Abstract:
A sound enhancing device for F-hole stringed instruments, banjos, and drums. The device includes at least one cross-shaped element and a timbre square, which may be part of a larger, user-constructed sound emitter. Strung like beads along a fastener, one or more cross-shaped elements and timbre squares are arrayed between a bridge and terminal retainer. In one embodiment, the cross-shaped element and timbre square are juxtaposed, forming a sound emitter which is mounted within an F-hole instrument&#39;s sound chamber; the bridge, positioned above it and astraddle opposing F-hole side edges, collects inaudible sound surface waves and transmits them through the fastener —a knot-free, waxed string under tension—to the sound emitter. There sound waves are amplified by constructive interference, timbre characteristics added, and sound waves transferred into the sound chamber&#39;s air. The latter then increase the sound surface waves at the F-hole&#39;s edges, setting up a positive feedback loop.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is both a continuation in part of application Ser. No. 10/459,961, filed Jun. 12, 2003, now U.S. Pat. No. 6,861,581 and a non-provisional application of the earlier filed provisional application Ser. No. 60/700,104 filed Jul. 19, 2005, and claims the benefit of the priority date of the filing date Jul. 19, 2005, pursuant to U.S.C. Sec. 119(e). 

   FIELD OF INVENTION 
   This present invention relates generally to F-hole guitars, F-hole mandolins, and other stringed instruments having elongated sound openings, as well as to banjos and openable drums, and in particular to devices for enriching and amplifying the output sound of such instruments without the use of electronics. 
   BACKGROUND OF THE INVENTION 
   The volume, sound duration and richness of tone needed to create beautiful music with today&#39;s acoustic stringed instruments is difficult, at best, to achieve. The problem stems in large part from the fact that few adjustments can be made to change the sound characteristics of these instruments once they have been manufactured. An added handicap for small guitars, mandolins and acoustic-electric guitars is the small size of their sound chambers which tends to hinder the production of musical notes of low frequency. 
   Traditionally, success in making good sounding acoustic guitars, acoustic-electric guitars, mandolins, banjos and drums was largely determined by the quality of the materials used in construction, the quality of skilled craftsmanship in the manufacturing process, and a degree of good fortune as the various parts were brought together and the instrument was tested, primarily after completion. The intricacies of this approach insured that good sounding acoustic instruments made following its techniques would be expensive. 
   Further, tuning guitars and mandolins for optimum performance (defined herein as a state in which they exhibit a noticeable maximum available volume with a noticeably high quality of sound) was left up to the manufacturer. Banjos and drums, while tuneable for optimum performance to a degree, required the expenditure of considerable effort on the part of experienced players. 
   Players have had so little control over the characteristic sound or timbre (hereinafter “timbre”) of their acoustic stringed instruments that musicians often resorted to using several instruments to meet their needs for different sounds. 
   Not until recently has this situation improved significantly and only with respect to round-hole acoustic musical instruments. As described by Geiger in U.S. Pat. No. 6,861,581, a resonating and amplifying device, capable of improving the sound quality and volume of a conventional guitar, includes a cross-shaped resonator which when mounted within the guitar&#39;s sound chamber is cantilevered beneath its sound hole, partially covering it. Holding the device in position is a set of prongs formed in an extended arm of the resonator. In use, opposing upper and under prongs clip the device to the edge of the sound hole which then forms a wedge between them, Unfortunately, the geometry of this device is such that it cannot be readily attached to the edge of elongated sound openings such as are found in F-hole guitars, F-hole mandolins, and the like. Moreover, in placing the resonator on a guitar, one risks harming its body unless the prongs are handled gently. 
   SUMMARY OF INVENTION 
   The object of the present invention is to provide a mechanical device capable of increasing the volume, sound duration and richness of tone of all musical notes, the device being readily attachable to and removable from a wide variety of conventional musical instruments including those with F-holes and similar elongated sound openings, as well as banjos, drums and the like. 
   A further object is to provide such a mechanical device which the player of a musical instrument can use to easily change temporarily and significantly its volume, sound duration, and timbre. 
