Abstract:
A stringed musical instrument including a soundbox. The soundbox has a back, a side adjoining the back to define a hollow interior, a soundboard covering the hollow interior, and a soundboard support structure including a plurality of kerfing members for securing the soundboard on the side opposite the back to cover the hollow interior and a plurality of bracing members for reinforcing the soundboard. The soundboard support structure includes a plurality of adjoining members selected from the group consisting of the plurality of kerfing members and the plurality of bracing members. The plurality of adjoining members are integrally formed as a single piece of polyurethane containing a plurality of half inch glass fibres.

Description:
FIELD OF THE INVENTION 
     The invention relates in general to stringed musical instruments, and more particularly to an acoustic support structure for stringed musical instruments. 
     BACKGROUND OF THE INVENTION 
     The manufacture of wooden musical instruments by conventional methods is both expensive and time-consuming. Typically, wooden musical instruments are made of many different components which must be first manufactured and then assembled by skilled workers, thereby increasing manufacturing expense. 
     Prior art stringed musical instruments have been devised to address these problems. For example, U.S. Pat. No. 5,396,823 (Hoshino) discloses a guitar that is made largely of plastic. A typical guitar would include a soundbox, and a neck extending therefrom to a head. The soundbox includes a wooden side, an adjoining wooden back portion, and a wooden soundboard on top of the side opposite to the back portion. In Hoshino, the side and back portion are integrally formed of plastic as a single piece. This considerably reduces manufacturing time and expense. However, the resulting guitar may suffer in terms of both its appearance and acoustic properties. 
     Accordingly, a stringed musical instrument that retains the desirable acoustic characteristics resulting from a wooden construction, but is less expensive and time-consuming to manufacture, is desirable. 
     SUMMARY OF THE INVENTION 
     An object of one aspect of the present invention is to provide an improved stringed musical instrument. 
     In accordance with this aspect of the present invention, there is provided a stringed musical instrument comprising a soundbox. The soundbox has a back, a side adjoining the back to define a hollow interior, a soundboard covering the hollow interior, and a soundboard support structure including a plurality of kerfing members for securing the soundboard on the side opposite the back to cover the hollow interior, and a plurality of bracing members for reinforcing the soundboard. The soundboard support structure includes a plurality of adjoining members selected from the group consisting of the plurality of kerfing members and the plurality of bracing members. The plurality of adjoining members are integrally formed as a single piece of hardenable plastic material. 
     In accordance with another aspect of the present invention, there is provided an improved method of manufacturing a stringed musical instrument having a sound box. The soundbox has a back, a side adjoining the back to define a hollow interior, and a soundboard covering the hollow interior. The method comprises forming a soundboard support structure for supporting the soundboard on the soundbox. The soundboard support structure includes a plurality of kerfing members for securing the soundboard on the side opposite the back to cover the hollow interior, a plurality of bracing members for reinforcing the soundboard, and a plurality of adjoining members selected from the group consisting of the plurality of kerfing members and the plurality of bracing members, the plurality of adjoining members being formed as a single piece of a hardenable plastic material. The method further comprises the steps of shaping the back, the side and the soundboard of the soundbox to substantially conform to a dimension of the single piece of a hardenable plastic material, securing the soundboard on the side using the soundboard support structure, and securing the back on the side opposite the soundboard. 
