Abstract:
An apparatus and method are disclosed for compensating for string tension acting upon the body of an acoustic instrument. An acoustic instrument incorporating the string tension compensating apparatus is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/431,612, entitled “ACOUSTIC STRING TENSION COMPENSATING METHOD AND APPARATUS,” filed Jan. 11, 2011, which application is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure is generally directed to acoustic instruments, and is more particularly directed to an apparatus and method for compensating for string tension acting upon the instrument body. 
     BACKGROUND 
     In many acoustic instruments, strings are terminated to a bridge that is attached to the body of the acoustic instrument. In the normal design of an acoustic instrument, such as a guitar, the bridge of the instrument feels substantial force from the tension of the strings. This force can be in excess of 150 lbs and the torque on the order of several foot pounds. This places substantial stress on the top sound producing surface of the instrument and requires elaborate bracing of the top in an attempt to balance strength with the freedom to vibrate for sound production. Heavy bracing or thick top surfaces are strong but do not vibrate well. Light bracing and/or thin tops vibrate well but with time can bulge (belly) and lose sound quality, or mechanically fail altogether. 
     There is a need for an effective apparatus and method for compensating for string tension acting upon the body of an acoustic instrument. 
     Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs. 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment there is disclosed a method for compensating for string tension in an acoustic musical instrument comprising a neck, a soundboard, strings and a bridge. The method includes coupling at least one tension coupling between the bridge of the musical instrument and structural members of the musical instrument; and adjusting the at least one tension coupling to counter forces applied to the soundboard by the strings. 
     In another embodiment the disclosure includes a counteracting lever system for an acoustic instrument comprising a neck, a soundboard, strings and a bridge. The counteracting lever system includes a tension coupling attached at a first end to a surface of the acoustic instrument. 
     In yet another embodiment, what is disclosed is an acoustic instrument. The acoustic instrument includes a bridge and a counteracting lever system. The counteracting lever system includes tension couplings attached proximate to the bridge. 
     This invention transfers the forces to more substantial structural members of the guitar that are not a significant part of the sound forming surfaces, e.g., an end block or an area of the end pin. 
     An advantage of the present invention is that lighter braced and/or thinner tops are possible since stresses are transferred from the top to the edges and sides. This gives an instrument that is more responsive to the touch and potentially more volume, dynamic range, and or tonal complexity. 
     Another advantage of the present invention is that heavier gage strings can be used on lighter braced instruments. Heavier strings typically give more volume and fullness to the tone. 
     Another advantage of the present invention is that more or less symmetry of the bracing is possible for more unique voicing (tonal quality as a function of pitch or position that it is played on the fretboard) of an instrument. 
     Another advantage of the present invention is that the voice can be adjusted by the musician or luthier and is reversible. 
     Another advantage of the present invention is that new design and tonal property instruments are now possible since conventional braces that have always been there for structural integrity can be moved or removed all together giving more design freedom based on tone and volume than ever before. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a reverse or internal side of a soundboard of an exemplary acoustic musical instrument. 
         FIG. 2  shows a cross-sectional elevational view of an exemplary instrument. 
         FIG. 3  shows a partial top view of a guitar soundboard in the bridge area. 
         FIG. 4  shows a cross-sectional elevational view of an exemplary instrument with a tension coupling device. 
         FIG. 5  shows a cross-sectional view of an exemplary acoustic instrument having a compound pulley tension system. 
         FIG. 6  shows a partially cut-away top view of an exemplary instrument having a compound pulley tension system. 
         FIG. 7  shows a partially cut-away top view of an exemplary instrument having a pair of eyelet anchors for separate control of tension force and torque compensation. 
         FIG. 8  shows a rear view of a soundboard of another embodiment of an exemplary instrument having a plurality of springs and tensioning eyelets. 
         FIG. 9  shows a partial cross-sectional view of an exemplary instrument having a plurality of eyelet adjustments. 
         FIG. 10  shows a partial cross-sectional view of an exemplary instrument having a tensioning bracket. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , the invention herein relieves stresses from the bridge  12  and/or soundboard  30 . A stress relief device or counteracting lever system  410  ( FIG. 4 ) may be an integral part of the bridge  12  or an area  14  immediately adjacent to bridge  12  on sound board  30  (blue in  FIG. 1 ). In an embodiment, stress relief device  410  ( FIG. 4 ) attaches on one end to a bridge plate  16 , or to area  14  for already built guitars), or to the cross-bracing on the rear of soundboard  30  near bridge  12  or to the underside of the soundboard  30 . The opposite end of stress relief device  410  is attached to internal structural members of instrument  10 , and transfer the forces to more substantial structural members of the guitar  10  that are not a significant part of the sound forming surfaces, e.g., an end block  38 , area of end pin  42 , backboard  44  and internal backboard bracing  46 . 
     Referring to  FIGS. 2 and 3 , it can be seen that the strings  22  generate a tension that is pulling toward the neck  24 , which acts to pull bridge  12  towards the neck and the top of the guitar  10 . The bracing  18  must be strong enough to resist the applied string tension. In addition strings  22  create a torque that causes bridge  12  to be twisted in a counterclockwise direction. 
     Even new guitars will show some of the phenomenon discussed above, but significant problems can develop due to the torque and tension on the bridge as time passes. Referring to  FIG. 3 , the top surface  28  of soundboard  30  may become deformed, in particular in the regions  26 ,  32  above and below bridge  12 . Top surface region  26 , located between the sound hole  34  and bridge  12 , may become concave in region  26  due to torque applied to bridge  12  by strings  22 . On the opposite side of bridge  12  opposite top surface region  26 , the top surface region  32  may become convex, or belly up to form a hump, due to torque applied to bridge  12  by strings  22 . 
