Patent Publication Number: US-8983099-B2

Title: Electrostatic loudspeaker

Description:
TECHNICAL FIELD 
     The present invention relates to an electrostatic loudspeaker. 
     BACKGROUND ART 
     The push-pull electrostatic loudspeaker disclosed in Patent Document 1 includes two flat electrodes opposed to each other with a clearance therebetween and a membranous vibrating plate (vibrating member) having conductibility and disposed between the flat electrodes; when a predetermined bias voltage is applied to the vibrating plate and the voltage to be applied across the flat electrodes is changed, the electrostatic force exerted to the vibrating plate is changed, whereby the vibrating plate is displaced. When the applied voltage is changed depending on an acoustic signal to be input, the vibrating plate is displaced repeatedly depending on the change, and an acoustic wave depending on the acoustic signal is generated from both faces of the vibrating plate. The generated acoustic wave passes through through-holes formed in the flat electrodes and is radiated to the outside. 
     Furthermore, as an electrostatic loudspeaker having flexibility and being foldable or bendable, the electrostatic loudspeaker disclosed in Patent Document 2 is available. In the electrostatic loudspeaker, a polyester film (vibrating member) on which aluminum is evaporated is held between two pieces of cloth (electrodes) woven with conductive threads, and ester wool is disposed between the film and the cloth. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: JP-A-2007-318554 
     Patent Document 2: JP-A-2008-54154 
     SUMMARY OF THE INVENTION 
     Problem that the Invention is to Solve 
     A push-pull electrostatic loudspeaker generates an acoustic wave from both faces of the vibrating plate (vibrating member) thereof. However, in the case that the push-pull electrostatic loudspeaker is installed so as to be made contact with a shield through which the acoustic wave hardly passes, such as a floor face or a wall face, the acoustic wave generated toward the shield is blocked by the shield, and there occurs a problem that the acoustic wave is not radiated to the outside of the electrostatic loudspeaker. 
     Under the circumstances described above, an object of the present invention is to provide a push-pull electrostatic loudspeaker capable of radiating the acoustic wave generated from both faces of the vibrating member thereof to the outside of the electrostatic loudspeaker even if the electrostatic loudspeaker is installed so as to be made contact with a shield through which the acoustic wave hardly passes. 
     Means for Solving the Problems 
     In order to solve the above problems, according to the invention, there is provided an electrostatic loudspeaker comprising: a first electrode having acoustic transmission property; a second electrode having acoustic transmission property, and disposed so as to be opposed to the first electrode; a vibrating member having conductibility, and disposed between the first electrode and the second electrode; a first elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the first electrode; a second elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the second electrode; and a first separation member having insulation property and acoustic transmission property, and disposed on an opposite side of a face of the first electrode, which is opposed to the first elastic member. 
     In the invention, the electrostatic loudspeaker may further include a second separation member having insulation property and acoustic transmission property, and disposed on an opposite side of a face of the second electrode, which is opposed to the second elastic member. 
     In the invention, the first separation member may have a hole opening from an inside of the first separation member toward a face on an opposite side of a face of the first separation member, which is opposed to the first electrode. 
     In the invention, a holding member may be inserted into the hole. 
     In the invention, the first separation member may have a hole in a circumferential face thereof. 
     In the invention, a hook member may be inserted into the hole. 
     In the invention, the first separation member may have elasticity. 
     In the invention, the first separation member may be integrated with a main body having at least the first electrode, the second electrode, the vibrating member, the first elastic member, and the second elastic member using a restraining member so as to be formed into one body. 
     In the invention, the restraining member may have a belt shape. 
     In the invention, the restraining member may be a member for covering the first separation member and the main body. 
     In the invention, the first separation member may have one face formed into a convex shape, and a main body having at least the first electrode, the second electrode, the vibrating member, the first elastic member, and the second elastic member may be provided on the one face. 
     In the invention, the first separation member may have one face formed into a concave shape, and a main body having at least the first electrode, the second electrode, the vibrating member, the first elastic member, and the second elastic member may be provided on the one face. 
     In the invention, the first separation member may have one face formed into a curved shape, and a main body having at least the first electrode, the second electrode, the vibrating member, the first elastic member, and the second elastic member may be provided on a face on an opposite side of the one face. 
     In the invention, the first separation member may have a base and a plurality of protrusions provided on one face of the base. 
     In the invention, the first separation member may be a member in which a plurality of spaces having a predetermined shape are joined together. 
     In the invention, the predetermined shape is a hexagonal shape. 
     In order to solve the above problems, according to the invention, there is provided a speaker system comprising: a loudspeaker&#39;s main body including: a first electrode having acoustic transmission property; a second electrode having acoustic transmission property, and disposed so as to be opposed to the first electrode; a vibrating member having conductibility, and disposed between the first electrode and the second electrode; a first elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the first electrode; and a second elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the second electrode; and a separation member having insulation property and acoustic transmission property, and disposed on an opposite side of a face of the first electrode of the loudspeaker&#39;s main body, which is opposed to the first elastic member. 
     In order to solve the above problems, according to the invention, there is provided a separation member mounted on a loudspeaker&#39;s main body having a first electrode having acoustic transmission property, a second electrode having acoustic transmission property, and disposed so as to be opposed to the first electrode, a vibrating member having conductibility, and disposed between the first electrode and the second electrode, a first elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the first electrode, and a second elastic member having elasticity, insulation property, and acoustic transmission property, and disposed between the vibrating member and the second electrode, wherein the separation member has insulation property and acoustic transmission property and is disposed on an opposite side of a face of the first electrode of the loudspeaker&#39;s main body, which is opposed to the first elastic member. 
