied to multiple points of the constituent elements, which are thus adhered together and are restrained in position. When multiple points of the adhesive agent are each formed to slightly project from the constituent elements with certain thickness, space may be formed between the constituent elements. That is, the adhesive agent can be used as a spacer (or spacers).

Moreover, a quilting member is attached to the conductive cloth20U at a prescribed position opposite to the elastic member30U, while another quilting members is attached to the conductive cloth20L at a prescribed position opposite to the elastic member30L. The quilting members are woven together with the vibrator10, the conductive cloths20, and the elastic members30. In this structure, even when the electrostatic speaker1is bent or folded, the quilting members may expand so as to press the conductive cloths20, thus prevent the spaces between the vibrator10and the conductive cloths20from being unexpectedly broadened.

Lastly, the present invention is not necessarily limited to the foregoing embodiment and variations, which can be further modified in a variety of ways within the scope of the invention as defined in the appended claims.