Patent Publication Number: US-2011075868-A1

Title: Electrostatic speaker

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrostatic speakers (or capacitor speakers) constituted of parallel planar electrodes and diaphragms. 
     The present application claims priority on Japanese Patent Application No. 2009-228543, the content of which is incorporated herein by reference. 
     2. Description of the Related Art 
     Patent Document 1 discloses an electrostatic speaker in which a diaphragm having conductivity is slightly distanced from and interposed between a pair of fixed electrodes having conductivity, which are disposed opposite to each other. Patent Document 2 discloses a planar speaker in which a pair of planar electrodes is disposed in proximity to the surface and backside of a diaphragm (i.e. a thin-film member) via damping members. 
     Patent Document 1: Japanese Patent Application Publication No. 2007-274341 
     Patent Document 2: Japanese Patent Application Publication No. 2008-54154 
     The technologies of Patent Documents 1 and 2 may not always demonstrate a normal functionality as an electrostatic speaker when adjacent conductive layers unexpectedly conduct to each other due to a wrong installation of an electrostatic speaker. Even when an electrostatic speaker is installed with a holding member tightly holding end portions thereof, the electrostatic speaker may not function normally due to a short-circuiting of adjacent conductive layers under a high pressure applied to end portions thereof. Even when an electrostatic speaker is installed with a holding member having conductivity (e.g. a screw or hook) being inserted into a through-hole (which runs through the electrostatic speaker), the electrostatic speaker may not function normally due to a short-circuiting of adjacent conductive layers (which are partially exposed on the interior wall of a through-hole) being pressed by a holding member, In addition, a high pressure applied to the periphery of a through-hole may cause a short-circuiting of adjacent conductive layers, thus disturbing a normal function of an electrostatic speaker. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrostatic speaker which does not cause a short-circuiting of adjacent conductive layers regardless of installation using various types of holding members. 
     An electrostatic speaker of the present invention is constituted of a diaphragm in which a first conductive layer is formed on a first surface, and an electrode in which a second conductive layer is formed on a second surface. The diaphragm is disposed opposite to and/or slightly distanced from the electrode in such a way that the first surface is disposed opposite to the second surface. A holding region is formed on the main body of an electrostatic speaker in relation to the first surface of the diaphragm and the second surface of the electrode. The first conductive layer circumvents the holding region of the first surface whilst the second conductive layer circumvents the holding region of the second surface. 
     In the above, the holding region is formed along a predetermined edge of the main body of an electrostatic speaker. That is the holding region is formed on the first surface along the predetermined edge whilst the holding region is formed on the second surface along the predetermined edge. 
     In addition, a through-hole can be formed to run through the diaphragm and the electrode. The holding region of the first surface is formed in the periphery of a through-hole running through the diaphragm, whilst the holding region of the second surface is formed in the periphery of a through-hole running through the electrode, 
     The installation equipment is adapted to the electrostatic speaker in such a way that a holding member holds the holding region of the electrostatic speaker, thus installing the electrostatic speaker at a predetermined position (e.g. a wall surface). The present invention guarantees the normal functionality of an electrostatic speaker irrespective of installation measures. Even when a through-hole of an electrostatic speaker is hung at a predetermined position via a holding member, the present invention guarantees normal functionality of the electrostatic speaker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings. 
         FIG. 1  is a perspective view showing an exterior appearance of an electrostatic speaker according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the electrostatic speaker of  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the electrostatic speaker of  FIG. 1 , 
         FIG. 4  is an electric circuit showing an electronic configuration of the electrostatic speaker. 
         FIG. 5  is a perspective view showing an example of installation equipment including a suspension-type holding member for holding the electrostatic speaker of  FIG. 1 . 
         FIG. 6  is a perspective view showing an exterior appearance of an electrostatic speaker according to a second embodiment of the present invention. 
         FIG. 7  is a cross-sectional view of the electrostatic speaker of  FIG. 6 . 
         FIG. 8  is an exploded perspective view of the electrostatic speaker of  FIG. 6 . 