     Advantage of the Invention 
     The electrostatic loudspeaker according to the present invention can radiate the acoustic wave generated from both faces of the vibrating member thereof to the outside of the electrostatic loudspeaker even if the electrostatic loudspeaker is installed so as to be made contact with a shield through which the acoustic wave hardly passes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view showing an electrostatic loudspeaker according to an embodiment of the present invention; 
         FIG. 2  is a schematic view showing the cross-section and electrical configuration of the electrostatic loudspeaker; 
         FIG. 3  is an exploded perspective view showing the electrostatic loudspeaker; 
         FIGS. 4(   a ) and  4 ( b ) are views illustrating the transmission of an acoustic wave; 
         FIGS. 5(   a ) and  5 ( b ) are views showing an electrostatic loudspeaker in which the positional displacement thereof is suppressed according to a modification of the present invention; 
         FIG. 6  is a view showing an electrostatic loudspeaker equipped with an amplifier according to a modification of the present invention; 
         FIG. 7  is a sectional view showing an electrostatic loudspeaker according to a modification of the present invention; 
         FIGS. 8(   a ) and  8 ( b ) are external perspective views showing a separation member according to a modification of the present invention; 
         FIGS. 9(   a ) and  9 ( b ) are external perspective views showing a separation member according to a modification of the present invention; 
         FIG. 10  is a schematic view showing a separation member and a shield according to a modification of the present invention; 
         FIGS. 11(   a ),  11 ( b ), and  11 ( c ) are views showing the structure of a separation member according to a modification of the present invention; 
         FIGS. 12(   a ),  12 ( b ), and  12 ( c ) are views showing the structure of a separation member according to a modification of the present invention; 
         FIG. 13  is an exploded perspective view showing an electrostatic loudspeaker according to a modification of the present invention; 
         FIG. 14  is a view showing the lower face of a separation member according to a modification of the present invention; 
         FIG. 15  is a view showing an electrostatic loudspeaker secured to a shield according to a modification of the present invention; 
         FIGS. 16(   a ) and  16 ( b ) are views showing a separation member and a holding member according to a modification of the present invention; 
         FIGS. 17(   a ) and  17 ( b ) are views showing an electrostatic loudspeaker secured to a shield according to a modification of the present invention; and 
         FIG. 18  is a view showing the structures of hook members and a separation member according to a modification of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     [Embodiment] 
       FIG. 1  is an external view showing an electrostatic loudspeaker  1  according to an embodiment of the present invention, and  FIG. 2  is a schematic view showing the cross-section and electrical configuration of the electrostatic loudspeaker  1 . In addition,  FIG. 3  is an exploded perspective view showing the electrostatic loudspeaker  1 . In this embodiment, the electrostatic loudspeaker  1  has a rectangular parallelepiped shape. In the following descriptions of the figures, the X, Y, and Z axes perpendicular to one another indicate directions, and it is assumed that the left-right direction as viewed from the front of the electrostatic loudspeaker  1  is the X-axis direction, that the depth direction is the Y-axis direction, and that the height direction is the Z-axis direction. Besides, it is assumed that “•” written in “o” in each figure means an arrow directed from the back to the front of the figure. Moreover, “x” written in “o” in each figure means an arrow directed from the front to the back of the figure. The term “front” herein denotes the direction of a face for the convenience of description, but does not denote that the electrostatic loudspeaker  1  is oriented in the front direction when it is placed. When the electrostatic loudspeaker  1  is placed, it may be placed in any direction as necessary. Still further, the dimensions of the respective components shown in the figure are made different from the actual dimensions thereof so that the shapes of the components can be understood easily. 
     (Configurations of the Respective Components of the Electrostatic Loudspeaker  1 ) 
     The electrostatic loudspeaker  1  is roughly divided into a main body  11  and a separation member  12 . 
     First, the configurations of various sections constituting the main body  11  of the electrostatic loudspeaker  1  will be described. 
     The main body  11  of the electrostatic loudspeaker  1  is the so-called push-pull electrostatic loudspeaker and has a vibrating member  10 , electrodes  20 U and  20 L, spacers  30 U and  30 L, and elastic members  40 U and  40 L. In this embodiment, the configurations of the electrodes  20 U and  20 L are the same, and the configurations of the spacers  30 U and  30 L are the same. Furthermore, the configurations of the elastic members  40 U and  40 L are also the same. Hence, in the case that it is not particularly necessary to distinguish between the two in the respective members, the descriptions of “U” and “L” are omitted. 
     The vibrating member  10  has a configuration in which a metal having conductibility is evaporated or a conductive coating material is applied to both faces of a film made of PET (polyethylene terephthalate), PP (polypropylene), or the like to form conductive membranes. The vibrating member  10  has a rectangular shape as viewed from the Z-axis direction, and the dimension in the Z-axis direction is approximately several pm to several ten pm. Furthermore, the vibrating member  10  has flexibility and is deflected when a force is applied thereto. 
     The spacer  30  has insulation property and has a rectangular frame shape as viewed from the Z-axis direction. Furthermore, the spacer  30  has flexibility and is deflected when a force is applied thereto. The dimension of the spacer  30  in the X-axis direction is the same as the dimension of the electrode  20  in the X-axis direction, and the dimension of the spacer  30  in the Y-axis direction is the same as the dimension of the electrode  20  in the Y-axis direction. The dimension of the spacer  30 U in the Z-axis direction is the same as the dimension of the spacer  30 L in the Z-axis direction. The elastic member  40  is a member obtained by heating and compressing cotton and allows air and sound to pass therethrough. In other words, the elastic member  40  has acoustic transmission property. Furthermore, the elastic member  40  has insulation property and elasticity, and it is deformed when an external force is applied thereto and returns to its original shape when the external force is removed. In addition, the elastic member  40  has a rectangular shape as viewed from the Z-axis direction. 
     The electrode  20  has a configuration in which a metal having conductibility is evaporated or a conductive coating material is applied to one face of a film having insulation property and made of PET, PP, or the like. The electrode  20  has a plurality of through-holes  21  passing through from the front face to the back face. The electrode  20  allows air and sound to pass therethrough. In other words, the electrode  20  has acoustic transmission property. In addition, the electrode  20  has flexibility and is deflected when a force is applied thereto. The electrode  20  has a rectangular shape as viewed from the Z-axis direction. The dimensions of the electrode  20  in the X-axis direction and in the Y-axis direction are longer than the dimensions of the vibrating member  10  in the X-axis direction and in the Y-axis direction. 
     Next, the configuration of the separation member  12  of the electrostatic loudspeaker  1  will be described. The separation member  12  is a member that is used to separate the main body  11  from a shield to provide an air layer. The term “shield” is an object, such as a floor face, a wall face, or a pillar, which can make contact with the electrostatic loudspeaker  1 ; an acoustic wave incident to the shield hardly passes therethrough and is easily reflected thereby. The shape of the surface of the shield is not limited to a flat face, but may be a curved face or a face having unevenness. The term “separation” means a state in which a certain object is placed away from a certain position. 
