Abstract:
A plurality of force sensing transducer elements are enclosed in a stringed musical instrument bridge height adjuster, designed to be installed as one of a pair of height adjusters in the legs of the bridge. The transducers are disposed to allow rotation of the adjuster to control how the modes of vibration in the bridge affect the transducers, thus allowing the player to adjust the tonal response of the transducers to the instrument and to their own sound preference. An inline jack-plug pair allows the output cable of the transducer to be quickly disconnected and reconnected to avoid straining or tangling the cable while adjusting the tone and the bridge height.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to musical instrument transducers for use with stringed musical instruments employing a bridge for a portion of their string support. More particularly, the invention pertains to a stringed instrument such as a bass violin.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     N/A  
       BACKGROUND OF THE INVENTION  
       [0003]     There are numerous musical instrument transducers in existence, and several of them have been designed specifically in an attempt to solve the problem of producing an accurate electrical replica of the sound of an instrument such as a bass violin. A conventional musical instrument transducer of the force sensing transducer type for use with a bass violin is disclosed in U.S. Pat. No. 4,356,754 issued Nov. 2, 1982 and entitled Musical Instrument Transducer. The conventional transducer described herein has a plurality of piezoelectric elements attached with clips onto one of the faces of the bridge of the instrument, and in the preferred embodiment an output cable connected to a jack and mounting plate that is secured to the strings between the bridge and the tailpiece. This style of transducer allows good reproduction of the sound of plucked strings, but is deficient at reproducing the sound of bowed strings. Another drawback includes the risk of the transducer being dislodged and possibly damaged with handling or while in transit. This style of construction leaves both the piezoelectric elements and their cable connections exposed and vulnerable to damage. Additionally, there is a need to attach a ground wire to all of the strings to prevent their acting as antennae for electromagnetic interference, while requiring no irreversible modifications to the instrument.  
         [0004]     It would therefore be desirable to have a transducer that allows accurate reproduction of both plucked and bowed strings, adjustibility of the tonal characteristics, that is less at risk of being dislodged or damaged, is feedback resistant, and is fully shielded from electromagnetic interference.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In accordance with the present invention, a musical instrument transducer of the force sensing transducer type is disclosed that is formed in the shape of a bass violin bridge height adjuster, and that allows the position of the internal transducer elements to be rotationally altered to optimize the sound of the pickup on each specific instrument.  
         [0006]     While the process of installing this transducer requires the bridge to be modified, it is a modification already present on many bridge-equipped stringed instruments, one that is considered very standard, doesn&#39;t impair the non-amplified function of the instrument, and allows regular height adjuster wheels to be installed if the transducer should be removed. In addition, this style of transducer does not require mechanical re-biasing after bridge height adjustment, as some other types do.  
         [0007]     In a preferred embodiment, the presently disclosed transducer assembly is configured to contain four piezoelectric transducer disks arrayed in a circle, inside an enclosure that has the outer shape of a bass violin bridge height adjuster. The enclosure is composed of a cylindrical base with a threaded post, and a cover with a non-threaded cylindrical post. The base and cover are mechanically and electrically joined with an electrically conductive adhesive to ensure good electromagnetic shielding continuity when the enclosure is grounded. Within the enclosure, an interior or bottom surface of the cover is in physical contact with the piezoelectric transducer disks. Thus, the ground path extends from the upper surface of the transducer disks through the cover, the electrically conductive adhesive, and the base to a cable connected thereto. The transducer disks themselves are mounted on a disk of copper-clad circuit board with an electrically conductive adhesive to complete the electrical path between the bottom of the transducer disks, across the metalized circuit board, and to a conductor of a connected cable. A rigid, electrically isolating spacer is disposed between the transducer disks. This disk assembly sits on a resilient, insulating support inside the enclosure. A center conductor of a coaxial cable makes contact with the copper-clad portion of the circuit board, and an outer shield of the cable makes contact with the enclosure. The cable is terminated in this preferred embodiment at a jack-plug pair to allow quick disconnection and reconnection when the enclosure is rotated, thereby preventing tangling or damage to the cable.  
         [0008]     In a presently preferred embodiment, the lowest frequency string on the instrument is the E string, and the leg on that side of the bridge will be referred to as the bass leg. Additionally in this embodiment, the highest frequency string on the instrument is the G string, and the leg on that side of the bridge will be referred to as the treble leg.  