   A still further object is to provide such a mechanical device which a player can easily use to “tune” an acoustic instrument for optimum performance. 
   A still further object is to provide such a mechanical device which not only can be easily attached to and removed from a musical instrument without damaging it but also can be fabricated by unskilled craftsmen from common inexpensive materials, making good musical sound available from less expensive instruments and therefore available to more people. 
   In accordance with the present invention, there is provided an improved sound enhancing device which includes a sound emitter, an elongated fastener, and a bridge. The sound emitter comprises a stacked array having at least two nested cross-shaped elements and a timbre square, each of which is small and thin in shape and defines a central hole sized for slideably receiving the fastener. Aligned with the cross-shaped elements and the timbre square along the elongated fastener, the bridge contacts the body of the musical instrument itself, collecting inaudible sound surface waves thereon and transmitting them through the fastener to the sound emitter. The latter is mounted within the instrument&#39;s sound chamber. 
   The bridge, on the other hand, is mounted outside of the sound chamber whenever the device is used to enhance the performance of F-hole instruments and the like. Preferably formed as a wooden half-ball which has a generally flat bottom and defines a reverse-tapered hole extending perpendicularly thereto, the bridge is sized to straddle the instrument&#39;s elongated sound opening. 
   In use, opposing edges of the sound opening are wedged between the bridge&#39;s flat bottom and the sound emitter. Holding them together in assembled relation is the fastener which, in the preferred embodiment, includes a waxed, knot-free string, a retainer ring, and a tapered pin. The pin fits tightly in the smallest transverse cross-section of the reverse-tapered hole and, when so fitted, does not protrude from the bridge&#39;s flat bottom. The waxed string, which is doubled upon itself except where it contacts the retaining ring, passes through both the reverse-tapered hole and the central hole of each of the cross-shaped elements. Seated in the reverse-tapered hole, the pin is used to hold a length of the doubled waxed string securely against the hole&#39;s upper edge at the top of the half-ball once the string has been pulled tight, drawing the retaining ring and the sound emitter together. 
   In an alternate embodiment of the sound enhancing device which is used to enhance the performance of banjos, openable drums, and the like, the bridge is mounted inside the sound chamber. Compatible with the cylindrical wood rim which typically encloses the sound chamber in such instruments, the bridge is formed as a brass half-donut which has concentric, generally flat bottom edges for contacting the wood rim. Also defined by the half-donut is a reverse-tapered hole with a centerline which extends perpendicularly to the plane in which the concentric bottom edges lie. 
   In use, the concentric bottom edges of the bridge are pressed against the wood rim. The bridge is sized to have sufficient height or standoff to keep portions of the sound emitter which are contiguous thereto free of direct physical contact with the curved wood rim while the sound enhancing device is operating. Holding the bridge and the sound emitter together in assembled relation is the fastener which, in the alternate embodiment, includes a bolt or machine screw with threads which fit the banjo&#39;s (or drum&#39;s) existing “shoe” bracket. The bolt passes through both the reverse-tapered hole of the half-donut and the central hole of each of the cross-shaped elements and the timbre square. When the bolt is tightened by screwing it into the “shoe” bracket, the head of the bolt, which is positioned inwardly of the sound emitter, presses against it, drawing the nested cross-shaped elements, the timbre square, the half-donut, and the cylindrical wood rim together in assembled relation. 
   Common to both embodiments of the improved sound enhancing device is the sound emitter which receives surface waves, including those collected by the bridge, through a fastener slideably held within a central hole in each of the sound emitter&#39;s crossed-shaped elements and timbre squares. Sound waves are also transferred by direct physical contact to the sound emitter whenever one or its crossed-shaped elements or timbre squares touches vibration-active surfaces on the body of the musical instrument or the bridge itself. 
   As confirmed by testing, noticeable amplification of the instrument&#39;s sound results with the use of the improved sound enhancing device. Specifically, the volume was found to increase with every addition, at least up to a quantity of four, of a crossed-shaped element or timbre square to the sound emitter. Importantly, because of high frequency amplification, and the fact that the “pleasantness” of the sound depends upon the presence and high energy level in the first several harmonics, not only could one play the instrument louder but also it sounded better at all volume levels. While amplification was highly noticeable at all levels of playing effort, the sound increase was especially impressive when input energy was moderate to high, such as when the instrument was played vigorously. 