     The separation member  12  is a member obtained by heating and compressing cotton and allows air and sound to pass therethrough. The separation member  12  has insulation property and elasticity, and it is deformed when an external force is applied thereto and returns to its original shape when the external force is removed. The separation member  12  has a rectangular parallelepiped shape. In the separation member  12 , the face in the positive direction of the Z-axis is referred to as the upper face thereof, the face in the negative direction of the Z-axis is referred to as the lower face thereof, and the faces other than the upper face and the lower face are referred to as the circumferential faces thereof. The electrode  20 L of the main body  11  is firmly bonded to the upper face of the separation member  12  using an adhesive. The dimension of the separation member  12  in the X-axis direction is the same as the dimension of the main body  11  in the X-axis direction, and the dimension of the separation member  12  in the Y-axis direction is the same as the dimension of the main body  11  in the Y-axis direction. The dimension of the separation member  12  in the Z-axis direction is approximately 5 to 6 cm, that is, a dimension adequate to allow an acoustic wave having passed through the through-holes  21  to be radiated from the circumferential faces of the separation member  12  to the outside of the electrostatic loudspeaker  1 . The dimension of the separation member  12  in the Z-axis direction is not limited to 5 to 6 cm, but may be determined appropriately depending on the intensity of the acoustic wave radiated from the main body  11 . It is supposed that the separation member  12  has acoustic transmission property higher than that of the spacer  30 . 
     (Structure of the Electrostatic Loudspeaker  1 ) 
     Next, the structure of the electrostatic loudspeaker  1  will be described. 
     In the electrostatic loudspeaker  1 , the spacer  30 U and the spacer  30 L are firmly bonded to each other with one side of the vibrating member  10  held between the lower face of the spacer  30 U and the upper face of the spacer  30 L. Furthermore, in the electrostatic loudspeaker  1 , the electrode  20 L is firmly bonded to the lower face of the spacer  30 L with the conductive face thereof oriented toward the vibrating member  10 , and the electrode  20 U is firmly bonded to the upper face of the spacer  30 U with the conductive face thereof oriented toward the vibrating member  10 . Inside the frame-shaped spacer  30 L, the elastic member  40 L is disposed. The elastic member  40 L makes contact with the vibrating member  10  and the electrode  20 L. Furthermore, inside the frame-shaped spacer  30 U, the elastic member  40 U is disposed. The elastic member  40 U makes contact with the vibrating member  10  and the electrode  20 U. The separation member  12  is firmly bonded to the lower face of the electrode  20 L using an adhesive. 
     In this embodiment, only one side of the vibrating member  10  is held between the spacer  30 U and the spacer  30 L, and the other three sides are in a state of not being held between the spacer  30 U and the spacer  30 L. In other words, the vibrating member  10  is placed between the electrode  20 U and the electrode  20 L in a state that no tension is applied thereto. However, since the elastic member  40 U and the elastic member  40 L support the vibrating member  10  while holding it therebetween, when the vibrating member  10  is not in a state of being driven, the vibrating member  10  is placed at an intermediate position between the electrode  20 U and the electrode  20 L. Moreover, since no tension is applied to the vibrating member  10 , even if the electrostatic loudspeaker  1  is deflected, no tension is applied to the vibrating member  10 , and no elongation occurs in the vibrating member  10 . 
     (Electrical Configuration of the Electrostatic Loudspeaker  1 ) 
     Next, the electrical configuration of the electrostatic loudspeaker  1  will be described. As shown in  FIG. 2 , a driver  100  is connected to the electrostatic loudspeaker  1 . The driver  100  is equipped with a transformer  50 , an input section  60 , and a bias supply  70 . An acoustic signal is input to the input section  60  from the outside. The bias supply  70  is connected to the conductive portion of the vibrating member  10  and to the middle point on the output side of the transformer  50 . The bias supply  70  supplies a DC bias to the vibrating member  10 . The conductive portion of the electrode  20 U is connected to one terminal on the output side of the transformer  50 , and the conductive portion of the electrode  20 L is connected to the other terminal on the output side of the transformer  50 . The input side of the transformer  50  is connected to the input section  60 . In this configuration, when an acoustic signal is input to the input section  60 , a voltage corresponding to the input acoustic signal is applied across the electrodes  20 , whereby the electrostatic loudspeaker  1  operates as a push-pull electrostatic loudspeaker. 
     (Operation of the Electrostatic Loudspeaker  1 ) 
     Next, the operation of the electrostatic loudspeaker  1  will be described. When an acoustic signal is input to the input section  60 , a voltage corresponding to the input acoustic signal is applied across the electrode  20 U and the electrode  20 L from the transformer  50 . When a potential difference occurs between the electrode  20 U and the electrode  20 L due to the applied voltage, an electrostatic force is exerted to the vibrating member  10  placed between the electrode  20 U and the electrode  20 L in a direction in which the vibrating member  10  is attracted to either the electrode  20 U or the electrode  20 L. 
     For example, it is assumed that an acoustic signal is input to the input section  60 , this acoustic signal is supplied to the transformer  50 , a plus voltage is applied to the electrode  20 U, and a minus voltage is applied to the electrode  20 L. Since a plus voltage is applied from the bias supply  70  to the vibrating member  10 , the vibrating member  10  repels the electrode  20 U to which the plus voltage is applied, but is attracted to the electrode  20 L to which the minus voltage is applied, thereby being displaced toward the electrode  20 L. Furthermore, it is assumed that an acoustic signal is input to the input section  60 , this acoustic signal is supplied to the transformer  50 , a minus voltage is applied to the electrode  20 U, and a plus voltage is applied to the electrode  20 L. The vibrating member  10  repels the electrode  20 L to which the plus voltage is applied, but is attracted to the electrode  20 U to which the minus voltage is applied, thereby being displaced toward the electrode  20 U. 
     In this way, the vibrating member  10  is displaced toward the electrode  20 U or toward the electrode  20 L depending on the acoustic signal and the direction of the displacement changes sequentially, whereby vibration is generated and an acoustic wave corresponding to the vibration state (frequency, amplitude, and phase) is generated from the vibrating member  10 . The generated acoustic wave passes through the elastic members  40  and the electrodes  20 , and is radiated to the outside of the main body  11  of the electrostatic loudspeaker  1 . 
