Patent Publication Number: US-9406288-B2

Title: Actuator for vibrating a sound board in a musical instrument and method for attaching same

Description:
TECHNICAL FIELD 
     The present invention relates to a voice coil type actuator for positively imparting vibration to a sound board of a musical instrument and a method for attaching the actuator to the musical instrument, as well as a musical instrument provided with the actuator and a method for manufacturing the same. 
     BACKGROUND ART 
     In electronic pianos, electronic tones (sounds) are audibly generated or sounded through an electromagnetic speaker. In some of the electronic pianos too, a sound board is provided to generate not only electronic tones but also natural spreading of tones and rich low-pitched tones. Patent Literature 1 discloses a technique in accordance with which an electromagnetic speaker is mounted on the sound board to vibrate the sound board with the electromagnetic speaker so that a tone is radiated from the sound board. 
     PRIOR ART LITERATURE 
     Patent Literature 1: Japanese Translation of PCT International Application No. HEI-4-500735 
     To vibrate the sound board, there is employed, for example, a voice coil type actuator that generates drive force by inputting a drive signal to a voice coil disposed on a path of magnetic lines of force (magnetic path). Because such an actuator is similar in construction to a voice coil type speaker, it is possible to reduce necessary cost. In order to obtain stable drive force, it is desirable that the actuator be mounted in such a manner that variation in the number of coil winding turns of the vibrating voice coil present in the magnetic path is minimized. For example, such variation decreases as a dimension, in a vibrating direction, of the voice coil is increased. But, as such a dimension, in the vibrating direction, of the voice coil increases, inductance increases, so that frequencies at which good responsiveness can be obtained would be limited to low frequencies. To avoid such an inconvenience, it is necessary that the dimension, in the vibrating direction, of the voice coil be set to equal a length of a dimension, in the vibrating direction, of the magnetic path plus a maximum amplitude of the voice coil or such a length plus a length of play (or clearance). In that case, in order to obtain stable drive force, there arises a need to accurately mount a vibration section vibrating together with the voice coil and a magnetic path formation section, constructed to form a magnetic path, in such a manner that relative positions, in the vibrating direction, of the vibration section and the magnetic path formation section, have predetermined relationship. According to the technique disclosed in Patent Literature 1, a bobbin and a yoke are component parts independent of each other, and thus, the yoke is fixed to a strut or the like after the bobbin has been connected to the sound board. In such a case, there is a need to finely adjust a position, in the vibrating direction, of the bobbin in order to mount the bobbin and the yoke at their respective accurate position, and such an adjusting operation tends to be cumbersome and complicated. 
     Further, in the electromagnetic speaker used as the actuator for vibrating the sound board as in the aforementioned prior art technique, the voice coil attached to the bobbin is positioned in a path of magnetic lines of force (magnetic path) formed, for example, by a magnet and yokes, and a drive signal is input to the voice coil to generate drive force. In such a construction, the magnetic path is formed between the yokes opposed to each other, and the bobbin is positioned between the yokes. When a human operator mounts such an actuator on a musical instrument, it is necessary to mount the bobbin and the yokes at their respective positions in such a manner that the bobbin and the yokes do not contact each other. Patent Literature 1 discloses that the bobbin is fixed to the sound board and then the yokes are mounted in accordance with the fixed position of the bobbin. In such a case, however, cumbersome and complicated operations would be required because the human operator has to perform the operations for fixing the magnet and the yokes while finely adjusting the positions of the yokes in various directions in such a manner that the bobbin and the yokes do not contact each other. 
     SUMMARY OF INVENTION 
     It is therefore an object of the present invention to provide a voice coil type actuator which can be attached to the sound board with ease. It is another object of the present invention to provide a voice coil type actuator which can be attached to the sound board in such a manner that the voice coil is positioned at a desired ideal position within a magnetic path space of the voice coil. 
     It is still another object of the present invention to provide a voice coil type actuator constructed to be easily attachable to a musical instrument in such a manner that the bobbin and a magnetic path formation section do not contact each other. 
     In order to accomplish the above-mentioned objects, the present invention provides an actuator for vibrating a sound board of a musical instrument, which comprises: a magnetic path formation section constructed to form a magnetic path space; a bobbin having a voice coil attached thereto in such a manner that the voice coil is disposed within the magnetic path space; and a connection member connected to the bobbin and constructed to vibrate in response to vibration of the bobbin, the connection member having a connection end adapted for connection to the sound board of the musical instrument, the connection member being constructed to be adjustable in length. 
     According to the present invention arranged in the aforementioned manner, the end member connected to the bobbin connects the bobbin indirectly to the sound board of the musical instrument so as to transmit vibration of the bobbin (voice coil) to the sound board. The connection member is constructed to be adjustable in length, and thus, when the actuator is to be attached to the sound board, the connection member of the actuator can be connected to the sound board by mere adjustment of the length of the connection member without the magnetic path formation section and the bobbin (voice coil) being moved in position. In this way, the actuator can be attached to the sound board with an increased ease. Further, because the connection member can be connected to the sound board, by mere adjustment of the length of the connection member, with relative positional relationship between the magnetic path formation section and the bobbin (bobbin coil) maintained in a predetermined reference mounting position. Thus, according to the present invention, operations for attaching the actuator to the sound board with relative positional relationship between the magnetic path formation section and the bobbin (bobbin coil) maintained in the reference mounting position can be performed with an increased ease. 
     In an embodiment, the connection member may include a rod-shaped member, and a screw structure for converting rotational displacement of the rod-shaped member to linear displacement of the rod-shaped member. 
     In another embodiment, the connection member may include: a first member connected to the bobbin: a second member connected to the first member in such a manner that the second member is displaceable relative to the first member; and a tightening tool adapted to tighten and fix a connected portion between the first member and the second member, i.e. tighten and fix the first member and the second member relative to each other. 
     According to another aspect of the present invention, there is provided a musical instrument, which comprises: the aforementioned actuator; the support section supporting the magnetic path formation section; the sound board having the connection end connected thereto; a performance operator; and a signal generation section constructed to generate a drive signal indicative of an audio waveform corresponding to an operation of the performance operator, the drive signal being supplied to the actuator for driving the voice coil. 
     According to still another aspect of the present invention, there is provided a method for attaching the aforementioned actuator to a musical instrument, which comprises: a step of providing a support section in association with an actuator-attaching position of the sound board to which the actuator is to be attached and installing the magnetic path formation section on the support section; a step of connecting the connection end to the sound board after adjusting a length of the connection member in such a manner that the connection end is moved toward the sound board; and a step of fixing the length of the connection member having been adjusted in such a manner that the connection end is connected to the sound board. 
     Further, by incorporating the aforementioned actuator attaching method into the aforementioned musical instrument manufacturing method, the present invention can provide a novel and useful musical instrument manufacturing method. 
     According to still another aspect of the present invention, there is provided an actuator for vibrating a sound board of a musical instrument, which comprises: a magnetic path formation section constructed to form a magnetic path space; a bobbin having a voice coil attached thereto in such a manner that the voice coil is disposed within the magnetic path space; and a connection member joined to an end of the bobbin and connected to the sound board of the musical instrument, the magnetic path formation section having a portion inserted in an inner space of the bobbin, the portion inserted in the inner space having a through-hole portion formed therethrough in an axial direction of the voice coil, a mark provided on a portion of the end member opposed to the through-hole portion, the mark designating a position at which a fixation member for connecting the end member to the sound board is to be fastened. 
     In this actuator, the through-hole portion is formed in the portion of the magnetic path formation section inserted in the inner space of the bobbin, and the mark designating a position at which the fixation member is to be fastened is provided on the portion of the end member opposed to the through-hole portion. By the provision of such a mark, the operation for connecting the connection member to the sound board by means of the fixation member can be performed with an increased ease. Further, because the through-hole portion is formed in the portion of the magnetic path formation section inserted in the inner space of the bobbin, a tool (e.g., screwdriver) to be used in the operation for connecting the end member to the sound board by means of the fixation member (e.g., screw) can be readily introduced through the through-hole portion to a predetermined connection point. In this way, the present invention can provide a construction that effectively facilitates the operations for attaching the actuator to the sound board. Further, because, with the bobbin (voice coil) disposed within the magnetic path formation section, the fixation member (e.g., screw) can be readily introduced through the through-hole portion to the predetermined connection point so that the connection member fixing operation is performed. Thus, it is possible to eliminate a need for employing an operational sequence of first connecting the bobbin (voice coil) to the sound board and combining the magnetic path formation section to the bobbin (voice coil) as done in the prior art technique. As a result, the operations for attaching the actuator to the sound board can be performed in such a manner that the bobbin and the magnetic path formation section do no contact each other. 
     According to still another aspect, the present invention provides a method for attaching the aforementioned actuator to a musical instrument, which comprises: a step of providing a support section in association with an actuator-attaching position of the sound board to which the actuator is to be attached and installing the magnetic path formation section on the support section; a step of introducing, through the through-hole portion of the magnetic formation section, the fixation member to a position of the mark of the end member; and a step of fixing the end member to the sound board by means of the fixation member introduced to the position of the mark. Further, by incorporating the aforementioned actuator attaching method into the aforementioned musical instrument manufacturing method, the present invention can provide a novel and useful musical instrument manufacturing method. 
     According to still another aspect of the present invention, there is provided a device for vibrating a sound board of a musical instrument, which comprises: an actuator including: a magnetic path formation section constructed to form a magnetic path space; a bobbin having a voice coil attached thereto in such a manner that the voice coil is disposed within the magnetic path space; and a connection member connected to the bobbin and to the sound board of the musical instrument and adapted to transmit vibration of the bobbin to the sound board; a support section disposed in association with an actuator-attaching position of the sound board to which the actuator is to be attached; and an adjustment device constructed to adjust a relative distance of the support section to the sound board. 
     According to that aspect, when the actuator is to be attached to the sound board, the support section and the actuator can be moved as a unit to a position where the connection member of the actuator is to be connected to the sound board, by mere adjustment of the relative distance of the support section to the sound board, without the magnetic path formation section and the bobbin (voice coil) being moved in position within the actuator. In this way, the actuator can be attached to the sound board with an increased ease. Further, because the connection member can be connected to the sound board by mere adjustment of the support section with relative positional relationship between the magnetic path formation section and the bobbin (bobbin coil) maintained in the predetermined reference mounting position, the operations for attaching the actuator to the sound board with the relative positional relationship between the magnetic path formation section and the bobbin (bobbin coil) maintained in the reference mounting position can be performed with an increased ease. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Hereinbelow, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         FIG. 1  is a perspective view showing an outer appearance of a grand piano according to an embodiment of the present invention; 
         FIG. 2  is a view explanatory of an internal construction of the grand piano; 
         FIG. 3  is a view explanatory of a configuration of a vibration device; 
         FIG. 4  is a view showing an outer appearance of a first embodiment of the vibration device of the present invention; 
         FIG. 5  is a vertical sectional view of the vibration device shown in  FIG. 4 ; 
         FIG. 6  is a flow chart showing a sequence of operations for attaching the vibration device to the grand piano; 
         FIG. 7  is a plan view and a front view showing an outer appearance of a fixing jig; 
         FIG. 8  is a view showing the fixing jig mounted to a magnetic circuit member; 
         FIG. 9  is a view showing the magnetic circuit member supported by the support section; 
         FIG. 10  is a view showing a spacer connected to a sound board; 
         FIG. 11  is a view showing a shaft fixed to a cap; 
         FIG. 12  is a view showing the sound board and the support section positionally displaced relative to each other; 
         FIG. 13  is a view showing the vibration device mounted at a position where a sound board rib is located above a yoke; 
         FIG. 14  is a block diagram showing a construction of a control device; 
         FIG. 15  is a block showing functional components of the grand piano; 
         FIG. 16  is a view showing a modified fixing jig mounted; 
         FIG. 17  is a view showing a modified magnetic circuit member; 
         FIG. 18  is a view showing a modified vibration device; 
         FIG. 19  is a view showing a modified cap; 
         FIG. 20  is a view showing a modified shaft; 
         FIG. 21  is a view showing a modified shaft; 
         FIG. 22  is a view showing an outer appearance of a second embodiment of the vibration device of the present invention; 
         FIG. 23  is a vertical sectional view of the second embodiment of the vibration device shown in  FIG. 22 ; 
         FIG. 24  is a flow chart showing a sequence of operations for attaching the second embodiment of the vibration device to the grand piano; 
         FIG. 25  is a view showing the vibration member and the magnetic circuit member provisionally fixed in position by means of the fixing jig; 
         FIG. 26  is a view showing the magnetic circuit member supported by the support section; 
         FIG. 27  is a view showing the cap fixed to the sound board; 
         FIG. 28  is a view showing a modified cap; 
         FIG. 29  is a view showing a modified cap; 
         FIG. 30  is a view showing a modified cap; 
         FIG. 31  is a view showing a modified fixing jig mounted in place; 
         FIG. 32  is a view showing a modified vibration device; 
         FIG. 33  is a view showing a modified vibration device; 
         FIG. 34  is a view showing a modified vibration member; 
         FIG. 35  is a vertical sectional view of a third embodiment of the vibration device of the present invention; 
         FIG. 36  is a vertical sectional view of a fourth embodiment of the vibration device of the present invention; and 
         FIG. 37  is a schematic side elevational view showing a mechanism for adjusting a height of a fifth embodiment of the vibration device of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a perspective view showing an outer appearance of a grand piano  1  according to a first embodiment of the present invention. Like the conventionally-known grand pianos, the grand piano  1  includes a keyboard having a plurality of keys  2  arranged on a front surface thereof for manual performance operations by a user or human player, and performance controlling pedals  3 . The grand piano  1  also includes a control device  10  having an operation panel  13  on a front surface thereof and a touch panel  60  provided on a music stand. User&#39;s instructions can be input to the control device  10  by the user operating the operation panel  13  and the touch panel  60 . 
     The grand piano  1  is constructed to be capable of generating sounds or tones in any one of a plurality of tone generation modes selected in accordance with an instruction by the user. Examples of such a plurality of tone generation modes include: (1) a normal tone generation mode in which is performed only tone generation based on vibration of a string set (one or more string) by a corresponding hammer as in a conventional or ordinary grand piano; (2) a weak tone mode in which is performed only tone generation based on active sound board vibration sound (that is typically a tone smaller in volume than a normal performance tone, but may be a tone larger in volume than a normal performance tone) generated from a sound board of a vibration device by, while preventing string-striking action or movement of the hammer by means of a stopper, positively physically vibrating the sound board with a drive signal based on an audio waveform signal generated by a tone generator section, such as an electronic tone generator: and (3) a vibration device strong tone mode in which is performed tone generation based on string vibration sound responsive to string striking by a corresponding hammer as in the normal tone generation mode simultaneously with tone generation based on active sound board vibration sound generated by the sound board being positively physically vibrated by a drive signal as in the weak tone mode. In the strong tone mode, not only volume is raised but also a first acoustic tone having a piano&#39;s inherent timber or tone color obtained by a hammer striking a string set and a second acoustic tone having an additional tone color obtained by compulsorily vibrating the sound board with a drive signal having a desired tone color waveform other than piano tone colors (including tone colors similar to the piano tone color) are generated simultaneously, so that a tone color layer effect can be achieved. Thus, the strong tone generation mode can function also as a performance mode achieving a tone color layer effect. 
     Note that the above-mentioned plurality of tone generation modes may include other tone generation modes, such as a silence mode. In the silence mode, the same construction as in the weak tone generation mode is employed, but an electronic tone waveform signal (audio waveform signal) generated by the tone generator section is supplied to a headphone terminal, instead of being used as a drive signal for vibrating the sound board, so that the human player is allowed to personally listen to a tone based on the electronic tone waveform signal (i.e. the tone is not audibly generated to an external space). 
     Table 1 below lists the aforementioned various tone generation modes. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 function for preventing string striking by a hammer 
               
            
           
           
               
               
               
            
               
                   
                 invalid (string striking effected) 
                 valid (string striking not effected) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 vibration by a 
                 capable of playing with 
                 silent piano whose tone is listened 
               
               
                 vibration 
                 performance specific to a 
                 to with a headphone without the 
               
               
                 section not 
                 piano without an acoustic 
                 tone being output outside 
               
               
                 effected 
                 piano sound board 
                 (silence mode) 
               
               
                   
                 characteristic being 
               
               
                   
                 influenced (normal tone 
               
               
                   
                 generation mode) 
               
               
                 vibration by the 
                 capable of achieving an effect 
                 obtain natural resonance effect with 
               
               
                 vibration section 
                 like Honky-tonk piano by not 
                 resonance of weak tone (strong 
               
               
                 effected 
                 only raising volume but also 
                 tone) piano string kept valid 
               
               
                 (piano tone color) 
                 consciously shifting tuning 
                 (weak tone mode) 
               
               
                   
                 (strong tone mode) 
               
               
                 vibration by the 
                 obtain an effect where a tone of 
                 mode for enjoying a performance 
               