   These test results are consistent with the theory that in the sound emitter, surface sound waves radiate outwardly from the center of each cross-shape element and timbre square toward its outer edges. There, because of the difference in media density between the various materials in the sound emitter—primarily wood and metal—and air, the sound waves are reflected backwardly. In the process, they meet sound waves, with the same or similar frequencies, moving from different directions and set up patterns of constructive interference, causing amplification of the fundamental tones in the sound waves as well as their harmonics (frequency multiples). 
   In the preferred embodiment, each of the crossed shaped elements includes a generally flat central section and four three-sided arms which are formed integrally therewith. Contiguous arms in each cross-shaped element are disposed generally perpendicularly to each other, but only three of the arms have square edges. The remaining arm is preferably trapezoidal in shape. 
   In assembled relation, the generally flat central sections of the nested cross-shaped elements are in direct physical contact; but their respective arms, although they are paired in an orthogonal array, are spaced apart in such a way as to create small diverging air spaces which extend outwardly between the paired arms. Moreover, each of the arms is adjustable in position and, in use, is bent slightly so that its curvature differs substantially from that of the arm with which it is paired in the orthogonal array. 
   Transfer of surface sound waves from the sound emitter to the sound chamber&#39;s air occurs when their small motion in the diverging surfaces of the paired arms, as well as between an arm and a contiguous portion of the timbre square, compresses the air in the smallest spaces between these surfaces. In the case of nested cross-shaped elements, these air spaces range in size from zero where the contiguous center sections touch to approximately ⅛-inch or more at the outer extremities of the paired arms. The air compression creates audible sound in these smallest spaces; and the increasing amount of air space toward the outer edges of the paired arms, or alternately, an arm and a contiguous portion of the timbre square, due to their divergence, cause the sound in air to be amplified. In effect, the orthogonal array of paired arms in the nested cross-members amplifies sound in a manner analogous to that of four open-sided megaphones. Since the four sets of paired arms in the nested cross-shaped elements are disposed perpendicularly and are open on their sides, amplification in air also occurs between these open sides. 
   As found in practice, both the spacing between the paired arms of the nested cross-shaped elements and the arms&#39; curvatures effect the quality and volume of instruments on which an improved sound enhancing device is mounted. When the sound emitter is mounted in a banjo, a player can easily change the spacing between the paired arms and their respective curvatures directly by hand, using only the sense of touch. For F-hole instruments, on the other hand, a simple tool is provided to help the player make these adjustments which are critical for optimizing the instrument&#39;s performance. 
   Not only is the instrument&#39;s timbre changed when sound surface waves move across the timbre square and cross-shaped elements of different materials but also the volume is affected. Preferably, the timbre square and cross-shaped elements included in the sound emitter are selected on the basis of the timbre and volume desired and are changed to meet different purposes. With the improved sound enhancing device, a wide variety of combinations using different materials and shapes (whether timbre squares or cross-shaped elembers) and also varying their order and the number of each in the sound emitter is possible. 
   Moreover, the timbre square and the cross-shaped element disposed contiguous thereto, in combination, comprise means for adjusting the sound duration of an instrument using the improved sound enhancing device. The sound duration is maximized whenever the timbre square is oriented generally diagonally with respect to the square shaped arms of the contiguous cross-shaped element. 
