Patent Publication Number: US-8126179-B2

Title: Diaphragm and sound output apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2007-191596 filed in the Japanese Patent Office on Jul. 24, 2007, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to diaphragms and sound output apparatuses. More specifically, the present invention relates to a diaphragm and a sound output apparatus in which no sound degradation due to the weight of a sound output portion occurs. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2007-67538 discloses a screen speaker unit that functions as a speaker for outputting sound as well as a screen for dividing a room or hiding undesirable views. 
     Screen speakers typically use a rectangular diaphragm. Japanese Patent No. 3905814 and Japanese Unexamined Patent Application Publication No. 2004-356868, for example, disclose structures for improving sound quality of speakers that use a rectangular diaphragm. 
     SUMMARY OF THE INVENTION 
       FIG. 1  shows a diaphragm retainer mechanism of a screen speaker unit disclosed in Japanese Unexamined Patent Application Publication No. 2007-67538, viewed from above. Fixing members  2  having screws are fixed to a main frame  1  by nuts  3 . A diaphragm  4  is fixedly supported by the fixing members  2  through the intermediary of cushioning members  5 . 
     However, the diaphragm  4  may gradually slip down under its own weight because the cushioning members  5  exert a weak urging force on the diaphragm  4 . As a result, the diaphragm  4  may weigh on a supporting member (not shown) provided below the diaphragm  4 , and friction between the supporting member and the diaphragm  4  may produce undesirable sound. 
     The diaphragm retainer mechanism disclosed in Japanese Unexamined Patent Application Publication No. 2007-67538 retains the left and right edges of the diaphragm  4  with the diaphragm retainers having a U-shaped cross section. However, the mechanism is not designed to support the weight of the diaphragm  4 . Thus, the diaphragm  4  may gradually slip down under its own weight. If the diaphragm retainers support the weight of the diaphragm  4 , the diaphragm retainers may interfere with the diaphragm  4 , resulting in frictional and fluttering sounds. 
     The speakers disclosed in Japanese Patent No. 3905814 and Japanese Unexamined Patent Application Publication No. 2004-356868 have mechanisms that support the diaphragms by applying pressure. This may make it difficult to mount the diaphragms. Further, the diaphragms may be damaged by the pressure. 
     The present invention has been made in view of these situations, and it is desirable to provide a sound output apparatus that outputs high-quality sound. 
     A diaphragm according to an embodiment of the present invention outputs sound by vibrating, and has a hole of a predetermined shape that allows another member to extend therethrough. 
     The hole may have a size allowing a cushioning member to be disposed between the other member and the hole in the diaphragm. 
     The diaphragm may be rectangular, the hole may be provided in the vicinity of an edge of the diaphragm, and the edge may be fixed. 
     The hole may be provided in the vicinity of a short edge of the diaphragm, and the short edge may be fixed. 
     A diaphragm according to an embodiment of the present invention has a hole that allows another member to extend therethrough. 
     A sound output apparatus according to an embodiment of the present invention has a first member, a diaphragm having a hole of a predetermined shape through which the first member extends, and a second member into which the first member is screwed. 
     A cushioning member may be disposed between the diaphragm and the first member extending through the hole. 
     A first plate may connect to the first member, the first plate being attached to one surface of the diaphragm. A second plate may have a hole, one surface of the second plate being attached to the other surface of the diaphragm. A frame to which the diaphragm is fixed may be arranged adjacent to the other surface of the second plate and have a hole. The first member may extend through the hole in the diaphragm, the hole in the second plate, and the hole in the frame. The diaphragm may be fixed to the frame by the first and second members being screwed together, while being disposed between the first and second plates. 
     The diaphragm may be rectangular, the first and second plates may be attached to a short edge of the diaphragm, and a cushioning member may be disposed along a long edge of the diaphragm, between the diaphragm and the frame. 
     The second plate may have a thickness sufficient to prevent the diaphragm from contacting the frame when the diaphragm vibrates. 
     The size of a vibrating surface of the diaphragm may be changed by changing the width of the second plate. 
     The hole in the second plate may be elongated in a longitudinal direction of the diaphragm. The second plate may be movable in the longitudinal direction of the diaphragm. 
     The diaphragm and a cushioning member may be disposed between the first and second plates. 
     In the sound output apparatus according to an embodiment of the present invention, the first member extends through the hole in the diaphragm and screws into the second member, whereby the diaphragm is fixed to a predetermined frame. 