     The transmission paths of the acoustic wave generated from the vibrating member  10  will be described. 
       FIGS. 4(   a ) and  4 ( b ) are views illustrating the transmission of the acoustic wave.  FIG. 4(   a ) shows an electrostatic loudspeaker  900  according to a related art, not equipped with the separation member  12 , and  FIG. 4(   b ) shows the electrostatic loudspeaker  1  according to this embodiment, equipped with the separation member  12 . Respective components constituting the electrostatic loudspeaker  900  are the same as those constituting the main body  11  of the electrostatic loudspeaker  1 . Hence, the descriptions of the respective components constituting the electrostatic loudspeaker  900  are omitted. 
     First, the transmission paths of the acoustic wave radiated from the electrostatic loudspeaker  900  will be described. The electrostatic loudspeaker  900  is installed such that the electrode  20 L is made contact with a shield S 1 . It is assumed that the shield S 1  is a floor face, for example, on which objects can be placed. The acoustic wave generated from the vibrating member  10  is radiated in the positive direction of the Z-axis and in the negative direction of the Z-axis. The acoustic wave generated in the positive direction of the Z-axis passes through the elastic member  40 U and the electrode  20 U and is radiated to the outside of the electrostatic loudspeaker  900 . On the other hand, the acoustic wave generated in the negative direction of the Z-axis passes through the elastic member  40 L and enters the through-holes  21 L of the electrode  20 L. However, since the electrode  20 L makes contact with the shield S 1 , the through-holes  21 L are blocked by the shield S 1 . As a result, the acoustic wave having entered the through-holes  21 L is reflected by the shield S 1  and cannot pass through the through-holes  21 L. In other words, the acoustic wave generated in the negative direction of the Z-axis is not radiated to the outside of the electrostatic loudspeaker  900 . 
     Next, the transmission paths of the acoustic wave radiated from the electrostatic loudspeaker  1  according to the present invention equipped with the separation member  12  shown in  FIG. 4(   b ) will be described. The electrostatic loudspeaker  1  is installed such that the lower face of the separation member  12  is made contact with the shield S 1 . The acoustic wave generated from the vibrating member  10  is radiated in the positive direction of the Z-axis and in the negative direction of the Z-axis. The acoustic wave generated in the positive direction of the Z-axis passes through the elastic member  40 U and the electrode  20 U and is radiated to the outside of the electrostatic loudspeaker  1 . On the other hand, the acoustic wave generated in the negative direction of the Z-axis passes through the elastic member  40 L and enters the through-holes  21 L of the electrode  20 L. In this case, since the electrode  20 L makes contact with the separation member  12 , the through-holes  21 L are blocked by the separation member  12 . However, since the separation member  12  allows air and sound to pass therethrough, the acoustic wave having entered the through-holes  21 L can pass through the through-holes  21 L. As a result, the acoustic wave having passed through the through-holes  21 L passes through the separation member  12  and is reflected by the shield S 1 , and then radiated from the circumferential faces of the separation member  12  to the outside of the electrostatic loudspeaker  1 . 
     As described above, in the electrostatic loudspeaker  1 , the through-holes  21 L are not blocked by the shield. Hence, in the electrostatic loudspeaker  1 , the acoustic wave having passed through the through-holes  21 L can be radiated from the circumferential faces of the separation member  12 . In other words, the electrostatic loudspeaker  1  can radiate the acoustic wave generated from both faces of the vibrating member to the outside of the electrostatic loudspeaker. 
     For example, in the case that the separation member  12  is not provided between the vibrating member  10  and the shield and that no distance is securely obtained between the vibrating member  10  and the shield, the air being present between the vibrating member  10  and the shield is difficult to move even if the vibrating member  10  vibrates, and the viscosity of the air being present between the vibrating member  10  and the shield affects the vibration of the vibrating member  10 , whereby the sound pressure is lowered. On the other hand, in the electrostatic loudspeaker  1  according to this embodiment, a distance is securely obtained between the vibrating member  10  and the shield by virtue of the separation member  12 , and the air being present between the vibrating member  10  and the shield is easy to move. Hence, when this case is compared with the case in which the separation member  12  does not exist between the vibrating member  10  and the shield and no distance is securely obtained therebetween, the vibrating member  10  is less affected by the viscosity of the air being present between the shield and the vibrating member  10 , whereby the sound pressure of the sound to be output can be raised. 
     In addition, the electrostatic loudspeaker  1  is formed of components that are deflected when a force is applied thereto. Hence, the electrostatic loudspeaker  1  can be deflected, thereby being able to be installed not only on a flat face but also on a curved face. 
     [Modifications] 
     The above-mentioned embodiment is just one example of the embodiment according to the present invention. The present invention can be implemented in embodiments in which the following modifications are applied to the above-mentioned embodiment. The following modifications may be appropriately combined and implemented as necessary. 
     (Modification 1) 
     In the above-mentioned embodiment, the vibrating member  10  is a member obtained by evaporating a conductive metal or by applying a conductive coating material onto both faces of a film, but may be a member obtained by evaporating a conductive metal or by applying a conductive coating material onto one face of the film. In addition, the vibrating member  10  is not limited to be made of PET or PP, but may be a member obtained by evaporating a conductive metal or by applying a conductive coating material onto a film of another synthetic resin. 
     In the above-mentioned embodiment, the electrode  20  is provided with the plurality of through-holes  21  passing therethrough from the front face to the back face. However, the electrostatic loudspeaker  1  is not limited to have the through-holes  21 , but should only have a configuration in which at least an acoustic wave can be radiated to the outside of the electrostatic loudspeaker  1 . For example, the electrode  20  may be a cloth-like electrode woven with conductive fiber or may be made of conductive non-woven cloth; the electrode should only have conductibility and flexibility and allow air and sound to pass therethrough. Furthermore, the electrode  20  is a member obtained by evaporating a conductive metal or by applying a conductive coating material onto one face of a film, but may be a member obtained by evaporating a conductive metal or by applying a conductive coating material onto both faces of the film. In addition, the electrode  20  is not limited to be made of PET or PP, but may be a member obtained by evaporating a conductive metal or by applying a conductive coating material onto a sheet of another synthetic resin. 
