Patent Publication Number: US-7897856-B2

Title: Casing structure of electronic musical instrument

Description:
BACKGROUND 
     The present invention relates an electronic musical instrument casing structure suited for application to electronic pianos having an outer appearance like that of a grand piano. 
     Heretofore, there have been known electronic pianos (electronic musical instruments) having an outer appearance like that of a grand piano, one example of which is disclosed in Japanese Patent Application Laid-open Publication No. 2007-233190 (hereinafter referred to as “the patent literature”). The electronic piano disclosed in the patent literature includes a casing structure where an accommodating section is provided behind a keyboard and surrounded by side plates defining an outer shape of the electronic piano. Back lid is provided on an opening portion at the top of the accommodating section in such a manner that it can open or close the opening portion as necessary. Plate-shaped member, referred to as “sound board” in the patent literature, having a plurality of speakers arranged thereon is provided within the accommodating section. 
     In the acoustic piano, where strings are provided within the accommodating section, a sound board corresponding to the aforementioned plate-shaped member is provided in the accommodating section beneath the strings and a frame. In the electronic piano, on the other hand, the plate-shaped member is provided near the top opening portion of the accommodating section close to the back lid. 
     Thus, when the back lid is in the opened position, the plate-shaped member undesirably appears on the exterior of the electronic piano; namely, the plate-shaped member is undesirably visible from outside the electronic piano. 
     Further, in the electronic piano disclosed in the patent literature, a fixation structure comprising fastener members, such as bolts, is used for fixing the plate-shaped member to side plates etc. of the body section of the electronic piano. However, because the plate-shaped member is an externally exposed component part in the electronic piano, the bolts fixing the plate-shaped member may also be undesirably visible from outside the electronic piano, which would undesirably impair the outer appearance of the electronic piano. Further, the plate-shaped member provided in the accommodating section is relatively large in size, and thus, if the plate-shaped member is fastened with many bolts, it must be bolted at many portions one by one over a relatively wide range, so that the mounting operations of the plate-shaped member would require much time and labor. 
     If the plate-shaped member is fixed by adhesive, no fastener members, such as bolts, would not be exposed outside of the electronic piano. However, such fixation by adhesive can not achieve a high degree of freedom of mounting and connection between the component parts of the electronic piano. Further, the fixation by adhesive alone may not be able to fix the component parts with a sufficient strength. 
     Further, if the plate-shaped member is formed of a natural material, such as wood, there would occur a deviation, from a designed size, of an actual size of the plate-shaped member. Thus, it is desirable that the fixation structure for the plate-shaped member be one capable of absorbing (tolerating) as much as possible influences of a deviation in actual size of the plate-shaped member and deformation of the plate-shaped member. Further, if the plate-shaped member influences acoustic characteristics of electronic component parts, such as the sound board, it is desired that the fixation structure for the plate-shaped member be constructed so as to enhance an acoustic effect of the casing including the plate-shaped member. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an improved casing structure of an electronic musical instrument which allows the plate-shaped member to be assembled to the casing with an enhanced efficiency, can enhance tolerances against deformation and deviation in actual size of the plate-shaped member, and which permits an enhanced acoustic effect of the casing. 
     In order to accomplish the above-mentioned object, the present invention provides an improved casing structure of an electronic musical instrument, which comprises: a body section; an accommodating section provided in said body section and having at least one portion thereof adapted to be opened; a plate-shaped member to be mounted to said accommodating section; a fitting section provided on said body section for fitting therein part of an end edge portion of said plate-shaped member; fixation portions provided on left and right side regions of a surface of said plate-shaped member facing inwardly of said accommodating section and adapted to be fixed to said body section; and fastener members for fastening and fixing said fixation portions to corresponding portions provided on said body section in correspondence with said fixation portions, wherein said plate-shaped member is mounted to said accommodating section by said fixation portions being fastened and fixed to said corresponding portions by means of said fastener members with the part of the end edge portion of said plate-shaped member fitted in said fitting section. 
     With the casing structure of the present invention, where the plate-shaped member is mounted to the accommodating section by the end edge portion of the plate-shaped member being fitted into the fitting section, it is possible to minimize the number of portions to be fixed by fastener members, such as bolts. Thus, the casing structure of the present invention can facilitate mounting operations of the plate-shaped member and thereby permits an enhanced assembling efficiency of the casing of the electronic musical instrument. Further, because the plate-shaped member is mounted to the accommodating section by the end edge portion of the plate-shaped member being fitted into the fitting section, the casing structure of the present invention can achieve enhanced tolerances against a deviation, from a designed size, of an actual size of the plate-shaped member and deformation of the plate-shaped member, as compared to cases where the plate-shaped member is fixed to the body section by fastener members, such as bolts, alone. As a result, the casing structure of the present invention can not only facilitate the mounting operations of the plate-shaped member but also stabilize a fixed state of the plate-shaped member after the mounting. Further, because the fixation portion to be fixed by the fastener member is provided on the surface of the plate-shaped member facing inwardly of the accommodating section, the present invention can prevent the fastener member from appearing on the exterior of the electronic musical instrument, i.e. from being visible from outside the electronic musical instrument. As a result, the casing structure of the present invention allows the electronic piano to have an improved outer appearance with, for example, a sense of high quality. 