   In an alternate embodiment, provided to facilitate changing timbre in F-hole instruments, both the bridge and at least one cross-shaped element are mounted outside of the sound chamber. Very easily added without removing the sound emitter from the sound chamber, this externally mounted cross-shaped element greatly increases the volume as well as the timbre. Brightness and clarity are also increased if one or more of the cross-shaped element&#39;s arms is positioned over the F-hole. This brightness is further enhanced when a hole, preferably about ¼ inch in diameter is formed in each of the two opposing square-shaped arms of the elements; and these opposing arms are then positioned so that their holes are disposed over the F-hole, 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an outside perspective of a the invention of a sound enhancing device according to the present invention, the device being depicted with its half-ball bridge astraddle the F-hole sound opening of a conventional mandolin, the mandolin being shown for illustrative purposes only and forming no part of the claimed invention; 
       FIG. 2  is close up perspective view of the sound enhancing device according to  FIG. 1  and a fragment of the mandolin, portions of the device which are mounted beneath the F-hole sound opening within the mandolin&#39;s sound chamber, as well as part of the half-ball bridge above it, being shown; 
       FIG. 3  is a exploded perspective view of the sound enhancing device according to  FIG. 1 ; 
       FIG. 4  is a plan view of the cross-shaped element and a timbre square, components which individual players can use in constructing the sound emitter device according to  FIG. 1 , an alignment of its timbre square with the cross-shaped element in which maximum sound duration is achieved being shown; 
       FIG. 5  is an exploded perspective view of the sound enhancing according to  FIG. 1 , portions of the device, as well as a fragment of the mandolin surrounding its F-hole sound opening, being shown in cross-section; 
       FIG. 6  shows schematically various positions along the length of an F-hole sound opening where one can mount the sound-enhancing device according to  FIG. 1 , the best sounding location for a particular musical instrument being selected experimentally by sliding the half-ball bridge along the sound opening; 
       FIG. 7  is a plan view of a tool which can be used to install the sound emitter of the sound enhancing device according to  FIG. 1  within the sound chamber of an instrument having an F-hole opening; 
       FIGS. 8 and 9  are perspective and exploded views, respectively, of an alternate embodiment of the sound enhancing device according to  FIG. 1  which is mountable inside a banjo&#39;s sound chamber, the fragmentary portions of the banjo depicted in  FIGS. 8 and 9  being shown for illustrative purposes only and forming no part of the invention; and 
       FIGS. 10 and 11  are outside and closeup inside perspective views, respectively, of a further alternate embodiment of the sound enhancing device according to  FIG. 1 , the device being depicted with its half-ball bridge and a cross-shaped element contiguous thereto astraddle the F-hole sound opening of a conventional mandolin, the mandolin being shown for illustrative purposes only and forming no part of the claimed invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the drawings, an improved sound enhancing device for use with a stringed instrument  30  having elongated sound openings  41 ,  41 ′ is indicated generally by the reference numeral  10 . The device  10  includes a sound emitter, a bridge  35  and a fastener which, in the first embodiment, is a waxed, knot-free string  20 . 
   Constructed of thin metal and wood strips in a stacked array, the sound emitter comprises at least two nested cross-shaped elements  11 ,  21  and one or more timbre squares  31 , which define central holes  16 ,  17 ,  18 , respectively. Preferably, both the cross-shaped elements  11 ,  21  and the timbre square  31  are fabricated from metal or two-ply veneer wood. 
   Metal timbre squares  31  are typically thin carbon steel, which measures approximately 0.007-inch thick and 1-inch square, and brass squares of the same size but which measure approximately 0.010-inch in thickness. Wood veneer squares are typically made of maple or mahogany or glued combinations of these or similar woods. Cross-shaped elements  11 ,  21  are typically brass pieces of approximately 0.010-inch thickness and two-ply maple or mahogany veneer. Timbre is changed when sound surface waves move across timbre squares  31  and cross-shaped elements  11 ,  21  made of different materials. 
   In operation, the sound emitter is mounted within the instrument&#39;s sound chamber beneath the sound opening  41  ( FIG. 2 ). Aligned with the sound emitter along the string  20 , the bridge  35 , on the other hand, is mounted outside of the sound chamber. 
   Preferably formed as a wooden half-ball which has a generally flat bottom and defines a reverse-tapered hole  19  extending perpendicularly thereto, the bridge  35  is sized to straddle the sound opening  41 . The bridge  35  collects a portion of the sound surface waves which typically move to and travel along F-hole edges. There the inaudible sound surface waves create active vibration centers which add their sound to the air as air with sound leaves the instrument&#39;s sound chamber through sound openings  41 ,  41 ′. Tests have shown that the amount of sound energy around F-hole edges varies considerably. As suggested in  FIG. 6 , the device  10  is designed to facilitate searches, along the length of an F-hole  41 , for the best location to mount the bridge  35 . 