     Preferably, the hardenable plastic material is a thermoplastic polymer. Preferably, this thermoplastic polymer is polyurethane containing a plurality of half inch glass fibres. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of the preferred embodiments is provided herein below with reference to the following drawings, in which: 
     FIG. 1, in a front view, illustrates a guitar according to the prior art; 
     FIG. 2 is a side view of the guitar of FIG. 1; 
     FIG. 3, in an exploded perspective view, illustrates the soundboard support structure under the soundboard of the guitar of FIG. 1; 
     FIG. 4, in an exploded perspective view, illustrates the back support structure under the back of the guitar of FIG. 1; 
     FIG. 5, in a disassembled exploded perspective view, illustrates the soundboard support structure of FIG. 3; 
     FIG. 6, in an exploded clam shell view, illustrates an acoustic support structure according to a preferred embodiment of the present invention; 
     FIG. 7, in an enlarged sectional view, illustrates a side of a soundbox of a guitar incorporating an acoustic support structure in accordance with the present invention; 
     FIG. 8, in an exploded clam shell view, illustrates an acoustic support structure according to a second preferred embodiment of the present invention; and, 
     FIG. 9, in an exploded clam shell view, illustrates an acoustic support structure according to a third preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is illustrated in a front view, a guitar  20  in accordance with the prior art. The guitar  20  includes a head  24  that is connected to a soundbox  28  by a neck  22 . The soundbox  28  includes a sound hole  34  in a soundboard  32 . Strings  26  extend from the head  24  of the guitar  20  along the neck  22  across the sound hole  34  and partly along the soundboard  32  to a bridge  36  attached to the soundboard  32 . Referring to FIG. 2, the guitar of FIG. 1 is shown in a side view. As shown in FIG. 2, the guitar  20  further includes a back  38  and a side  30  of the soundbox  28 . 
     The tone of the guitar  20  depends mainly on the vibration of the soundboard  32 , although the side  30  and the back  38  also help to determine the tone. Generally speaking, the more freely the soundboard  32  is able to vibrate, the better the tone of the guitar  20 . The soundboard  32  acts analogously to a speaker in a stereo—the more the soundboard  32  moves, the louder and better the tone. Typically, the soundboard  32 , back  38  and side  30  are made of wood; however, these components may also be made of graphite or other suitable material. 
     The guitar  20  must also, however, be strong enough to resist the compressive force provided by the tension in the string  26 . While the neck  22  and head  24  are typically well able to withstand the compressive stress exerted by the tension in the strings  26 , it may be otherwise with the soundboard  32 . Precisely because the soundboard  32  should be able to vibrate as freely as possible, the soundboard  32  must be quite thin. However, a thin soundboard is likely to buckle as a consequence of the compressive stress exerted on the soundboard by the tension in the strings  26 . 
     In order to address this problem traditional guitars have relied on a soundboard and back support structure. A support structure according to the prior art is shown in the exploded perspective views of FIGS. 3,  4  and  5 . FIG. 3, in an exploded perspective view, illustrates soundboard braces that extend across the soundboard  32 , inside the soundbox  38 , of the guitar  20  in order to strengthen the soundboard  32 . The outline of the soundboard  32 , shown in dotted line, has been exploded up from the bracing, leaving a dotted line to mark its original position around kerfing  50 . 
     The kerfing  50  increases the gluing surface available to attach the soundboard  32  to the side  30 . This is necessary as the thickness of the soundboard  32 , back  38  and the side  30  is typically only about ⅛ of an inch—not enough to securely attach two pieces of wood at a right angle. The kerfing  50 , is about ½ inch in height, and about ¼ inch wide, and is attached to the side  30  and soundboard  32  at their juncture, as well as to the side  30  and back  38  at their juncture, in order to increase the available gluing space. The bridge  36  of the guitar  120  requires additional reinforcement due to the tension in the strings  26 . Accordingly, the soundboard  32  is reinforced underneath the bridge  36  by a bridge plate  52 . 
     FIG. 4 in an exploded perspective view, illustrates back braces  58  that extend laterally across the back  38  of the guitar and back strips  60  that extend longitudinally along the back  38  of the guitar in order to strengthen the back  38 . The outline of the back  38 , shown in dotted line, has been exploded up from the bracing, leaving a dotted line to mark its original position around kerfing  50 . 
     Soundboard  32  is typically made of a different species of wood then side  30  (back  38  may also be made of a different species of wood then side  30 ). This difference arises from the different primary functions that the soundboard  32  and the side  30  perform. Specifically, soundboard  32  must be able to vibrate in order to satisfy its acoustic function, while side  30  must be relatively rigid in order to perform its structural function. Accordingly, there will be a transition between these two species of wood where the side  30  meets the soundboard  32 . At this juncture, a channel is routed into the side  30  and soundboard  32 . Then, several binding pieces  54  are typically inserted into the channels where the side  30  meets the soundboard  32  in order to mask this transition. If the back  38  is also made of a different species of wood from the side  30 , then a channel may be similarly routed into the side  30  and the back  38  at their juncture, and several binding pieces  54  inserted in order to mask this transition. 