         FIG. 9  is a perspective view showing an example of installation equipment including a suspension-type holding member for holding the electrostatic speaker of  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in further detail by way of examples with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a perspective view showing an exterior appearance of an electrostatic speaker  10  according to a first embodiment of the present invention,  FIG. 2  is a cross-sectional view of the electrostatic speaker  10 .  FIG. 3  is an exploded perspective view of the electrostatic speaker  10 . 
     The electrostatic speaker  10  is constituted of an electrode  112 , a diaphragm  102 , an electrode  114 , and a pair of cushion materials  132 . The electrostatic speaker  10  has a laminated structure sequentially laminating the electrode  112  (i.e. an uppermost portion), the cushion material  132 , the diaphragm  102 , the cushion material  132 , and the electrode  114  (i.e. a lowermost portion), which are mutually connected together via tapes or bonds (or adhesives). The electrostatic speaker  10  has an integral structure including these constituent elements as shown in  FIG. 1 . The diaphragm  102 , the electrodes  112  and  114  are composed of thin films having flexibility. In addition, the diaphragm  102 , the electrodes  112  and  114  have rectangular planar shapes. For example, the diaphragm  102 , the electrodes  112  and  114  are composed of PET (i.e. polyethylene terephthalate) or PP (i.e. polypropylene). A plurality of apertures  112 C is formed in the electrode  112  with predetermined spacing therebetween, while a plurality of apertures  114 C is formed in the electrode  114  with predetermined spacing therebetween. 
     A main body of the electrostatic speaker  10  has a holding region  10 A, which is held by a holding member (not shown) in an installation of the electrostatic speaker  10 . The holding region  10 A is laid along an edge of the main body of the electrostatic speaker  10 . That is, the holding region  10 A having a width W is formed along one side of the electrostatic speaker  10  having a rectangular shape. 
     The diaphragm  102  is sandwiched between the electrodes  112  and  114  via the cushion materials  132  with one end portion thereof being held between the electrodes  112  and  114 , One cushion material  132  is interposed between the diaphragm  102  and the electrode  112 , while the other cushion material  132  is interposed between the diaphragm  102  and the electrode  114 . The cushion materials  132  have insulating property, air permeability, and elasticity. The cushion materials  132  are composed of compressed cottons. An internal space  10 B which allows for an upper-side vibration of the diaphragm  102  is secured between the diaphragm  102  and the electrode  112 , while another internal space  10 B which allows for a lower-side vibration of the diaphragm  102  is secured between the diaphragm  102  and the electrode  114 . It is possible to insert a spacer between the diaphragm  102  and the electrode  112 , thus securing the internal space  10 B therebetween. In addition, it is possible to insert a spacer between the diaphragm  102  and the electrode  114 , thus securing the internal space  10 B therebetween. 
     A vibrating portion of the diaphragm  102  other than one edge thereof has a shape and size which can be stored inside the internal space  10 B. The vibrating portion of the diaphragm  102  is disposed approximately at an intermediate position of the internal space  10 B in a vertical direction and interposed between the electrodes  112  and  114 . An upper surface  102 A of the diaphragm  102  is disposed opposite to a lower surface  112 A of the electrode  112  via the internal space  10 B which is sufficiently large to accept an upper-side vibration of the diaphragm  102 . A lower surface  102 B of the diaphragm  102  is disposed opposite to an upper surface  114 A of the electrode  114  via the internal space  10 B which is sufficiently large enough to accept a lower-side vibration of the diaphragm  102 . 
     A conductive layer  103  is formed on the upper surface  102 A of the diaphragm  102 , while a conductive layer  104  is formed on the lower surface  102 B of the diaphragm  102 . A conductive layer  113  is formed on the lower surface  112 A of the electrode  112 , while a conductive layer  115  is formed on the upper surface  114 A of the electrode  114 . The conductive layers  103 ,  104 ,  113 , and  115  are formed on the surfaces  102 A,  102 B,  112 A, and  114 A in such a way that conductive metals are deposited on these surfaces or conductive coatings are applied onto these surfaces. 
     As described above, the holding region  10 A is formed along one edge of the electrostatic speaker  10  with the predetermined with W; that is, the holding region  10 A having the width W is formed along one edge of the upper surface  102 A of the diaphragm  102  and is also formed along one edge of the lower surface  102 B of the diaphragm  102 . In addition, the holding region  10 A having a width W is formed along one edge of the lower surface  112 A of the electrode  112  and is further formed along one edge of the upper surface  114 A of the electrode  114 . 
     The electrostatic speaker  10  is designed to satisfy at least one of design choices (a) and (b). 
     (a) The conductive layer  103  is formed to bypass the holding region  10 A on the upper surface  102 A of the diaphragm  102 .
 