               
                 vibration section 
                 an acoustic piano itself and a 
                 with a non-piano color while 
               
               
                 effected 
                 color, such as that of a string 
                 obtaining natural sound field 
               
               
                 (non-piano tone 
                 instrument, compatible with the 
                 feeling and string resonance effect 
               
               
                 color) 
                 piano tone mix together 
                 (weak tone mode) 
               
               
                   
                 (strong tone mode) 
               
               
                   
               
            
           
         
       
     
     Further, the grand piano  1  can operate in a user-instructed performance mode of a plurality of performance modes. Examples of such a performance modes include a normal performance mode in which a tone is generated in response to a user&#39;s performance operation, and an automatic performance mode in which a tone is generated by automatic driving of a key. In order to carry out the present invention, it just suffices that the grand piano  1  be constructed to realize at least one of the performance modes. 
     [Construction of the Grand Piano  1 ] 
       FIG. 2  is a view explanatory of an internal construction of the grand piano  1 , where, for structural components provided in corresponding relation to the individual keys  2 , only the structural components for one of the keys  2  are illustrated with illustration of the structural components for the other keys  2  omitted. 
     Underneath a rear end portion (i.e., an end portion remote from a user performing the grand piano  1 ) of each of the keys  2  is provided a key drive section  30  that drives the key  2  by use of a solenoid when the performance mode is the automatic performance mode. The key drive section  30  drives the solenoid in accordance with a control signal given from the control device  10 . Namely, the drive section  30  reproduces the same state as when the user has depressed the key by driving the solenoid to cause the plunger to ascend and reproduces the same state as when the user has released the key by causing the plunger to descend. Namely, the difference between the normal performance mode and the automatic performance mode is whether the key  2  is driven by a user&#39;s operation or by the key drive section  30 . 
     Hammers  4  are provided in corresponding relation to the keys  2 , so that, when any one of the keys  2  has been depressed, the corresponding hammer  2  moves in response to force being transmitted to the hammer  2  via an action mechanism (not shown) and thereby strikes a string set (tone generating member)  5  corresponding to the depressed key  2 . A damper  8  is brought out of or into contact with the string set  5  in accordance with a depressed amount of the key  2  and a depressed amount of a damper pedal of the pedals  3  (hereinafter, “pedal  3 ” refers to the damper pedal unless specified otherwise). When in contact with the string set  5 , the damper  8  suppresses vibration of the string set  5 . 
     A key sensor  22  is provided underneath the corresponding key  2  for outputting to the control device  10  a detection signal corresponding to behavior of the key  2 . In the illustrated example, the key sensor  22  detects a depressed amount of the key  2  and outputs to the control device  10  a detection signal indicative of a result of the detection. Note that, whereas the key sensor  22  has been described above as outputting a detection signal corresponding to a depressed amount of the key  2 , it may output a detection signal indicating that the key  2  has passed through a particular depressed position. The “particular depressed position” is any one, or preferably more, of positions from a rest position to an end position of the key  2 . Namely, the detection signal output from the key sensor  22  may be any form of signal as long as the control device  10  is allowed to identify behavior of the key  2  on the basis of the detection signal. 
     Hammer sensors  24  are provided in corresponding relation to the hammers  4 , and each of the hammer sensors  24  outputs to the control device  10  a detection signal corresponding to behavior of the corresponding hammer  4 . In the illustrated example, each of the hammer sensors  24  detects a moving velocity of the hammer  4  immediately before the hammer  4  strikes the string set  5  and outputs to the control device  10  a detection signal indicative of a result of the detection. Note that the detection signal need not necessarily be indicative of a moving velocity itself of the hammer  4  and may be another form of detection signal as long as the control device  10  can calculate a moving velocity of the hammer  4  on the basis of the detection signal. For example, a detection signal indicating that the hammer shank has passed two predetermined positions during movement of the hammer  4  may be output, or a detection signal indicative of a time length from a time point when the hammer shank has passed through one of the two positions to a time point when the hammer shank has passed through the other of the two positions. Namely, the detection signal output from the hammer sensor  24  may be any form of detection signal as long as the control device  10  is allowed to identify behavior of the hammer  4  on the basis of the detection signal. 
     Pedal sensors  23  are provided in corresponding relation to the pedals  3 , and each of the pedal sensors  23  outputs to the control device  10  a detection signal indicative of behavior of the corresponding pedal  3 . In the illustrated example, the pedal sensor  23  detects a depressed amount of the corresponding pedal  3  and outputs to the control device  10  a detection signal indicative of a result of the detection. Whereas the pedal sensor  23  has been described as outputting a detection signal corresponding to a depressed amount of the pedal  3 , the pedal sensor  23  may output a detection signal indicating that the pedal  3  has passed through a particular depressed position of the pedal  3 . The “particular depressed position” is any of positions within a range from a rest position to an end position of the pedal and preferably a depressed position that permits distinction between a state where the dampers  8  and the string sets  5  are in complete contact with each other and a state where the dampers  8  and the string sets  5  are out of contact with each other. It is even further desirable that a plurality of such particular depressed positions be employed so that a half pedal state too can be detected. Namely, the detection signal output from the pedal sensor  23  may be any form of detection signal as long as the control device  10  is allowed to identify behavior of the pedal  3  on the basis of the detection signal. 
     The key sensor  22 , the pedal sensor  23  and the hammer sensor  24  may output results of detection of the corresponding key  2 , pedal  3  and hammer  4  as other forms of detection signals as long as the control device  10  is allowed to identify, for each of the keys  2  (key numbers), a time of striking by the hammer  4  of the corresponding string set  5  (key-on time), a velocity of the striking by the hammer  4  of the corresponding string set  5  and a time of suppression by the damper  8  of vibration of the corresponding string set  5  on the basis of the detection signals output from the key sensor  22 , the pedal sensor  23  and the hammer sensor  24 . 
     The sound board  7  is a plate-shaped member formed of wood. The sound board  7  has bridges  6  on its front face, and a plurality of sound board ribs (second rod-shaped members)  75  on its reverse face. In a normal piano performance, vibration of the string set  5  struck by the hammer  4  is transmitted via the bridge  6  to the sound board  7 . 
     Further, a vibration device (actuator)  50  is mounted on the sound board  7 . The vibration device  50  includes a vibration member  51  connected to the sound board  7 , and a magnetic circuit member (magnetic path formation section)  52  supported by a support section  55 . The support section  55  is formed of non-magnetic metal, such as aluminum material, suited for supporting the magnetic circuit member  52 . Further, the support section  55  is fixed to a vertical strut  9  with a strength great enough to support a load of the magnetic circuit member  52 . The vertical strut  9  is a plate-shaped member which is a part of a casing supporting a weight of the grand piano  1 . A drive signal can be supplied or input from the control device  10  to the vibration device  50 . The vibration member  51  of the vibration device  50  vibrates, in accordance with a waveform indicated by the input drive signal, to thereby vibrate the sound board  7 , so that the bridge  6  too is vibrated. Namely, the vibration device  50  is an actuator for vibrating the sound board  7  and the bridge  6 . 
       FIG. 3  is a view explanatory of a configuration of the vibration device  50 . In the illustrated example, two vibration devices  50 H and  50 L are provided as the vibration device  50 . In the following description, the vibration devices  50 H and  50 L will be collectively referred to simply as “vibration device  50 ” when the vibration devices  50 H and  50 L need not be particularly described distinctively from each other. In the illustrated example, the vibration devices  50 H and  50 L are connected to the reverse face of the sound board  7  between two adjoining ones of the sound board ribs  75 . The vibration device  50 H is disposed at a position corresponding to the long bridge  6 H of the two bridges (long and short bridges  6 H and  6 L), and the other vibration device  50 L is disposed at a position corresponding to the short bridge  6 L. Namely, the sound board  7  is sandwiched between the vibration devices  50 H.  50 L and the bridges  6 H.  6 L. 
     Note that the mounting position of the vibration device  50  is not limited to underneath the bridge. Namely, the sound board  7  may be mounted at any desired position, without necessarily being sandwiched between the vibration devices and the bridges, as long as the vibration device  50  is positioned in such a manner as to be capable of driving the sound board  7  by a necessary amount singly or in combination of a plurality of the vibration devices. Further, the number of the vibration devices  50  mounted on the sound board  7  is not necessarily limited to two and may be more or less than two. If only one vibration device  50  is mounted, it is desirable that the one vibration device  50  be disposed at a position corresponding to the long bridge  6 H. The long bridge  6 H is a bridge supporting the string sets  5  belonging to a high pitch range, while the short bridge  6 L is a bridge supporting the string sets  5  belonging to a low pitch range. In the following description, the long and short bridges  6 H and  6 L will be collectively referred to simply as “bridge  6 ” when the bridges  6 H and  6 L need not be particularly described distinctively from each other. 
     [First Embodiment of the Vibration Device] 
       FIG. 4  is a view showing an outer appearance of a first embodiment of the vibration device  50  of the present invention. The vibration device  50  includes the vibration member  51 , the magnetic circuit member  52  and a damper  53 . The vibration member  51  includes: a voice coil  513  attached to a bobbin  511 ; a cap  512  connected to a distal end portion of the bobbin  511 ; a shaft  514 ; and a spacer  516 . The cap  512  is a disk-shaped member. The shaft  514  is a rod-shaped member and has one longitudinal end portion fixed to the center of the circular surface of the cap  512 , and the spacer  516  is mounted on another longitudinal end portion of the shaft  514 . The spacer  516  is a member of a circular columnar shape and has a flat end surface opposite from its end portion mounted on the shaft  514 . The flat end surface, which has a circular shape having a diameter φ, is a surface to be connected to the sound board  7 . In the following description, a direction along a normal line to the flat end surface of the spacer  516  will be referred to as “normal line direction A 1 ”, and let it be assumed here that a positive direction of the normal line direction A 1  is a direction in which the flat end surface is oriented. Further, in each of figures to be described hereinbelow, a positive direction side, in the normal line direction A 1 , of the vibration device  50  is assumed to be an upper side, while a negative direction side, in the normal line direction A 1 , of the vibration device  50  is assumed to be a lower side. Further, surfaces oriented in the upper side direction will be referred to as upper surfaces, while surfaces oriented in the lower side direction will be referred to as lower surfaces. The aforementioned flat end surface of the spacer  516  will be referred to as “upper surface  516 A”. 
     The magnetic circuit member  52  includes a top plate  521 , a magnet  522  and a yoke  523 , and these elements  521 ,  522  and  523  are vertically superposed on one another from above in the order they were mentioned here. Namely, in the magnetic circuit member  52 , the top plate  521  is located uppermost, and the yoke  523  is located lowermost. The damper  53  is a member formed of fibers or the like in a disk shape, and it has an accordion-like wavy shape (such an accordion-like wavy shape is shown in a simplified manner in  FIG. 4 ). The damper  53  has an outer peripheral end portion mounted to the upper surface  521 A of the top plate  521  and an inner peripheral end portion mounted to the vibration member  51 , so that the damper  53  supports the vibration member  51  in such a manner that the vibration member  51  can vibrate in the normal line direction A 1 . The vibration device  50  vibrates the sound board  7  by vibrating the vibration member  51  in the normal line direction A 1 . 
       FIG. 5  is a vertical sectional view of the vibration device  50  shown in  FIG. 4 . The vibration member  51  includes the bobbin  511 , the cap  512 , the voice coil  513 , the shaft  514 , a nut  515  and the spacer  516 . The bobbin  511  is a cylindrical member of an outer diameter L 1  formed of non-magnetic metal, such as aluminum material. Opposite end portions, in an axial direction A 2 , of the bobbin  511  are open. The axial direction A 2  is a direction along an axis line B 2  of the cylindrical shape of the bobbin  511 , and a positive direction of the axial direction A 2  is a lower-to-upper direction. The voice coil  513  is provided on and around the outer peripheral surface  511 D and transforms an electric current into vibration, and the voice coil  513  is formed of a conductive wire wound around the outer peripheral surface  511 D. 
     The cap  512 , which is a member formed of non-magnetic metal having a high thermal conductivity, such as aluminum material, is connected to an upper end open portion, in the axial direction A 2 , of the bobbin  511  to thereby close the upper open end portion of the bobbin  511 . As shown in  FIG. 4 , the cap  512 , which has a disk shape as a whole, includes an upper, large disk-shaped portion (upper side portion) and a lower, small disk-shaped portion (lower side portion). An outer diameter of the lower side portion equals an inner diameter of the bobbin  511 , so that the lower side portion is fitted in the bobbin  511 . Further, the upper side portion of the cap  512  is engaged by an end portion of the bobbin  511  so that the cap  512  does not enter deep into the bobbin  511 . The underside  512 B of an outer peripheral region of the upper side portion of the cap  512  contacts the end portion of the bobbin  511 . The underside  512 B protrudes laterally outward beyond the outer periphery of the bobbin  511 . Further, the cap  512  has a hole portion  512 G ending centrally through the upper side portion and the lower side portion. A female thread (internal thread) is formed in the hole portion  512 G. 
     The shaft  514  is a member formed of metal, such as aluminum material, in a rod shape and extending in the axial direction A 2 . A male thread (external thread) is formed on a more-than-half portion, in a longitudinal direction, of the shaft  514  in such a manner that it is meshingly engageable with the female (internal) thread of the hole portion  512 G. The male (external) thread continuously extends to one end portion, in the longitudinal direction, of the shaft  514 . Another end portion of the shaft  514  has a hexagonal columnar shape like a so-called bolt head shape (see  FIG. 4 ), and the hexagonal columnar portion is turnable or rotatable with a spanner wrench or the like. By the hexagonal columnar portion being rotated like this, the shaft  514  moves relative to the cap  512  in the axial direction A 2  within a predetermined range. The “predetermined range” is, for example, from a position of the shaft  514  moved upward until the lower end of the shaft  514  aligns with the lower end of the hole portion  512 G (such a position will be referred to as “upper limit position”) to a position of the shaft  514  moved downward until the hexagonal columnar portion cannot rotate any more (such a position will be referred to as “lower limit position”). This predetermined range will hereinafter be referred to as “shaft moving range”. 
     The nut  515  has a female thread formed therein and meshingly engageable with the male thread of the shaft  514 . The nut  515  is fitted over a portion of the shaft  514  closer to the hexagonal columnar portion than the cap  512 . As the nut  515  is pressed against the cap  512  by being rotated with a spanner wrench or the like, the shaft  514  is fixed with respect to the cap  512 . The spacer  516  is a member fixed to an upper end portion, in the axial direction A 2 , of the shaft  514  and sandwiched between the shaft  514  and the sound board  7 . The spacer  516  is formed of synthetic resin or the like and has a lower thermal conductivity than the shaft  514  and cap  512  formed of aluminum material. The above-mentioned upper surface  516 A is the upper surface of the spacer  516  opposite from the upper side of the spacer  516 , i.e. the side of the spacer  516  fixed to the shaft  514 . 
     With the various portions of the vibration member  51  joined to one another in the aforementioned manner, the normal line direction A 1  of the upper surface  516 A matches the axial direction A 2  of the bobbin  511 . The upper surface  516 A of the spacer  516  constitutes an upper end of the vibration member  51  to be connected to the sound board  7  (such an upper end will hereinafter be referred to as “connection end”); namely, the spacer  516  is an end member forming such a connection end. A distance between the connection end and the bobbin  511  constitutes a predetermined range, i.e. a range within which the distance between the connection end and the bobbin  511  varies as the connection end moves in response to the shaft  514  moving within the above-mentioned shaft moving range. Such a range will hereinafter be referred to as “end moving range”. Further, a combination of the cap  512 , the shaft  514 , the nut  515  and the spacer  516  coupled to one another in the aforementioned manner functions as a connection member for connecting the bobbin  511  to the sound board  7  with an overall length (i.e., length from the upper end of the bobbin  511  to the connection end  516 A) adjusted as appropriate. In short, the connection member comprises the rod-shaped member (shaft  514 ), and a screw structure (a combination of the male thread of the shaft  514  and the female thread of the cap  512 ) for converting rotational displacement of the rod-shaped member (shaft  514 ) into linear displacement of the rod-shaped member (shaft  514 ). 
     Note that the term “length” is used herein to refer to a length, for example, in the axial direction A 2 . The connection member is fixed at the connection end to the sound board  7  with its overall length adjusted as appropriate while positioning the voice coil  513 , provided on the bobbin  511 , at a predetermined position within a magnetic path space  525  shown in  FIG. 5 . Positioning the voice coil  513  at the predetermined position within the magnetic path space  525  means, in other words, placing the voice coil  513  and the top plate  521  in predetermined positional relationship, e.g. in mutually-opposed relationship. 