   In use, opposing edges of the sound opening are wedged between the bridge&#39;s flat bottom and the sound emitter. Holding them together in assembled relation is the waxed string  20 , a terminal retaining ring  33 , and a tapered pin  36  ( FIGS. 3 and 5 ). The pin  36  fits tightly in the smallest transverse cross-section of the reverse-tapered hole  19 . So fitted, the pin  36  does not protrude from the bridge&#39;s flat bottom. Doubled upon itself except where it contacts the ring  33 , the waxed string  20 , which preferably measures about 1/32-inch in thickness, passes through both the reverse-tapered hole  19  and the central holes  16 ,  17 ,  18 , as well as through openings in threadless brass nut spacers  32 . The brass fittings  32 ,  33  help to reduce damping effects of the string  20  on the sound emitter. 
   Seated in the reverse-tapered hole  19 , the pin  36  is used to hold a length of the doubled waxed string  20  securely against the hole&#39;s upper edge at the top of the half-ball once the string  20  has been pulled tight, drawing the retaining ring  33  and the sound emitter together. 
   Under tension, the waxed string  20 , an unusual but efficient medium for sound waves, performs three functions in the device  10 : (1) it holds the sound emitter securely against the bottom surface of the instrument&#39;s top; (2) it serves as the medium for sound surface waves between the half-ball and the sound emitter; (3) it provides necessary flexibility so that the sound emitter can be inserted into the elongated sound opening  41 , one component at a time, and allows the sound emitter to be “self-constructed” as the various pieces of the sound emitter are drawn together when the string  20  is pulled taut. 
   The excellent acoustic efficiency of the waxed string  20  is also evident in the noticeable change in timbre which can be achieved by using different materials, such as rosewood, ebony, and plastic, for the pin  36 . Because of the remote location of the pin  36  relative to the sound emitter, this timbre effect, which is dependent upon the presence of high frequency sounds passing over and/or through the pin  36 , most likely enters the instrument&#39;s sound through the string  20  and is then transferred to the sound emitter in the sound chamber. Conversely, sound also travels from the sound emitter to the pin  36  where the half-ball/pin combination detects these sounds and broadcasts them to the instrument&#39;s top. 
   Not only does sound move to and from the sound emitter through the string  20  but also directly through the timbre square  31  where it touches the bottom surface of the instrument&#39;s top and where the cross-shaped elements  11 ,  21  and the timbre square  31  touch each other. 
   Because of the very short distance involved and the fast speed of sound through and over brass and hardwood materials, sound on the string  20  enters all wood and metal components strung thereon at almost the same time and is amplified, throughout surfaces in the sound emitter, where surface sound waves with similar frequencies meet. 
   The sound emitter not only amplifies the sound surface waves in the cross-shaped elements  11 ,  21  and timbre square  31  by constructive interference but also adds timbre characteristics and transfers these waves into the air of the sound chamber. The amplified sound in air in the chamber further increases the sound surface waves at the sound hole edges which are again sent back to the sound emitter for amplification in the manner of positive feedback. Because the device  10  is made to respond efficiently to high frequencies, primarily through the use of thin geometries and very short distances, harmonics are amplified, improving sound quality. The positive feedback effect also increases sound duration unless the latter is reduced by using softer materials in the components, or alternately fewer components, in the sound emitter. 
   Much of the uniqueness of the F-hole embodiment revolves around the ease with which a player can construct and then modify the device  10  to achieve different timbres and volumes. The flexible string  20  allows the sound emitter is be easily inserted, withdrawn and also “self-constructed” in the sound chamber immediately beneath the F-hole opening  41  when the string  20  is pulled tight. 
   Illustrated in  FIG. 7  is a simple tool  42  which can be used to facilitate insertion and removal of the device  10  through the F-hole  41 . The player first constructs the device  10  in loose form by threading desired components including cross-shaped elements  11 ,  21  and timbre square  31  on the string  20 . Since the components are either small or almost flat, they can be placed sideways through the sound opening  41 , one component at a time. 