(b) The conductive layer  113  is formed to bypass the holding region  10 A on the lower surface  112 A of the electrode  112 .
 
     Specifically, the conductive layer  103  is not formed in the holding region  10 A on the upper surface  102 A of the diaphragm  102 , so that the conductive layer  103  bypasses the holding region  10 A of the upper surface  102 A. The conductive layer  113  is not formed in the holding region  10 A on the lower surface  112 A of the electrode  112 , so that the conductive layer  113  bypasses the holding region  10 A of the lower surface  112 A. 
     The electrostatic speaker  10  is designed to satisfy at least one of design choices (c) and (d). 
     (c) The conductive layer  104  is formed to bypass the holding region  10 A on the lower surface  102 B of the diaphragm  102 .
 
(d) The conductive layer  115  is formed to bypass the holding region  10 A on the upper surface  114 A of the electrode  114 .
 
     That is, the conductive layer  104  is not formed in the holding region  10 A on the lower surface  1028  of the diaphragm  102 , so that the conductive layer  104  bypasses the holding region  10 A of the lower surface  102 B. The conductive layer  115  is not formed in the holding region  10 A on the upper surface  114 A of the electrode  114 , so that the conductive layer  115  bypasses the holding region  10 A of the upper surface  114 . 
       FIG. 4  is a circuit diagram showing an electronic configuration of the electrostatic speaker  10 . The electrostatic speaker  10  is a push-pull electrostatic speaker including a transformer  42 , an input unit  44  for inputting audio signals from an external device (not shown), and a bias power source  46  for applying a DC bias voltage to the diaphragm  102 . A neutral point of the output side of the transformer  42  is connected to one terminal of the bias power source  46 , while the other terminal of the bias power source  46  is connected to the conductive layers  103  and  104 . One terminal of the output side of the transformer  42  is connected to the conductive layer  113 , while the other terminal of the output side of the transformer  42  is connected to the conductive layer  115 . Terminals of the input side of the transformer  42  are connected with the input unit  44 , A voltage is applied to the conductive layers  113  and  115  in correspondence with an audio signal input into the input unit  44 . When a voltage difference occurs between the conductive layers  113  and  115 , an electrostatic force is exerted on the conductive layers  103  and  104 , each of which is attracted toward either the conductive layer  113  or the conductive layer  115 . 
     For example, a positive voltage is applied to the conductive layers  103  and  104 , wherein a positive voltage is applied to the conductive layer  113  while a negative voltage is applied to the conductive layer  115 . In this situation, the diaphragm  102  is displaced toward the conductive layer  115  in such a way that the conductive layers  103  and  104  sandwiching the diaphragm  102  are repelled by the “positively charged” conductive layer  113  while being attracted toward the “negatively charged” conductive layer  115 . Alternatively, a positive voltage is applied to the conductive layers  103  and  104 , wherein a negative voltage is applied to the conductive layer  113  while a positive voltage is applied to the conductive layer  115 . In this situation, the diaphragm  102  is displaced toward the conductive layer  113  in such a way that the conductive layers  103  and  104  are repelled by the conductive layer  115  while being attracted toward the conductive layer  113 . The diaphragm  102  is forced to vibrate as the conductive layers  103  and  104  repeat displacements toward the conductive layers  113  and  115 . The diaphragm  102  vibrates to produce sound based on vibration factors (i.e. frequency, amplitude, and phase). Sound caused by the diaphragm  102  permeates at least one of the apertures  112 C of the electrode  112  and the apertures  114 C of the electrode  114 , so that the electrostatic speaker  10  emits sound into the external space. 
       FIG. 5  shows an example of installation equipment  500  including a suspension-type holding member  510  for holding the electrostatic speaker  10 . The electrostatics speaker  10  is suspended by the holding member  510  in such a way that the holding region  10 A is directed upward and tightly held by the holding member  510 . That is, the holding member  510  is limited to hold the holding region  10 A of the electrostatic speaker  10 , which is thus subjected to a high pressure (which is sufficient for the holding member  50  to tightly hold the holding region  10 A of the electrostatic speaker  10 ). Since no conductive layers are formed and disposed opposite to each other in the holding region  10 A of the diaphragm  102 , the electrodes  112  and  114 , it is possible to reliably prevent conductive layers from contacting each other irrespective of a high pressure applied to the holding region  10 A. Even though the electrostatic speaker  10  is installed at a certain position while being tightly held by the holding member  510  or the like, the electrostatic speaker  10  is able to function normally. Alternatively, the electrostatic speaker  10  can be installed at a certain position by way of a through-hole formed in the holding region  10 A. In this case, the electrostatic speaker  10  is able to function normally because no conductive layers are formed and disposed opposite each other in the holding region  10 A of the diaphragm  102 , the electrodes  112  and  114 . 
     Second Embodiment 