     The top plate  521  is formed, for example, of soft magnetic material, such as soft iron, in a disk shape having a central hole (i.e., in a ring shape). Further, the yoke  523  is formed, for example, of soft magnetic material, such as soft iron, in such a shape that a disk portion  523 E of a disk shape and a circular columnar portion  523 F, having a smaller outer diameter than the disk portion  523 E, are formed concentrically with each other. The outer diameter of the circular columnar portion  523 F is smaller than the inner diameter of the top plate  521 . The magnet  522  is a ring-shaped permanent magnet, and it has a smaller inner diameter than the top plate  521 . 
     The top plate  521 , the magnet  522  and the yoke  523  are superposed on one another in substantial axis alignment (i.e., with their respective axis lines substantially coinciding with one another) in the order they were mentioned such that the top plate  521  is located uppermost. A height of the circular columnar portion  523 F from the disk portion  523 E, i.e. a dimension, in an axial direction A 3 , of the circular columnar portion  523 F, is substantially equal to a sum of respective dimensions, in the axial direction A 3 , of the top plate  521  and the magnet  522 . The axial direction A 3  is a direction along the axis line B 3  of the circular column of the circular columnar portion  523 F, and let it be assumed here that a down-to-up direction of the axial direction A 3  is a positive direction of the axial direction A 3 . The top plate  521 , the magnet  522  and the yoke  523  arranged in the aforementioned manner form a magnetic path indicated by broken-line arrows in  FIG. 5 . The vibration member  51  is supported by the damper  53  in such a manner that the voice coil  513  is positioned in a magnetic path space  525  which is sandwiched between the top plate  521  and the circular columnar portion  523 F and in which the magnetic path is formed. The top plate  521 , the magnet  522  and the yoke  523  cooperate with one another to function as a magnetic path formation means for forming the magnetic path space  525 . A drive signal input to the vibration device  50  is input to the voice coil  513 . In response to receipt of the magnetic force in the magnetic path space  525 , drive force is generated such that the bobbin  511  moves and vibrates in the axial direction A 2  in accordance with a waveform indicated by the input drive signal. Namely, the vibration member  51  is a vibration means that vibrates in the axial direction A 2  in accordance with the drive signal input to the voice coil  513 . Further, the vibration device  50  is a voice coil type actuator that imparts vibration to the sound board by the drive force generated in the voice coil  513 . 
     The voice  513  has a dimension in the axial direction A 2  (hereinafter referred to as “coil length dimension”) greater than a dimension in the axial direction A 2  of the magnetic path space  525  (hereinafter referred to as “magnetic path width dimension”). Further, the less variation in the number of coil winding turns present in the magnetic path space  525  when the vibration member  513  is vibrating (during vibration of the vibration member  513 ), the more stable drive force can the voice coil  513  generate. Conversely, as variation in the number of coil winding turns present in the magnetic path space  525  during vibration of the vibration member  513  increases, the drive force generated by the voice coil  513  varies more, so that desired vibration (amplitude in particular) cannot be obtained. For example, once there occurs a state where an end portion, in the axial direction A 2 , of the voice coil  513  (hereinafter referred to as “coil end portion”) has entered the magnetic path space  525  during the vibration of the vibration member  513 , in other words, once there occurs a state where the magnetic path space  525  has protruded out beyond the voice coil  513 , the number of turns varies so greatly that desired vibration cannot be obtained and thus a desired tone cannot be generated. The more the middle, in the axial direction A 2  (length direction), of the voice coil  513  (hereinafter referred to as “coil length middle”) is deviated from the middle, in the axial direction A 2  (length direction), of the magnetic path space  525  (hereinafter referred to as “magnetic path width middle”) when the vibration member  51  is not vibrating, the more one coil end portion of the voice coil  513  approaches the magnetic path space  525 , so that it becomes more likely for the aforementioned states to occur during vibration of the vibration member  51 . Conversely, if the above-mentioned coil length middle and the magnetic path width middle coincide with each other, it becomes least likely for the aforementioned states to occur, so that a desired tone can be obtained in the most stable manner. In the illustrated example of  FIG. 5 , the vibration member  51  and the magnetic circuit member  52  are positioned in such a manner that the above-mentioned coil length middle and the magnetic path width middle coincide align with each other, and a height from the top plate  521  (i.e., the upper surface  521 A) to the upper end of the bobbin  511  is depicted as L 2 . 
     By increasing the coil length dimension, the aforementioned phenomena can also be made less likely to occur. Further, if the coil length dimension is increased, it becomes less likely for the coil end portion to enter the magnetic path space  525  even where the coil length middle and the magnetic path width middle are deviated from each other. However, if the number of coil winding turns per unit length is not changed, inductance of the voice coil  513  increases as the coil length dimension is increased, so that frequencies at which good responsiveness can be obtained would be limited to low frequencies. Therefore, it is desirable that the coil length dimension be equal to a sum of the magnetic path width middle and a maximum amplitude of vibration of the vibration member  51  or such a sum plus a length of play; in the illustrated example, the coil length dimension of the voice coil  513  is set to equal the latter sum (i.e., sum of the magnetic path width middle, the maximum amplitude of vibration of the vibration member and the length of play. Therefore, it is necessary that the vibration member  51  and the magnetic circuit member  52  be mounted accurately so that their relative positions in the axial direction A 2  have predetermined relationship. Here, the predetermined relationship means that the vibration member  51  and the magnetic circuit member  52  are positioned relative to each other such that the coil length middle and the magnetic path width middle coincide with each other. 
     Note that, although the coil length dimension is greater than the magnetic path width dimension in the instant embodiment, the coil length dimension may be smaller than the magnetic path width dimension. Even in that case, it becomes least likely for the coil end portion to protrude out beyond the magnetic path space  525  during vibration of the vibration member  51  and least likely for the aforementioned phenomena to occur. 
     Further, in  FIG. 5 , the bobbin  511  is supported by the damper  53  in such a manner that the axis line B 2  of the bobbin  511  aligns with (substantially coincides with) the axis line B 3  of the circular columnar portion  523 F. Such a state is referred to as a state where the axes of the bobbin  511  and the circular columnar portion  523 F align with each other, in other words, a state where the bobbin  511  and the circular columnar portion  523 F are in axis alignment with each other. When the bobbin  511  and the circular columnar portion  523 F are in axis alignment with each other like this, the bobbin  511  is less likely to contact the circular columnar portion  523 F as compared to when the bobbin  511  and the circular columnar portion  523 F are not in axis alignment with each other, i.e. when a portion of the inner peripheral surface  511 C of the bobbin  511  is located closer to the circular columnar portion  523 F than the remaining portion of the inner peripheral surface  511 C. 
     Because the top plate  521 , magnet  522  and yoke  523  of the magnetic circuit member  52  are formed of soft magnetic material or magnet as noted above and greater in volume than the vibration member  51 , they are much heavier than the vibration member  51  formed of resin or aluminum material. Further, because the load of the magnetic circuit member  52  acts on the vertical strut  9  via the support section  55 , most of the load of the vibration device  50  is prevented from acting on the sound board  7 . Although the load of the vibration member  51  acts on the sound board  7 , such a load acting on the sound board  7  is nominal, an influence of the load on a vibration characteristic of the sound board  7  can be minimized. 
     Next, with reference to  FIGS. 6 to 11 , a description will be given about a sequence of operations performed when a human operator attaches the vibration device  50  to the grand piano  1 . 
       FIG. 6  is a flow chart showing the sequence of operations for attaching the vibration device  50  to the grand piano  1 . First, the grand piano  1  to which the vibration device (actuator)  50  has not been attached yet is provided. Then, the support section  55  is mounted on a predetermined portion, such as the vertical strut  9 , of the grand piano  1 . In this case, a position of the support section  55  is determined properly in association with a predetermined actuator-attaching position of the sound board  7  to which the vibration device (actuator)  50  is to be attached. The sequence of operations shown in  FIG. 6  is started up with the support section  55  connected to the vertical strut  9 . Then, the human operator mounts a predetermined fixing jig to the magnetic circuit member  52  (step S 11 ). Here, the fixing jig is a reference position instructing member (jig) for automatically indicating that the relative positions, in the axial direction A 2 , of the vibration member  51  and the magnetic circuit member  52  are in the above-mentioned desired relationship (i.e., ideal position or reference mounted position of the voice coil within the magnetic path space). 
       FIG. 7  is a view showing an outer appearance of the fixing jig  54  that is formed of magnetic material, such as iron, in a plate shape. (a) of  FIG. 7  is a plan view showing the fixing jig  54  as viewed from a side of the upper surface  54 A that is the largest of all of the surfaces of the fixing jig  54 . In the fixing jig  54 , a side the upper surface  54 A faces is assumed to be an upper side. Further, in (a) of  FIG. 7 , the fixing jig  54  has a shape of a letter U, which has two straight portions  541  and  542  and a curve portion  543  connecting between respective one ends of the two straight portions  541  and  542 . Respective distal end portions of the straight portions  541  and  542  are spaced from each other by a distance L 1  to define an inner space therebetween. 
     (b) of  FIG. 7  is a front view of the fixing jig  54 . In the fixing jig  54 , a side where the respective distal end portions of the straight portions  541  and  542  are visible, i.e. where the inner space of a U shape is visible, will be referred to as “front side”, a side opposite from that front side will be referred to as “back side”, and a side where a side surface of any one of the straight portions  541  and  542  is visible will be referred to as “side surface”. Further, for convenience of the following description, a side where the inner space interposed between the straight portions  541  and  542  is located will be referred to as “inner side”, and a side opposite from the inner space across any one of the straight portions  541  and  542  from the inner space will be referred to as “outer side”. Further, the side the upper surface  54 A faces will be referred to as “upper side” as noted above, and a side opposite from the upper side will be referred to as “lower side”. Further, a direction from the upper side to the lower side will be referred to as “up-down direction”. Further, the fixing jig  54  has its lower surface  54 B that is located in a portion opposite from the upper surface  54 A and closest to the outer side. In the illustrated example of (a) of  FIG. 7 , the lower surface  54 B is located opposite from an outermost region of the upper surface  54 A outside a broken line (hidden line). A distance between the upper surface  54 A and the lower surface  54 B, i.e. a thickness, in the up-down direction, of the outermost region of the fixing jig  54 , is depicted as L 2 . This thickness L 2  is equal to the height from the upper surface  521 A of the top plate  521  to the upper end of the bobbin  511  when the above-mentioned coil length middle and magnetic path width middle are coincident with each other. Further, the fixing jig  54  has a thickness L 3  (in the up-down direction), smaller than the thickness L 2 , in its region inside the lower surface  54 B (L 3 &lt;L 2 ), so that a space is defined between the lower surface  54 B and the lower surface of the small-thickness region. The straight portions  541  and  542  have inner side surfaces  541 C and  542 C, respectively, extending in the up-down direction. The inner side surfaces  541 C and  542 C are opposed to each other and each define a corner with the upper surface  54 A. 
       FIG. 8  is a view showing a state where a position and orientation of the vibration member  51  relative to the magnetic circuit member  52  are restricted by means of the fixing jig  54 . In  FIG. 8 , the shaft  514  has been lowered, with the nut  515  fittingly engaging with the root of the male thread portion of the shaft  514 , to a position immediately before the lower surface of the nut  515  contacts the upper surface of the cap  512 . Note, however, that the shaft  514  may be lowered until the lower surface of the nut  515  contacts the upper surface of the cap  512 . The fixing jig  54  is installed with the lower surface  54 B placed in contact with the upper surface  521 A of the top plate  521 . Because the fixing jig  54  is formed of magnetic material as noted above, it is fixed to the upper surface  521 A by magnetic attractive force of the top plate  521  magnetized by the magnetic force of the magnet  522 . Then, the fixing jig  54  is mounted in place so as to sandwich the bobbin  511  between the straight portions  541  and  542  (i.e., to accommodate the bobbin  511  in the U-shaped inner space of the jig  54 ). Because the outer diameter of the bobbin  511  and the distance between the straight portions  541  and  542  are both L 1  as noted above, the outer peripheral surface  511 D of the bobbin  511  are placed in contact with the side surfaces  541 C and  542 C. Thus, the bobbin  511  does not move in any other direction than the direction along the side surfaces  541 C and  542 C, unless force capable of moving in that other direction the fixing jig  54  fixed to the upper surface  521 A by the magnetic attractive force as noted above is applied to the fixing jig  54 . At that time, it is desirable that the fixing jig  54  be mounted such that the axis line B 2  of the bobbin  511  and the axis line B 3  of the circular columnar portion  523 F align (substantially coincide) with each other as in the state shown in  FIG. 5 . 
     Further, although the bobbin  511  is supported by the damper  53  in such a manner that it can vibrate in the normal line direction A 1 , it is prevented from moving more downward than the position where the lower surface  512 B of the cap  512  contacts the upper surface  54 A of the fixing jig  54 . When these surfaces are in contact with each other, the distance between the upper end of the bobbin  511  and the upper surface  521 A of the top plate  521  equals the distance between the upper and lower surfaces  54 A and  54 B of the fixing jig  54 , i.e. the thickness L 2  of the fixing jig  54 , and thus, the above-mentioned coil length middle and the magnetic path width middle substantially coincide with each other as noted above. Namely, because a range over which the vibration member  51  can move downward is limited by the fixing jig  54 , the relative positions, in the axial direction A 2 , of the vibration member  51  and the magnetic circuit member  52  can be maintained in the above-mentioned desired relationship. 
     Referring back to  FIG. 6 , the human operator causes the magnetic circuit member  52  to be supported by the support section  55  (i.e., installs the magnetic circuit member  52  on the support section  55 ) (step S 12 ). At that time, the human operator causes the magnetic circuit member  52  to be supported by the support section  55  after securing a height position of the magnetic circuit member  52  such that a distance from the magnetic circuit member  52  to the sound board  7  falls within the abovementioned end moving range. For example, in a case where the magnetic circuit member  52  is mounted above the support section  55  via a plurality of support rods, a height of the magnetic circuit member  52  to be supported via the plurality of support rods is set properly. In other words, the human operator causes the magnetic circuit member  52  to be supported by the support section  55  at a proper height such that, with the overall length of the connection member adjusted as described later, the connection member can be connected at the connection end to the sound board  7 . Also, the human operator causes the magnetic circuit member  52  to be supported by the support section  55  after determining a position of the support section  55  such that the vibration member  51  including the spacer  516  is opposed from below to a vibration area preset on the lower surface  7 B of the vibration member  51 . This vibration area is preset as an area for connecting the upper surface  516 A of the spacer  516  to the sound board  7  and includes, for example, the position of the bridge  6 H or bridge  6 L shown in  FIG. 3 . 
       FIG. 9  is a view showing the magnetic circuit member  52  supported by the support section  55  in the aforementioned manner. In  FIG. 9 , the positions of the sound board  7 , bridge  6  and support section  55  are indicated by two-dot-dash lines in order to show positional relationship among the vibration device  50 , the sound board  7 , the bridge  6  and the support section  55 . Further, in  FIG. 9 , the state where the magnetic circuit member  52  has been supported by the support section  55  is shown as viewed in such a direction where a width direction A 4  of the bridge  6  corresponds to a left-right direction of the figure. The bridge  6  is mounted on the upper surface  7 A of the sound board  7 . Further, the vibration area C 1  is preset on the lower surface  7 B of the sound board  7 . The vibration area C 1  is an area to which force is applied from the vibration device  50  and which is set such that a middle, in the width direction A 4 , of the bridge  6  aligns with the normal line A 1  passing centrally through the width of the bridge  6 . Further, the vibration area C 1  has a shape similar to that of the upper surface  516 A of the spacer  516 ; more specifically, the vibration area C 1  is a circular area whose dimension in the width direction A 4  (i.e., diameter) is φ1. 
     The top plate  521  has a plurality of through-holes formed in predetermined positions thereof close to the outer periphery of the lower surface  521 B. The support section  55  has a plurality of through-holes extending vertically therethrough in positions corresponding to the positions of the through-holes of the top plate  521 . Each of the plurality of support rods  551  has male threads formed on opposite end portions thereof. Such opposite end portions having the male threads are inserted through corresponding ones of the through-holes of the top plate  521  and the support section  55  and fastened to the top plate  521  and the support section  55  by means of a plurality of nuts  552 , so that the magnetic circuit member  52  is fixed to the support section  55  as shown in the figure. Note that a female thread may be formed in each of the through-holes. As noted above in relation to  FIG. 3 , the support section  55  is fixed to the vertical strut  9  with a strength great enough to support the load of the magnetic circuit member  52 . Thus, the load of the magnetic circuit member  52  acts on the vertical strut  9  via the support section  55 . Also, the magnetic circuit member  52  is supported by the support section  55  in such a manner that a distance L 4  between the magnetic circuit member  52  and the sound board  7  falls within the aforementioned end moving range, i.e. a range where the distance between the connection end (upper surface  516 A) and the bobbin  511  varies. Because the position in the normal line direction A 1  or axial direction A 2  (height position) of the magnetic circuit member  52  when supported by the support section  55  only has to be such that the distance L 4  falls within the end moving range, no particular severe accuracy is required of the position of the magnetic circuit member  52 . Thus, the human operator can perform step S 12  with an increased ease as compared to the case where severe accuracy is required, e.g. where the position (height position) of the magnetic circuit member  52  should be matched with a predetermined position (height position) in the axial direction A 2 . The operation of step S 12  is an example of a “support step” in the present invention. 