     The sound output apparatus according to an embodiment of the present invention outputs high-quality sound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a structure of a related art retainer mechanism; 
         FIG. 2  shows a structure of a screen speaker unit; 
         FIG. 3  shows a retainer mechanism according to an embodiment of the present invention; 
         FIGS. 4A and 4B  are a plan view and a side view of a cushioning member, respectively; 
         FIG. 5  shows a detailed structure of the retainer mechanism; 
         FIG. 6  shows a detailed structure of another retainer mechanism; 
         FIG. 7  is a graph showing frequency characteristics of two retainer mechanisms; 
         FIGS. 8A and 8B  schematically show shapes of diaphragms; 
         FIGS. 9A and 9B  schematically show directions of sound propagation in the diaphragms; 
         FIG. 10  shows a structure for customizing sound quality; 
         FIG. 11  shows a structure for customizing sound quality; and 
         FIG. 12  shows a structure for customizing sound quality. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described. The correspondence relationship between the claimed elements and the embodiments disclosed in the specification or the drawings is as follows. This description confirms that the embodiments supporting the present invention are disclosed in the specification or the drawings. Accordingly, even if the correspondence between an embodiment disclosed in the specification or the drawings and a claimed element is not described herein, it does not mean that there is no correspondence between the embodiment and the claimed element. By contrast, even if the correspondence between an embodiment and a claimed element is described herein, it does not mean that there is no correspondence between the embodiment and another claimed element. 
     A diaphragm according to an embodiment of the present invention (e.g., a diaphragm  31 - 2  in  FIG. 3  or diaphragms  31  in  FIGS. 8A and 8B ) outputs sound by vibrating. The diaphragm has a hole (e.g., a hole  53 A- 1  in  FIG. 3 ) of a predetermined shape. Another member (e.g., a bolt  51 A- 1  in  FIG. 3 ) is configured to extend through the hole. 
     The hole may have a size allowing a cushioning member (e.g., cushioning members  52  in  FIG. 3 ) to be disposed between the other member and the hole in the diaphragm. 
     The diaphragm may be rectangular, the hole may be provided in the vicinity of an edge of the diaphragm, and the edge may be fixed (e.g., the diaphragm  31 - 2  in  FIG. 3 ). 
     The hole may be provided in the vicinity of a short edge of the diaphragm, and the short edge may be fixed (e.g., the diaphragm  31 - 2  in  FIG. 3 ). 
     A sound output apparatus according to an embodiment of the present invention (e.g., a screen speaker unit  11  in  FIG. 2 ) has a first member (e.g., the bolt  51 A- 1  in  FIG. 3 ), a diaphragm (e.g., the diaphragm  31 - 2  in  FIG. 3  or the diaphragms  31  in  FIGS. 8A and 8B ) having a hole (e.g., the hole  53 A- 1  in  FIG. 3 ) of a predetermined shape through which the first member extends, and a second member (e.g., a nut  58 A- 1  in  FIG. 3 ) into which the first member is screwed. 
     A cushioning member (e.g., the cushioning member  52 A- 1  in  FIG. 3 ) may be disposed between the diaphragm and the first member extending through the hole. 
     A first plate (e.g., a plate  25 A- 2  in  FIG. 3 ) may connect to the first member, the first plate being attached to one surface of the diaphragm. A second plate (e.g., a plate  54 A in  FIG. 3 ) may have a hole, one surface of the second plate being attached to the other surface of the diaphragm. A frame (e.g., a frame  24  in  FIG. 3 ) to which the diaphragm is fixed may be arranged adjacent to the other surface of the second plate and have a hole. The first member may extend through the hole (e.g., the hole  53 A- 1  in  FIG. 3 ) in the diaphragm, the hole (e.g., a hole  55 A- 1  in  FIG. 3 ) in the second plate, and the hole (e.g., a hole  57 A- 1  in  FIG. 3 ) in the frame. The diaphragm may be fixed to the frame by the first and second members being screwed together, while being disposed between the first and second plates (e.g., the diaphragm  31 - 2  in  FIG. 3 ). 
     The diaphragm may be rectangular, the first and second plates may be attached to a short edge of the diaphragm, and a cushioning member may be disposed along a long edge of the diaphragm, between the diaphragm and the frame (e.g., a cushioning member  56 A in  FIG. 5 ). 
     The second plate may have a thickness sufficient to prevent the diaphragm from contacting the frame when the diaphragm vibrates (e.g., the plates  54 A and  54 B in  FIG. 10 ). 
     The size of a vibrating surface of the diaphragm may be changed by changing the width of the second plate. 
     The hole in the second plate may be elongated (e.g., a hole  55 A″- 1  in  FIG. 12 ) in a longitudinal direction of the diaphragm. The second plate may be movable in the longitudinal direction of the diaphragm. 
     Embodiments of the present invention will now be described with reference to the drawings. 
       FIG. 2  shows a structure of the screen speaker unit  11  according to an embodiment of the present invention. The screen speaker unit  11  functions as a speaker as well as a screen, and is an exemplary sound output apparatus of the present invention. 