     In addition to the potential structural problems occurring with time, the volume, tonal characteristics, playability, and other factors associated with musical quality, can degrade. 
     The string generated forces may be transferred to the outer, stronger edges of the guitar and/or to the end block, via more substantial structural member. This is accomplished by use a counteracting lever system, pulleys, and/or springs. Ideally the spring tension could be adjusted by the luthier as well as the musician. 
       FIG. 4  shows an embodiment of an acoustic instrument  400  including a tension coupling device  410  according to the invention. As can be seen in  FIG. 4 , acoustic tension coupling device  410  is attached to the inner or bottom surface  420  of soundboard  430 . The acoustic tension coupling device  410  allows the torque and the tension of strings  22  on bridge  12  to be adjusted. In another embodiment, acoustic tension coupling device  410  may be attached to the outside surface of soundboard  430 . In yet another embodiment, strings  22  may be terminally attached to bridge  12 , the outside surface of the soundboard, the inside surface of the soundboard, and any combination thereof. 
     Acoustic tension coupling device  410  includes an elastic member  412  and an adjustment device  414 . In another embodiment, one or more acoustic tension coupling devices  410  may be used on guitar  400 . In this embodiment, the elastic member  412  may be a wire spring. In another embodiment, the elastic member  412  may be an elastic band, spring, counteracting lever system, pulley, or combinations thereof, or any other device, similar to a spring, which retracts to its initial length after a force stretches the device to an elongated length. In another embodiment, one or more elastic members may be used. In another embodiment, one or more acoustic tension coupling devices may be used. Additionally, in this embodiment, the adjustment device  414  is an adjustable screw. In another embodiment, the adjustment device  414  may be any device capable of adjusting the length of the elastic member  412 . In another embodiment, one or more adjustment devices  414  may be used. 
     Referring next to  FIG. 5  and  FIG. 6 , an exemplary embodiment of acoustic instrument  400  includes a compound pulley system  50 . Pulley system  50  includes a pulley wheel  52  connected by a bracket  54  to adjustment device  414  on end block  38 . A tensioning line  56  is attached at an eyelet anchor  58  at one end. Tensioning line  56  is threaded around pulley wheel  52  and terminated at the opposite end to side wall  58  adjacent the heel  60 . In an alternate embodiment the termination points of the tensioning  56  line may be at any point along the sidewall  58 , e.g., points that are off-center of the guitar neck. Pulley tension may be adjusted at eyelet anchor  58  or tension adjustment device  414 . It should be noted that while the eyelet is used as a termination point at bridge  12 , any suitable fastener for terminating line  56  may be substituted for the eyelet within the scope of the disclosure. Similarly, line  56  may be any suitable line material. Non-limiting examples include wire, rope, wire rope, cord, belt, chain, rubber, or woven fabric which is capable of withstanding the tension forces and torques applied to the acoustic instrument  400 . In addition, additional pulleys may be employed in multiple-pulley arrangements to increase the force applied by line  56  to bridge  12  and sound board  430 , as will be appreciated by those skilled in the art. 
       FIG. 7  shows a partial cut-away view of another embodiment of acoustic instrument  400  including a pair of eyelet anchors  58 ,  59 , attached to tension coupling device  410 . The double anchor variable tension coupling device  410  allows separate control of tension force and torque compensation. Eyelet anchor  58  applies torque compensation independently of string tension compensation which is provided by eyelet anchor  59 . 
       FIG. 8  shows a bottom plan view of soundboard  430  of another embodiment of an exemplary acoustic instrument having a plurality of springs  410  and tensioning eyelet anchors  58 ,  59 . An eyelet anchor  58  is disposed adjacent bridge  12  or bridge area  14  at opposite ends of bridge  12 . Springs  410  are attached between eyelet anchors  58  at one end and at a common eyelet anchor  59  adjacent end block  38 . Eyelet anchors  58  apply torque compensation that is distributed to either end of bridge  12 , and separately, string tension compensation is provided by eyelet anchor  59 . 
       FIG. 9  shows a partial cross-sectional view of an exemplary instrument having a plurality of eyelets  62  in eyelet anchor  58 . Torque compensation on bridge  12  may be increased or decreased by changing the eyelet  62  to which spring or springs  410  are attached. The opposite end of the spring or springs  410  are attached to adjustment device  414  on end block  38 , as described above with respect to  FIGS. 5 and 6 . 
       FIG. 10  shows a partial cross-sectional view of an exemplary instrument having a tensioning bracket  64  fastened to bridge  12  or area  14  beneath soundboard  430 . Bracket  64  may include one or more eyelets  62  for varying torque applied to bridge  12 , as described above with respect to  FIG. 9 . Bracket  64  provides an offset clearance on the underside of soundboard  430 , to allow spring  410  and eyelet anchors  58  sufficient clearance below structural bracing  18  to avoid interference with the bracing  18 . Bracket  64  may be applied to any or all of the disclosed embodiments to provide necessary clearance for tension coupling device  410  and associated elements to function. Bracket  64  may be adapted in different shapes for specific configurations of soundboard bracing and other structure of the acoustic instrument  400 , which may vary from one instrument to another as will be appreciated by those skilled in the art. 
     It should be noted that a fixed tension coupling may be employed based upon the teachings in the above disclosure, using the method and apparatus. It would be appreciated by one skilled in the art to determine the appropriate ratio of arm lengths and to arrive at the disclosed invention with an adjustable one and provide a fixed, non-adjustable tension coupling on an acoustic instrument, within the scope of the appended claims. 
     It is important to note that the construction and arrangement of the acoustic tension coupling device as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. 
     While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.