     Referring back to  FIG. 6 , the human operator then applies an adhesive agent to the upper surface  516 A of the space  516  (step S 13 ). The adhesive agent used here may be any desired adhesive, such as one capable of adhering wood and resin together, as long as it can adhere the sound board  7  and the spacer  516  together. Then, the human operator connects the upper surface  516 A of the spacer  516  to the sound board  7  by rotating the shaft  514  with a spanner wrench or the like to thereby move the shaft  514  upward. At that time, the upper surface  516 A can surely reach and connect to the sound board  7 , because the distance L 4  is set to fall within the end moving range as noted above. By such operations, the upper surface  516 A having the adhesive agent applied thereto can be adhesively connected to the sound board  7 . A series of the operations of steps S 13  and S 14  is an example of a “connection step” in the present invention. 
       FIG. 10  is a view showing the spacer  516  connected to the sound board  7 . In  FIG. 10 , the shaft  514  has been moved upward from the position shown in  FIG. 9 , so that the upper surface  516 A of the spacer  516  has been connected to the sound board  7 . In  FIG. 9 , the upper surface  516 A is located underneath and connects to the vibration area C 1 . At that time, the spacer  516  is pressed against the sound board  7 . Further, the range over which the vibration member  51  can move downward is limited by the fixing jig  54  as noted above, and thus, even if force acts on the vibration member  51  in the negative direction of the normal line direction A 1  due to reaction from the sound board  7 , the position of the vibration member  51  relative to the magnetic circuit member  52  can be maintained appropriately such that the coil length middle and the magnetic path width middle coincide with each other. 
     Further, as noted above, the position of the shaft  514  moved upward until the lower end of the shaft  514  aligns with the lower end of the hole portion  512 G is preset as the upper limit position. Thus, following the operation of step S 14 , the lower end of the shaft  514  aligns with the lower end, i.e. lower surface  512 B, of the cap  512 , or protrudes downward beyond the lower surface  512 E of the cap  512  in the illustrated example of  FIG. 10 . Because the shaft moving range is set in the aforementioned manner, an axial length of a region of the shaft  514  supported by the hole portion  512 G is large and thus the shaft  514  can be made less likely to incline in a direction, such as the width direction A 4  of  FIG. 9 , intersecting the axial direction A 2 , as compared to a case where the lower end of the shaft  514  is located above the lower surface  512 B of the cap  512 . 
     Referring back to  FIG. 6 , the human operator then rotates the nut  515 , for example, with a spanner wrench to move the nut  515  in the negative direction of the normal line direction A 1 . By moving downward the nut  515  until the nut  515  is pressed against the cap  512 , the human operator fixes the shaft  514  to the cap  512  (step S 15 ). By that operation, a length of the shaft  514  from the bobbin  511  to the upper surface  516 A is fixed with the upper surface  516 A connected to the sound board  7 . The operation of step S 15  is an example of a “fixation step” in the present invention. Finally, the human operator detaches or dismount the fixing jig  54  (step S 16 ) and finishes the sequence of operations for attaching the vibration device  50  to the grand piano  1 . With the vibration device  50  attached to the grand piano  1  in the aforementioned manner, the sound board  7  is pushed upward as the bobbin  511  moves in the positive direction of the normal line direction A 1 . But, as the bobbin  511  moves in the negative direction of the normal line direction A 1 , the sound board  7  is pulled downward by the bobbin  511  instead of the bobbin  511  being disconnected from the sound board  7 . Thus, vibration of the bobbin  511  is imparted to the bridge  6  by way of the sound board  7  and then to the string set  5 .  FIG. 11  shows the vibration device  50  having been attached to the grand piano  1 . 
       FIG. 11  is a view showing a state when the sequence of operations for attaching the vibration device  50  has been completed. In  FIG. 11 , the upper surface  516 A of the spacer  516  has been connected to the vibration area C 1  of the sound board  7 , and the magnetic circuit member  52  has been supported by the support section  55 . At that time, the relative positions, in the normal line direction A 1 , of the vibration member  51  and the magnetic circuit member  52  are in desired relationship such that the coil length middle and the magnetic path width middle coincide with each other. Thus, the vibration device  50  can be mounted with ease at a desired position in the normal line direction A 1 , i.e. in the direction where the vibration member  51  vibrates (vibrating direction of the vibration member  51 ). Further, if the fixing jig  54  was mounted with the axis line B 2  of the bobbin  511  and the axis line B 3  of the circular columnar portion  523 F aligned with (substantially coinciding with) each other, and if such aligned state is maintained till completion of the operation of step S 15 , axis alignment between the bobbin  511  and the circular columnar portion  523 F is achieved. Thus, in this case, contact between the bobbin  511  and the circular columnar portion  523 F is less likely to occur as compared to a case where such axis alignment is not achieved. 
     Because the magnetic circuit member  52  is supported by the vertical strut via the support section  55 , most of the drive force generated in the voice coil  513  is used as thrust force for vibrating the bobbin  511 . Further, the vibration member  51  is supported by the sound board  7  and the damper  53  by being connected to the sound board  7 . Further, the sound board  7  and the damper  53  are formed respectively of wood and fibers or the like, and thus, the damper  53  is much lower in modulus of rigidity than the sound board  7 . Therefore, most of the load of the vibration member  51  would act on the sound board  7 . The magnetic circuit member  52  is supported by the support section  55  and connected with the vibration member  51  only via the damper  53 . The damper  53  is much lower in modulus of rigidity than any one of the vibration member  51  (aluminum material or resin), the magnetic circuit member  52  (soft magnetic material or magnet) and the support section  55  (metal). Thus, even when the relative positions of the vibration member  51  and the magnetic circuit member  52  have changed, for example, only the damper  53  deforms, and force applied from the damper  53  to the vibration member  51  becomes extremely small. Therefore, almost no load except for that of the vibration member  51  is applied to the sound board  7 . Note that the support section  55  may support the magnetic circuit member  52  in any other desired manner than the aforementioned as long as no load other than that of the vibration member  51  acts on the sound board  7 . 
     Note that, after the acceleration device  50  has been attached as shown in  FIG. 11 , relative positions of the support section  55  and the sound board  7  may deviate from each other due to deformation of the grand piano  1 , positional deviation of any of the various members.  FIG. 12  is a view showing the sound board  7  displaced relative to the support section  55 . In the illustrated example of  FIG. 12 , the sound board  7  has been displaced, relative to the support section  55 , by a length L 5  in the width direction A 4  of the bridge  6 . In the vibration member  51 , only the bobbin  511  is supported at its outer peripheral surface by the damper  53 , apart from the portion (more specifically, the upper surface  516 A) at which the spacer  516  is connected to the sound board  7 . Thus, if the spacer  516  shifts in the width direction A 4  together with the sound board  7 , the vibration member  51  will turn about an axis passing through a center P 1  of the portion supported by the damper  53  and perpendicularly intersecting the width direction A 4 . At that time, the upper end portion of the shaft  514  slightly inclines, and the spacer  516 , formed of resin, deforms in response to such inclination of the shaft&#39;s upper end portion. Here, a distance between the upper surface  516 A moving by the length L 5  in the axial direction A 4  and the center P 1  is depicted as L 6 , and a distance between the center P 1  and the middle, in the axial direction A 2 , of the voice coil  513  is depicted as L 7 . The distance L 6  includes the length of the shaft  514 , and thus, the distance L 6  is larger than the distance L 7 . If displacement, in the width direction A 4 , of the middle, in the axial direction A 2 , of the voice coil  513  is given as L 8 , then L 8  can be expressed by an expression “L 8  =L 5 /L 6 ×L 7 ”. Because L 6 &gt;L 7  as noted above, L 8 &lt;L 5 . Namely, when the sound board  7  and the support section  55  have been displaced relative to each other in the width direction A 4 , an amount of displacement, in the width direction A 4 , of the voice coil  513  in the vibration device  50  can be made smaller than the amount of displacement. 
     Further, because the magnetic circuit member  52  in the vibration device  50  is supported spaced from the sound board  7  by an amount equal to the length, in the normal line direction A 1 , of the shaft  514  and the spacer  516 , the vibration device  50  can be mounted near the sound board rib  75 .  FIG. 13  is a view showing the vibration device  50  mounted at a position where the sound board rib  75  is located above the top plate  521 . Namely, the sound board rib  75  is provided on the surface of the sound board  7  to which the spacer  516  is connected, i.e. on the lower surface  7 B of the sound board  7 . A distance between the lower surface  7 B and the upper surface  521 A of the top plate  521 , i.e. a height, from the upper surface  521 A, of the upper surface  516 A of the spacer  516  connected to the sound board  7 , in this state is given as L 9 , and a height of the sound board rib  75  from the sound board  7  (lower surface  7 B) is given as L 10 . The distance L 9 , the height L 10  and the height L 2  from the upper surface  521 A to the end of the bobbin  511  are in a relationship of L 9 &gt;L 10 &gt;L 2 . Namely, the aforementioned connection member  51 , comprising the cap  512 , shaft  514 , nut  515  and spacer  516 , is constructed to fix the upper surface  516 A to the bobbin  511  in such a manner that the distance (L 9 ) of the surface  516 A from the magnetic circuit member  52  is greater than the distance (L 10 ) of the sound board rib  75  from the sound board  7 . In other words, the connection member can connect the upper surface  516 A to the bobbin  511  with its overall length adjusted in such a manner that the distance between the connection end and the bobbin  511  is greater than the distance from the sound board  7  to the sound board rib  75 . A modification of the vibration device may, for example, be constructed so as to directly connect and mount the bobbin  511  to the sound board  7 . In such a case, however, the height of the bobbin  511  from the upper surface  521 A, i.e. the distance between the upper surface  521 A and the lower surface  7 B becomes L 2 , and, thus, the vibration device  50  cannot be attached because the sound board rib  75  having the height L 10  contacts the top plate  521 . The above-described embodiment of the vibration device  50 , where the connection end can move in the aforementioned manner, can be attached to the sound board  7  and the support section  55  without the sound board rib  75  contacting the top plate  521 . 
     [Construction of the Control Device  10 ] 
       FIG. 14  is a block diagram showing a construction of the control device  10  which includes a control section  11 , a storage section  12 , the operation panel  13 , a communication section  14 , a signal generation section  15 , and an interface  16 . These components  11 ,  12 ,  13 ,  14 ,  15  and  16  are interconnected via a bus. 
     The control section  11  includes an arithmetic device, such as a CPU (Central Processing Unit), and storage devices, such as a ROM (Read-Only Memory) and a RAM (Random Access Memory). On the basis of control programs stored in any of the storage devices, the control section  11  controls various components of the control device  10  and various components connected to the interface  16 . In the illustrated example, the control section  11  causes the control device  10  and some of the components connected to the control device  10  to function as the musical instrument of the present invention, by executing any of the control programs. 
     The storage section  12  stores therein setting information indicative of various settings to be used during execution of the control programs. The setting information is information for determining content of a drive signal (audio waveform signal) to be generated by the signal generation section  15  on the basis of detection signals output, for example, from the key sensor  22 , pedal sensor  23  and hammer sensor  24 . Further, the setting information also includes information indicative of a tone generation mode and performance mode set by the user. 
     The operation panel  13  includes operating buttons operable by the user (capable of receiving user&#39;s operations), etc. Upon receipt of a user&#39;s operation via any one of the operating buttons, an operation signal corresponding to the user&#39;s operation is output to the control section  11 . The touch panel  60  connected to the interface  16  includes a display screen, such a liquid crystal display, and a touch sensor for receiving user&#39;s operations are provided on a surface portion of the display screen. On the display screen of the touch panel  60  are displayed, under control via the interface  16  of the control section  11 , a setting change screen for changing any of the settings of the setting information stored in the storage section  12 , setting screens for setting various modes etc., and various information, such as a musical score. Further, upon receipt of a user&#39;s operation via the touch sensor, an operation signal corresponding to the user&#39;s operation is output to the control section  11  via the interface  16 . Namely, user&#39;s instructions to the control device  10  are input through operations received via the operation panel  13  and the touch panel  60 . 
     The communication section  14  is an interface for executing communication with other equipment in wireless, wired and other desired manners. To the interface may be connected a disk drive that reads out various data recorded on a recording medium, such as a DVD (Digital Versatile Disk) or CD (Compact Disk), and outputs the thus-read-out data. Data input to the control device  10  via the communication section  14  are, for example, music piece data for use in an automatic performance. 
     The signal generation section  15  includes a tone generator section  151  for outputting an audio signal (audio waveform signal), an equalizer (EQ) section  152  for adjusting a frequency characteristic of the audio signal, and an amplification section  153  for amplifying the audio signal (see  FIG. 15 ). The signal generation section  15  outputs, as a drive signal, the audio signal amplified after having been adjusted in frequency characteristic. 
     The interface  16  is an interface for connecting the control device  10  with various external elements. In the illustrated example, examples of the external elements connected to the interface  16  include the key sensors  22 , pedal sensors  23 , hammer sensors  24 , key drive sections  30 , stoppers  40 , vibration device  50  and touch panel  60 . The interface  16  outputs to the control section  11  detection signals output from the key sensors  22 , pedal sensors  23  and hammer sensors  24  and detection signals output from the touch panel  60 . Further, the interface  16  outputs to the key drive sections  30  control signals output from the control section  11  and outputs to the vibration device  50  a drive signal output from the signal generation section  15 . 
     [Functional Arrangements of the Grand Piano  1 ] 
     The following describe functions implemented by the control section  11  executing the control program.  FIG. 15  is a block showing functional components of the grand piano  1 . Once any one of the keys  2  is operated, the hammer  4  strikes the corresponding string set  5 , so that the string set  5  vibrates. Such vibration of the string set  5  is transmitted via the bridge  6  to the sound board  7 . Further, the corresponding damper  8  operates in response to operations of the key  2  and the pedal  3 . Vibration suppression state of the string set  5  is changed by the action of the damper  8 . 
     A setting section  110  is implemented as a functional component having the following functions by means of the touch panel  60  and the control section  11 . First, the touch panel  60  receives a user&#39;s operation for setting a tone generation mode. The control section  11  changes the setting information in accordance with a performance mode and a tone generation mode set by the user and outputs to a performance information generation section  120  and a prevention control section  130  a control signal indicative of the selected tone generation mode in accordance with these modes. 
     Further, the touch panel  60  receives user&#39;s operations for setting various control parameters for use in the signal generation section  15 . The various control parameters are parameters for determining a color (timbre) of an audio signal (audio waveform signal) output from the tone generator section  51 , a frequency characteristic adjustment style in the equalizer section  52  and an amplification factor in the amplification section  153 . The user may either individually set such control parameters, or set such control parameters by selecting a preset data set from among a plurality of preset data sets, each predefining respective values of the control parameters, stored in the storage section  12 . The control section  11  changes the setting information in accordance with the various control parameters and controls a drive signal to be output from the signal generation section  15  in accordance with the control parameters. Predetermined parameters are set in the equalizer  152  and the amplification section  153 , which need not necessarily be constructed to be changeable by the control section  11 . 
     The performance information generation section  120  is constructed of the control section  11 , the key sensors  22 , the pedal sensor  23  and hammer sensors  24  as a functional component having the following functions. Behavior of the pedal  3  and each of the hammers  4  is detected by the corresponding key sensor  22 , pedal sensor  23  and hammer sensor  24 , and on the basis of detection signals consequently output from these sensors  22 ,  23  and  24 , the control section  11  identifies, as information (performance information) to be used in the tone generator section  151 , timing of striking by the hammer  4  of the string set  5  (key-on timing), No. of the key  2  corresponding to the hammer-struck string set  5  (key No.), striking velocity (velocity) and timing of vibration suppression by the damper  8  of the string set  5  (key-off timing). In the illustrated example, the control section  11  identifies the striking timing and key No. of the key  2  on the basis of the behavior of the key  2 , the striking velocity on the basis of the behavior of the hammer  4 , and the time of vibration suppression on the basis of the behavior of the key  2  and pedal  3 . Note that the striking timing may be identified on the basis of the behavior of the hammer  4  and the striking velocity may be identified on the basis of the behavior of the key  2 . Further, the performance information may be represented in control parameters of a MIDI (Musical Instrument Digital Interface) format. 