     In an embodiment of the present invention, a resilient shock absorbing portion is provided on at least one of the fitting section and the end edge portion of the plate-shaped member to be fitted into the fitting section. With such an arrangement, the present invention allows the end edge portion of the plate-shaped member to resiliently fit into the fitting section and thereby can even further facilitate the mounting operations of the plate-shaped member. Further, the present invention can achieve even further enhanced tolerances against a deviation of the actual size and deformation of the plate-shaped member but also stabilize the fixed state of the plate-shaped member after the mounting. 
     In an embodiment of the present invention, a speaker is provided in the accommodating section, and, by the plate-shaped member mounted to the accommodating section, at least part of the speaker is hidden to be invisible from outside the accommodating section. This arrangement can even further enhance the outer appearance design of the electronic musical instrument. 
     In an embodiment of the present invention, the speaker comprises a plurality of speakers placed on a speaker placing surface in the accommodating section, the speaker placing surface facing the plate-shaped member mounted to the accommodating section, and the plate-shaped member has sound emitting holes formed in positions thereof corresponding to individual ones of the plurality of speakers, a gap being defined between the plate-shaped member mounted to the accommodating section and the speaker placing surface. Sounds emitted through the sound emitting holes are combinations of so-called direct sounds generated by the speakers and emitted directly through the sound emitting holes and so-called indirect sounds generated by the speakers and then emitted through the sound emitting holes after being mixed together by being reflected in the gap defined between the plate-shaped member mounted to the accommodating section and the speaker placing surface. With the direct sounds alone, the sounds of the speakers would sound separately and give a listener an impression as if a plurality of point sound sources were generating the sounds. However, by the indirect sounds being combined with the direct sounds, it is possible to give the human listener an impression as if a plurality of surface sound sources were generating the sounds. Thus, with the casing structure of the present invention constructed in the aforementioned manner, an acoustic effect very similar to that achieved by a soundboard of an acoustic piano or the like can be obtained by the casing of the electronic musical instrument. As a result, the casing structure of the present invention can significantly improve the acoustic effect provided by the casing of the electronic musical instrument. 
     In an embodiment of the present invention, the accommodating section is disposed in a rear region of the body section opposite from a human player of the electronic musical instrument, the fitting section is provided on a rear side plate surrounding a rear side of the accommodating section or surrounding a region of the accommodating section extending from the rear side to at least portions of left and right sides of the accommodating section, and the end edge portion of the accommodating section is fitted into the fitting section as the plate-shaped member is moved in the accommodating section from a human player side toward the rear side. Thus, when the plate-shaped member is to be mounted to the accommodating section, the end edge portion of the plate-shaped member can be fitted into the fitting section and mounted in place by the plate-shaped member being merely slid in one direction. Therefore, the casing structure of the present invention can facilitate the mounting operations of the plate-shaped member and achieve an enhanced mounting ease of the plate-shaped member. 
     In a preferred implementation of the present invention, the plate-shaped member comprises a first plate-shaped member to be fitted into a first setting section provided in the body section and a second plate-shaped member to be mounted to the mounting section together with the first plate-shaped member, and further comprises: a second fitting section provided on another end edge portion of the first plate-shaped member than the end edge portion to be fitted into the first setting section, part of an end edge portion of the second plate-shaped member being fitted into the second fitting section; a second fixation portion provided on a surface of the second plate-shaped member facing inwardly of the accommodating section and adapted to be fixed to the body section; and a second fastener member for fastening and fixing the second fixation portion to the body section. In this case, the second plate-shaped member is mounted to the accommodating section by the part of the end edge portion of the second plate-shaped member being fitted into the second fitting section and the second fixation portion being fastened and fixed to the body section by means of the second fastener member with the first plate-shaped member mounted to the accommodating section. With such an arrangement, the second plate-shaped member can be mounted to the accommodating section using the second fitting section provided on the first plate-shaped member. Thus, although two (i.e., first and second) plate-shaped members are to be mounted to the accommodating section, the present invention can minimize the number of portions to be fixed by fastener members, such as bolts. Further, because the second fixation portion is provided on the surface of the second plate-shaped member facing inwardly of the accommodating section, it can be made invisible from outside the accommodating section and hence the electronic musical instrument, and thus, the electronic musical instrument can have an even further enhanced outer design. Furthermore, if an arrangement is made for causing only a selected one of the two plate-shaped members to vibrate in response to tone generation by the electronic musical instrument, it is also possible to diversify the acoustic effect achievable by the casing of the electronic musical instrument. Furthermore, different materials can be used for one of the plate-shaped members that influences the acoustic effect and the other plate-shaped member. Thus, it is possible to effectively reduce the necessary manufacturing cost while enhancing the acoustic effect of the electronic musical instrument. 
