Patent Abstract:
An optimally coupled stringed musical instrument bridge having an individual bridge assembly supporting and retaining each string. Each assembly comprises an action (height) and intonation (length) adjustable string support assembly and string retention assembly integrally incorporated into the instrument body. The bridge minimizes acoustic energy lost to friction, thereby increasing sustain, minimizes fundamental or harmonic interaction between strings, and maximizes acoustic energy transmitted to the instrument body, thereby allowing the natural instrument resonances to emanate. The bridge and its attributes are especially suited for use with bass guitars.

Full Description:
BACKGROUND OF THE INVENTION 
     The art of the present invention relates to musical instrument bridges in general and more particularly to a musical instrument bridge which efficiently transmits string energy into an instrument body yet maximally isolates individual string energy from other strings on the instrument. 
     Conventional stringed musical instruments such as guitars have one or more strings affixed or mounted along the length of the instrument. Said strings typically pass over a nut distal the musician and are fixed and tensioned by a tensioning adjustment, tuner, or tuning pegs at a first end. At a second end, said strings pass over a bridge and are anchored to a bridge plate or the instrument body itself. The vibrating length of the string is between said nut and bridge with said bridge typically having parallel adjustment with the string axis in order to shorten or lengthen said vibrating length. Vibrating length adjustment is necessary in order to achieve perfect intonation. That is for the western tonal system, an octave (i.e. twice the fundamental vibrating frequency) represents 12 half steps or logarithmic chromatic frequency divisions between notes of equivalent type. (e.g. A to A, C to C, etc.) Especially for fretted instruments such as a guitar, depression of a string located at the 12 th  fret position away from the nut must produce a perfect octave relative to an open string. This intonation adjustment is only achievable if the vibrating length is adjustable since intonation is dependent on string mass and elastic properties. 
     For playability ease and optimization, it is desirable to minimize the musician imposed force between a string and the fretboard or neck in order to create a desired note. This is typically known as an easy “action” and means that the musician minimizes his or her effort during play. Unfortunately, too easy of an action, i.e. a string positioned very close to the fretboard or neck, creates a “buzz” or nonlinear resonance. Conventional stringed musical instruments thereby require adjustment of the string height relative to the neck or fretboard. Since said nut is usually affixed to the instrument, optimal string height is typically achieved by adjusting the bridge height. 
     Prior art bridges often provide bridge height adjustment via one or more semi-pointed setscrews threaded substantially perpendicularly through a saddle and seating or bearing upon a metal base plate attached with the instrument body. This prior art configuration transmits string vibration into the instrument body via the tip of said setscrews. Unfortunately, the acoustic impedance mismatch between said setscrew point and said plate and the frictional movement between the aforesaid fails to achieve high quality string tone and sustain. That is, without a solid connection between a string and the instrument body, the string energy attenuates rapidly and does not readily transmit into the body. The resulting poor tonal quality and sustain is especially noticeable for low frequency notes such as found in bass guitars. This is especially true for a bass guitar which often relies upon body and neck resonance for high quality note representation. 
     The aforesaid prior art bridge systems utilize said base plate mounted via screws to the body of the instrument without an integral attachment there between. Upon this base plate are mounted said bridge saddles that are aligned with and support each string. Unfortunately, the prior art often retains the string via this plate whereby string force tends to pull said plate away from the instrument body. This force further limits the energy transmitted to the instrument body, especially when a minute gap forms there between. That is, the string force prevents a solid connection between the string and instrument body. Variations of the prior art mounting methods are shown and described in U.S. Pat. No. 4,208,941 entitled Adjustable Bridge Saddle by Wechter with issue date of Jun. 24, 1980, U.S. Pat. No. 5,285,710 entitled Adjustable Bridge for a Stringed Musical Instrument by Chapman with issue date of Feb. 15, 1994, and U.S. Pat. No. 5,295,427 entitled Bridge for String Instruments by Johnsen with issue date of Mar. 22, 1994. 
     Said prior art bridge systems also generate undesirable fundamental or harmonic interaction between the strings on a multi string instrument. Since the bridge comprises a continuous metallic base plate of different acoustic impedance than the wood, polymer, or composite material of the body, acoustic energy is reflected from the interface and retained within said bridge. Since the metallic base plate structure is not highly attenuating, said energy is transmitted to other strings retained by said base plate and induces unwanted vibration thereon. 
     The present art overcomes the prior art limitations with a uniquely constructed and body attached bridge apparatus which minimizes string energy loss and maximizes acoustic energy transmission into the instrument body. Unlike the prior art, each bridge piece of the present art is a solid construction which is secured to the instrument body and thereby maximizes tonal purity and sustain and minimizes harmonic interaction between the strings. 