     At the identified key-on timing, the control section  11  outputs to the tone generator section  151  of the signal generation section  15  performance information indicative of the key No., velocity and key-on instruction. Further, at the identified key-off timing, the control section  11  outputs to the tone generator section  15  performance information indicative of the key No. and key-off instruction. When the user-set tone generation mode is the weak tone mode or strong tone mode, the control section  11  performs the aforementioned functions, while, when the user-set tone generation mode is the normal tone mode, the control section  11  in the illustrated example outputs no performance information to the tone generator section  151 . In the normal tone generation mode, it just suffices to prevent a drive signal from being generated/output from the signal generation section  15 ; thus, even where the embodiment is constructed to generate/output performance information, it just suffices for the control section  11  to perform control such that no drive signal is generated/output from the signal generation section  15 . The performance information generation section  120  and the signal generation section  15 , cooperating in the aforementioned manner, function as an output means for outputting to the vibration device (actuator)  50  a drive signal indicative of a sound or tone corresponding to operations of performance operators comprising the key  2  and pedal  3 . 
     The prevention control section  130  is implemented by the control section  11  as a component having the following function. When the user-set tone generation mode is the weak tone mode, the control section  11  moves the stopper  40  to a position for preventing the hammer  4  from striking the corresponding string set  5 , while, when the user-set tone generation mode is the normal tone generation mode or strong tone mode, the control section  11  moves the stopper  40  to a position for not preventing the hammer  4  from striking the string set  5 . 
     The tone generator section  151  outputs an audio signal (audio waveform signal) on the basis of performance information generated from the performance information generation section  120  (control section  11 ). For example, the tone generator section  151  outputs an audio signal (audio waveform signal) with a tone pitch corresponding to the key number and with a tone volume corresponding to the velocity. This audio signal (audio waveform signal) is adjusted in frequency characteristic by the equalization section  152 , amplified by the amplification section  153  and then supplied to the vibration device  50  as a drive signal, as noted above. As also noted above, the vibration device  50  vibrates in response to the supplied drive signal to thereby vibrate the sound board  7 . The vibration of the sound board  7  is transmitted to the bridge  6 , by way of which it is transmitted to the string set  5 . 
     By the audio waveform signal being generated with the tone pitch (frequency) corresponding to the key No. of the key operated for a performance as noted above, a vibration sound generated by the sound board  7  vibrating in accordance with the audio waveform signal (drive signal) will have a tone pitch corresponding to the tone pitch of the operated key. The vibration sound generated by the sound board  7  can also be subjected to velocity control (i.e., volume control corresponding to a key touch). However, the frequency etc. of the audio waveform signal may be modified variously without being limited to the aforementioned processing. For example, a signal obtained by mixing audio waveform signals of a plurality of tone pitches, such as those of a chord, may be used as a drive signal to vibrate the sound board  7 . 
     [Modifications of the First Embodiment] 
     The above-described embodiment is only one example of the first embodiment of the present invention, and the first embodiment may be modified variously as follows. Further, the above-described embodiment and the following modifications may be practiced in combination as necessary. 
     &lt;Modification 1&gt; 
     The fixing jig may have a different shape than the above-described fixing jig  54  and need not necessarily have the function of being capable of being automatically positioned in desired positional relationship. Namely, the fixing jig may have any desired shape as long as, with the fixing jig mounted to the top plate  521 , the height of the upper end of the bobbin  511  from the upper surface  521 A of the top plate  521  is L 2  (the voice coil  513  is positioned at a predetermined reference mounting position within the magnetic path space), i.e. the fixing jig functions as the reference position instructing member indicating whether the voice coil  513  is positioned in desired positional relationship with respect to the magnetic path space  525  in such a manner that such positional relationship is automatically or visually checked by the human operator. 
       FIG. 16  is a view showing the modified fixing jig  54   q  mounted to the magnetic circuit member  52 . This modified fixing jig  54   q  does not have an automatic positioning function like that of the fixing jig  54 ; instead, it performs a function of presenting a reference position indicative of whether the voice coil  513  is currently positioned in desired positional relationship with respect to the magnetic path space  525  in such a manner that the reference position can be visually checked by the human operator. More specifically, the fixing jig  54   q  is shaped such that it is devoid of a portion located inward of the lower surface  54 B of the fixing jig  54  shown in (b) of  FIG. 7 . In  FIG. 16 , the fixing jig  54   q  is mounted out of contact with its lower surface  54 Bq placed in contact with the upper surface  521 A of the top plate  521 . Namely, the fixing jig  54   q  may be mounted to the magnetic circuit member  52 . In this case, the human operator may mount the fixing jig  54   q  to the magnetic circuit member  52  at step S 11  of  FIG. 6 , then move the shaft  514  until the upper surface  516 A (connection end) contacts the sound board  7  and then adjust the length of the shaft  514 , while visually checking the length, so that the upper end of the bobbin  511  is brought into alignment with the upper surface  54 Aq of the fixing jig  54   q . In this manner, the human operator connects the upper surface  516 A to the sound board  7  (step S 14 ) in such a manner that the coil length middle and the magnetic path width middle substantially coincide with each other, i.e. relative positions of the vibration member  51  and the magnetic circuit member  52  are set in the above-mentioned desired relationship. 
     Note that the fixing jig mounted in place need not necessarily have the height L 2  from the upper surface  512 A; for example, the fixing jig may be mounted in such a manner that the upper surface  512 A of the cap  512  is at the height L 2  from the top plate  521  (upper surface  521 A), or that a mark put somewhere on the vibration member  51  is at the height L 2  from the upper surface  521 A. In short, the fixing jig may be at any desired height from the upper surface  521 A as long as the height from the upper surface  521 A can function as a reference for the human operator to visually check a position of the vibration member  51  when the coil length middle and the magnetic path width middle substantially coincide with each other. 
     &lt;Modification 2&gt; 
     In place of the fixing jig, the magnetic circuit member  52  may include a portion formed thereon so as to permit checking of the position of the vibration member  51  when the coil length middle and the magnetic path width middle substantially coincide with each other.  FIG. 17  is a view showing a modified magnetic circuit member  52   r  whose top plate  521   r  has an upper surface  521 Ar and a projecting portion  521 E formed on the upper surface  521 Ar and having the height L 2  from the upper surface  521 Ar. When moving upward the shaft  514  at step S 14  of  FIG. 6 , the human operator adjusts the position of the shaft  514  in such a manner that the upper end of the bobbin  511  is located at a position along (in alignment with) the upper surface  521 F of the projecting portion  521 E. Namely, the modified magnetic circuit member (magnetic path formation section)  52   r  has the projecting portion  512 E indicating a relative position of the voice coil  513  to the vibration member  51 , i.e. whether the voice coil  513  is positioned in desired positional relationship with the magnetic path space  525 . Namely, the projecting portion  512 E functions as the reference position instructing member indicating whether relative positions, in the axial direction of the bobbin  511 , of the voice coil  513  and the magnetic path space  525  are currently set in desired relationship. Thus, the human operator can adjust, while visually checking, the position of the vibration member  51  relative to the magnetic circuit member  52  in such a manner that the coil length middle and the magnetic path width middle substantially coincide with each other. 
     &lt;Modification 3&gt; 
     As another modification, the magnetic circuit member  52  may be supported by the support section in a manner different from the above-described. For example, through-holes may be formed in the yoke  523 , not in the top plate  521 , to extend through the thickness, i.e. from the upper surface to the lower surface, of the yoke  523 , so that the magnetic circuit member  52  can be supported by the support section  55  by means of the support rods  551  and the plurality of nuts  552 . Further, although the magnetic circuit member  52  is supported out of contact with the support section  55  in the illustrated example of  FIG. 9 , it may be supported in contact with the support section  55 . Further, whereas the support section  55  is fixed to the casing of the grand piano  1  in the above-described embodiment, it may be fixed to any other suitable part than the grand piano casing, such as the ground surface (floor). In any case, it just suffices for the magnetic circuit member  52  to be supported in such a manner that the distance from the bobbin  511  to the sound board  7  falls within the aforementioned end moving range. 
     &lt;Modification 4&gt; 
     As still another modification of the vibration device  50 , a heat sensor for measuring a temperature may be mounted on the flat upper surface  512 A of the cap  512  shown in  FIG. 5  for measuring heat produced from the voice coil  513 .  FIG. 18  is a view showing the modified vibration device  50   s . The heat sensor  56  is mounted on the vibration member  51  of the vibration device  50   s . The heat sensor  56  is a temperature measurement means provided in contact with the upper surface  512 A of the cap  512  for measuring a temperature of the upper surface  512 A. 
     In order to measure heat produced from the voice coil  513 , it is desirable that the heat sensor  56  be placed in contact with a position to which the heat can easily transfer. For example, the bobbin  511  is placed in direct contact with the voice coil  513  and is the most easily-heat-transferable member of all of the component members of the vibration device  50 . However, because the bobbin  511  is a circular cylindrical member and thus the heat sensor  56  has to be mounted on a curved surface of the bobbin  511 , it is difficult to mount the heat sensor  56  on the bobbin  511 . Further, although a surface of the top plate  521  facing the magnetic path space  525  is located closest to the voice coil  513 , heat from the voice coil  513  would not sufficiently transfer to the top plate  521  due to a space interposed between the top plate  521  and the voice coil  513 . It has been experimentally known that the heat would not sufficiently transfer to the top plate  521  even by way of the damper  53 , and thus, even if the heat sensor  56  is mounted on the top plate  521 , only a value considerably different from an actual temperature of the voice coil  513  can be measured by the heat sensor  56 . 
     Because the upper surface of the cap  512  is a flat surface and has a necessary area for mounting thereon the heat sensor  56 , it is easier to mount the heat sensor  56  on the upper surface of the cap  512  than on the bobbin  511 . Further, the cap  512  is formed of metal aluminum material and has a greater thermal conductivity, for example, at a temperature of 25° C. than iron or resin, such as polyethylene. Thus, as compared to the case where the cap  512  is formed of iron or resin, the cap  512  can easily transfer heat and can measure a value close to an actual temperature of the voice coil  513 . Note that the heat sensor  56  may be mounted on the lower surface of the cap  512 . If a wire connecting to the heat sensor  56  is passed between the bobbin  511  and the yoke  523 , the wire may undesirably contact the yoke  523 , and force may be produced due to magnetic force in the magnetic path space  525  and an electric current flowing through the wire, so that force to be imparted to the sound board  7  may vary. Thus, the wire connecting to the heat sensor  56  is preferably passed through a hole, which is formed to extend through the cap  512  up to the upper surface  512 A, so that the need for passing the wire between the bobbin  511  and the yoke  523  can be eliminated. 
     The heat sensor  56  mounted on the cap  512  in the aforementioned manner supplies the control section  11  of  FIG. 14  with data indicative of the measured temperature. If the temperature indicated by the data supplied from the heat sensor  56  is greater than a threshold value, the control section  11  controls the signal generation section  15  in such a manner that the signal generation section  15  generates such a drive signal as to reduce the heat produced from the voice coil  513 , more specifically to reduce the electric current flowing to the voice coil  513 . Thus, as the temperature measured by the heat sensor  56  gets greater than the threshold value, it is possible to lower the temperature of the voice coil  513  by eliminating heat having been produced from the voice coil  513 . Note that the control section  11  may control the signal generation section  15  to progressively change the drive signal so that heat produced from the voice coil  513  is progressively reduced. 
     &lt;Modification 5&gt; 
     The cap  512  may be shaped to radiate heat with an increased ease. Heat produced from the voice coil  513  is radiated into the air by way of the top plate and yoke  521 ,  523  or the bobbin  511 . If the heat produced from the voice coil  513  is radiated into the air by way of the top plate and yoke  521 ,  523 , an amount of heat transferred from the voice coil  513  tends to be small because these yokes are separated from the voice coil  513  by the air, although these yokes have a great surface area and thus can radiate much heat. As compared to the above-mentioned yokes, the bobbin  511  can radiate only a small amount of heat because an area contacting the air is small, although a great amount of heat is transferred to the bobbin  511  by virtue of direct contact between the bobbin  511  and the voice coil  513 . However, because the heat transferred to the bobbin  511  transmits to the cap  512  as well, it is radiated from the cap  512  into the air via the cap  512 . Therefore, in a case where it is necessary to increase heat radiation, the cap  512  may be shaped to radiate heat with an increased ease. 
       FIG. 19  is a view showing an example of such a modified cap. The cap  512   t  is formed of aluminum material and has a plurality of fins  512 E formed on the upper surface  512 At and projecting upward from the upper surface  512 At. With such fins  512 E, the modified cap  512   t  has a greater surface area than the cap  512  employed in the above-described surface area. Thus, the cap  512   t  can radiate air with an increased ease as compared to other caps, such as the cap  512 , having no such fin. Note, however, the modified cap need not necessarily be of the type having fins; in short, it just suffices for the cap to be shaped to radiate heat with an increased ease. Heat transferred from the voice coil  513  also transmits to the shaft  514  and the nut  515 , and thus, in a case where it is necessary to increase heat radiation, the shaft  514  and the nut  515  too may be shaped to radiate heat with an increased heat as long as they can be rotated to move axially with no difficulty. 
     &lt;Modification 6&gt; 
     Whereas the vibration member  51  in the above-described embodiment has the spacer  516 , the spacer  516  may be dispensed with or omitted, in which case the upper end surface of the shaft  514  directly connects to the sound board  7 . In the above-described embodiment, the bobbin  511 , the cap  512  and the shaft  514  are each formed of aluminum material. If, in that case, the vibration member  51  connects to the sound board  7  directly, i.e. not via the spacer  516 , more of heat produced from the voice coil  513  can be transmitted to the sound board  7  than in the case where the vibration member  51  connects to the sound board  7  via the spacer  516 . Thus, in this case, the sound board  7  would be influenced more by the heat, particularly if the sound board  7  is formed of wood as in the above-described embodiment. This is true even where the nut  515 , a part of the nut  515 , a part of the shaft  514 , etc. are formed of material of smaller conductivity than the spacer  516 . Namely, if the vibration member  51  includes the spacer  516  and a portion greater in thermal conductivity than the spacer  516 , heat transmitted via the spacer  516  to the sound board  7  would be reduced and thus influences given by the heat to the sound board  7  can be reduced, as compare to the case where heat is transmitted to the sound board  7  not via the spacer  516 . 
     On the other hand, if the influence of the heat on the sound board  7  is nominal, e.g. because the heat produced from the voice coil  513  is of a small amount, the heat may be transmitted to sound board  7  not via the spacer  516 . In such a case, because the heat is transmitted to sound board  7  not via the spacer  516 , energy loss would be small and thus vibration of the vibration member  51  would give great force to the sound board  7 , as compared to the case where the spacer  516  is sandwiched between the shaft  514  and the sound board  7 . 
     &lt;Modification 7&gt; 
     The bobbin  511 , the cap  512 , the shaft  514 , the nut  515  and the spacer  516  may be formed of material different from the material employed in the above-described embodiment. For example, whereas the bobbin  511 , the cap  512  and the shaft  514  have been described as formed of metal aluminum material, they may be formed of any other material, such as copper, resin, plastic or the like, as long as the material satisfies conditions required of the voice coil type actuator, such as a strength, weight, non-magnetic/magnetic property, absence/presence of heat resistant property, etc. 
     &lt;Modification 8&gt; 
     As still another modification, the shaft  514  may have a shape different from that in the above-described embodiment.  FIG. 20  is a view showing an outer appearance of an example of the modified shaft  514   u . The modified shaft  514   u  includes a tubular member  514   u   1 , an axially-extending member  514   u   2  extending in the axial direction A 2 , and a bolt  514   u   3 . The axially-extending member  514   u   2  includes a circular columnar portion formed in a circular columnar shape having a diameter smaller than the inner diameter of the tubular member  514   u   1 , and a male screw portion extending integrally from the circular columnar portion and having a male thread formed thereon. The axially-extending member  514   u   2  is fixed to the hole portion  512 G of the cap  512  by means of the nut with the male screw portion screwed in the hole portion  512 G. The circular columnar portion of the axially-extending member  514   u   2  has a single hole formed in the circular columnar portion and extending diametrically therethrough, i.e. perpendicularly to the axial direction A 2 . The tubular member  514   u   1  is fixed, at its one end portion in the axial direction A 2 , to the spacer  516  by an adhesive agent or the like. Further, the tubular member  514   u   1  has holes formed therein at a plurality of (e.g., four) different positions spaced from one another in the axial direction A 2  so as to extend diametrically through the entire shaft  514   u  (i.e., the tubular member  514   u   1  and the axially-extending member  514   u   2 ) perpendicularly to the axial direction A 2 . A female thread is formed in each of the plurality of holes formed through the tubular member  514   u   1  and the axially-extending member  514   u   2  so that the bolt  514   u   3  can be screwed in any one of the holes. A portion of the bolt  514   u   3  which has a male thread formed thereon has a length greater than the outer diameter of the tubular member  514   u   1  so as to extend diametrically through the tubular member  514   u   1 . Further, the circular columnar portion of the axially-extending member  514   u   2  is inserted inside the tubular member  514   u   1 , and the bolt  514   u   3  is screwed through any one of the holes formed in the tubular member  514   u   1  and the single hole of the circular columnar portion of the axially-extending member  514   u   2  with the one hole of the tubular member  514   u   1  and the single hole of the circular columnar portion aligned with each other. In this manner, the axially-extending member  514   u   2  and the tubular member  514   u   1  are fixed. The shaft  514   u  is changeable in height position in a plurality of steps (e.g., four steps) by changing the hole of the tubular member  514   u   1  in which the bolt  514   u   3  is to be screwed. 