     As of these parts of the support structure are individually machined and installed during the manufacture of the guitar. Specifically, kerfing  50  which is typically made up to 12 pieces, is glued around the circumference of the side  30  in order to secure the soundboard  32  and back  38  to the side  30 . Once the soundboard  32  and back  38  are attached to the side  30 , there is a noticeable seam where the two pieces of wood—usually of different species—meet. In order to cover the seam to make the instrument more cosmetically pleasing, a channel is routed into the soundboard  32  and side  30  where they meet, as well as where the back  38  and side  30  meet. Then, plastic binding  54  is glued into the channel in order to cover up the seam. 
     This support structure typically requires 36 or more pieces including 12 pieces of cedar kerfing (this number may vary depending of the length of each piece of kerfing), up to 13 spruce soundboard braces  56 , up to four space back braces  58 , up to four back strip components  60 , up to four pieces of plastic binding  54  and a bridge plate  52 . To assemble all of these pieces into a guitar will require skilled labour and will take a considerable amount of time. 
     Referring to FIG. 5, there is illustrated in an exploded perspective view, illustrates the soundboard braces  56  prior to assembly. The soundboard braces are formed to have recesses that engages the recesses in other soundboard braces  56  to secure the braces  56  together. 
     Referring to FIG. 6, there is illustrated in an exploded clam shell view, an acoustic support structure according to a preferred embodiment of the present invention. The acoustic support structure comprises a soundboard support structure  130  and a back support structure  150 . The soundboard outline is shown in dotted lines and is exploded upwards from the soundboard support structure  130 . The outline of the back is also shown in dotted lines and is exploded downward from the back support structure  150 . The sides of a soundbox of a guitar embodying the invention are shown in dotted outline extending upwardly from the back support structure  150 . 
     The back support structure  150  of FIG. 6 includes a back binding portion  152 , a back kerfing portion  154 , a back bracing portion  158  and a back strip portion  160 . The entire back support structure  150  is formed from plastic as a single piece which is glued to the side of the guitar within the hollow interior to reinforce the back of the guitar. 
     The soundboard support structure  130  of FIG. 6 includes a soundboard kerfing portion  138 , a bridge plate portion  132 , a soundboard binding portion  134 , and a soundboard bracing portion  136 . However, all of these portions are formed from plastic as a single piece. The soundboard kerfing portion  138  provides an extended gluing surface for fastening the soundboard to the sides of the soundbox of the guitar. The bridge plate portion  132  reinforces the bridge of the guitar. The soundboard binding portion  134  masks the seam where the soundboard meets the sides of the guitar and the soundboard bracing portion  136  reinforces the soundboard of the guitar. 
     As the soundboard must be free to vibrate, but must also be sufficiently reinforced by the soundboard support structure  130  to resist the compressive stress of the strings, the material that the soundboard support structure  130  is made of must be carefully selected. Specifically, as soundboard bracing components have traditionally been made of spruce, the plastic material selected should preferably be similar to spruce, at least in terms of its acoustic properties, in order to mimic guitars made in the traditional way. Important features in selecting the plastic include the following: 
     1. The ratio of the plastic&#39;s modulus of elasticity to its density should resemble that of spruce. 
     2. The plastic should provide good adhesion using glue. 
     3. The plastic should be aesthetically attractive, as well as lightweight and is resistant. 
     4. The plastic should be injection moldable. 
     5. The plastic should have a low coefficient of thermal expansion. 
     6. The plastic, should, other things being equal, be inexpensive. 
     7. The plastic should have a tangent delta value of approximately 0.0256 at a frequency of 100 hertz—approximately the tangent delta value of spruce. 
     Preferably, the acoustic support structure is made from a thermoplastic polymer such as thermoplastic polyurethane containing half inch glass fibers, which suitably mimics the acoustic properties of spruce, while also being comparatively inexpensive. 
     FIG. 7, in a sectional view, illustrates the side of a soundbox of a guitar incorporating the acoustic support structure of FIG.  6 . The side is shown at its junctures with both the soundboard and the back of the guitar. Specifically, a soundboard  112  and a side  110  are secured to each other by the soundboard kerfing portion  138  and a soundboard binding portion  134  of the soundboard support structure  130 . Similarly, the side  110  and a back  114  of the guitar are joined by the back kerfing portion  154  and the back binding portion  152  of the back support structure  150 . 