     (Modification 2) 
     In the above-mentioned embodiment, the main body  11  and the separation member  12  of the electrostatic loudspeaker  1  are firmly bonded to each other using an adhesive. However, without the main body  11  and the separation member  12  firmly bonded to each other, they may be configured so that their positions are not displaced relative to each other. 
       FIGS. 5(   a ) and  5 ( b ) are views showing an electrostatic loudspeaker  1   a  in which the positional displacement thereof is suppressed according to a modification of the present invention. In  FIG. 5(   a ), a restraining member  131  and a restraining member  132  are an endless belt, have insulation property, and allow air and sound to pass therethrough. The restraining member  131  is wound in the Y-axis direction so that the main body  11  and the separation member  12  are integrated into one body, whereby the position of the main body  11  and the position of the separation member  12  are suppressed from being displaced relative to each other in the Y-axis direction and in the Z-axis direction. Furthermore, the restraining member  132  is wound in the X-axis direction so that the main body  11  and the separation member  12  are integrated into one body, whereby the position of the main body  11  and the position of the separation member  12  are suppressed from being displaced relative to each other in the X-axis direction and in the Z-axis direction. As a result, the main body  11  and the separation member  12  are suppressed from being displaced relative to each other as in the case that they are firmly bonded to each other using an adhesive. 
     Furthermore, although the relative positional displacement is suppressed by winding the restraining members on the surfaces of the main body  11  and the separation member  12  as shown in  FIG. 5(   a ), the relative positional displacement may be suppressed by covering the entire areas of the surfaces of the main body  11  and the separation member  12  using a restraining member as shown in  FIG. 5(   b ). In  FIG. 5(   b ), a restraining member  133  is a piece of cloth formed to cover the surfaces of the main body  11  and the separation member  12  by integrating them into one body, and the cloth has insulation property and allows air and sound to pass therethrough. The restraining member  133  covers the main body  11  and the separation member  12  by integrating them into one body, whereby the positions of the main body  11  and the separation member  12  are suppressed from being displaced relative to each other in the X-axis direction, in the Y-axis direction, and in the Z-axis direction. As a result, the main body  11  and the separation member  12  are suppressed from being displaced relative to each other as in the case that they are firmly bonded to each other using an adhesive. 
     (Modification 3) 
     The electrostatic loudspeaker may be configured so as to be integrated with an amplifier for amplifying an acoustic signal. 
       FIG. 6  is a view showing an electrostatic loudspeaker  1   b  equipped with an amplifier according to a modification of the present invention. In the electrostatic loudspeaker  1   b , an amplifier  14  is mounted on a circumferential face thereof. The amplifier  14  amplifies an acoustic signal input from the outside and outputs the acoustic signal. The acoustic signal output from the amplifier  14  is input to the input section  60  of the driver  100  provided for the main body  11 . In the electrostatic loudspeaker  1   b  configured as described above, no amplifier is required to be connected thereto separately, and it is not required to consider the disposition of the amplifier. In other words, the installation of the electrostatic loudspeaker  1   b  is made easy. Furthermore, in the electrostatic loudspeaker  1   b,  the main body  11  is not required to be equipped with the driver  100 . In this case, a function equivalent to that of the driver  100  may be provided as the function of the amplifier  14 , for example. 
     (Modification 4) 
     In the above-mentioned embodiment, the separation member  12  is provided between the shield and the electrode  20 L opposed to the shield. However, the position in which the separation member  12  is provided is not limited to this position. 
       FIG. 7  is a sectional view showing an electrostatic loudspeaker  1   c  according to a modification of the present invention. As shown in the figure, in the electrostatic loudspeaker  1   c , a separation member  12 L is firmly bonded to the lower face of the electrode  20 L, and a separation member  12 U is firmly bonded to the upper face of the electrode  20 U. In other words, in the electrostatic loudspeaker  1   c , the main body  11  is held between the separation member  12 U and the separation member  12 L. In the electrostatic loudspeaker  1   c  configured as described above, even if the separation member  12 U is made contact with a shield, the through-holes  21 U are not blocked by the shield. Furthermore, even if the separation member  12 L is made contact with a shield, the through-holes  21 L are not blocked by the shield. In other words, in the electrostatic loudspeaker  1   c , even if either the separation member  12 U or the separation member  12 L is made contact with a shield, the acoustic wave generated from both faces of the vibrating member can be radiated to the outside of the electrostatic loudspeaker  1   c.    
     Moreover, since the electrostatic loudspeaker  1   c  is configured so that the main body  11  is held between the separation members  12  having elasticity, it may be possible that an impact applied to the electrostatic loudspeaker  1   c  is absorbed by the separation members  12  and the impact transmitted to the main body  11  is reduced. Still further, since the electrostatic loudspeaker  1   c  is configured so that the electrode  20  is covered with the separation members  12 , it may be possible that the occurrence of electric shock and short-circuit is suppressed. 
     (Modification 5) 
     The shape of the separation member is not limited to a cube, but may be a pillar or a cone. In addition, the face of the separation member on which the main body is provided is not limited to be a flat face, but may be a curved face. 
       FIG. 8(   a ) is an external perspective view showing a separation member  12   d , and  FIG. 8(   b ) is a schematic view showing the transmission paths of an acoustic wave. As shown in the figures, the upper face of the separation member  12   d  is formed into a convex shape. In the case that an electrostatic loudspeaker is configured by bonding the main body to the area  127   d  on the upper face of the separation member  12   d , the shape of upper face of the main body becomes a convex shape similar to the shape of the separation member  12   d . In this case, since the acoustic wave radiated from the main body is diffused along the transmission paths Ld shown in  FIG. 8(   b ), the wave is diffused to a space wider than the space of the area  127   d  in the Z-axis direction. 
       FIG. 9(   a ) is an external perspective view showing a separation member  12   e , and  FIG. 9(   b ) is a schematic view showing the transmission paths of an acoustic wave. As shown in the figures, the upper face of the separation member  12   e  is formed into a concave shape. In the case that an electrostatic loudspeaker is configured by bonding the main body to the area  127   e  on the upper face of the separation member  12   e , the shape of the upper face of the main body becomes a concave shape similar to the shape of the separation member  12   e . In this case, since the acoustic wave radiated from the main body is diffused along the transmission paths Le shown in  FIG. 9(   b ), the wave is diffused to a space narrower than the space of the area  127   e  in the Z-axis direction. 