     The casing structure of an electronic musical instrument of the present invention allows the plate-shaped member to be assembled to the casing of the electronic musical instrument with an enhanced efficiency and ease, can enhance tolerances against deformation and deviation in actual size of the plate-shaped member, and permits an enhanced acoustic effect of the casing. 
     The following will describe embodiments of the present invention, but it should be appreciated that the present invention is not limited to the described embodiments and various modifications of the invention are possible without departing from the basic principles. The scope of the present invention is therefore to be determined solely by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For better understanding of the object and other features of the present invention, its preferred embodiments will be described hereinbelow in greater detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing an overall construction of an electronic piano employing a casing structure according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view showing a construction of a body section of the electronic piano; 
         FIG. 3A  is an upper perspective view of a middle plate,  FIG. 3B  is a lower perspective view of the middle plate,  FIG. 3C  is a side sectional view showing in enlarged scale a section encircled at A of  FIG. 3A , and  FIG. 3D  is a side sectional view showing in enlarged scale a section encircled at B of  FIG. 3B ; 
         FIG. 4A  is an upper perspective view of a soundboard,  FIG. 4B  is a lower perspective view of the soundboard,  FIG. 4C  is an enlarged front view showing a section encircled at C of  FIG. 4A , and  FIG. 4D  is an enlarged side view showing the section encircled at C; 
         FIGS. 5A to 5C  are conceptual views explanatory of a sequence of operations for mounting the middle plate to an accommodating section; 
         FIG. 6  is a perspective view showing the body section with the middle plate appropriately mounted to the accommodating section; 
         FIGS. 7A to 7C  are conceptual views explanatory of a sequence of operations for mounting a soundboard to the accommodating section; and 
         FIG. 8  is a perspective view showing the body section with the middle plate and the soundboard appropriately mounted to the accommodating section. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show an electronic piano (electronic musical instrument)  1  equipped with a casing structure according to an embodiment of the present invention, of which  FIG. 1  is a perspective view showing an overall construction of the electronic piano  1  while  FIG. 2  is an exploded perspective view showing a construction of a body section  10  of the electronic piano  1 . The electronic piano  1  includes the body section  10 , three legs  2  supporting the body section  10 , a pedal unit  3  mounted to the underside of the body section  10 , etc. Note that illustration of the legs  2  and the pedal unit  3  is omitted in  FIG. 2  and succeeding figures. Further, in the following description, one side region of the body section  10  closer to a human player will be referred to as “front side”, and another side region of the body section  10  opposite from the human player or front side will be referred to as “rear side”. Further, a direction in which keys  61  of a keyboard  60  are arranged or arrayed will be referred to as “horizontal direction” or “left-right direction”. 
     In the body section  10 , the keyboard  60  having a plurality of keys  61  arrayed thereon is provided on the front side, and an accommodating section  20  is provided behind the keyboard  60 . The accommodating section  20  is defined by a pair of left and right side plates  11  surrounding the left and right sides of the body section  10  and a rear side plate  12  surrounding the rear side of the body section  10 . The accommodating section  20  has, at its upper end, an opening portion  20   a  that opens upwardly, and a back lid  4  openable and closeable by vertically pivoting about its one side is provided on the opening portion  20   a . Further, a lid prop  5  is provided for supporting the back lid  4  in a raised position. Further, as shown in  FIG. 2 , a speaker box  50  having a plurality of speakers  51  is accommodated in a rear region of the accommodating section  20 . Two horizontal support members  23  and  24 , each having a rectangular columnar shape, are provided in the accommodating section  20  in front of the speaker box  50  and spaced from each other by a predetermined distance in the front-rear direction, and the support members  23  and  24  span between and are fixed to respective inner surfaces  11   a  of the left and right side plates  11 . A mounting plate  25  having a flat plate shape is provided on and spans between the support members  23  and  24 , and electronic component parts, such as a circuit board, are mounted on the mounting plate  25  although not specifically shown. Further, in the accommodating section  20  are mounted a middle plate (first plate-shaped member)  30  closing a rear region of the opening portion  20   a  and a soundboard (second plate-shaped member)  40  closing a front region of the opening portion  20   a  in front of the middle plate  30 . Furthermore, a music rest  55  is provided on a horizontally middle portion of the upper surface  43  of the soundboard  40 , and a pair of decorative rests  57  are provided adjacent to the left and right sides of the music rest  55 . 