     The present art not only provides the aforesaid benefits via a string support assembly but further utilizes a unique string retention assembly whereby acoustic separation and body transmission is assured. That is, the string retention assembly of the present art is integral with and internal to the instrument body. This arrangement provides an acoustic energy feed directly into the body of the instrument for any energy transmitted past the string support assembly via the strings. 
     Accordingly, an object of the present invention is to provide an optimally coupled string instrument bridge and method of manufacture which maximizes acoustic energy transmission into the body of the instrument. 
     Another object of the invention is to provide an optimally coupled string instrument bridge and method of manufacture which maximally isolates fundamental and harmonic vibratory interaction between strings on the instrument. 
     A further object of the present invention is to provide an optimally coupled string instrument bridge and method of manufacture having strings secured to the instrument body and not the bridge whereby said bridge is not forcibly pulled away from said body. 
     A still further object of the invention is to provide an optimally coupled string instrument bridge and method of manufacture which provides all of the length and height adjustment features of a conventional bridge without the undesirable coupling and transmission characteristics. 
     A yet further object of the invention is to provide an optimally coupled string instrument bridge and method of manufacture which minimizes the acoustic impedance mismatch between the bridge assembly and the instrument body. 
     SUMMARY OF THE INVENTION 
     To accomplish the foregoing and other objects of this invention there is provided an optimally coupled string instrument bridge and method of manufacture for obtaining maximum energy transmission, sustain, and tonal quality without string harmonic interaction. The apparatus and method is useful with stringed instruments and more particularly with guitars, especially bass guitars. 
     The apparatus is provided as a bridge comprised of individual assemblies for each string of the instrument. Each individual assembly comprises a string support assembly and a string retention assembly. For a preferred embodiment, each string support assembly comprises an internally threaded base sleeve mounted into the instrument body, a bridge piece capable of adjustable retention within said threaded base sleeve, and a saddle piece within said bridge piece onto which a string is accepted within a groove. Within the preferred embodiment, each string retention assembly comprises an upper guide tube, a retention ferrule into which a string ball end or eyelet seats, and a lower guide tube, all of which are mounted within the instrument body rearward of the support assembly. 
     Each string support assembly anchors and mates intimately with the instrument body via the base sleeve at an optimal intonation site. Each base sleeve has a substantial cylindrical surface area contacting with and preferably bonded within said body. This large contact area assures maximum transmission of acoustic energy into the instrument body. Each string retention assembly is also bonded or pressed into said body whereby a string is held by the body and not the support assembly. The combination of the aforesaid efficiently transmits vibratory energy into the body of the instrument while also isolating vibrations or energy coupling between adjacent strings. 
     The threaded mate between the bridge piece and base sleeve further provides the desired string height adjustment via rotation of said bridge piece. Movement of the saddle piece within a channel within the bridge piece further allows intonation adjustment. The aforesaid adjustments are typically performed without tension on the supported string. That is, the strings are removed or partially removed. 
     The art of the present invention may be manufactured from a plurality of materials including but not limited to brass or copper materials, steels, titanium, aluminum, (and alloys thereof), composites, polymers, woods, or ceramics. In the preferred embodiment, said bridge assemblies are each manufactured from brass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Numerous other objects, features and advantages of the invention should now become apparent upon a reading of the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front plan view of an optimally coupled string instrument bridge mounted with a bass guitar and showing the complete guitar for clarity of placement. 
         FIG. 2  is an exploded front face plan view of an optimally coupled string instrument bridge also mounted with a bass guitar. 
         FIG. 3  is a perspective view of a preferred optimally coupled string instrument bridge mounted with a body portion of a four string bass guitar. 
         FIG. 4  is a cross section view taken along line  4 - 4  of  FIG. 2 . 
         FIG. 5  is a top plan view of an optimally coupled string instrument bridge mounted with a stringed instrument. 
         FIG. 6  is an assembly view of a string support assembly. 
         FIG. 7  is an assembly view of a string retention assembly. 
         FIG. 8  is a top plan view of an alternative embodiment showing the string support assembly canted rearward or towards the body rear portion. 
         FIG. 9  is a cross section view of an alternative embodiment bridge piece taken along the same line as the cross sectional bridge piece of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, there is shown in  FIGS. 1-7  a preferred embodiment and in  FIGS. 8 &amp; 9  an alternative embodiment of an optimally coupled string instrument bridge  10 . The bridge  10  provides height and intonation adjustments and also provides better coupling of the string  22  vibration into the instrument body  14 . The apparatus further provides superior acoustic isolation between the strings  22  on the instrument. 