     The screen speaker unit  11  includes a base  21 , casters  22 A to  22 D, supporting members  23 A to  23 D, the frame  24 , the plates  25 A- 1  to  25 B- 3 , the diaphragms  31 - 1  to  31 - 3 , and vibrators  41 A to  43 C. 
     The base  21  is made of a material strong enough to support the frame  24 , for example, a metal such as iron, aluminum, magnesium, or titanium. The base  21  has the casters  22 A to  22 D (the caster  22 D is not shown) at the four corners of the lower surface thereof, and the supporting members  23 A to  23 D (the supporting members  23 C and  23 D are not shown) adjacent to the casters  22 A to  22 D. A user can move the screen speaker unit  11  placed in a room, for example, by pushing it to cause the casters  22 A to  22 D to roll on the floor. The supporting members  23 A to  23 D contact the floor to support the screen speaker unit  11 . 
     That is, a user can move the screen speaker unit  11  to a desired position. 
     The frame  24  is, for example, welded to the upper surface of the base  21  and stands upright on the base  21 . 
     Although a detailed description will be given below, the frame  24  has a mechanism for supporting the weight of the diaphragms  31 - 1  to  31 - 3 , and the plates  25 A- 1  to  25 B- 3  for fixing the diaphragms  31 - 1  to  31 - 3  so as not to move in the front-back direction in  FIG. 2 . The diaphragms  31 - 1  to  31 - 3  are removably fixed to the frame  24  by the mechanism and the plates  25 A- 1  to  25 B- 3 . Although a detailed description will be given below, the frame  24  and the plates  25 A- 1  to  25 B- 3  support the diaphragms  31 - 1  to  31 - 3  so as not to move downward or in the front-back direction. 
     The weight of the diaphragm  31 - 1  is supported by the below-described mechanism, and the plates  25 A- 1  and  25 B- 1  support the diaphragm  31 - 1  so as not to move in the front-back direction. Similarly to the diaphragm  31 - 1 , the weight of the diaphragm  31 - 2  is supported by the below-described mechanism, and the plates  25 A- 2  and  25 B- 2  support the diaphragm  31 - 2  so as not to move in the front-back direction. The weight of the diaphragm  31 - 3  is supported by the below-described mechanism, and the plates  25 A- 3  and  25 B- 3  support the diaphragm  31 - 3  so as not to move in the front-back direction. 
     The diaphragms  31 - 1  to  31 - 3  are arranged vertically along the frame  24  and removably fixed thereto. The screen speaker unit  11  is structured to serve as a screen having a predetermined height from the floor. 
     The diaphragms  31 - 1  to  31 - 3  are formed in a plate shape. Examples of the material of the diaphragms  31 - 1  to  31 - 3  include plasterboard, wood such as medium density fiberboard (MDF), aluminum plate, resin such as carbon resin or acrylic resin, and glass. The diaphragms  31 - 1  to  31 - 3  may also be formed from a composite material made by combining or laminating different materials together. 
     Each of the diaphragms  31 - 1  to  31 - 3  has a plurality of vibrators (three vibrators in  FIG. 2 ) arranged horizontally in a line. The diaphragm  31 - 1  has vibrators  41 A to  41 C, the diaphragm  31 - 2  has vibrators  42 A to  42 C, and the diaphragm  31 - 3  has vibrators  43 A to  43 C arranged horizontally in a line. 
     When the vibrators  41 A to  43 C are driven by a sound source (not shown), such as an amplifier, they, according to a sound signal from the sound source, cause the diaphragms  31 - 1  to  31 - 3  to vibrate and output sound. Thus, the screen speaker unit  11  serves as a speaker for converting a sound signal into sound. 
     The vibrators  41 A to  43 C are removably attached to predetermined positions of the diaphragms  31 - 1  to  31 - 3 , depending on the vibration characteristics of the diaphragms  31 - 1  to  31 - 3 . 
     Although  FIG. 2  shows the screen speaker unit  11  having three diaphragms, namely, the diaphragms  31 - 1  to  31 - 3 , the number of the diaphragms  31  does not necessarily have to be three in the present invention, and one or more diaphragms  31  may be removably fixed to the frame  24 . That is, a user can customize the height of the screen speaker unit  11  by vertically arranging a desired number of the diaphragms  31 . 
     In the following description, the plates  25 A- 1  to  25 B- 3  will be referred to as the plates  25 , the plates  25 A- 1 ,  25 A- 2 , and  25 A- 3  will be referred to as the plates  25 A, and the plates  25 B- 1 ,  25 B- 2 , and  25 B- 3  will be referred to as the plates  25 B, when they do not have to be distinguished. 