     The rear side plate  12  of the body section  10  is a curved plate-shaped member formed of wood or the like and surrounds a rear portion of the accommodating section  20  extending from the rear end of the accommodating section  20  to left and right sides of the accommodating section  20 . The left and right side plates  11 , which are each a generally flat plate-shaped member formed of wood or the like, extend in the front-rear direction to interconnect the left and right rear ends of the rear side plate  12  and the left and right ends of the keyboard  60 . A fitting section  21 , into which a rear end edge portion  30   a  of the middle plate  30  is fitted, is provided on the inner surface  12   a  (facing the accommodating section  20 ) of the rear side plate  12 . The fitting section  21 , which is a laterally-inwardly facing channel-shaped section, includes a stepped portion  12   b  provided on and along the upper end of the rear side plate  12  and projecting into the accommodating section  20 , and a plurality of angle members  13  provided immediately beneath the stepped portion  12   b . More specifically, the stepped portion  12   b  is in the form of a projection having a generally rectangular cross-sectional shape formed on and along the inner periphery of the opening portion  20   a . Each of the angle members  13  is a metal member of an L shape having two portions, and one of the two portions is fixed to the inner surface  12   a  of the rear side plate  12  while the other portion  12  extends horizontally from the inner surface  12   a  of the rear side plate  12  inwardly of the accommodating section  20 . The fitting section  21  is defined by or between the angle members  13  and the stepped portion  12   b . The fitting section  21  has a vertical dimension substantially equal to the thickness of the rear end edge portion  30   a  of the middle plate  30 , so that the rear end edge portion  30   a  of the middle plate  30  is sandwiched vertically or in its thickness direction by the fitting section  21 . The angle members  13  are provided at predetermined horizontal intervals along the inner peripheral edge of the rear side plate  12 . Further, a cushion member (i.e., shock absorbing member)  13   a , formed of a resilient material like urethane, is affixed to the upper surface of the above-mentioned other portion of each of the angle members  13 . 
       FIG. 3A  is an upper perspective view of the middle plate  30 ,  FIG. 3B  is a lower perspective view of the middle plate  30 ,  FIG. 3C  is a side sectional view showing in enlarged scale a section encircled at A of  FIG. 3A , and  FIG. 3D  is a side sectional view showing in enlarged scale a section encircled at B of  FIG. 3B . The middle plate  30 , which is a flat plate-shaped member formed of wood, has a shape defined by: the rear end edge portion  30   a  curved along the inner periphery of the rear side plate  12  and left and right side plates  11  defining the accommodating section  20 ; generally straight left and right side edge portions  30   b ; and a slightly curved front end edge portion  30   c . A thin plate-shaped cushion member  31 , formed of a resilient material like urethane, is affixed at least to the rear end edge portion  30   a . Further, the middle plate  30  has a plurality of (four in the illustrated example) sound emitting holes  32 . Each of the sound emitting holes  32  is constructed by fixing a net-like perforated metal sheet  32   a , having a multiplicity of small holes, to the edge of a through-hole formed in the middle plate  30  and shaped along the outer periphery of one of the speakers  50 . Each of the sound emitting holes  32  is formed in a portion of the middle plate  30  positionally corresponding to a respective one of the speakers  51  of the speaker box  50  ( FIG. 2 ) provided in the accommodating section  20 . 
     The middle plate  30  has a fitting section  35  provided on the underside  34  of the front end edge portion  30   c  for fitting therein of a rear end edge portion  40   a  of the soundboard  40 . The fitting section  35  is a forwardly facing channel-shaped section which includes the underside  34  of the front end edge portion  30   c  and a plurality of angle members  36  fixed to the underside  34 . Each of the angle members  36  is in the form of a plate-shaped metal member formed to have three portions: an upper horizontal portion fixed to the underside  34  of the front end edge portion  30   c ; a vertical portion bent generally perpendicularly from the front end of the horizontal portion, i.e. generally vertically downward away from the underside  34 ; and a lower horizontal portion extending forward in parallel to the underside  34 . Namely, the fitting section  35  is defined by or between the angle members  36  and the underside  34  of the front end edge portion  30   c . As shown in  FIGS. 3A and 3B , the angle members  36  are provided at predetermined intervals along the underside  34  of the front end edge portion  30   c  of the middle plate  30 . The fitting section  35  has a vertical dimension substantially equal to the thickness of the rear end edge portion  40   a  of the soundboard  40 , so that the rear end edge portion  40   a  of the soundboard  40  is sandwiched vertically or in its thickness direction by the fitting section  35 . 
     As shown in  FIGS. 3B and 3D , fixing pieces (fixation portions)  37  are provided on left and right side regions of the underside  34  of the middle plate  30  near the front end edge portion  30   c , and the fixing pieces  37  have the same shape. More specifically, each of the fixing pieces  37  is in the form of a generally L-shaped metal plate having two portions, and one of the two portions is fixed to the underside  34  while the other portion extends downward from the front end of the one portion away from the underside  34 . These fixing pieces  37  are provided for fastening and fixing the middle plate  30  to the body section  10  and each have a bolt hole  37   a  for passage therethrough of a bolt (fastener member)  16  (see  FIG. 5 ). 