     A stringed musical instrument incorporating the present art comprises a body  14  having a body face  16 , a body back  18 , and a body rear portion  20 , a neck  12 , and one or more strings  22  supported by a bridge assembly  24  and a nut  11  opposite said bridge  24 . The strings  22  are retained via the tension imparted thereto between a retention assembly  52  mounted with said body  14  and a tensioning adjustment or tuning peg apparatus opposite said retention assembly  52 . 
     For the preferred embodiment, each string  22  is supported and retained by an individual bridge assembly  24  comprising a string support assembly  26  and a string retention assembly  52 . The string support assembly  24  first comprises a base sleeve  28  mounted within the body  14  through the body face  16  and within a body face hole  17 . That is, in a preferred embodiment, the base sleeve  28  is a cylindrical tube  30  which is recessed and held into the instrument body  14  through the body face  16  and sized to fit said face hole  17 . In a preferred embodiment said sleeve  28  is pressed and adhesively epoxy bonded into said body  14 . Alternative embodiments may utilize only a frictional fit, other adhesives than epoxy, other cross sectional sleeve  28  shapes, or forgo use of said sleeve  28  as a separated element and form said sleeve  28  as an integral portion of said body  14 . 
     In a preferred embodiment, the base sleeve  28  is a cylindrical tube  30  having internal threads  32  and a flat bottom side  33  which contacts the base  19  of the body face hole  17 . Also in a preferred embodiment, when recessed into the instrument body  14 , a top side  35  is finished substantially flush with the body face  16 , whether said face  16  is curved or flat. The central axis of the base sleeve  28  is mounted substantially perpendicular to the axis of the string  22  in a preferred embodiment or angled whereby the top side  35  is closer to the body rear portion  20  relative to the bottom side  33 , in an alternative embodiment. The alternative mounting method places substantially more of the vectorial string  22  force onto the central axis of the base sleeve  28  and also aids in intonation compensation during string  22  height adjustment. 
     The string support assembly  24  next comprises a bridge piece  34  which is a substantially solid cylinder  36  in a preferred embodiment. Said cylinder  36  has external threads  38  which are capable of mating with said internal threads  32  of the base sleeve  28 . That is, the bridge piece  34  may be adjustably accepted by said base sleeve  28 . The bridge piece  34  further has a channel  42  on a top surface  40  of preferably rectangular cross section which is capable of accepting a saddle piece  48 . Also in the preferred embodiment, a threaded hole  44  within said piece  34  is substantially perpendicular to and intersecting the run of said channel  42 . Said threaded hole  44  is located to accept a setscrew  46  externally and allow said setscrew  46  to forcibly lock or retain said saddle piece into position. In a preferred embodiment, said setscrew  46  is externally adjustable with the instrument fully assembled. Alternative embodiments may forego use of said channel  42  and incorporate the features of said saddle piece  48  into said bridge piece  34  as an integral saddle piece  48  or utilize channels  42  of various geometric cross sections or utilize said channel  42  for string  22  support. Alternative embodiments may also utilize other methods for adjustment of said bridge piece  34  within said base sleeve  28  including but not limited to steps, notches, pins, screws, or frictional mating. 
     Further alternative embodiments of said bridge piece  34  minimize the acoustic impedance mismatch between the string support assembly  26  and the body  14  whereby maximum acoustic energy is transmitted into the body  14 . That is, the acoustic impedance of a material is proportional to the material density (ρ) multiplied by the acoustic velocity (c) or the square root of the density (ρ) divided by the modulus of elasticity (λ, Young&#39;s modulus) within the material. 
               Z   O     ∝     ρ   ·   c     ∝       ρ   λ             
Since the bridge piece  34  is typically of a metallic material such as brass and the body is of a wood, composite, or polymer material, the density, elasticity, and velocity differences within the relative materials create an acoustic mismatch. The acoustic mismatch between the body  14  and string support assembly  26  may be more closely matched and thereby maximize acoustic energy transmission if the aforesaid solid cylinder  36  has a recess or hollow portion  37  which reduces volumetric density. The recess or hollow portion  37  is of a volume determined by a diameter and depth which produces the most desirable amount of energy coupling for the musician. Thus, a musician may have varied and multiple volume bridge pieces  34  on a single instrument in order to minimize or maximize the acoustic energy coupled with the body  14  for each string  22 .