       FIG. 21  is a view showing an outer appearance of another example of the modified shaft  514   v . The modified shaft  514   v  includes a tubular member  514   v   1 , an axially-extending member  514   v   2  extending in the axial direction A 2 , and two bolts  514   v   3 . The tubular member  514   v   1  has two holes formed therein at one position (not four positions) and extending diametrically through the entire shaft  514   v  perpendicularly to the axial direction A 2 . Namely, the modified shaft  514   v  is similar to the aforementioned modified shaft  514   u  except that the two holes are formed opposed to each other in the direction perpendicular to the axial direction A 2 . In other words, the modified shaft  514   v  is similar to the aforementioned modified shaft  514   u  except that no hole is formed in the circular columnar portion. In a portion of the volt  514   v   3  having a male thread formed therein has a predetermined length such that the distal end of the threaded portion can reach the circular columnar portion when the threaded portion is screwed through the hole of the tubular member  514   v   1 . Further, in the shaft  514   v , the two bolts  514   v   3  are screwed in corresponding ones of the two holes of the tubular member  514   v   1  with the circular columnar portion of the axially-extending member  514   v   2  inserted inside the tubular member  514   v   1 , and the tubular member  514   v   1  and the axially-extending member  514   v   2  are fixed relative to each other by the respective distal ends of the two bolts  514   v   3  pressed against the circular columnar portion. The shaft  514   v  can be continuously changed in height from the cap  512 , by changing the position where the respective distal ends of the two bolts  514   v   3  are pressed against the circular columnar portion. 
     Because the height of the modified shaft from the cap  512  is changeable, the vibration member having the modified shaft can be fixed at the connection end to the bobbin  511  in such a manner that the distance from the bobbin  511  to the upper surface  516 A of the spacer  516  falls within a predetermined range. Thus, the aforementioned connection member, i.e. the cap  512 , shaft  514 , nut  515  and spacer  516 , can be fixed after being adjusted in overall length in such a manner that it is connected at the connection end to the sound board  7  while allowing the voice coil  513 , provided on the bobbin  511 , to be positioned at a predetermined position within the magnetic path space  525  as shown in  FIG. 5 . In short, the shaft may be of any shape as long as the connection member including the shaft can be fixed after being adjusted in overall length as noted above. 
     &lt;Modification 9&gt; 
     A position where the lower end of the shaft  514  is located higher than the lower end of the hole portion  512 G may be preset as an upper limit position within the shaft moving range. Even in this case, it just suffices that the connection member be capable of being fixed after being adjusted in overall length in such a manner that it is connected at the connection end to the sound board  7  while allowing the voice coil  513 , provided on the bobbin  511 , to be positioned at a predetermined position within the magnetic path space  525 . Here, “allowing the voice coil  513 , provided on the bobbin  511 , to be positioned at a predetermined position” means allowing the voice coil  513  and the top plate  521  to have predetermined positional relationship, e.g. allowing the voice coil  513  to be opposed to the top plate  521 . 
     &lt;Modification 10&gt; 
     In the sequence of operations for attaching the vibration device  50  to the grand piano  1 , the operation of step S 11  may be performed after other operations (steps S 12  and S 13 ) as long as it is performed before the operation of step S 14 . In short, it just suffices that the fixing jig  54  be fixed in such a manner as to allow the human operator to automatically or visually confirm, at the time of the movement of the shaft  514  at step S 14 , that relative positional relationship of the vibration member  51  to the magnetic circuit member  52  achieves a state where the coil length middle and the magnetic path width middle substantially coincide with each other. 
     &lt;Modification 11&gt; 
     Further, in the above-described embodiment of the vibration device  50 , the damper  53  may be dispensed with. In such a case, because the assembly of the vibration member  51  and the assembly of the magnetic circuit member  52  are not connected with each other prior to attachment of the vibration device  50  to the sound board  7 , the operations of steps S 13  and S 14  of  FIG. 16  are performed before step S 12  so as to first attach the assembly of the vibration member  51  to a predetermined position of the sound board  7 . Then, the operation of step S 12  is performed for installing the magnetic circuit member  52  on the support section  55  in such a manner that the bobbin  511  provided with the voice coil  513  is appropriately accommodated within the magnetic path space of the magnetic circuit member  52 . After that, the operation of step S 14  is performed for adjusting the length of the shaft  514  in such a manner that relative positional relationship of the vibration member  51  to the magnetic circuit member  52  achieves a state where the coil length middle and the magnetic path width middle substantially coincide with each other. 
     [Second Embodiment of the Vibration Device] 
       FIG. 22  is a view showing an outer appearance of a second embodiment of the vibration device  50 A of the present invention. The second embodiment of the vibration device  50 A does not include the mounting shaft  514  as employed in the first embodiment of the vibration device  50 . Although the second embodiment of the vibration device  50 A is different from the first embodiment of the vibration device  50  in terms of the structure by which the vibration device  50 A is attached to the sound board  7 , it may be similar to the first embodiment of the vibration device  50  in terms of the other structures by which it performs its primary function as a vibration device. Thus, in the following description and drawings pertaining to the second embodiment, similar elements to the first embodiment are indicated by the same reference numerals as used in the first embodiment and will not be described here to avoid unnecessary duplication. 
     According to the second embodiment, as shown in  FIG. 22 , a vibration section  51  of the vibration device  50 A comprises the bobbin  511  and the cap  512 . The cap  512  is a disk-shaped end member mounted at the distal end of the bobbin  511 . In the second embodiment, the upper surface  512 A of the cap or end member  512  functions as the “connection end” for connection to the sound board  7 . 
       FIG. 23  is a vertical sectional view of the second embodiment of the vibration device  50 A. The second embodiment of the vibration device  50 A is different from the first embodiment of the vibration device  50  shown in  FIG. 5  in that it does not include the mounting parts depicted at reference numerals  514 ,  515  and  516  in  FIG. 5 , in that no male thread is formed in the central hole portions  512 G of the cap  512  of the bobbin  511 , in that the cap  512  is formed of material different from the material in the first embodiment, and in that a through-hole portion  523 G is formed through the disk portion  523 E and circular columnar portion  523 F of the yoke  523 . The other structures in  FIG. 23  are substantially similar to the corresponding structures shown in  FIG. 5 . 
     The cap  512  in the second embodiment shown in  FIGS. 22, 23 , etc. is formed of material like resin and fixedly mounted on and closes an upward opening portion of the bobbin  511 . The cap  512  has a hole portion  512 G′ extending centrally through upper and lower portions thereof. The axis line B 1  of the hole portion  512 G′ coaxially aligns with the axis line B 2  of the bobbin  511 . Further, the yoke  523  has the through-hole portion  523 G extending through both of the disk portion  523 E and the circular columnar portion  523 F in the axial direction A 3 . Namely, the through-hole portion  523 G extends through the magnetic circuit member  52  in the axial direction A 3 . As described later, the through-hole portion  523 G has an inner diameter size to permit passage therethrough of a wood screw (fastening member)  61  for connecting the cap (end member)  512  to the sound board  7 . The hole portion  512 G′ is formed in the cap  512  at a position corresponding to the hole portion  523 G of the yoke  523  and in axial alignment with the hole portion  523 G. The hole portion  512 G′, which is formed for passage therethrough of a threaded portion of the wood screw (fastening member)  61 , functions as a mark for designating a position where the wood screw (fastening member)  61  is to be fastened in the surface of the cap (end member)  512  opposed to the hole portion  523 G. 
     Next, with reference to  FIGS. 24 to 27 , a description will be given about a sequence of operations performed by the human operator for attaching the second embodiment of the vibration device  50 A to the grand piano  1 .  FIG. 24  is a flow chart showing the sequence of operations for attaching the vibration device  50 A to the grand piano  1 . First, as in the above-described first embodiment, the grand piano  1  to which the vibration device  50 A has not been attached yet is provided, and the support section  55  is mounted to a predetermined portion, such as the vertical strut  9 , of the grand piano  1 . Like the sequence of operations shown in  FIG. 6 , the sequence of operations shown in  FIG. 24  is started up with the support section  55  connected to the vertical strut  9 . The human operator mounts a predetermined fixing jig to the magnetic circuit member  52  (step S 21 ). The same fixing jig  54  ( FIG. 7 ) used in the first embodiment may be used in the second embodiment. 
       FIG. 25  is a view showing the vibration member  51  restricted in position and orientation relative to the magnetic circuit member  52  by means of the fixing jig  54 . As in the illustrated example of  FIG. 8 , the fixing jig  54  is installed with its lower surface  54 B in contact with the upper surface  521 A of the top plate  521  and fixed to the upper surface  521 A by attractive force (magnetic attractive force) from the top plate  521 . The fixing jig  54  is mounted in place so as to sandwich the bobbin  511  between the straight portions  541  and  542  (i.e., to accommodate the bobbin  511  in the U-shaped inner space). 
     Referring back to  FIG. 24 , the human operator then causes the cap portion  512  to contact a predetermined position of the sound board  7  (step S 22 ). The “predetermined position” is preset as a position at which the vibration device  50 A should impart vibration to the sound board  7 , and it is, for example, a position located opposite to the bridge  6 H or  6 L across the sound board  7 . Then, the human operator causes the magnetic circuit member  52  to be supported by the support section  55  (step S 23 ). Step S 23  is an example of the “support step” in the present invention. 
       FIG. 26  is a view showing the magnetic circuit member  52  supported by the support section  55  in the aforementioned manner. In  FIG. 26 , the positions of the sound board  7 , bridge  6  and support section  55  are indicated by two-dot-dash lines in order to show positional relationship among the addition device  50 A, the sound board  7 , the bridge  6  and the support section  55 . Further, in  FIG. 26 , the state where the magnetic circuit member  52  is supported by the support section  55  is shown as viewed in such a direction where the width direction A 4  of the bridge  6  corresponds to a left-right direction of the figure. The bridge  6  is mounted on the upper surface  7 A of the sound board  7 . Further, the vibration area C 1  is preset on the lower surface  7 B of the sound board  7 , as noted above. Note that the support section  55  has a suitable opening  55   a  formed therein such that a screwdriver held in a human operator&#39;s hand can be inserted into the opening  55   a  from below during the attachment operations. 
     The top plate has a not-shown hole portion extending therethrough from the upper surface to the lower surface, and a female thread formed in the inner surface of the hole. Similarly, the support section  55  has a not-shown hole portion extending therethrough from the upper surface to the lower surface, and a female thread formed in the inner surface of the hole. Like in the above-described first embodiment, the magnetic circuit member  52  is fixed to the support section  55  by a combination of the plurality of support rods  551  each having male threads formed on opposite end portions thereof and the nuts  552  screwed on the respective male threads of the support rods  551 . Thus, like in the above-described first embodiment, the load of the magnetic circuit member  52  supported by the support section  55  acts on the vertical strut  9  via the support section  55 . 
     Then, when the human operator performs the operation of step S 23 , the vibration member  51  is prevented from moving downward of the position where the lower surface  512 B of the cap  512  contacts the upper surface  54 A of the fixing jig  54  by means of the fixing jig  54 , i.e. where coil length middle and the magnetic path width middle substantially coincide with each other, as noted above. By thus preventing formation of a gap between the lower surface  512 E and the upper surface  54 A, the human operator allows the magnetic circuit member  52  to be supported by the support section  55  in such a manner that a relative position, in the normal line direction A 1 , of the vibration member  51  to the magnetic circuit member  52  has predetermined relationship. 
     Referring, back to  FIG. 24 , the human operator then removes or dismount the fixing jig  54  (step S 24 ). Then, the human operator moves the fastening member (e.g., wood screw), provided for fixing the cap  512  to the sound board  7 , to a mounting position of the cap  512  where the fastening member (e.g., wood screw) should be fastened (step S 25 ) and then fastens the fastening member to the mounting position and to the sound board  7  to thereby fix the cap  512  to the sound board  7  (step S 26 ). Step S 25  is an example of a “movement step” in the present invention, and step S 26  is an example of a “fixation step” in the present invention. Details of the operations performed by the human operator at steps S 25  and S 26  will be described below with reference to  FIG. 27 . 
       FIG. 27  is a view showing the cap  512  fixed to the sound board  7 . More specifically, the cap  512  is fixed to the sound board  7  by means of the wood screw  61  that is a fastening member fastened through the hole portion  512 G to the sound board  7 . The wood screw  61  is formed of non-magnetic metal, such as brass or stainless steel, and includes a head portion having a greater diameter than the hole portion  512 G of the cap  512 . Here, the “non-magnetic metal” is substance other than ferromagnetic substance. The wood screw  61  is screwed through the hole portion  512 G to the sound board  7  and then into the bridge  6 . The cap  512  is fixed to the sound board  7  by being pressed against the sound board  7  via the head portion. Further, a part of an externally-threaded portion of the wood screw  61  closer to the head portion (i.e., the root of the wood screw  61 ) has a diameter matching the diameter of the hole portion  512 G. Thus, in the state of  FIG. 27 , the root of the wood screw  61  is accurately snugly fitted in the lower end opening of the hole portion  512 G. Namely, the cap  512  is fixed at one position relative to the position where the wood screw  61  is screwed into the sound board  7  and the bridge  6 . 
     The screwdriver  62  is formed of non-magnetic metal, such as brass or stainless steel, and the distal end of the screwdriver  62  has a shape corresponding to a shape of a tapped hole of the wood screw  61 . For example, if the wood screw  61  is a cross-head screw having a “+” tapped hole, the distal end of the screwdriver  62  has a “+” shape, but, if the wood screw  61  is a slotted-head screw having a “−” tapped hole, the distal end of the screwdriver  62  has a “−” shape. At step S 25 , the human operator uses the screwdriver  62  to perform the operation. Namely, with the wood screw  61  fitted in the distal end of the screwdriver  62 , the human operator inserts the distal end of the screwdriver  62  into the hole portion  523 G extending through the yoke  523 . Before the wood crew  61  of  FIG. 23  is fastened through the hole portion  512 G to the sound board  7 , the axis line B 2  of the bobbin  511  and the axis line B 3  of the circular columnar portion  523 F are in alignment with (substantially coincident with) each other for connection via the damper  53 . Thus, the axis line of the hole portion  512 G of the cap  512  is substantially coincident with the axis of the hole portion  523 G. The human operator uses the screwdriver  62  to move the wood screw  61 , inserted into the hole portion  523 G until the wood screw  61  passes through the hole portion  523 G to reach the hole portion  512 G. 
     Then, once the wood screw  61  passes through the hole portion  512 G into contact with the sound board  7 , the human operator rotates the screwdriver  62  to screw the wood screw  61  into the sound board  7 . During that time, the driver  62  and the wood screw  61  substantially align with each other in the axial direction, because the screw driver  62  turns the wood screw  61  while continuing to push the wood screw  61 . Thus, the wood screw  61  is fastened to the hole portion  512 G and the sound board  7 . Further, the cap  512  is fixed at one position relative to the position where the wood screw  61  is screwed into the sound board  7  and the bridge  6  as noted earlier, and thus, even if the axis line B 1  of the hole portion  512 G and the axis line B 3  of the yoke  523  are in misalignment with each other when the operation of step S 25  is to be stared, the root of the wood screw  61  will accurately snugly fitted in the lower end opening of the hole portion  512 G as the wood screw  61  is screwed into the sound board  7 . As a consequence, the hole portion  512 G and the hole portion  523 G will axially align in a straight line, and thus, the axis line B 1  of the hole portion  512 G and the axis line B 3  of the yoke  523  will axially align with each other. Also, the axis line B 1  axially aligns with the axis line B 2  of the bobbin  511 . Namely, by the human operator performing the operation of step S 25 , the bobbin  511  and the yoke  523  are brought into axis alignment with each other. Thus, the human operator can attach the vibration device  50 A in such a manner that the bobbin  511  and the yoke  523  do not contact each other. Further, when the vibration member  511  vibrates, the bobbin  511  and the yoke  523  are less likely to contact each other as compared to the where the bobbin  511  and the yoke  523  are not in axis alignment with each other. 
     When an object is to be moved through the hole portion  523 G to reach the hole portion  512 G, the object and a tool for moving the object both pass through the magnetic path formed by the magnetic circuit member  52 . If the object and the tool are formed of magnetic material, they are attracted to the yoke  523  by attractive force produced by the magnetic path, so that it becomes difficult to move them. On the other hand, the wood screw  61  and the screwdriver  62  are both formed of non-magnetic material as noted above, and thus, force which they receive due to the magnetism of the magnetic path when they pass through the two hole portions is so small to ignore. Therefore, the human operator can perform the operation of step S 25  without minding force which the wood screw  61  and the screwdriver  62  receive from the magnetic force. In this manner, the cap  512  is fixed to the sound board  7  as shown in  FIG. 27 . 