     Further, as shown in  FIG. 3B , connecting members  38  are fixed to the underside  34  of the middle plate  30 . Each of the connecting members  38  is in the form of a plate-shaped metal member formed to have three portions: an upper horizontal portion fixed to the underside  34  of the middle plate  30 ; a vertical portion bent generally perpendicularly from the rear end of the horizontal portion, i.e. generally vertically downward away from the underside  34 ; and a lower horizontal portion extending rearward from the lower end of the vertical portion in parallel to the underside  34 . Thus, a gap is defined by or between each of the connecting members  38  and the underside  34  of the middle plate  30 , as seen in  FIG. 5A . The connecting members  38  are disposed near the front end edge portion  30   c , one on each of left and right side regions of the underside  34  of the middle plate  30 . Further, a cushion member  38   a , formed of a resilient material like urethane, is affixed to the upper surface of the lower horizontal portion of each of the connecting members  38 . 
       FIG. 4A  is an upper perspective view of the soundboard  40 ,  FIG. 4B  is a lower perspective view of the soundboard  40 ,  FIG. 4C  is an enlarged front view showing a section encircled at C of  FIG. 4A , and  FIG. 4D  is an enlarged side view showing the section encircled at C. The soundboard  40  is a flat plate-shaped member formed of wood and has a horizontally elongated rectangular shape, which has a rear end edge portion  40   a  slightly curved along the slightly curved front end edge portion  30   c  of the middle plate  30 , generally straight left and right side edge portions  40   b , and a generally straight front edge  40   c . The soundboard  40  has an opening  40   d  elongated in the front-rear direction and formed through the thickness of a middle region thereof to permit passage therethrough of a support rod (not shown) for supporting the music rest  55 . Further, small openings  40   e  elongated in the front-rear direction are formed through the thickness of regions of the soundboard  40  adjacent to the left and right side edge portions of the soundboard  40  to permit insertion therethrough of pins  26   a  of mounting members  26  provided on the body section  10 . 
     Furthermore, a plurality of transducers (vibration generators)  58  are mounted on the underside  44  of the soundboard  40  near the front end edge portion  40   c  for imparting the soundboard  40  with vibrations corresponding to a tone to be performed by the electronic piano  1  (i.e., a tone signal to be electrically generated by the electronic piano  1 ). In the illustrated example, one such transducer  58  is provided on each of left and right side regions of the underside  44  of the soundboard  40 . The transducers  58  are connected via connectors to a circuit board mounted beneath the soundboard  40 , for vibrating the soundboard  40  in accordance with an input tone signal. Note that the transducers  58  may be caused to operate only in response to a tone signal of a high pitch (or treble) range. A plurality of fixing pieces (fixation portions)  47  are fixed to the undersurface  44  of the soundboard  40  and at predetermined horizontal intervals along the front end edge portion  40   c , and the fixing pieces  47  have the same shape. More specifically, as shown in  FIGS. 4C and 4D , each of the fixing pieces  47  is in the form of a generally L-shaped metal plate having two portions, and one of the two portions is fixed to the underside  44  of the soundboard  40  while the other portion extends downward from the front end of the one portion away from the underside  44 . These fixing pieces  47  are provided for fastening and fixing the sound board  40  to the accommodating section  20  by being fixed to the support member (fixation portion)  23  of the accommodating section  20  by means of bolts (fastener members)  48  (see  FIG. 7 ). For that purpose, each of the fixing pieces  47  has a bolt hole  47   a  for passage therethrough of a bolt (fastener member)  48 . 
     As shown in  FIG. 2 , the music rest  55  is formed in a generally rectangular flat plate shape. The music rest  55  is pivotably mounted at its front (lower) end edge portion  55   a  to the support member  23  immediate beneath the soundboard  40  by means of hinges  56  in such a manner that an inclination angle of the music rest  55  is adjustable via a support rod (not shown) horizontally movably connected to a guide member  27 . Further, the decorative rests  57  are fixed adjacent to left and right side edge portions of the music rest  55  by means of the pins  26   a  projecting upwardly from the mounting members  26  through the openings  40   e  formed in the soundboard  40 . The decorative rests  57  can be used for placing thereon small articles, candle holders or the like. 
     The speaker box  50  is accommodated in a rear lower region of the accommodating section  20 , and a plurality of (four sets in the illustrated example) of speakers  51  are placed at predetermined horizontal intervals on the upper surface (i.e., speaker placing surface)  50   a  of the speaker box  50 . Further, spacer members  52  each having a small rectangular columnar shape are provided at suitable horizontal intervals between the speakers  51 . A cushion member  52   a , formed of a resilient material like urethane, is affixed to the upper surface of each of the spacer members  52 . During operations for mounting the middle plate  30  to the accommodating section  20 , the spacer members  52  having the cushion member  52   a  affixed thereto can function as shock absorbing members that prevent the rear end edge portion  30   a  and the underside of the middle plate  30  from colliding against the speaker box  50  and speakers  51 . 