     Using the acoustic support structure of the present invention, a guitar can be assembled in a fraction of the time required to assemble conventional guitars. Further, the resulting guitar will not differ substantially either in appearance or acoustic properties from guitars manufactured in accordance with conventional techniques. Using the acoustic support structure of the present invention also reduces the skill level required of the workers in assembling the guitar. 
     Prior to assembly, the soundboard support structure  130  and the back support structure are formed by injection molding. The side portions, soundboard and back portions of the guitar are then cut for assembly. Unlike conventional guitar manufacture, where the support structure can be modified slightly to accommodate discrepancies in the dimensions of the soundboard, side portions and back portions of a guitar, in the assembly of a guitar according to the present invention, the soundboard, side portions and back portions should be cut to substantially the same measurement as the acoustic support structure. 
     Referring to FIG. 8, there is illustrated in an exploded clam shell view, an acoustic support structure according to a second preferred embodiment of the invention. The acoustic support structure comprises a soundboard support structure  130 ′ and a back support structure  150 ′. The soundboard outline is shown in dotted lines and is exploded upwards from the soundboard support structure  130 ′. The outline of the back is also shown in dotted lines and is exploded downwards from the back support structure  150 ′. The sides of a soundbox of a guitar embodying the invention are shown in dotted outline extending upwardly from the back support structure  150 ′. 
     The soundboard support structure  130 ′ of FIG. 8 includes a soundboard bracing portion  136 ′ and a bridge plate portion  132 ′, but does not include a kerfing portion or binding portion. Instead, the guitar includes a kerfing portion  50 ′ and a binding portion  54 ′. The soundboard bracing portion  136 ′ and bridge plate portion  132 ′ are formed from plastic as a single piece which is glued to the kerfing portion  50 ′ underneath the soundboard to reinforce the soundboard. 
     The back support structure  150 ′ of FIG. 8 includes a back bracing portion  158 ′ and a back strip portion  160 ′, but does not include a kerfing portion or binding portion. The back bracing portion  158 ′ and back strip portion  160 ′ are formed from plastic as a single piece which is glued to the kerfing portion  50 ′ underneath the back to reinforce the back. 
     Referring to FIG. 9, there is illustrated in an exploded clam shell view, an acoustic support structure according to a third preferred embodiment of the invention. The acoustic support structure comprises a soundboard support structure  130 ″ and a back support structure  150 ″. The soundboard outline is shown in dotted lines and is exploded upwards from the soundboard support structure  130 ″. The outline of the back is also shown in dotted lines and is exploded downwards from the back support structure  150 ″. The sides of a soundbox of a guitar embodying the invention are shown in dotted outline extending upwardly from the back support structure  150 ″. 
     The soundboard support structure  130 ″ of FIG. 9 includes a soundboard kerfing portion  138 ″ and a soundboard binding portion  134 ″, but does not include a soundboard bracing portion or a bridge plate portion. The soundboard kerfing portion  138 ″ and soundboard binding portion  134 ″ are formed from plastic as a single piece which is glued to the side of the guitar underneath the soundboard to reinforce the soundboard. The soundboard kerfing portion  138 ″ includes recesses  160  spaced to receive the ends of soundboard braces that stretch across the soundbox underneath the soundboard. 
     The back support structure  150 ″ of FIG. 9 includes a back kerfing portion  154 ″ and a back binding portion  152 ″, but does not include a back bracing portion or a bridge plate portion. The back kerfing portion  154 ″ and back binding portion  152 ″ are formed from plastic as a single piece which is glued to the side of the guitar underneath the back to reinforce the back. The back kerfing portion  154 ″ includes recesses  160  spaced to receive the ends of back braces that stretch across the soundbox underneath the back. 
     Other variations and modifications are possible. In particular, while an acoustic support structure for a guitar has been described above, such an acoustic support structure could readily be modified for incorporation in other wooden musical instruments. Accordingly, all such modifications or variations are believed to be within the scope of the invention as defined by the claims appended hereto.