     Thus, as the bobbin  511  moves upward, the sound board  7  is pressed upward. But, as the as the bobbin  511  moves downward, the sound board  7  is pulled downward instead of the bobbin  511  getting away from the sound board  7 . In this manner, vibration of the bobbin  511  is transmitted to the bridge  6  via the sound board  7  and then to the string set  5 . 
     The bobbin  511  and the cap  512  together constitute an example of a “bobbin section” in the present invention, and the wood screw  61  is an example of a “fixation member” in the present invention. Further, the cap  512 , which covers one end of the bobbin section, is an example of a “lid section” in the present invention. As noted earlier, the bobbin section is fixed at one end to the sound board  7  by means of the fixation member of non-magnetic material. Further, the magnetic circuit member  52  functions as a magnetic path formation section that forms the magnetic path space  525  between inside the inner peripheral surface  511 C of the bobbin section and outside the outer peripheral surface  511 D of the bobbin section shown in  FIG. 5 . Further, the hole portion  523 G formed in the yoke  523  of the magnetic circuit member  52  is an example of a “hole” in the present invention. As shown in  FIG. 23 , the hole portion  523 G extends through the magnetic path formation section in the axial direction A 3  and has one end portion opening from the circular columnar portion  523 F into the inner space of the bobbin section of the magnetic path formation section. The circular columnar portion  523 F is a portion located inwardly of the bobbin section of the magnetic path formation section. Further, the axial direction A 3  is an example of a “first direction” in the present invention. Further, the hole portion  523 G has a size to permit passage therethrough of the wood screw  61  as noted above in relation to step S 25  of  FIG. 6 . The bobbin section (more specifically, the cap  512  thereof) has the hole portion  512 G extending therethrough in the axial direction A 3 . The hole portion  512 G, which also indicates that it is a position to which the wood screw  61  should be fastened, is an example of a “designated region” in the present invention. When the hole  512 G is in alignment with the hole portion  523 G in the axial direction A 3 , it is indicated that the bobbin section and the magnetic path formation means are in a state where they do not contact each other as seen in  FIG. 10 . 
     Because the magnetic circuit member  52  is fixed in position by being supported by the support section  55 , most of the drive force produced by the voice coil  513  is used as thrust force for vibrating the bobbin  511 . Further, the magnetic circuit member  52  is supported by the support section  55  in spaced-apart positional relation to the vibration member  51  and in such a manner as to not contact with the sound board  7 . Further, because the vibration member  51  is spaced from the magnetic circuit member  52 , the vibration member  51  is supported by the sound board  7  by being fixed to the sound board  7 . By the vibration device  50 A being supported by the support section  55  in the aforementioned manner, no load other than that of the vibration member  51  acts on the sound board  7 . The support section  55  may support the magnetic circuit member  52  in any other desired manner than the aforementioned as long as no load other than that of the vibration member  51  is applied to the sound board  7 . Like in the above-described first embodiment, the support section  55  may support the magnetic circuit member  52  in any other desired manner than the aforementioned as long as no load other than that of the vibration member  51  acts on the sound board  7 . 
     In the second embodiment, there may be employed a control system similar in function and construction to the functional arrangements of the control device  10  and grand piano  1  in the first embodiment shown in  FIGS. 14 and 15 . 
     [Modifications of the Second Embodiment] 
     The above-described is only one example of the second embodiment of the present invention, and the second embodiment may be modified variously as follows. Further, the above-described embodiment and the following modifications may be practiced in combination as necessary. 
     &lt;Modification 12&gt; 
     Whereas the cap  512  in the second embodiment has been described as fixed to the sound board  7  by means of the wood screw  61  as the fixation member, any other suitable fixation members may be used. For example, the cap  512  may be fixed to the sound board  7  by means of a bolt and a nut, a nail or an adhesive agent. Desirably, the cap  512  is fixed at its central portion by means of a wood screw passed through the hole portion  512 G′ and fixed at an outer peripheral end region of the upper surface  512 A by means of an adhesive agent. Force pulling downward the bobbin  512  is applied by the bobbin  511  to the outer peripheral end region of the upper surface  512 A. By fixing such an outer peripheral end region of the upper surface  512 A in the aforementioned manner, it is possible to prevent the outer peripheral end region of the upper surface  512 A from floating off the sound board  7 . 
     &lt;Modification 13&gt; 
     As another modification, a washer may be used in fixing the cap  512  to the sound board  7  by means of the wood screw  61 . In such a case, the washer is positioned beneath the cap  512 , and the wood screw  61  is passed through the washer and the hole portion  512 G′ to be screwed into the sound board  7 . Thus, the wood screw  61  can be made less likely to come loose as compared to a case where no such washer is used. 
     &lt;Modification 14&gt; 
     As still another modification, the cap mounted on the bobbin  511  may have a different shape from the cap  512  in the above-described embodiment.  FIG. 28  is a view showing an example of the modified cap  512   m . (a) of  FIG. 28  shows a state before the cap  512   m  is fixed to the sound board  7  by means of the wood screw  61 . The cap  512   m  has a shape gradually dented downward in a direction from an outer peripheral portion to a central portion. (b) of  FIG. 28  shows the cap  512   m  fixed to the sound board  7  by means of the wood screw  61  passed through the hole portion  512 Gm into the sound board  7 . By the wood screw  61  pressing the cap  512   m  against the sound board  7 , the downwardly dented central portion of the cap  512   m  is uplifted in a direction of arrows into contact with the sound board  7 . 
     For example, let it be assumed here that the cap is fixed to the sound board  7  by means of an adhesive agent and the wood screw  61  as noted above in relation to Modification 12. In this case, the human operator fixes the magnetic circuit member  52  to the support section  55  at step S 23  of  FIG. 24  and then uses an adhesive-pouring tool  63 , shown in two-dot-dash line, to pour an adhesive agent through the hole portion  512 Gm into a space between the cap  512   m  and the sound board  7  placed in the state shown in (a) of  FIG. 28 . Then, the human operator presses the cap  512   m  against the sound board  7  by use of the wood screw  61  at step S 15  as shown in (b) of  FIG. 28 . At that time, the poured adhesive spreads between the upper surface  512 Am of the cap  512   m  and the sound board  7 . In this manner, the human operator fixes the cap  512   m  to the sound board  7  by means of the wood screw and the adhesive agent. According to this modification, even in a case where the cap  512   m  is fixed by means of the wood screw and the adhesive agent, the human operator can cause the magnetic circuit member  52  to be supported by the support section  55  without minding an exact position of the cap  512   m , by performing the operations without applying the adhesive agent to the upper surface  512 Am till step S 24 . Further, after causing the magnetic circuit member  52  to be supported by the support section  55 , the human operator can easily apply the adhesive agent at step S 15  as compared to a case where, for example, the tool  63  is inserted from a lateral side into a gap between the sound board  7  and the upper surface  512 Am to apply the adhesive agent all over the upper surface  512 Am. 
     Further, whereas the second embodiment has been described above as using the cap  512  mounted on the end of the bobbin  511 , what is mounted on the end of the bobbin  511  is not limited to the cap or other member of a shape closing the end opening of the bobbin.  FIG. 29  is a view showing an example of the member  512   n  mounted on the end of the bobbin  511 . The member  512   n  has the upper surface  512 An. Specifically,  FIG. 29  shows the member  512   n  as viewed from over the upper surface  512 An. The member  512   n  has a hole portion  512 G and opening regions  512 H shaped to surround the outer periphery of the hole portion  512 Gn. As the member  512   n  is mounted on the upper end of the bobbin  511 , the interior of the bobbin  511  opens to outside the bobbin  511  through the opening regions  512 H. The member  512   n  may be fixed to the sound board  7 , for example, by the wood screw  61  fastened to the hole portion  512 Gn and the sound board  7  and the adhesive agent applied to the upper surface  512 An. In short, it suffices that the member mounted on the bobbin  511  be one having a hole for fitting therein the wood screw  61 , such as the above-described cap  512  or the member  512   n.    
     Further, whereas the hole portion  512 G′ in the second embodiment has been described above as extending axially through the cap  512 , it need not necessarily extend axially through the cap  512 .  FIG. 30  is a view showing an example of such a modified cap  512   p . (a) of  FIG. 30  shows the cap  512   p  before the wood screw  61  is fitted in the cap  512   p . The cap  512   p  has a hole portion  512 Gp formed therein to extend from the lower surface  512 Bp to a position short of the upper surface  512 Ap. The hole  512 Gp is formed by denting the lower surface  512 Bp in a conical shape and extends short of the upper surface  512 Ap. A portion of the cap  512   p  from the bottom of the hole portion  512 Gp to the upper surface  512 Ap has such a thickness that, by the human operator screwing the distal end of the wood screw  61  into the resin of the bottom to form an additional hole, the hole portion  512 Gp can be extended through the additional hole to the upper surface  512 Ap. In short, the hole portion of the cap need not necessarily extend through the cap as long as it can function as a mark indicating that the hole portion is a position where the wood screw  61  is to be fitted or fastened and can fix the cap to the sound board  7  by fitting therein the wood screw  61 . The aforementioned cap  512   m , the member  512   n  or cap  512   p , and the bobbin  511  constitute an example of the “bobbin section” in the present invention. 
     &lt;Modification 15&gt; 
     In the above-described second embodiment, the human operator merely positions the upper surface  512 A of the cap  512  in contact with the sound board  7  at step S 22  of  FIG. 24 . As a modification, however, there may be used an adhesive agent that takes time before curing to a degree where the position of the upper surface  512 A contacting the sound board  7  can be shifted if desired, until the time required for the operations of steps S 23  to S 25  elapses. Even before completely curing, this adhesive agent fixes the cap  512  to such a degree where the position of contact between the upper surface  512 A and the sound board  7  would not be shifted, for example, by force applied due to flexure of the damper  53 . In this manner, the position of contact between the upper surface  512 A and the sound board  7  can be preventing from shifting due to mere slight inclination of the magnetic circuit member  52  during the operation of step S 23 , so that the human operator can perform the operation for fixing the magnetic circuit member  52  to the support section  55  with an increased ease. 
     &lt;Modification 16&gt; 
     The bobbin  511  and the cap  512  in the above-described second embodiment may be formed of material different from the aforementioned. For example, whereas the bobbin  511  has been described as formed of metal aluminum material, it may be formed of any other material, such as copper, resin, plastic or the like. Further, whereas the cap  512  has been described as formed of resin, it may be formed of metal, such as aluminum material or copper, plastic or the like. In any case, any desired material may be used as long as the material satisfies conditions required of the voice coil type actuator, such as strength, weight, non-magnetic/magnetic property, absence/presence of heat resistant property, etc. 
     &lt;Modification 17&gt; 
     As still another modification, the magnetic circuit member  52  may be fixed to the support section  55  in a manner from the above-described manner. For example, through-holes may be formed in the yoke  523 , not in the top plate  521 , to extend through the thickness, i.e. from the upper surface to the lower surface, of the yoke  523 , so that the magnetic circuit member  52  can be supported by the support section  55  by means of the support rods  551  and the plurality of nuts  552 . Further, although the magnetic circuit member  52  is supported out of contact with the support section  55  in the illustrated example of  FIG. 26 , it may be supported in contact with the support section  55 . In such a case, the position, in the axial direction A 2 , of the support section  55  may be made adjustable, so that, by adjusting the position (height position) in the axis direction A 2  of the support section  55 , the vibration device  50 A can be attached to the sound board  7  with the relative positions relative (height) positions), in the axial direction A 2 , of the vibration member  51  and the magnetic circuit member  52  maintained in an ideal state. 
     &lt;Modification 18&gt; 
     In the second embodiment, like in Modification  1  of the first modification, the fixing jig may have a different shape from the above-described fixing jig  54 , and a fixing jig similar to the fixing jig  54   q  shown in  FIG. 16  may be used in the second embodiment.  FIG. 31  shows an example where a fixing jig similar to the fixing jig  54   q  is used in the second embodiment. In this case, at step S 23  of  FIG. 24 , the human operator causes the magnetic circuit member  52  to be supported by the support section  55 , while visually checking their positions, in such a manner that the upper end of the bobbin  511  is brought into alignment with the upper surface  54 Aq of the fixing jig  54   q  with the upper surface  512 A of the cap  512  contacting the sound board  7 . In this manner, the human operator can make setting such that the coil length middle and the magnetic path width middle substantially coincide with each other, i.e. relative positions of the vibration member  51  and the magnetic circuit member  52  have the above-mentioned desired relationship. 
     Further, as noted above, the fixing jig mounted to the magnetic circuit member  52  need not necessarily have the height L 2  from the upper surface  512 A; for example, the fixing jig may be mounted to the magnetic circuit member  52  in such a manner that the upper surface  512 A of the cap  512  is at the height L 2  from the top plate  521  (upper surface  521 A), or a mark put somewhere on the vibration member  51  is at the height L 2  from the upper surface  521 A. In short, the fixing jig may be at any desired height from the upper surface  521 A as long as the height can function as a reference for the human operator to visually check a position of the vibration member  51  when the coil length middle and the magnetic path width middle substantially coincide with each other. 
     &lt;Modification 19&gt; 
     In the second embodiment, the fixing jig may be dispensed with; instead, the magnetic circuit member  52  may include a portion formed thereon so as to permit checking of the position of the vibration member  51  when the coil length middle and the magnetic path width middle are substantially coincident with each other, like in Modification  2  ( FIG. 17 ) of the first embodiment.  FIG. 32  is a view showing a modified magnetic circuit member  52   r  whose top plate  521   r  has an upper surface  521 Ar and a projecting portion  521 E formed on the upper surface  521 Ar and having the height L 2  from the upper surface  521 Ar. In this case, the human operator at step S 23  of  FIG. 24  causes the magnetic circuit member  52  to be supported on the support section  55  while making adjustment such that the upper end of the bobbin  511  is located at a position along (in alignment with) the upper surface  521 F of the projecting portion  521 E. 
     &lt;Modification 20&gt; 
     In the above-described second embodiment, the hole portion  512 G′ and the hole portion  523 G extend through the cap  512  and the yoke  523 , respectively, in the axial direction A 2 , they may extend through the cap  512  and the yoke  523 , respectively, in a different direction from the above-described.  FIG. 33  is a view showing such a modified vibration device  50 B. The vibration device  50 B includes a cap  512   s  and a yoke  523   s . The cap  512   s  has a hole portion  512 Gs, and the yoke  523   s  has a hole portion  523 Gs. The hole portion  512 Gs and the hole portion  523 Gs extend in a direction A 5  at an angle to the axial direction A 2 . In  FIG. 33 , a distance between magnetic flux line directions A 6  and A 7  that are directions of lines of magnetic flux of the bobbin  511  and the yoke  523  (i.e., directions indicated by broken lines in  FIG. 23 ) is L 4 . This represents a state where the bobbin  511  and the yoke  523  are in axis alignment as shown in  FIG. 23 . In this state, the hole portion  512 Gs of the cap  512  is formed to extend obliquely in alignment with the direction A 5  of the hole portion  523 Gs. The hole portion  523 Gs is an example of a “hole portion” in the present invention. Further, of the hole portion  512 Gs, an opening appearing in the upper surface of the cap  512  is an example of a “designating region” in the present invention. Further, the direction A 5  is an example of the “first direction” in the present invention. In the aforementioned manner, the cap  512   s  can be fixed to the sound board  7  with the screwdriver  62  and the wood screw  61  of  FIG. 27  passed obliquely through the hole portions  512 Gs and  523 Gs so that the hole portions  512 Gs and  523 Gs axially align with each other in a straight line. 
     &lt;Modification 21&gt; 
     Whereas the second embodiment has been described above in relation to the case where the cap  512  is mounted on the upper end of the bobbin  511 , the bobbin  511  itself may be shaped to include the cap  512 .  FIG. 34  is a view showing such a modified vibration member  51   t , which includes a bobbin  511   t  and the voice coil  513 . The bobbin  511   t  is formed of aluminum material and shaped to correspond to a combination of the shapes of the bobbin  511  and cap  512  shown in  FIG. 23 . The bobbin  511   t  has a hole portion  511 Gt extending through an upper end portion thereof in the axial direction A 2 . The bobbin  511   t  is an example of the “bobbin section” in the present invention. 
     &lt;Modification 22&gt; 
     As still another modification, the magnetic circuit member  52  may be supported by the support section  55  in a manner from the above-described manner. For example, through-holes may be formed in the yoke  523 , not in the top plate  521 , to extend through the thickness, i.e. from the upper surface to the lower surface, of the yoke  523 , so that the magnetic circuit member  52  can be supported by the support section  55  by means of the support rods  551  and the plurality of nuts  552 . Further, although the magnetic circuit member  52  is supported out of contact with the support section  55  in the illustrated example of  FIG. 26 , it may be supported in contact with the support section  55 . Further, whereas the support section  55  is fixed to the casing of the grand piano  1  in the above-described embodiment, it may be fixed to any other suitable part than the grand piano casing, such as the ground surface (floor). In any case, it just suffices for the magnetic circuit member  52  to be supported in such a manner that the distance from the bobbin  511  to the sound board  7  falls within the aforementioned end moving range. 