     Hence, for example, in the case that an acoustic wave is desired to be radiated to a wide space, the main body should only be provided on the separation member formed into a convex shape. Furthermore, in the case that an acoustic wave is desired to be radiated to a narrow space, the main body should only be provided on the separation member formed into a concave shape. The shape of the separation member and the position in which the main body is provided on the separation member are arbitrary and should only be determined depending on the direction in which the acoustic wave is desired to be radiated. 
     The shape of the separation member may be determined to a shape matched to the shape of a shield. 
       FIG. 10  is a schematic view showing a separation member  2   f  and a shield S 3  according to a modification of the present invention. In  FIG. 10 , the shield S 3  is a cylinder having a radius of R 1 . In this case, the separation member  12   f  should only be determined so as to have a shape to be wound around the outer circumferential face of the shield S 3 , that is, so that a curved face of a radius of R 1  becomes the inner circumferential face thereof. The separation member  12   f  configured as described above can be provided for the shield S 3  without being deflected. Furthermore, it is assumed that the separation member  12   f  is determined so that a curved face of a radius R 2  (R 1 &lt;R 2 ) becomes the outer circumferential face thereof. In this case, an electrostatic loudspeaker is configured by bonding the main body to the outer circumferential face of the separation member  12   f . The outer circumferential face of the separation member  12   f  is not limited to a curved face, but may be formed into a flat face. 
     The separation member may be configured so as to be deformed more easily than that having a cubic shape.  FIGS. 11(   a ),  11 ( b ), and  11 ( c ) are views showing the structure of a separation member  12   g  according to a modification of the present invention.  FIG. 11(   a ) is a bottom view showing the separation member  12   g ,  FIG. 11(   b ) is a front view showing the separation member  12   g , and  FIG. 11(   c ) is a side view showing the separation member  12   g.  An electrostatic loudspeaker is configured by bonding the main body to the upper face of the separation member  12   g.  The separation member  12   g  has a rectangular shape as viewed from the Z-axis direction and is equipped with a base  124   g  and a plurality of protrusions  125   g . The base  124   g  and the protrusions  125   g  are obtained by heating and compressing cotton and allow air and sound to pass therethrough. The separation member  12   g  has insulation property and elasticity, and it is deformed when an external force is applied thereto and returns to its original shape when the external force is removed. On the lower face of the base  124   g , the plurality of protrusions  125   g  are provided at predetermined intervals (spacing  126   g ) in the X-axis direction and in the Y-axis direction. The protrusions  125   g  have a quadrangular prism shape, and each protrusion  125   g  has a rectangular parallelepiped shape in which the side in the X-axis direction is equal to the side in the Y-axis direction. Furthermore, one end of the protrusion  125   g  is a fixed end secured to the base  124   g , and the other end of the protrusion  125   g  is a free end not secured to the base  124   g . For example, it is assumed that the base  124   g  is bent convexly at the center of the lower face. In this case, the spacing  126   g  between the protrusions  125   g  adjacent to each other becomes wider in the direction from the fixed end to the free end. In addition, it is assumed that the base  124   g  is bent concavely at the center of the lower face. In this case, the spacing  126   g  between the protrusions  125   g  adjacent to each other becomes narrower in the direction from the fixed end to the free end. In other words, the separation member  12   g  is configured so that the free end of the protrusion  125   g  is movable as the base  124   g  is bent, whereby the separation member  12   g  can be bent without causing expansion or contraction of the lower face of the separation member  12   g . Hence, the separation member  12   g  having the plurality of protrusions  125   g  can be bent more flexibly depending on the shape of a shield than a separation member having no protrusions. Furthermore, since the separation member  12   g  can be wound, it is stored and carried easily. Although the plurality of protrusions  125   g  are provided at predetermined intervals in the X-axis direction and in the Y-axis direction on the lower face of the base  124   g , the protrusions  125   g  may be provided at predetermined intervals either in the X-axis direction or in the Y-axis direction. 
       FIGS. 12(   a ),  12 ( b ), and  12 ( c ) are views showing the structure of a separation member  12   h  according to a modification of the present invention.  FIG. 12(   a ) is a bottom view showing the separation member  12   h ,  FIG. 12(   b ) is a front view showing the separation member  12   h,  and  FIG. 12(   c ) is a side view showing the separation member  12   h . An electrostatic loudspeaker is configured by bonding the main body to the upper face of the separation member  12   h , and the separation member is provided by making the lower face thereof into contact with a shield. The separation member  12   h  has a rectangular shape as viewed from the Z-axis direction and is equipped with a base  124   h  and a plurality of protrusions  125   h . It is assumed that the base  124   h  and the protrusions  125   h  are formed of the same material as that of the base  124   g  and the protrusions  125   g . On the lower face of the base  124   h,  the plurality of protrusions  125   h  are provided at predetermined intervals (spacing  126   h ) in the Y-axis direction. The protrusions  125   h  have a quadrangular prism shape, and each protrusion  125   h  has a rectangular parallelepiped shape extended in the X-axis direction in which the side in the X-axis direction is longer than the side in the Y-axis direction. Furthermore, one end of the protrusion  125   h  is a fixed end secured to the base  124   h,  and the other end of the protrusion  125   h  is a free end not secured to the base  124   h . For example, it is assumed that the base  124   h  is bent convexly at the center of the lower face. In this case, the spacing  126   h  between the protrusions  125   h  adjacent to each other becomes wider in the direction from the fixed end to the free end. In addition, it is assumed that the base  124   h  is bent concavely at the center of the lower face. In this case, the spacing  126   h  between the protrusions  125   h  adjacent to each other becomes narrower in the direction from the fixed end to the free end. In other words, the separation member  12   h  is configured so that the free end of the protrusion  125   h  is movable as the base  124   h  is bent, whereby the separation member  12   h  can be bent without causing expansion or contraction of the lower face of the separation member  12   h . Hence, the separation member  12   h  having the plurality of protrusions  125   h  can be bent more flexibly depending on the shape of a shield than a separation member having no protrusions. Furthermore, since the separation member  12   h  can be wound, it is stored and carried easily. 