       FIG. 6  is a perspective view showing the exterior appearance of the electrostatic speaker  10  according to a second embodiment of the present invention. Since the second embodiment is similar to the first embodiment, the following description refers to differences between the first and second embodiments; hence, similarities between the first and second embodiments are not discussed below. 
     In the second embodiment, through-holes  10 C pierce through the main body of the electrostatic speaker  10  from the upper surface of the electrode  112  to the lower surface of the electrode  114 , That is, the through-holes  10 C run through the electrode  112 , the diaphragm  102 , and the electrode  114 .  FIG. 6  shows that the through-holes  10 C are each formed in a rectangular shape in plan view. In addition, holding regions  10 D are formed in proximity to the through-holes  10 C in the main body of the electrostatic speaker  10 . During an installation of the electrostatic speaker  10 , the holding regions  10 D are being held by holding members. Specifically, the holding regions  10 D are formed in the periphery of the through-holes  10 C. In plan view, the holding regions  10 D have rectangular shapes which are lager than the rectangular shapes of the through-holes  10 C. 
       FIG. 7  is a cross-sectional view of the electrostatic speaker  10  of the second embodiment.  FIG. 8  is an exploded perspective view of the electrostatic speaker  10  of the second embodiment. The holding regions  10 D are formed in the periphery of the through-holes  10 C in a vertical direction of the electrostatic speaker  10 , so that the holding regions  10 D are formed in the periphery of the through-holes  10 C on the upper surface  102 A of the diaphragm  102 , while the holding portions  10 D are formed in the periphery of the through-holes  10 C on the lower surface  102 E of the diaphragm  102 . In addition, the holding regions  10 D are formed in the periphery of the through-holes  10 C on the lower surface  112 A of the electrode  112 , while the holding regions  10 D are formed in the periphery of the through-holes  10 C on the upper surface  114 A of the electrode  114 . 
     The conductive layer  103  is not formed in the holding regions  10 D on the upper surface  102 A of the diaphragm  102 ; hence, the conductive layer  103  circumvents the holding regions  10 D of the upper surface  102 A of the diaphragm  102 . In addition, the conductive layer  104  is not formed in the holding regions  10 D on the lower surface  102 E of the diaphragm  102 ; hence, the conductive layer  104  circumvents the holding regions  10 D of the lower surface  102 B of the diaphragm  102 . 
     The conductive layer  113  is not formed in the holding regions  10 D on the lower surface  112 A of the electrode  112 ; hence, the conductive layer  113  circumvents the holding regions  10 D of the lower surface  112 A of the electrode  112 . In addition, the conductive layer  115  is not formed in the holding regions  10 D on the upper surface  114 A of the electrode  114 ; hence, the conductive layer  115  circumvents the holding regions  10 D of the upper surface  114 A of the electrode  114 . 
       FIG. 9  is a perspective view showing an example of installation equipment  500  including the holding members  510  for holding the electrostatic speaker  10 . The electrostatic speaker is suspended by the holding members  510  on a wall surface  920 . The holding members  510  are fixed to the wall surface  920 . As described above, the holding regions  10 D are formed in the periphery of the through-holes  10 C in the electrostatic speaker  10 . The holding members  510  have L-shapes whose base portions are fixed to the wall surface  920  and whose projections are inserted into the through-holes  10 C of the electrostatic speaker  10 , so that the electrostatic speaker  10  is hung at the wall surface  920  and prevented from falling down from the wall surface  920 . Since no conductive layers are formed in the holding regions  10 D in the diaphragm  102 , the electrodes  112  and  114 , no conductive layers are exposed on the interior walls of the through-holes  10 C. Even when the holding members  510  are made of conductive materials, it is possible to prevent the conductive layers  103 ,  104 ,  113 , and  115  from being short-circuited in the electrostatic speaker  10 . That is, the second embodiment guarantees the normal functionality of the electrostatic speaker  10  irrespective of the through-holes  10 C with which the electrostatic speaker  10  is installed at a certain position. 
     Variations 
     The present invention is not necessarily limited to the first and second embodiments, which can be further modified in various ways as follows. 
     (1) The structure of the electrostatic speaker  10  is not necessarily limited to the first and second embodiments. In short, the electrostatic speaker  10  needs to be configured of a diaphragm having a first conductive layer on a first surface and a substrate having a second conductive layer on a second surface. Namely, the electrostatic speaker  10  needs at least the diaphragm  102  having the conductive layer  103  on the upper surface  102 A and the electrode  112  having the conductive layer  113  on the lower surface  112 A. In addition, the diaphragm  102 , the electrode  112  and  114  do not need conductivity in the holding region  10 A and the holding regions  10 D, whilst they need conductivity in other regions (other than the holding regions  10 A and  10 D). For example, at least one of the electrodes  112  and  114  is composed of a planar conductive cloth in which conductive materials are included in other regions (other than the holding regions  10 A and  10 D), whilst no conductive materials are included in the holding regions  10 A and  10 D.
 