     Also in the following description, the left-right direction with respect to the screen speaker unit  11  (the left-right direction in  FIG. 2 ) will be referred to as an x-axis direction, the front-back direction (the direction penetrating through the paper in  FIG. 2 ) will be referred to as a y-axis direction, and the top-bottom direction in  FIG. 2  will be referred to as a z-axis direction. 
       FIG. 3  shows a retainer mechanism for retaining the diaphragms  31 . Although  FIG. 3  shows the retainer mechanism for retaining the diaphragm  31 - 2 , basically the same retainer mechanisms are used for the diaphragms  31 - 1  and  31 - 3 . 
     The plates  25 A- 2  and  25 B- 2  are provided on the front surface (in the y-axis direction) of the diaphragm  31 - 2 . The plates  25 A- 2  and  25 B- 2  are attached to both edges in the x-axis direction of the diaphragm  31 - 2 . 
     The plate  25 A- 2  has the bolts  51 A- 1 ,  51 A- 2 , and  51 A- 3 , and the plate  25 B- 2  has the bolts  51 B- 1 ,  51 B- 2 , and  51 B- 3 . The bolts  51 A- 1  to  51 A- 3  are welded, for example, to the plate  25 A- 2 , and the bolts  51 B- 1  to  51 B- 3  are welded, for example, to the plate  25 B- 2 . 
     As shown in  FIG. 2 , the plates  25  are positioned on the front surface of the screen speaker unit  11 , in other words, they are viewed by a user. It is preferable that the surfaces of the plates  25  viewed by a user (i.e., the surfaces on the left, opposite to the surfaces provided with the bolts  51 A- 1  to  51 B- 3 , in  FIG. 3 ) be finished smoothly because the screen speaker unit  11  also serves as a screen. Thus, as shown in  FIG. 3 , it is preferable that the bolts  51 A- 1  to  51 B- 3  be welded to the plates  25 , so that they are not viewed by a user. 
     Although the plates  25  shown in  FIG. 3  are rectangular, they may be folded plates having an L-shaped cross section, for example, so that they can cover the sides of the frame  24 . That is, as shown in  FIG. 2 , the plates  25  may cover the sides of the frame  24  to conceal the frame  24  from a user. 
     Referring back to  FIG. 3 , the diaphragm  31 - 2  has the holes  53 A- 1  to  53 A- 3  and the holes  53 B- 1  to  53 B- 3  provided in the vicinity of both edges in the x-axis direction thereof. The holes  53 A- 1  to  53 A- 3  are provided such that the bolts  51 A- 1  to  51 A- 3  can respectively extend therethrough, and the holes  53 B- 1  to  53 B- 3  are provided such that the bolts  51 B- 1  to  51 B- 3  can respectively extend therethrough. 
     The cushioning member  52 A- 1  is disposed between the hole  53 A- 1  in the diaphragm  31 - 2  and the bolt  51 A- 1 , so that the diaphragm  31 - 2  and the bolt  51 A- 1  do not contact with each other. This structure will be described with reference to  FIGS. 4A and 4B .  FIG. 4A  shows the cushioning member  52 A- 1  viewed in the y-axis direction, and  FIG. 4B  shows the cushioning member  52 A- 1  viewed in the z-axis direction. 
     Referring to  FIG. 4A , the cushioning member  52 A- 1  having an outside diameter smaller than the diameter of the hole  53 A- 1  is placed in the hole  53 A- 1  in the diaphragm  31 - 2 . The bolt  51 A- 1  having a diameter smaller than the inside diameter of the cushioning member  52 A- 1  extends through the cushioning member  52 A- 1 . Referring to  FIG. 4B , the cushioning member  52 A- 1  is sized to be placed in the hole  53 A- 1  in the diaphragm  31 - 2 . 
     The inner periphery of the hole  53 A- 1  in the diaphragm  31 - 2  and the outer periphery of the cushioning member  52 A- 1  may be in contact (tight contact) with each other. In other words, the diameter of the hole  53 A- 1  in the diaphragm  31 - 2  and the outer diameter of the cushioning member  52 A- 1  may be either substantially the same, or different to leave a gap therebetween. Similarly, the inner periphery of the cushioning member  52 A- 1  and the outer periphery of the bolt  51 A- 1  may be in contact (tight contact) with each other. In other words, the inner diameter of the cushioning member  52 A- 1  and the diameter of the bolt  51 A- 1  may be either substantially the same, or different to leave a gap therebetween. 
     This configuration prevents the diaphragm  31 - 2  and the bolt  51 A- 1  from contacting each other when the diaphragm  31 - 2  vibrates, and makes the cushioning member  52 A- 1  absorb noise produced by the bolt  51 A- 1  and the diaphragm  31 - 2  contacting each other, thereby reducing the noise. 