     Further, connection members  53  are fixed to the speaker placing surface  50   a . Each of the connection members  53  is in the form of a plate-shaped metal member formed to have three portions: a lower horizontal portion fixed to the speaker placing surface  50   a ; a vertical portion bent generally perpendicularly upward from the front end of the horizontal portion, i.e. generally vertically upward away from the speaker placing surface  50   a ; and an upper horizontal portion extending forward in parallel to the speaker placing surface  50   a . A gap is defined by or between each of the connection members  53  and the speaker placing surface  50   a , as seen in  FIG. 5 . The connection members  53  are disposed in positional corresponding relation to the connecting members  38  fixed to the underside  34  of the middle plate  30 . The connecting members  38  are disposed near the front end edge of the speaker placing surface  50   a , one on each of left and right side regions of the speaker placing surface  50   a . Further, a cushion member  53   a , formed of a resilient material like urethane, is affixed to the lower surface of the upper horizontal portion of each of the connection members  53 . 
     Further, fixation pieces  15  are provided on the inner surface  11   a  of each of the left and right side plates  11  in correspondence with the fixing pieces  37 . Each of the fixation pieces  15  is in the form of a generally L-shaped metal member having one portion fixed to the inner surface  11   a  of the corresponding side plate  11  and another portion extending inwardly of the accommodating section  20  from the one portion away from the inner surface  11   a . These fixation pieces  15  are provided for allowing the middle plate  30  to be mounted to the accommodating section  20  by fixedly engaging with the fixing pieces  37  of the middle plate  30  by means of the bolts  16  (see  FIG. 5 ). Furthermore, a support member  28  for supporting the soundboard  40  is provided on the inner surface  11   a  of each of the left and right side plates  11 . Each of the support members  28  is provided as a small protrusion of a generally rectangular columnar shape and supports thereon the underside  44  of one of the left and right side edge portions  40   b  of the soundboard  40  mounted to the accommodating section  20 . Note that only the fixation piece  15  and support member  28  fixed to the inner surface  11   a  of the left side plate  11  are shown in  FIG. 2 . 
     The following describe a sequence of operations for mounting the middle plate  30  and the soundboard  40  to the accommodating section  20  to assemble a casing in the aforementioned casing structure. The middle plate  30  and the soundboard  40  are mounted to the accommodating section  20  in the order mentioned, i.e. first the middle plate  30  and then the soundboard  40 .  FIGS. 5A to 5C  are conceptual views explanatory of a sequence of operations for mounting the middle plate  30  to the accommodating section  20 . The fixing piece  37  and angle member  36  of the middle plate  30  are shown in  FIGS. 5A to 5C  as partially overlapping with each other at the same position; actually, however, the fixing piece  37  and angle member  36  on each of left and right side regions of the middle plate  30  do not overlap with each other; namely, the fixing piece  37  is located closer to the corresponding side plate  11  than the angle member  36  as shown in  FIG. 3 . 
     To mount the middle plate  30  to the accommodating section  20 , the middle plate  30  shown in  FIG. 5A  is first inserted into the accommodating section  20  through the opening portion  20   a  and then placed in a horizontal orientation at a position slightly lower than the opening portion  20   a  (i.e., at a height position of the fitting section  21 ) as shown in  FIG. 5B . Then, the middle plate  30  is slid horizontally rearward, so that the rear end edge portion  30   a  of the middle plate  30  is moved to be fitted into the fitting section  21  and also each of the connecting members  38  is inserted into the corresponding connection member  53 , i.e. between the speaker placing surface  50   a  and the upper horizontal portion of the connection member  53 . Then, as shown in  FIG. 5C , each of the connecting members  38  and the corresponding connection member  53  engage with each other in a vertically overlapping state with the rear end edge portion  30   a  of the middle plate  30  fitted fully into the fitting section  21 . At that time, the rear end edge portion  30   a  of the middle plate  30  resiliently fits into the fitting section  21  by the provision of the cushion member  31  affixed to the rear end edge portion  30   a  and the cushion member  13   a  affixed to each of the angle members  13 , and each of the connecting members  38  and the corresponding connection member  53  resiliently engage with each other. Further, at that time, each of the fixing pieces  37  abuts against the corresponding fixation piece  15  of the accommodating section  20 , and then each of the fixing pieces  37  and the corresponding fixation piece  15  are fixed together by means of the bolt  16 . In this way, the mounting of the middle plate  30  to the accommodating section  20  is completed. 
       FIG. 6  is a perspective view showing the body section  10  with the middle plate  30  appropriately mounted to the accommodating section  20 . As shown, the middle plate  30  is mounted in a horizontal orientation at a position slightly lower than the opening portion  20   a  of the accommodating section  20  and thereby covers the speaker placing surface  50   a  (see  FIG. 1 ) of the speaker box  50  in a rear region of the accommodating section  20 . In this state, a gap A is defined between the speaker placing surface  50   a  and the middle plate  30  as shown in  FIG. 5C . 