     (Modification 6) 
       FIG. 13  is an exploded perspective view showing an electrostatic loudspeaker  1   i  according to a modification of the present invention. 
     A separation member  12   i  is a non-conductive member made of thin paper or the like allowing air and sound to pass therethrough and has a shape in which a plurality of spaces (cells) having a hexagonal shape as viewed from the above are joined together without clearances as in the case of a honeycomb. Innumerable holes may be formed in the thin paper to allow air and sound to easily pass through between the cells. When the electrostatic loudspeaker  1   i  is configured, one end face of the separation member  12   i  in the height direction thereof (in a direction orthogonal to the cross section of the hexagon) is made close contact with the surface of the electrode  20 L of the main body  11  and the separation member  12   i  is firmly bonded to the electrode  20 L using an adhesive or an adhesive tape. In this way, the electrostatic loudspeaker  1   i  having the separation member  12   i  is configured. In the electrostatic loudspeaker  1   i,  the electrode  20 L of the main body  11  is bonded to the separation member  12   i  that allows air and sound to passing therethrough; hence, the acoustic wave generated from both faces of the vibrating member can be radiated to the outside of the electrostatic loudspeaker  1   i . Although the shape of the cells of the separation member  12   i  is a hexagonal shape, the shape may be other shapes, such as a rectangular shape, a wavy shape or a trapezoidal shape. 
     (Modification 7) 
     The separation member may have a shape capable of being secured to a wall face or the like. 
       FIG. 14  is a view showing the lower face of a separation member  12   j  according to a modification of the present invention.  FIG. 15  is a sectional view taken on line A-A of an electrostatic loudspeaker  1   j  equipped with the separation member  12   j  shown in  FIG. 14  and is a view showing the electrostatic loudspeaker  1   j  secured to a shield S 2 . It is assumed that the shield S 2  is, for example, a wall on which no object can be placed. Furthermore, a holding member S 21   j  is, for example, a screw or a nail, and part thereof is inserted into the shield S 2 , thereby being secured to the shield S 2 . The description is herein returned to  FIG. 14 . In the separation member  12   j , a hole  128   j  opening from the inside to the lower face of the separation member  12   j  is provided. The hole  128   j  has a circular shape as viewed from the Z-axis direction and is open so as to have a size adequate to allow the holding member S 21   j  to be inserted therein. As shown in  FIG. 15 , the electrostatic loudspeaker  1   j  is configured by bonding the main body  11  to the upper face of the separation member  12   j . Then, the holding member S 21   j  is inserted into the hole  128   j , whereby the electrostatic loudspeaker  1   j  is secured to the shield S 2 . In other words, since the electrostatic loudspeaker  1   j  is not required to be separately equipped with members for securing the electrostatic loudspeaker to the shield S 2 , the electrostatic loudspeaker can be installed easily on a shield, such as a wall face, on which no object can be placed. 
     The hole provided in the separation member is not limited to a hole having a circular shape. 
       FIGS. 16(   a ) and  16 ( b ) are views showing a separation member  12   k  and a holding member S 21   k  according to a modification of the present invention.  FIG. 16(   a ) is a bottom view showing the separation member  12   k  according to the modification of the present invention.  FIG. 16(   b ) is a view showing the structures of the shield S 2  and the holding member S 21   k . Furthermore, the holding member S 21   k  is, for example, a screw or a nail, and includes a body S 211   k  and a head S 212   k . Part of the body S 211   k  of the holding member S 21   k  is inserted into the shield S 2 , whereby the holding member S 21   k  is secured to the shield S 2 . The head S 212   k  is formed so as to be thicker than the body S 211   k.    
     The description is herein returned to  FIG. 16(   a ). In the separation member  12   k , a hole  128   k  opening from the inside to the lower face of the separation member  12   k  is provided. The hole  128   k  has a rectangular shape as viewed from the Z-axis direction. In the hole  128   k , out of the two sides along the X-axis direction, the side in the positive direction of the Y-axis is referred to as a side X 1 , and the side in the negative direction of the Y-axis is referred to as a side X 2 ; and out of the two sides along the Y-axis direction, the side in the positive direction of the X-axis is referred to as a side Y 1 , and the side in the negative direction of the X-axis is referred to as a side Y 2 . Furthermore, the dimension of the side Y 1  and the side Y 2  is A 1 , and the dimension of the side X 1  and the side X 2  is A 2 . A convex  122   k  is provided on the wall face of the opening of the hole  128   k  so as to protrude therefrom. The convex  122   k  is equipped with a first convex  1221   k , a second convex  1222   k , and a third convex  1223   k . The first convex  1221   k  is provided so as to protrude by a dimension A 3  from the wall face of the opening along the side X 2 . The second convex  1222   k  is provided so as to protrude by the dimension A 3  in the negative direction of the X-axis from the wall face of the opening along the side Y 1 . The third convex  1223   k  is provided so as to protrude by the dimension A 3  in the positive direction of the X-axis from the wall face of the opening along the side Y 2 . In other words, the convex  122   k  is formed into a U-shape having two sides extending along the Y-axis direction and connected and one side extending along the X-axis direction, wherein each side is provided so as to protrude by the dimension A 3  from each wall face of the opening formed along each side. It is configured that the dimension (A 2 ) of the hole  128   k  in the X-axis direction is longer than the total of the dimension (A 3 ) of the protruding portion of the second convex  1222   k  and the dimension (A 3 ) of the protruding portion of the third convex  1223   k , and that the dimension (A 1 ) of the hole  128   k  in the Y-axis direction is longer than the dimension (A 3 ) of the protruding portion of the first convex  1221   k . The opening of the hole  128   k  formed as described above is roughly divided into a first space  1231   k  having the dimension A 2  in the X-axis direction and a second space  1232   k  having a dimension shorter than the dimension (A 2 ) of the first space  1231   k  by the total of the dimension (A 3 ) of the protruding portion of the second convex  1222   k  and the dimension (A 3 ) of the protruding portion of the third convex  1223   k . The first space  1231   k  is a space through which the head S 212   k  of the holding member S 21   k  can pass, and the second space  1232   k  is a space through which the head S 212   k  of the holding member S 21   k  cannot pass but only the body S 211   k  can pass. Furthermore, the first space  1231   k  and the second space  1232   k  are continuous to each other, and the holding member S 21   k  can move in the respective spaces. As shown in  FIGS. 17(   a ) and  17 ( b ), an electrostatic loudspeaker  1   k  is configured by bonding the main body  11  to the upper face of the separation member  12   k . Next, an example in which the electrostatic loudspeaker  1   k  is secured to the holding member S 21   k  provided in the shield S 2  is shown. 