     Referring back to  FIG. 3 , as described above, the cushioning member  52 A- 1  is disposed between the hole  53 A- 1  in the diaphragm  31 - 2  and the bolt  51 A- 1 . The cushioning member  52 A- 2  is disposed between the hole  53 A- 2  in the diaphragm  31 - 2  and the bolt  51 A- 2 , and the cushioning member  52 A- 3  is disposed between the hole  53 A- 3  in the diaphragm  31 - 2  and the bolt  51 A- 3 . In the same manner, the cushioning member  52 B- 1  is disposed between the hole  53 B- 1  in the diaphragm  31 - 2  and the bolt  51 B- 1 , the cushioning member  52 B- 2  is disposed between the hole  53 B- 2  in the diaphragm  31 - 2  and the bolt  51 B- 2 , and the cushioning member  52 B- 3  is disposed between the hole  53 B- 3  in the diaphragm  31 - 2  and the bolt  51 B- 3 . 
     The plate  54 A having the holes  55 A- 1  to  55 A- 3  that allow the bolts  51 A- 1  to  51 A- 3  to extend therethrough is fitted to the surface of the diaphragm  31 - 2 , opposite to the surface provided with the plate  25 A- 2 . In the same manner, the plate  54 B having the holes  55 B- 1  to  55 B- 3  that allow the bolts  51 B- 1  to  51 B- 3  to extend therethrough is fitted to the surface of the diaphragm  31 - 2 , opposite to the surface provided with the plate  25 B- 2 . 
     These plates  54 A and  54 B serve to create a space in which the diaphragm  31 - 2  vibrates in the front-back direction (y-axis direction). Although a detailed description will be given below with reference to  FIG. 5 , because the diaphragm  31 - 2  vibrates in the front-back direction to output sound, the plates  54 A and  54 B are provided to prevent the diaphragm  31 - 2  from contacting the frame  24 , and to prevent the frame  24  from inhibiting the vibration. 
     The cushioning members  56 A and  56 B are provided along the top and bottom edges (in the Z-axis direction) of the diaphragm  31 - 2 , to prevent the diaphragm  31 - 2  from contacting the frame  24  when the diaphragm  31 - 2  vibrates. The cushioning members  56 A and  56 B are made of a material that does not inhibit the vibration of the diaphragm  31 - 2  even when it contacts the diaphragm  31 - 2 , and a material that protects the diaphragm  31 - 2  from being damaged by contacting the frame  24 . 
     The frame  24  has the holes  57 A- 1  to  57 A- 3  that allow the bolts  51 A- 1  to  51 A- 3  of the plate  25 A- 2  to respectively extend therethrough, and the holes  57 B- 1  to  57 B- 3  that allow the bolts  51 B- 1  to  51 B- 3  of the plate  25 B- 2  to respectively extend therethrough. 
     The bolt  51 A- 1  extending through the hole  57 A- 1  screws into the nut  58 A- 1 , the bolt  51 A- 2  extending through the hole  57 A- 2  screws into the nut  58 A- 2 , and the bolt  51 A- 3  extending through the hole  57 A- 3  screws into the nut  58 A- 3 . 
     In the same manner, the bolt  51 B- 1  extending through the hole  57 B- 1  screws into the nut  58 B- 1 , the bolt  51 B- 2  extending through the hole  57 B- 2  screws into the nut  58 B- 2 , and the bolt  51 B- 3  extending through the hole  57 B- 3  screws into the nut  58 B- 3 . 
     Thus, the diaphragm  31 - 2  is fixed to the frame  24  by the bolts  51 A- 1  to  51 A- 3  and the nuts  58 A- 1  to  58 A- 3 , and the bolts  51 B- 1  to  51 B- 3  and the nuts  58 B- 1  to  58 B- 3  being screwed together. 
     Referring to  FIG. 5 , a mechanism for fixing the diaphragm  31 - 2  to the frame  24  will be described in detail.  FIG. 5  shows the diaphragm  31 - 2  fixed to the frame  24 , viewed from above (viewed in the z-axis direction). 
     As described above with reference to  FIGS. 4A and 4B , and as shown in  FIG. 5 , the cushioning member  52 A- 1  is thinner than the diaphragm  31 - 2  and is sized to be placed in the hole  53 A- 1  in the diaphragm  31 - 2 . Thus, the plates  25 A- 2  and  54 A contact the diaphragm  31 - 2 , as shown in  FIG. 5 . In the same manner, the cushioning member  52 B- 1  is thinner than the diaphragm  31 - 2  and is sized to be placed in the hole  53 B- 1  in the diaphragm  31 - 2 . Thus, the plates  25 B- 2  and  54 B contact the diaphragm  31 - 2 , as shown in  FIG. 5 . 