       FIGS. 7A to 7C  are conceptual views explanatory of a sequence of operations for mounting the soundboard  40  to the accommodating section  20 . To mount the soundboard  40  to the accommodating section  20 , the soundboard  40  shown in  FIG. 7A  is first inserted into the accommodating section  20  through the opening portion  20   a  and then placed in a horizontal orientation in front of the middle plate  30  and at a position lower than the middle plate  30  (i.e., at a height position of the fitting section  35 ) as shown in  FIG. 7B . At that time, the pins  26   a  of the mounting members  26  vertically project above the soundboard  40  through the openings  40   e  formed in the soundboard  40 , and the guide member  27  is positioned in opposed relation to the elongated opening  40   d  formed in the soundboard  40 , although not specifically shown. Then, the soundboard  40  is slid horizontally rearward, so that the rear end edge portion  40   a  of the soundboard  40  is moved to be fitted into the fitting section  35  of the middle plate  30 . In this case too, the rear end edge portion  40   a  of the soundboard  40  resiliently fits into the fitting section  35  by the provision of the cushion member  41  affixed to the rear end edge portion  40   a  and the cushion member  36   a  affixed to each of the angle members  36 . Then, as shown in  FIG. 7C , each of the fixing pieces  47  of the soundboard  40  abuts against the support member  23  with the rear end edge portion  40   a  of the soundboard  40  fitted fully into the fitting section  35 . Then, each of the fixing pieces  47  and the support member  23  are fixed together by means of the bolt  48 . In this way, the mounting of the soundboard  40  to the accommodating section  20  is completed. 
       FIG. 8  is a perspective view showing the body section  10  with the middle plate  30  and soundboard  40  appropriately mounted to the accommodating section  20 . As shown, the soundboard  40  is placed in a horizontal orientation in front of the middle plate  30  and at a position lower than the middle plate  30  and thereby covers an area between the keyboard  60  and the speaker box  50  in a front region of the accommodating section  20 . 
     Then, the music rest  55  is mounted to the upper surface  43  of the soundboard  40 , and the decorative rests  57  are mounted adjacent to the left and right sides of the music rest  55 . To mount the decorative rests  57 , respective outer side edge portions of the decorative rests  57  are fitted into the inner surfaces  11   a  of the corresponding side plates  11 , and then fixation portions (not shown) provided on the lower surfaces of the decorative rests  57  are fixed to the pins  26   a  of the mounting members  26  by means of not-shown bolts. Use of such a fixation structure can prevent the bolts, fixing the decorative rests  57 , from appearing on the exterior of the electronic piano  1 , i.e. from being visible from outside the electronic piano  1 . In the embodiment of the casing structure assembled in the aforementioned manner, the middle plate  30  and soundboard  40  appropriately mounted to the accommodating section  20  are visible from outside the electronic piano  1  when the back lid  4  is in the opened or raised position, and thus, the middle plate  30  and soundboard  40  constitute part of the outer appearance of the electronic piano  1 . 
     According to the above-described embodiment of the casing structure, when the middle plate  30  and the soundboard  40  are mounted to the accommodating section  20 , the rear end edge portion  30   a  of the middle plate  30  is fitted into the fitting section  21 , but also the rear end edge portion  40   a  of the soundboard  40  is fitted into the fitting section  35  of the middle plate  30 . In this way, the embodiment of the casing structure can minimize the number of the portions of the middle plate  30  to be fixed by the bolts  16  and the number of the portions of the soundboard  40  to be fixed by the bolts  48 . Consequently, the embodiment of the casing structure can enhance the assembling efficiency and ease of the middle plate  30  and the soundboard  40  and thereby allows the operations for mounting the middle plate  30  and soundboard  40  to be performed efficiently in a short time. Further, because not only the middle plate  30  and the soundboard  40  are mounted by being fitted into the fitting sections  21  and  35  as noted above but also the middle plate  30  and the soundboard  40  are resiliently fitted into the accommodating section  20  and the middle plate  30 , respectively, via the cushion members  31  and  13   a  and cushion members  41  and  36   a , the embodiment of the casing structure can effectively absorb (tolerate) influences of deviations, from designed sizes, of actual sizes of the middle plate  30  and soundboard  40  and deformation, such as warpage, of the middle plate  30  and soundboard  40 , during and after assemblage of the casing of the electronic piano  1 . As a result, the embodiment of the casing structure can not only facilitate the mounting operations of the middle plate  30  and soundboard  40  but also stabilize fixed states of the middle plate  30  and soundboard  40  after the mounting. Further, by the engagement between the connecting members  38  and the connection members  53 , the embodiment of the casing structure can prevent an inner portion of the middle plate  30  from undesirably lifting up due to deformation, such as warpage, of the middle plate  30 . 
     Further, with the embodiment of the casing structure, where the bolts  16  fixing the middle plate  30  and the bolts  48  fixing the soundboard  40  are disposed on the underside  34  of the middle plate  34  and the underside  44  of the soundboard  40 , the portions, fastened by the bolts  16  and  48 , of the middle plate  30  and soundboard  40  duly mounted on the accommodating section  20  can be prevent from being visible from outside the accommodating section  20  and hence the electronic piano  1 . As a result, the electronic piano  1  can have an improved outer appearance with, for example, a sense of high quality. Further, with the middle plate  30  mounted on the accommodating section  20 , the speakers  51  on the speaker placing surface  50   a  can be hidden or invisible from outside the electronic piano  1 . Thus, even when the back lid  4  is in the opened or raised position, the speaker box  50  and speakers  51  provided in the accommodating section  20  can be prevented from being directly visible from outside the electronic piano  1 , so that the electronic piano  1  can have an even further improved outer appearance. 