(2) It is possible to adopt other materials other than PET and PP for use in the diaphragm  102 , the electrodes  112  and  114 . For example, the diaphragm  102 , the electrodes  112  and  114  can be composed of synthetic resins. The cushion materials  132  need air permeability and elasticity; hence, they are not necessarily composed of compressed cottons. For example, the cushion materials  132  can be composed of ester wools. The outline shapes of the diaphragm  102 , the electrode  112  and  114  are not necessarily limited to rectangular shapes. For example, the diaphragm  102 , the electrodes  112  and  114  can be formed in circular shapes or polygonal shapes except for rectangular shapes. In addition, the main body of the electrostatic speaker  10  can be formed in a cylindrical shape, a conical shape, a pyramid shape, a lampshade shape, or parasol shape. In this case, it is preferable that one holding region be formed at one end of the cylindrical shape, whilst one holding region be formed at a top portion of the conical shape, the pyramid shape, the lampshade shape, or the parasol shape.
 
(3) It is possible to incorporate terminals with respect to the holding member  510  and the electrostatic speaker  10 . The terminal of the electrostatic speaker  10  comes in contact with the terminal of the holding members  510  when the electrostatic speaker  10  is held by the holding member  510 . The terminal of the electrostatic speaker  10  coupled with the terminal of the holding member  510  may serve as a power-supply terminal for supplying power to any one of the conductive layers  10 ,  104 ,  113 , and  115 . It is possible to incorporate a plurality of terminals (each serving as the above power-supply terminal) with respect to the electrostatic speaker  10  and the holding member  510  respectively. That is, it is possible to incorporate four power-supply terminals for supplying power to the four conductive layers  103 ,  104 ,  113 , and  115  with respect to the electrostatic speaker  10  and the holding members  510  respectively.
 
(4) In the first embodiment, the holding region  10 A is not necessarily formed along one edge of the “rectangular-shaped” electrostatic speaker  10 , and the holding region  10 A is not necessarily formed with a certain width. For example, the position, shape and size of the holding region  10 A can be determined in conformity with the position, shape and size of the holding member  510  holding the electrostatic speaker  10 . The holding member  510  does not necessarily hold the upper edge of the electrostatic speaker  10 , wherein the holding member  510  can hold both the left-side and right-side edges, both the upper and lower edges of the electrostatic speaker  10 , all the four corners of the electrostatic speaker  10 , all the four sides of the electrostatic speaker  10 , or the like. Herein, the holding region  10 A needs to be set to the position at which the holding region  10 A is held by the holding member  510 . The length of the holding member  510  can be shorter than the length of one side of the electrostatic speaker  10 . In this case, the length of the holding region  10 A needs to agree with the length of the holding member  510  along a side edge of the electrostatic speaker  10  being held by the holding member  510 .
 