     The diaphragm  31 - 2 , while being directly disposed between the frame  24  and the plates  25 A- 2  and  25 B- 2 , is fixedly fastened to the frame  24  by the bolt  51 A- 1  fixed to the plate  25 A- 2  and the nut  58 A- 1  being screwed together so as not to move in the front-back direction (y-axis direction). 
     Referring to  FIG. 5 , the cushioning member  56 A is disposed between the diaphragm  31 - 2  and the frame  24 . The thickness of the cushioning member  56 A is set such that it does not exert a force on the diaphragm  31 - 2  when the diaphragm  31 - 2  is not vibrated. The cushioning member  56 A serves to prevent the diaphragm  31 - 2  from contacting the frame  24  when the diaphragm  31 - 2  vibrates. Thus, the thickness of the cushioning member  56 A is set to be equal to or smaller than the distance between the diaphragm  31 - 2  and the frame  24 . Although it is not shown in  FIG. 5 , the cushioning member  56 B is disposed in the same manner as the cushioning member  56 A. 
     As can be seen from  FIG. 5 , the distance between the diaphragm  31 - 2  and the frame  24  is equal to the thickness of the plates  54 A and  54 B (the following description will be based on the plate  54 A). Accordingly, the cushioning member  56 A has a thickness equal to or smaller than the plate  54 A. 
     It is preferable that the diaphragm  31 - 2  do not contact the frame  24  while vibrating. Even if the diaphragm  31 - 2  contacts the frame  24 , the resulting noise should preferably be suppressed. Thus, the thickness of the plate  54 A is set such that it prevents the diaphragm  31 - 2  from contacting the frame  24  when the diaphragm  31 - 2  vibrates. 
     The plate  54 A is made of the same material as the frame  24  and has sufficient strength. The thickness of the plate  54 A is determined in relation to the diaphragm  31 - 2 , as described above. The plate  54 B has the same shape as the plate  54 A. 
       FIG. 6  shows another retainer mechanism using cushioning members. In the structure shown in  FIG. 5 , the diaphragm  31 - 2  directly contacts the plates  25 A- 2 ,  25 B- 2 ,  54 A, and  54 B. In contrast, in the structure shown in  FIG. 6 , the diaphragm  31 - 2  contacts the plates  25 A- 2 ,  25 B- 2 ,  54 A, and  54 B with the cushioning members therebetween. 
     A cushioning member  81 A- 1  is disposed between the plate  25 A- 2  and the diaphragm  31 - 2 . A cushioning member  81 A- 2  is disposed between the plate  54 A and the diaphragm  31 - 2 . In the same manner, a cushioning member  81 B- 1  is disposed between the plate  25 B- 2  and the diaphragm  31 - 2 , and a cushioning member  81 B- 2  is disposed between the plate  54 B and the diaphragm  31 - 2 . These cushioning members  81 A- 1 ,  81 A- 2 ,  81 B- 1 , and  81 B- 2  each have a hole (not shown) that allows the bolt  51 A- 1  or  51 B- 1  to extend therethrough. 
     The cushioning members  81  disposed between the diaphragm  31 - 2  and the plates  25  and between the diaphragm  31 - 2  and the plates  54  prevent the diaphragm  31 - 2  from contacting the plates  25  and  54  and producing undesirable noise, and prevent the diaphragm  31 - 2  from wearing. The cushioning members  81  are made of, for example, rubber or hard sponge. 
     As has been described, in the present embodiment, in order to prevent the diaphragms  31  from slipping down under their own weight, each diaphragm  31  has the holes  53  and allows the bolts  51  to extend therethrough, whereby the diaphragms  31  are supported. Further, the cushioning members  52  are provided to prevent the diaphragms  31  from contacting the bolts  51  and producing undesirable noise. Thus, the diaphragms  31  are prevented from slipping down under their own weight, while sound degradation is suppressed. In addition, a fluttering sound due to vibration can be reduced because the diaphragms  31  are fixedly fastened to the frame  24 . 
     Sound quality is further improved with the retainer mechanism according to the present embodiment shown in, for example,  FIG. 3  than with the related-art retainer mechanism shown in  FIG. 1 . In other words, sound quality is further improved with the structure shown in  FIG. 3 , in which two edges of each diaphragm  31  are free and the remaining two edges are fixed, than the structure shown in  FIG. 1 , in which all the four edges of the diaphragm  4  are free. 
       FIG. 7  is a graph showing frequency characteristics of sounds output from a diaphragm supported by the retainer mechanism shown in  FIG. 1 , and from a diaphragm supported by the retainer mechanism according to the present embodiment shown in  FIG. 3 . In  FIG. 7 , the frequency characteristic plotted as a solid line (denoted as “proposal”) shows the frequency characteristic for the retainer mechanism according to the present embodiment shown in  FIG. 3 , and the frequency characteristic plotted as a dashed line (denoted as “related art”) shows the frequency characteristic for the related-art retainer mechanism shown in  FIG. 1 . 