   When all the components, except for the bridge  30 , which are to be strung on the string  20  are hanging from it in the sound chamber, the player then presses the bridge half-ball down on the instrument&#39;s top and pulls the string taut (but not tight). Because the string  20  is, at this point, not very tight, the half-ball bridge  30  can be slid along the length of the F-hole  41 , while one intermittently picks the strings, to find the most responsive location for the device  10 . Once the best sounding location is found, the pin  36  is temporarily loosened, allowing the string  20  to be pulled very tight; and then the pin  36  is seated to secure it. 
   The tool  42  is next used to align the paired arms in an orthogonal array of the nested cross-shaped members  11 ,  21 . The tool is also used to orient the timbre square  31 , which is mounted contiguous with the bottom surface of the instrument&#39;s top, relative to the cross-shaped elements  11 ,  21  ( FIGS. 2 and 4 ). The relative angle between the timbre square  31  and the cross-shaped elements  11 ,  21  determines the amount of sustained sound duration. As is done to find the best sounding location in the F-hole  41 , one can determine this relative angle by intermittent playing of the instrument  30  between changes in the angle. So that adjustments can be made without loosening the string  20 , the tool  42  includes a vinyl-coated hook for “pulling” a cross-shaped element to a different angle. And an indented portion or notch formed on the hook can be used to “push” either the timbre square  31  or the element  11 ,  21 . 
   In addition, the tool  42  can be utilized to further adjust the sound quality of the instrument  30 , when the sound emitter is mounted in its sound chamber, by bending the paired arms  12 ,  22 :  13 ,  23 :  14 ,  24 :  15 .  25  so as to change the angles A, C, D, B between them, respectively. 
   In the second embodiment, a sound enhancing device  51  is provided for use with a banjo  50  or similar instruments such as openable drums. The device  51  employs a bolt  52  instead of the string  20  to mount both the sound emitter and a bridge  53  within the banjo&#39;s sound chamber in such a way that the bridge physically contacts the instrument&#39;s wood rim. 
   Preferably, one of the original bolts for engaging one of the banjo&#39;s existing “shoes”  55  used to hold a hook  56  (for securing the banjo&#39;s top) is replaced. Made of either steel or brass, the replacement  52  has the same diameter and thread but is slightly greater in length, by about 3/16 inch, than the original bolt. Moreover, central mounting holes  56 ,  57 ,  58  in the cross-shaped elements  11 ′.  21 ′ and timbre square  31 ′ and the opening in the bridge  53 , which is preferably a brass (or alternately, steel) finishing washer, are sized to receive the bolt  52 . 
   The metallic finishing washer  53  serves as a highly efficient circular vibration transfer bridge, giving excellent sound quality, and is used in part to standoff the sound emitter from the inside wall of the banjo  50 . In operation, the bridge washer  53  brings “wooden” sounds from the inside surface of the banjo&#39;s wood rim to the back side of the sound emitter, while the head of the bolt  52  brings “metallic” sounds from the “shoe”  55  to the front side of the sound emitter. 
   In a third embodiment, an improved sound enhancing device  60  is provided to facilitate changing timbre in F-hole instruments  30 . Both the bridge  35  and nested cross-shaped elements  61 ,  71  are mounted outside of the sound chamber. Very easily added without removing the timbre square  31  from the sound chamber, externally mounted cross-shaped elements  61 ,  71  and their paired arms  62 ,  72 ;  63 ,  73 ;  64 ,  74 ;  65 ,  75  greatly increase the volume as well as affecting the timbre. Brightness and clarity are also increased if at least one set of paired arms is positioned over the F-hole. This brightness is further enhanced when a hole, preferably about ¼ inch in diameter, is formed in each of the two opposing square shaped arms  72 ,  74  in the outermost cross-shaped element  71 ; and these opposing arms are then positioned so that their holes are disposed over the F-hole  41  in use. 
   Numerous modifications to and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. Details of the embodiment may be varied without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.