 
     Said saddle piece  48  is of preferably block form and designed to fit into the channel  42  of said bridge piece  34 . The preferred embodiment has a groove  50  in a top end  51  into which the string  22  is accepted and is supported. Preferably said groove  50  is of arcuate form whereby string  22  contact is minimized to a small portion of said groove  50 . If the string  22  contact with said saddle  48  is limited to a specific contact point, the vibrating string  22  length variation during play is minimized and tonal quality is maximized. 
     The string retention assembly  52  is preferably placed and held within a stepped body retention hole  21  within said body  14 . The assembly  52  first comprises an upper guide tube  54  which is mounted within said body  14  substantially flush with said body face  16 . A retention ferrule  58  having a retention hole  60  larger than said string  22  is positioned within said body  14  between said upper guide tube  54  and a lower guide tube  56 . Preferably said lower guide tube  56  is substantially flush with said body back  18 . That is, the string retention assembly  52  is substantially surrounded by said body  14  within said stepped body retention hole  21  except at the face  16  and back  18 . The lower guide tube  56  inside diameter is of greater diameter and the upper guide tube  54  inside diameter and retention hole  60  is of smaller diameter than a string  22  ball end or eyelet. Alternative embodiments may utilize a string retention assembly  52  having fewer or greater component parts or forgo use of said assembly  52  as a separated element and form said assembly  52  as an integral portion of said body  14 . 
     Assembly and manufacture of the present art instrument bridge  10  begins with forming or placement of the stepped body retention holes  21 . This is typically performed by drilling a smaller angled hole toward the body rear portion  20  from the body face  16  for upper guide tube  54  retention and counter-drilling said smaller hole to form a larger hole from the body back  18  for lower guide tube  56  retention. Preferably said holes are sized to intimately fit an outer diameter of said guide tubes  54 , 56 . Said upper guide tube  54  is then pressed and preferably adhesively bonded (i.e. epoxy) in place from said face  16 , said retention ferrule  58  is pressed and bonded from said back  18  and thereafter the lower guide tube  56  is also pressed and bonded in place. In the preferred embodiment, said tubes  54 ,  56  are finished substantially flush with said body face  16  and back  18  respectively. 
     In the preferred embodiment, each stepped body retention hole  21  is positioned on said body  14  in order to maintain a relatively and substantially constant distance from the respective individual string support assembly  26  for all of said assemblies  26 . That is, lighter gauge strings typically require said string support assembly  26  positioning slightly closer to said nut  11  in order to optimize intonation. The stepped body retention holes  21  are thereby positioned closer to said nut  11  in order to maintain said constant distance. On many stringed instruments, especially guitars, support assembly  26  and retention assembly  52  placement moves toward the nut  11  distally from the musician since the string gauge is lightest near the body bottom  23 . 
     The body face holes  17  are then placed in said body face  16 , said base sleeves  28  are pressed into said holes  17  with the bottom side  33  seated onto the base  19 , and each sleeve  28  is adhesively secured (i.e. epoxy) therein. Said placement is chosen to optimize said intonation placement conditions. Bridge pieces  34  are thereafter threaded within said sleeves  28  to the desired depth for optimum action. The saddle piece  48  is placed within said channel  42  and preferably secured with said setscrew  46 . 
     String  22  placement then proceeds with threading each string  22  through the respective lower guide tube  56 , retention ferrule  58  retention hole  60 , and the upper guide tube  54 . As stated, the ball or eyelet end of the string  22  is larger than the upper guide tube  54  and retention hole  60  inside diameter and thereby seats with said retention ferrule  58 . Each string  22  is then stretched across the respective saddle piece  48  within said top end  51  groove  50  towards the nut  11 , seated with said nut  11  and retained and tuned by the tuning assembly, tuning pegs, or tuners. Upon assembly, intonation is optimized via adjustment of the saddle pieces  48  toward or away from said nut  11 . 
     Those skilled in the art will appreciate that an optimally coupled string instrument bridge  10  apparatus and method of manufacture and use has been shown and described. Said present art utilizes a bridge assembly  24  with a large contact area between the support assembly  26  and instrument and also utilizes a retention assembly  52  incorporating the instrument body  14  for string retention whereby string forces and energy are concentrated onto and into the instrument body  14 . The present art provides optimum coupling into the instrument body  14  resulting in better tonal quality due to resonances within the instrument whereby different frequencies of the audio spectrum are diminished or reinforced. The integral body  14  mounting further provides an improved sustain characteristic, i.e. the decay time of a plucked string is longer. 
     Having described the invention in detail, those skilled in the art will appreciate that modifications may be made of the invention without departing from its spirit. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described. Rather it is intended that the scope of this invention be determined by the appended claims and their equivalents.

Technology Classification (CPC): 6