     In  FIG. 7 , a flatter line represents a better characteristic because it means that sound is output at an optimum level over the entire frequency range shown. Comparing the solid line with the dashed line in  FIG. 7 , the solid line is flatter than the dashed line. This shows that sound quality is improved more with the retainer mechanism according to the present embodiment shown in  FIG. 3  than with the related-art retainer mechanism shown in  FIG. 1 . 
     Thus, sound quality is improved with the retainer mechanism according to the present embodiment. 
     As shown in  FIG. 3 , in order to prevent the diaphragms  31  from slipping down under their own weight, each diaphragm  31  has the holes  53  and allows the bolts  51  to extend therethrough, whereby the diaphragms  31  are supported. The holes  53  are not necessarily of a circular shape having a larger diameter than the bolt  51  as shown in  FIG. 3 , and they may be of another shape. 
     For example, as shown in  FIG. 8A , the diaphragms  31  may have semi-elliptical notches. The diaphragms  31  having semi-elliptical notches provide the same effect as the diaphragms  31  having circular holes. The diaphragms  31  having semi-elliptical notches further contribute to prevent the diaphragms  31  from slipping down under their own weight, because they are slightly lighter than the diaphragms  31  having circular holes. 
     Alternatively, as shown in  FIG. 8B , the diaphragms  31  may have rectangular notches. In this case, the bolts  51  contact the upper edges of the rectangular notches with the cushioning members  52  therebetween, and support the diaphragm  31 . In this case, the plate  25 A- 2 , for example, has to have only one bolt, namely, the bolt  51 A- 1 . The diaphragms  31  as shown in  FIG. 8B  provide the same effect as the diaphragms  31  having circular holes, and the diaphragms  31  having semi-elliptical notches as shown in  FIG. 8A . 
     Although  FIGS. 3 and 8A  show the diaphragms  31  in which three holes (notches) are disposed along the right and left edges thereof, the number of the holes (notches) is not limited thereto. A diaphragm having a single hole (notch), for example, also falls within the scope of the present invention. That is, basically, the necessary number of holes (notches) for supporting the weight of each diaphragm  31  should be provided. 
     As described above, the diaphragms  31  have portions that allow other members to extend therethrough. The diaphragms  31  are fixed to the frame  24 , while the other members extend through the portions. As long as this structure is achieved, the shape of the diaphragms  31  and the shape of the portions that allow other members to extend therethrough may be modified. 
     As shown in  FIGS. 3 ,  8 A, and  8 B, the holes (notches) are disposed along the right and left edges (short edges) of each diaphragm  31 . In other words, the short edges of the diaphragms  31  are fixed, and the long edges of the diaphragms  31  are free. It is preferable to make the short edges fixed than to make the short edges free, taking the following points, which will now be described with reference to  FIGS. 9A and 9B , into consideration. 
     When the diaphragms  31  vibrate, the main vibration propagates parallel to the long edges ab and cd, as shown in  FIG. 9A . This is because the vibration propagates more easily in this direction than in the direction parallel to the short edges bc and da, as shown in  FIG. 9B . Thus, if the long edges, along which the main vibration propagates, are fixed, propagation of the main vibration is inhibited. Accordingly, it is preferable to make the short edges of the diaphragms  31  fixed. 
     As shown in  FIG. 9A , sound quality and sound volume can be adjusted by changing the length of the diaphragms  31  in the lengthwise direction because the main vibration propagates parallel to the long edges. When the length of the diaphragms  31  in the lengthwise direction is increased, the size of vibrating surfaces of the diaphragms  31  is increased. This enables the diaphragms  31  to output high-volume, low-pitched sound. In contrast, when the length of the diaphragms  31  in the lengthwise direction is decreased, the size of the vibrating surfaces of the diaphragms  31  is decreased. This enables the diaphragms  31  to output low-volume, high-pitched sound. 
     For example, the screen speaker unit  11  shown in  FIG. 2  has three diaphragms, namely, the diaphragms  31 - 1  to  31 - 3 . It is possible to make the diaphragms  31 - 1  to  31 - 3  of the screen speaker unit  11  output high-pitched sound, middle-pitched sound, and low-pitched sound, respectively, by changing the size of the vibrating surfaces thereof. 
     The size of the vibrating surfaces of the diaphragms  31  can be adjusted by changing the length of the diaphragms  31  in the lengthwise direction. More specifically, referring back to  FIG. 5 , the length of the diaphragm  31 - 2  in the lengthwise direction (the portion in the diaphragm  31 - 2  which actually vibrates) can be reduced by increasing the length of the plates  54 A and  54 B in the lengthwise direction of the diaphragms  31 . This will be described in more detail with reference to the drawings. 