     Further, with the embodiment of the casing structure, the rear end edge portion  30   a  of the middle plate  30  is fitted into the fitting section  21  as the middle plate  30  is slid horizontally in the front-to-rear direction in the accommodating section  20 , and the rear end edge portion  40   a  of the soundboard  40  is fitted into the fitting section  35  of the middle plate  30  as the soundboard  40  is slid horizontally in the front-to-rear direction, as set forth above. Namely, the middle plate  30  and the soundboard  40  can be fitted into the fitting sections  21  and  35  to be mounted in place by the middle plate  30  and the soundboard  40  being merely slid in one direction. Therefore, the embodiment of the casing structure can facilitate the mounting operations of the middle plate  30  and the soundboard  40 . 
     Further, according to the embodiment of the casing structure, the soundboard  40  can be mounted to the accommodating section  20  using the fitting section  35  provided on the middle plate  30 . Thus, although the plate-shaped member to be mounted to the accommodating section  20  comprises two separate plate-shaped members, i.e. the middle plate  30  and the soundboard  40 , the embodiment of the casing structure can effectively minimize the number of the portions of the middle plate  30  and soundboard  40  to be fixed by the bolts  16  and  48 . Further, because the plate-shaped member to be mounted to the accommodating section  20  comprises two separate plate-shaped members, i.e. the middle plate  30  and the soundboard  40 , the middle plate  30  and the soundboard  40  can be constructed of different materials. Thus, it is possible to construct the middle plate  30  using a relatively inexpensive material while using an optimal material for the soundboard  40  as an acoustic component, so that the necessary manufacturing cost can be reduced. Furthermore, because the middle plate  30  and the soundboard  40  are provided as separate plate-shaped members, the embodiment of the casing structure allows only the soundboard  40  to be vibrated by the transducers  58  as set forth above. In this way, the embodiment of the casing structure permits reduction in size and output power of the component parts, such as the transducers  58 , required for generation of vibrations, as compared to the case where only one plate-shaped member is mounted to the accommodating section  20  as in the conventionally-known structure discussed earlier in this specification. Furthermore, because the soundboard  40  provided in a front region of the accommodating section  20  is vibrated, the embodiment of the casing structure allows vibration sounds to be generated only from the soundboard  40  located near the human player, to thereby enhance responsiveness of the vibration sounds to be transmitted to the human player. Furthermore, with the rear end edge portion  40   a  of the soundboard  40  resiliently fitted in the second fitting section  35 , the embodiment of the casing structure can achieve an enhanced freedom of vibration of the soundboard  40  and thereby enhance an acoustic effect based on the vibrations of the soundboard  40 . 
     Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the preferred embodiment and may be variously modified within the scope of the technical idea presented in the specification and drawings and the following claims. For example, whereas the preferred embodiment has been described above in relation to the case where the cushion member (shock absorbing member) is provided both on the rear end edge portion  30   a  of the middle plate  30  and on the angle members  13 , such a cushion member (shock absorbing member) may alternatively be provided only on one of the rear end edge portion  30   a  of the middle plate  30  and the angle members  13 . Similarly, whereas the preferred embodiment has been described above in relation to the case where the cushion member (shock absorbing member) is provided both on the connecting members  38  and on the connection members  53 , such a cushion member may alternatively be provided only on one of the connecting members  38  and the connection members  53 . Furthermore, each of the aforementioned cushion members is only one example of the shock absorbing member to be employed in the present invention, and the shock absorbing member in the present invention may be constructed in a different manner from the above-described. 
     Further, whereas the fixing pieces  47  for fixing the soundboard  40  to the body section  10  by means of the bolts have been described as provided on the underside  44  of the soundboard  40 , the soundboard  40  may be fixed in a different manner than the aforementioned. For example, fastener-based fixation portions for fixing left and right side edge portion regions of the soundboard  40  from above the upper surface  43  may be provided, and the decorative rests  57  may be mounted in such a way to cover the fastener-based fixation portions, although not particularly shown. This construction too can prevent the fastener members, fixing the soundboard  40 , from appearing on the exterior of the electronic piano  1 . 
     Furthermore, whereas the preferred embodiment of the casing structure the present invention has been described above as applied to the grand-piano type electronic piano  1 , the casing structure the present invention may be applied to other types of electronic musical instruments. 
     The present application is based on, and claims priority to, Japanese Patent Application No. 2008-325686 filed on Dec. 22, 2008. The disclosure of the priority application, in its entirety, including the drawings, claims, and the specification thereof, is incorporated herein by reference.