     &lt;Modification 23&gt; 
     Whereas the vibration member  51 , the magnetic circuit member  52  and the damper  53  each have a circular shape as viewed in the normal line direction A 1  shown in  FIG. 23 , the present invention is not so limited, and the vibration member  51 , the magnetic circuit member  52  and the damper  53  may have any other shape, such as an elliptical or square shape. In short, the vibration member  51 , the magnetic circuit member  52  and the damper  53  may be of any desired shape as long as the vibration member  51  vibrates in accordance with a waveform indicated by a drive signal input to the voice coil. Even in such a case, a portion disposed inside the bobbin section of the magnetic path formation section like the aforementioned circular cylindrical portion  523 F is sized so that it can be disposed in such a manner to not contact the inner peripheral surface of the bobbin section, and a portion disposed outside the bobbin section of the magnetic path formation section like the aforementioned yoke  524  is sized so that it can be disposed in such a manner to not contact the outer peripheral surface of the bobbin section. 
     &lt;Modification 24&gt; 
     The end member (cap  512 ) mounted on the end of the bobbin  511  and suited for connection to the sound board  7  need not necessarily be a flat plate-shaped cap as set forth above. For example, the end member may be in the form of an elongated hollow rod projecting to some extent upward from the distal end of the bobbin  511 . In such a case, the hollow rod has a hole portion  512 G′ formed in a closed distal end surface for passage therethrough of a screw. Thus, the wood screw  61  that is a fixation member can pass through the hollow rod to reach the distal end hole portion  512 G′. 
     [Third Embodiment of the Vibration Device] 
       FIG. 35  is a vertical sectional view of a third embodiment of the vibration device  50 C. The third embodiment of the vibration device  50 C has a mounting-length-adjustable connecting shaft  514 A for mounting the connection member  51  to the sound board  7 , which is different in construction from the shaft  514  provided in the first embodiment of the vibration device  50 . The construction of the third embodiment of the vibration device  50 C for performing its primary function as a vibration device may be similar to that of the first or second embodiment of the vibration device  50  or  50 A. Thus, in the following description and drawings pertaining to the third embodiment, similar elements to the first or second embodiment are indicated by the same reference numerals as used in the first or second embodiment and will not be described here to avoid unnecessary duplication. 
     In  FIG. 35 , a housing formed of non-magnetic material (aluminum, synthetic resin or the like)  517  is joined to the upper end of the bobbin  513  of the voice coil  511 . The housing  517  has upper and lower openings  517   a  and  517   b , and a chuck  518  provided therein. The chuck  518  has a male thread portion  518   a  and a female thread portion  518   b . The chuck  518  has an axial central through-hole for passage therethrough of a shaft  514 A that is an object to be chucked by the chuck  518 . The male thread portion  518   a  is fixed within the housing  517 , and the female thread portion  518   b  is held in meshing engagement with the male thread portion  518   a  in such a manner that the through-hole of the chuck  518  aligns with the upper opening  517   a . As known in the conventional chucks, the male thread portion  518   a  has a plurality of axial cuts, and, in response to tightening by the female thread portion  518   b , the inner through-hole decreases in its diameter to clamp the shaft passed through the through-hole. The lower opening  517   b  of the housing  517  has a size suitably larger than the diameter of the chuck  518  so that the chuck  518  can be put inside the housing  517  during assembly. Further, the lower opening  517   b  is sized to allow a driver  64 , provided for turning the female thread portion  518   b  of the chuck  518 , to enter through the lower opening  517   b . Note that the chuck  518  has a key groove formed, in the lower surface of the female thread portion  518   b , for fitting engagement with a distal end key portion  64   a  of the driver  64 . Thus, the female thread portion  518   b  of the chuck  518  can be turned by the driver  64  with the distal end key portion  64   a  in the key groove. 
     Further, with the chuck  518  in a loosened state, the connecting shaft  514 A can be introduced into the housing  517  through the upper opening  517   a  of the housing  517 . Further, with the chuck  518  in the loosened state, the connecting shaft  514 A can be freely moved; thus, by setting the connecting shaft at a desired length and then tightening the chuck  518 , the connecting shaft  514 A can be fixed with a desired projecting length. Thus, an upper end portion of the shaft  514  is constructed to function as a connecting portion  514 Aa, and this connecting portion  514 Aa is connected to the sound board  7  by an adhesive agent or the like. 
     Like in the second embodiment, the yoke  523  in the third embodiment of the vibration device  50 C has a through-hole portion  523 G′ extending through both of the disk portion  523 E and the circular columnar portion  523 F in the axial direction. The driver  64  is inserted from below upward through the through-hole portion  523 G′ into the vibration device  50 C so that the female thread portion  518   b  of the chuck  518  can be turned by means of the driver  64 . 
     The following describe one example sequence of operations for attaching the third embodiment of the vibration device  50 C to the piano  1 . First, the support section  55  is mounted at a predetermined position in a manner to the aforementioned manner. Then, the connecting shaft  514 A is mounted singly at a predetermined position on the lower surface of the sound board  7 . Namely, the connecting portion  514 Aa is fixedly connected to the sound board  7  by an adhesive agent or the like. Then, the vibration device  50 C is installed on the support section  55  in a manner similar to the aforementioned. At the same time, the lower end of the connecting shaft  514 A is inserted into the chuck  518  through the upper opening  517   a  of the housing  517 . Then, the driver  64  is inserted from below upward into the through-hole portion  523 G′ of the yoke  523  from below, and the distal end key portion  64   a  of the driver  64  is fitted into the key groove and turned to fasten the chuck  518  and thereby fix the connecting shaft  514 A in position. Note that, at that time, the aforementioned fixing jig ( 54 ,  54   q  or the like) may or may not be used. The bobbin  511  can be set at a predetermined reference mounting position (at an ideal neutral position) by being held by the damper  53  (i.e., the distance L 2  from the upper surface  521 A of the top plate  521  to the upper end of the bobbin  511  can be set at the aforementioned ideal distance). Thus, ideal coil positioning can be achieved without the aforementioned fixing jig ( 54 ,  54   q  or the like) being used. Needless to say, the driver  64  is pulled out of the through-hole portion  523 G′ after completion of the tightening of the chuck  518 . As compared to the case where the operations for adjusting the length of the shaft  514  and fastening the shaft  514  by accessing from a lateral side, the aforementioned approach of accessing from below for the tightening operation can be applied advantageously under an environment where accessing from a lateral side is difficult. 
     The third embodiment may be summarized as follows. The connecting shaft  514 A, the housing  517  and the chuck  518  correspond to a connection member that is connected to the bobbin  511  and vibrates in response to vibration of the bobbin  511 . Such a connection member includes the connecting portion  514 Aa (connection end) suited for connection to the sound board  7  of the musical instrument and is adjustable in length. Namely, the connection member includes: the housing  517  (first member) connected to the bobbin  511 ; the connecting shaft  514 A (second member) connected to the housing  517  (first member) in such a manner that it is displaceable relative to the housing  517  (first member); and the chuck  518  (tightening tool) adapted to tighten and fix a connected portion between the first member and the second member. 
     [Fourth Embodiment of the Vibration Device] 
       FIG. 36  is a vertical sectional view of a fourth embodiment of the vibration device  50 D. The fourth embodiment of the vibration device  50 D has a mounting-length-adjustable connecting shaft  514 B for mounting the connection member  51  to the sound board  7 , which is different in construction from the shafts  514  and  514 A provided in the above-described first and third embodiments of the vibration device  50  and  50 D. The fourth embodiment is similar to the third embodiment in that the chuck  519  is used to adjust the length of the shaft  514 B but different from the third embodiment in terms of the construction of the chuck. In the following description and drawings pertaining to the fourth embodiment, similar elements to the first to third embodiments are indicated by the same reference numerals as used in the first to third embodiments and will not be described here to avoid unnecessary duplication. 
     In  FIG. 36 , a cap  512 ′ formed of non-magnetic material (aluminum, synthetic resin or the like) is joined to the upper end of the bobbin  513  of the voice coil  511 . A male thread portion  519   a  of the chuck  519  is joined to the upper surface of the chuck  512 ′. The cap  512 ′ and the male thread portion  519   a  of the chuck  519  may be formed integrally with each other, or formed as separate component parts and then interconnected with each other. A female thread portion  519   b  is held in meshing engagement with the male thread portion  519   a  of the chuck  519 . The chuck  519  has an axial central through-hole for passage therethrough of a shaft  514 B that is an object to be chucked, and this axial central through-hole is in communication with the hole portion of the cap  512 . Thus, the lower end of the shaft  514 B can pass through the axial central through-hole to project downward beyond the lower surface of the cap  512 ′, as necessary. The connecting shaft  514 B can be inserted into the chuck  519  through the upper opening of the chuck  519 . For example, a distal end region of the male thread portion  519   a  has a plurality of axial cuts formed therein and resiliently flares slightly radially outward. As the female thread portion  519   b  is turned to tighten the chuck, the female thread portion  519   b  moves upward to press the distal end region of the male thread portion  519   a  radially inward and thereby reduce the diameter of the axial central through-hole, so that the shaft passed through the axial central through-hole is tightened. 
     With the chuck  519  in the loosened state, the shaft  514 B can be freely moved. Thus, by setting the shaft  514 B at a desired height (length) projecting from the upper surface of the cap  512 ′ and then tightening the chuck  519 , the shaft  514 B can be fixed with a desired projecting height (length). Thus, an upper end portion of the connecting shaft  514 B is constructed to function as a connecting portion  514 Ba, and this connecting portion  514 Ba is connected to the sound board  7  by an adhesive agent or the like. 
     The following describe one example sequence of operations for attaching the fourth embodiment of the vibration device  50 D to the piano  1 . First, the support section  55  is mounted at a predetermined position in a similar manner to the aforementioned. Then, the vibration device  50 D having the connecting shaft  514 B attached thereto with the chuck  519  in the loosened state is installed on the support section  55  in a manner similar to the aforementioned. At that time, the upper end portion  514 Ba of the connecting shaft  514 B is positioned to correspond to a predetermined mounting position on the lower surface of the sound board  7 . Then, the shaft  514 B is moved upward and fixedly connected to the sound board  7  by means of an adhesive agent or the like. Then, the chuck  519  is tightened to fix the connecting shaft  514 B in position. Note that, at that time, the aforementioned fixing jig ( 54 ,  54   q  or the like) may or may not be used. The bobbin  511  can be set at a predetermined reference mounting position (at an ideal neutral position) by being held by the damper  53 . Thus, ideal coil positioning can be achieved without the aforementioned fixing jig ( 54 ,  54   q  or the like) being used. 
     As a modification of the fourth embodiment, the orientation of the chuck  519  may be reversed up and down. Namely, the shaft  514 B having the upper-end connecting portion  514 Ba is formed in a cylindrical shape having an inner through-hole, and the male thread portion  519   a  of the chuck  510  is formed on a lower portion of the cylindrical shaft  514 B in a downward orientation opposite from the orientation shown in  FIG. 36 . Then, a rod is provided to project upward beyond the upper surface of the cap  512 ′, and this rod is inserted through the through-hole of the chuck  519 . In this manner, the upwardly-projecting rod and the shaft  514 B are interconnected via the chuck  519  in such a manner that the shaft  514 B can be adjusted in height. 
     The fourth embodiment may be summarized as follows. The connecting shaft  514 B, the chuck  519  and the cap  512 ′ correspond to a connection member that is connected to the bobbin  511  so as to vibrate in response to vibration of the bobbin  511 . Such a connection member includes the connecting portion (connection end)  514 Ba suited for connection to the sound board  7  of the musical instrument and is adjustable in length. Namely, the connection member includes: the cap  512 ′ and the male thread portion (first member)  519   a  joined to the bobbin  511 ; the connecting shaft (second member)  514 B joined to the cap  512 ′ and the male thread portion (first member)  519   a  in such a manner that it is displaceable relative to the cap  512 ′ and the male thread portion (first member)  519   a : and the chuck (tightening tool)  519  adapted to tighten and fix a connected portion between the first member and the second member. 
     [Fifth Embodiment] 
       FIG. 37  is a schematic side elevational view showing a mechanism for adjusting a height of a fifth embodiment of the vibration device of the present invention. Like each of the above-described embodiments, the fifth embodiment of the vibration device  50 E comprises the vibration member  51 , the magnetic circuit member  52  and the damper  53 , the magnetic circuit member  52  includes the top plate  521 , the magnet  522  and the yoke  523 , and the vibration member  51  includes the bobbin  511  having the voice coil. The cap  512  is joined to the upper end of the bobbin  511 , a shaft  514 C extends upward from the upper surface of the cap  512 , and the upper end of the shaft  514 C is constructed to function as a connecting portion  514 Ca. Let it be assumed that, in the fifth embodiment, the shaft  514 C is fixed in length like the shaft in the above-described second embodiment. Note, however, that the shaft of the length-adjustable type provided in the first, third or fourth embodiment may be employed as the shaft  514 C. Further, like the vibration device described above in relation to  FIG. 9  or the like, the vibration device  50 E is connected to and supported by the support section  55  via the plurality of support rods  551 . The support section  55  is supported in such a manner as to be adjustable in length via a pair of height adjusting plates  71  provided on left and right side surfaces of the support section  55 . The pair of height adjusting plates  71  is fixed to a suitable base section  70  (e.g., the aforementioned vertical strut  9  of the piano, floor or the like). 
     Each of the height adjusting plate  71  has a pair of elongated guide holes  72   a  and  72   b  extending in a vertical (up-down) direction, and each of the side surfaces of the support section  55  has projections  552   a  and  552   b  fittable in the elongated guide holes  72   a  and  72   b  of a corresponding one of the height adjusting plates  71 . An upper edge portion of the height adjusting plate  71  is bent at the right angle or in the horizontal direction to provide an angle portion (or horizontal flange)  71   a . A lower edge portion of the height adjusting plate  71  is also bent at the right angle or in the horizontal direction to provide an angle portion (or horizontal flange)  55   a . An elongated bolt  73  is used to interconnect the upper and lower angle portions  71   a  and  55   a  with a length therebetween adjusted. For this purpose, the upper-edge angle portion  71   a  of the height adjusting plate  71  has a bolt passing hole, and the lower-edge angle portion  55   a  of the height adjusting plate  71  too has a bolt passing hole. A butterfly nut  74  is disposed on the lower surface side of the lower-edge angle portion  55   a  of the support section  55  and screwed on the bolt  73 . Further, a nut  75  is disposed on the upper surface side of the upper-edge angle portion  71   a  of the support section  55  and screwed on the bolt  73 . The support section  55  can be moved downward by loosening the butterfly nut  74  and moved upward by tightening the butterfly nut  74 . 
     According to the fifth embodiment constructed in the above-described manner, the support section  55  can be adjusted in height position as desired. Thus, during assembly, the support section  55  can be raised in position until the distal-end connecting portion  514 Ca of the vibration member  51  of the vibration device  50 E abuts against the reverse face of the sound board  7 , so that the connecting portion  514 Ca is adhesively joined to the sound board  7 ; also, the support section  55  is maintained at that raised height position. Note that the term “height” of the support section  55  does not necessarily mean a height in the vertical direction but means a distance between the support section  55  and the sound board  7  (relative distance between the support section  55  and the sound board  7 ) in a direction from the support section  55  toward the connection end portion  514 Ca (or  516 A or the like) of the vibration device  50 E (or  50  or the like). Therefore, in cases where the instant embodiment is applied to a piano of a type having the sound board standing in the vertical direction, height adjustment of the support section  55  means adjustment of a position, in a horizontal direction toward the sound board, of the support section  55 . 
     [Summary] 
     As described above in relation to each of the embodiments, the present invention can be implemented as a voice coil type actuator, such as the vibration device  50 - 50 E, which imparts vibration to the sound board  7 . According to another aspect, the present invention can be implemented as a keyboard musical instrument, such as the grand piano  1 , or other type of musical instrument provided with a voice coil type actuator, such as the vibration device  50 - 50 E as described above, which imparts vibration to the sound board  7 . Note that an object to which the vibration device  50 - 50 E is to be attached is not limited to an acoustic piano and may be an electronic piano or any other desired musical instrument that can be provided with a sound board, such as a guitar having a sound board, a new type of musical instrument where a speaker having a sound board is sounded in response to an operation of a performance operator. In any case, it just suffices that the vibration device  50 - 50 E be attached to the musical instrument having the sound board, a drive signal corresponding to an operation of the performance operator be output to the vibration device  50 - 50 E and the vibration device  50 - 50 E function as an actuator that drives the sound board in accordance with the drive signal. In these cases, the magnetic circuit member  52  is supported by a member like the support section fixed to the casing of any one of the musical instruments. Rather than being limited to the aforementioned, the present invention can also be implemented as a method for attaching a voice coil type actuator by performing operations as shown in  FIGS. 6 and 24 , and a method for manufacturing a musical instrument provided with a voice coil type actuator. 
     Although not particularly described in detail above, part of the constituent elements or features of any of the above-described various embodiments may be applied to any of the other embodiments wherever possible.