(5) The electrostatic speaker  10  of the first embodiment needs to be configured such that adjacent conductive layers cannot be short-circuited in the holding region  10 A. In other words, no conductivity is needed in at least one of the upper surface  102 A of the diaphragm  102  and the lower surface  112 A. of the electrode  112 . In addition, no conductivity is needed in at least one of the lower surface  102 E of the diaphragm  102  and the upper surface  114 A of the electrode  114 . That is, one of the conductive layers  103  and  113  is not necessarily formed in the holding region  10 A. In addition, one of the conductive layers  104  and  115  is not necessarily formed in the holding region  10 A. Alternatively, an insulating layer can be formed in the holding region  10 A in order to cover one of the conductive layers  103  and  113  therewith. In addition, an insulating layer can be formed in the holding region  10 A in order to cover one of the conductive layers  104  and  115  therewith.
 
(6) In the second embodiment, the through-holes  10 C are not necessarily formed in rectangular shapes in plan view. The through-holes IOC can be formed in circular shapes or polygonal shapes except for rectangular shapes, The number of the through-holes  10 C formed in the main body of the electrostatic speaker  10  is not necessarily limited to two. It is possible to form one through-hole  10 C or three or more through-holes  10 C in the main body of the electrostatic speaker  10 . The holding regions  10 D are not necessarily formed in rectangular shapes in plan view. The holding regions  10 D can be formed in circular shapes or polygonal shapes except for rectangular shapes. The shapes of the holding regions  10 D do not necessarily agree with the shapes of the through-holes  10 C. The shape, position and size of the holding region  10 D can be determined in conformity with the shape, position and size of the holding member  510  holding the electrostatic speaker  10 . The holding region  10 D can be set to a position at which the holding member  510  holds the electrostatic speaker  10 .
 
(7) In the second embodiment, an installation measure of the electrostatic speaker  10  having the through-holes  10 C is not necessarily limited to the “L-shaped” holding members  510  shown in  FIG. 9 . The holding member  510  can be formed in rod-like shapes (e.g. nails and stakes) which project from the wall surface  920 . That is, the electrostatic speaker  10  can be hung at the rod-shapes holding members  510  with the through-holes  10 C, so that the electrostatic speaker  10  is held and prevented from falling down from the wall surface  920 . The electrostatic speaker  10  can be fixed to the wall surface  920  by use of screws, which are inserted into the through-holes IOC and put into the wall surface  920 . In this connection, screws can be intensively fastened to certainly fix the electrostatic speaker  10  onto the wall surface  920 , wherein the electrostatic speaker  10  is intensively pressed onto the wall surface  920  with screw heads at a high pressure, That is, a high pressure, which is sufficient to press and fix the electrostatic speaker  10  onto the wall surface  920 , is applied to the holding regions  10 D via screw heads, Since no conductive layers are formed in the diaphragm  102 , the electrodes  112  and  114  in the holding region  10 D, adjacent conductive layers cannot be short-circuited with a high pressure applied to the holding regions  10 D. As described above, the second embodiment (and its variations) guarantees the normal functionality of the electrostatic speaker  10  even when the electrostatic speaker  10  is installed at a certain position.
 
(8) In the second embodiment, the electrostatic speaker  10  does not necessarily equipped with the through-holes  10 C in shipment. The electrostatic speaker  10  subjected to shipment can have the holding regions  10 D which do not surround the through-holes  10 C. This allows users to arbitrarily form the through-holes  10 C used for fixing the electrostatic speaker  10  onto the wall surface  920 . Before an installation of the electrostatic speaker  10  on the wall surface  920 , users may form the through-holes  10 C in the holding regions  10 D by use of a drill or punch in advance. Alternatively, users may form the through-holes  10 C simultaneously with fixing the electrostatic speaker  10  onto the wall surface  920 , wherein users may hammer nails into the holding regions  10 B of the electrostatic speaker  10 .
 
(9) It is possible to form an identification mark indicating the holding region  10 A or  10 D on the surface of the electrostatic speaker  10 . For example, the holding region  10 A or  10 D can be painted in a color which differs from a color of the other region on the surface of the electrostatic speaker  10 . Alternatively, the holding region  10 A or  10 D can be formed with a surface shape (or a texture) which differs from the texture of the other region on the surface of the electrostatic speaker  10 , This helps users to easily discriminate position, shape and size of the holding member  510  holding the electrostatic speaker  10 .
 
     Lastly, the present invention is not necessarily limited to the above embodiments and variations, which can be further modified within the scope of the invention as defined in the appended claims.