       FIGS. 17(   a ) and  17 ( b ) are views taken on line B-B of the electrostatic loudspeaker  1   k  equipped with the separation member  12   k  shown in  FIG. 16(   a ) and views showing the electrostatic loudspeaker  1   k  secured to the shield S 2 . First, as shown in  FIG. 17(   a ), the holding member S 21   k  is inserted into the hole  128   k  of the electrostatic loudspeaker  1   k . At this time, the head S 212   k  of the holding member S 21   k  is in a state of being positioned inside the hole  128   k , and part of the body S 211   k  is in a state of being positioned in the first space  1231   k . Then, as shown in  FIG. 17(   b ), in the state in which the holding member S 21   k  is inserted in the hole  128   k,  the electrostatic loudspeaker  1   k  is moved in the positive direction of the Y-axis direction until the first convex  1221   k  makes contact with the body S 211   k . At this time, the head S 212   k  is in a state of being positioned inside the hole  128   k , and part of the body S 211   k  is in a state of being positioned in the second space  1232   k . Since the second space  1232   k  is in a state of being enclosed with the convex  122   k  formed into a U-shape, the head S 212   k  cannot pass through the space, and only the body S 211   k  can pass through the space. Hence, the movement of the electrostatic loudspeaker  1   k  is restricted by the holding member S 21   k  not only in the directions around the convex  122   k  but also in the positive direction of the Z-axis direction. Since the gravitational force is applied in the positive direction of the Y-axis direction, the electrostatic loudspeaker  1   k  does not move in the negative direction of the Y-axis direction. In other words, the electrostatic loudspeaker  1   k  is restricted from moving in all the directions, thereby being secured to the shield S 2 . Hence, since the electrostatic loudspeaker  1   k  equipped with the separation member  12   k  shown in  FIG. 16(   a ) is not required to be separately equipped with members for securing the electrostatic loudspeaker to the shield S 2 , the electrostatic loudspeaker can be installed easily on a place, such as a wall face, on which no object can be placed. 
     One or more holes may be provided in the lower face of the separation member. In addition, the shape of the hole is not limited to a rectangular shape, but the hole should only be provided with a convex that is roughly divided into a space through which the head of the holding member can pass and a space through which the head of the holding member cannot pass and through which only the body can pass. 
     The shield S 2  is not limited to a fixed face, such as a wall face, but may be a movable face, such as a partition. In addition, the lower face of the electrostatic loudspeaker may be bonded to the shield S 2  using an adhesive or an adhesive tape, for example. The shape of the electrostatic loudspeaker is not limited to a rectangular shape, but may be other shapes, such as a polygonal shape, a circular shape, or an elliptic shape. 
     In the above-mentioned embodiment, the electrostatic loudspeaker is secured to the shield by inserting the holding member into the hole provided in the lower face of the separation member; however, the method for securing the electrostatic loudspeaker to the shield is not limited to this method. 
       FIG. 18  is a view showing the structures of hook members and a separation member according to a modification of the present invention. 
     It is assumed that a shield S 4  is an object, such as a floor face, a wall face, or a pillar, that can be made contact with the electrostatic loudspeaker and is an object through which an entered acoustic wave hardly passes and by which the entered acoustic wave is reflected easily. Furthermore, the shield S 4  is provided with hook members S 41  in the circumferential sections of a position where an electrostatic loudspeaker  1   m  is installed. In the electrostatic loudspeaker  1   m , holes  128   m  into which the hook members S 41  are inserted are provided in the circumferential faces of the separation member  12   m . Then, the hook members S 41  are inserted into the holes  128   m,  whereby it may be possible that the electrostatic loudspeaker  1   m  is secured to the shield S 4 . 
     (Modification 8) 
     The separation member is not limited to be made of cotton, but should only be made of a material, such as urethane foam, non-woven cloth, or glass wool, allowing air and sound to pass therethrough. Furthermore, the separation member is not limited to be formed by the method in which a material is compressed while being heated, but may be formed by providing a plurality of holes in a member formed into a plate shape, for example. The electrostatic loudspeaker may be formed of electrodes, spacers, elastic members, and a separation member having no flexibility and no elasticity. 
     (Modification 9) 
     In the above-mentioned embodiment, the vibrating member  10  is supported because one side of the vibrating member  10  is held between the lower face of the spacer  30 U and the upper face of the spacer  30 L. However, the main body  11  of the electrostatic loudspeaker  1  is not required to be equipped with the spacers  30 . In this case, it may be possible that, for example, the vibrating member  10  is disposed between the lower face of the elastic member  40 U and the upper face of the elastic member  40 L, an adhesive is applied in a width of several mm from the edges in the X-axis direction and from the edges in the Y-axis direction to the inside, and the vibrating member is firmly bonded to the elastic member  40 U and the elastic member  40 L. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
       1  . . . electrostatic loudspeaker,  11  . . . main body,  12  . . . separation member,  131 ,  132 ,  133  . . . restraining member,  14  . . . amplifier,  10  . . . vibrating member,  20  . . . electrode,  21  . . . through-hole,  30  . . . spacer,  40  . . . elastic member,  50  . . . transformer,  60  . . . input section,  70  . . . bias supply,  100  . . . driver, S 1 , S 2 , S 3 , S 4  . . . shield, S 21   j , S 21   k  . . . holding member, S 211   k  . . . body, S 212   k  . . . head, S 41  . . . hook member,  124   g ,  124   h  . . . base,  125   g ,  125   h  . . . protrusion,  126   g ,  126   h  . . . spacing,  127   d ,  127   e  . . . area,  128   j ,  128   k ,  128   m  . . . hole,  122   k  . . . convex,  1221   k  . . . first convex,  1222   k  . . . second convex,  1223   k  . . . third convex,  1231   k  . . . first space,  1232   k  . . . second space