       FIG. 10  shows only the diaphragm  31 - 2 , the plates  25 A- 2 ,  25 B- 2 ,  54 A, and  54 B, and the bolts  51 A- 1  and  51 B- 1  of the retainer mechanism shown in  FIG. 5 .  FIG. 10  schematically shows the diaphragm  31 - 2  while vibrating. 
     As shown in  FIG. 10 , the diaphragm  31 - 2  is disposed between the plates  25 A- 2  and  54 A at one end, and between the plates  25 B- 2  and  25 B at the other end. The diaphragm  31 - 2  vibrates using these portions (edges) disposed between the plates as supporting points. The thickness A of the plate  54 A ( 54 B) is set such that the diaphragm  31 - 2  does not contact the frame  24  (not shown in  FIG. 10 ) when the diaphragm  31 - 2  vibrates. That is, the thickness A of the plate  54 A ( 54 B) is set to be larger than half the maximum amplitude of vibration B of the diaphragm  31 - 2 . 
     The amplitude of vibration B of the diaphragm  31 - 2  depends on the material and thickness of the diaphragm  31 - 2 . A thinner diaphragm has larger amplitude of vibration B than a thicker diaphragm if they are made of the same material. Thus, the plate  54 A ( 54 B) has to be thickened according to the amplitude of vibration B. 
       FIG. 11  is a view similar to  FIG. 10 , showing a retainer mechanism in which the width of the plates  54 A and  54 B has been increased. As described above, the volume and quality of sound can be adjusted by changing the width of the plate  54 A. In  FIG. 11 , the plates  54 A and  54 B are denoted by plates  54 A′ and  54 B′ for distinction from the plates  54 A and  54 B shown in  FIG. 10 . 
     The plate  54 A′ shown in  FIG. 11  has a larger width C than the plate  54 A shown in  FIG. 10 . The plate  54 B′ shown in  FIG. 11  also has a larger width C than the plate  54 B shown in  FIG. 10 . Although the following description will be given under the assumption that the plates  54 A′ and  54 B′ have the same width C, the plates  54 A′ and  54 B′ may have different widths C. 
     When the width C of the plates  54 A′ and  54 B′ is increased, the supporting points are moved, that is, the supporting points approach each other. This reduces the amplitude of vibration B of the diaphragm  31 - 2 , whereby the diaphragm  31 - 2  outputs low-volume, high-pitched sound. 
     When the diaphragm  31 - 2  shown in  FIG. 10  and the diaphragm  31 - 2  shown in  FIG. 11  are supplied with sounds of the same volume and quality, the diaphragm  31 - 2  shown in  FIG. 11  outputs lower volume, higher-pitched sound than the diaphragm  31 - 2  shown in  FIG. 10 . 
     To output high-pitched sound while minimizing low-pitched sound, the width C of the plate  54 A ( 54 B) should be increased. To output low-pitched sound while minimizing high-pitched sound, the width C of the plate  54 A ( 54 B) should be decreased. The volume and quality of sound can be adjusted only by changing the width C of the plate  54 A ( 54 B). 
     This allows a user to customize the volume and quality of sound of the screen speaker unit  11  by changing the plate  54 , if the user does not like the volume and quality of sound of the screen speaker unit  11  at the time of purchase. Thus, a user does not have to buy another speaker unit because the user can customize it. 
     The width of the plates  54 , i.e., the distance between the supporting points of diaphragms  31 , may be changed using the plates as shown in  FIG. 12 . A plate  54 A″ shown in  FIG. 12  has elongated holes  55 A″- 1  to  55 A″- 3 . The holes  55 A- 1  to  55 A- 3  in the plate  54 A shown in  FIG. 3  are circular. In contrast, the holes  55 A″- 1  to  55 A″- 3  shown in  FIG. 12  are substantially elliptical. 
     Substantially elliptical holes (hereinafter, elliptical holes) allow the bolts  51  to move therein. For example, the bolt  51 A- 1  is movable between the ends of the hole  55 A″- 1 . To be more accurate, the bolts  51  do not move but the plate  54 A″ moves relative to the bolts  51  because the bolts  51  are fixed. 
     Accordingly, the distance between the supporting points of the diaphragm  31 - 2  can be changed by moving the plate  54 A″, not by replacing the plate  54 . A user can customize the volume and quality of sound by moving the plate  54 A″, for example. 
     According to the present embodiment, it becomes possible to reduce a negative influence of the weight of diaphragms and to adjust the quality of sound and the like. 
     Although the width of the plates  54  is changed to customize the volume and quality of sound in the above-described embodiment, the width of the plates  25 , not the plates  54 , may be changed. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.