         [0009]     Inside the body of a bass violin, there are two particular structures below the legs of the bridge. Under the treble leg there is a support known as a sound post, mechanically connecting the top and back parts of the body of the instrument. Under the bass leg, attached to the inside of the top part of the body, there is a longitudinal rib called the bass bar, a structural support that is also used to tune the response of the instrument. The rigidity of the sound post and the relative flexibility of the bass bar cause the bridge to effectively pivot around the sound post in response to the motion of the strings. Thus there is a major advantage to installing a force sensing mechanism in the bass leg of the bridge, where there is a much greater mechanical excursion. Bowing and plucking the strings of an instrument with this bridge support configuration will each give different modes of vibration.  
         [0010]     In a presently preferred embodiment, the transducer is installed by cutting a section out of the bass leg of the bridge, drilling holes into both leg sections for the posts, threading one of the holes, attaching the transducer into the leg sections, performing a matching set of actions on the treble leg with a regular bridge height adjuster, reinstalling the bridge on the instrument, and attaching the output connector through a signal cable to an amplifier or other signal processing electronic device.  
         [0011]     Additionally in the preferred embodiment, the resilient support is made of a material such as silicone rubber selected for a combination of thickness and durometer that distributes pressure evenly on the transducer disks and prevents over-clamping due to extreme height adjustment, thus preserving the dynamic range of the transducers. The resiliency of the material results in a self-aligning support which further limits the effects of over-clamping and serves to keep the transducers in an optimal range of clamping forces for maximum response. A typical combination would be a thickness in the range of 0.020″ to 0.040″, with a durometer in the range of 40 to 60 Shore A.  
         [0012]     The process of hole-drilling, threading and installation of the bridge height adjusters is well known to those skilled in the art, and may be found in the installation instructions in any standard after-market bass bridge height adjuster.  
         [0013]     Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0014]     The invention will be more fully understood with reference to the following Detailed Description of the Invention in conjunction with the drawings of which:  
         [0015]      FIG. 1  shows a perspective view of a bass violin with a force sensing transducer according to the present disclosure installed in the bridge;  
         [0016]      FIG. 2  shows a partial section view of a bass violin bridge with the force sensing transducer of  FIG. 1  and a standard adjuster;  
         [0017]      FIG. 3  shows a side view of a bass violin bridge with the force sensing transducer of  FIG. 1  and with a plug and jack pair shown disconnected;  
         [0018]      FIG. 4  shows a section view through the force sensing transducer of  FIG. 1 ;  
         [0019]      FIG. 5  shows a perspective, exploded view of the force sensing transducer of  FIG. 1 ; and  
         [0020]      FIG. 6  shows a section view of an alternative embodiment of the force sensing transducer of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     A musical instrument transducer of the force sensing transducer type is disclosed and shown mounted in the leg of the bridge of a bass violin.  
         [0022]     As described above, in a preferred embodiment, there is shown in  FIG. 1 a  stringed musical instrument in the form of a bass violin  50  comprising a body  52 , a neck  53 , a bridge  54 , and a plurality of strings  51 . Mounted in the bass leg  55  of the bridge  54  is a force sensing transducer  60 , and mounted in the treble leg  57  of the bridge  54  is a commonly available height adjuster  58 . Further shown is a coaxial cable  40  electrically connecting the force sensing transducer  60  to the jack and plug assembly  62 , and a foam rubber or neoprene isolation plug  56  that secures the coaxial cable  40  relative to the bridge  54 .  
         [0023]     A more detailed view of the mounting scheme of a presently preferred embodiment is shown in  FIG. 2 , including the location of both the bass bar  67  and the sound post  68 .  FIG. 3  depicts the unplugged jack subassembly  69 , where the RCA plug  44  at the end of the coaxial cable  40  is detached from the subassembly, which includes the RCA jack  46  electrically and mechanically connected to the ¼″ jack  48 , and the mounting plate  49 . In  FIG. 3 , the cable  40  has also been removed from the foam rubber isolation plug  56 . This unplugged form of the jack and plug assembly  62  allows easy and quick connection and disconnection of the cable  40  in such a way as to facilitate the rotation of the force sensing transducer  60  without tangling or straining the cable  40 .  
         [0024]     It is shown in  FIG. 1 ,  FIG. 2  and  FIG. 3  how the force sensing transducer  60  is positioned between the upper bass leg section  63  and the lower bass leg section  64 , and the height adjuster  58  is positioned between the upper treble leg section  65  and the lower treble leg section  66 . The lower leg sections terminate in the bass and treble feet  59 ,  61 , respectively. These feet rest on the top, outer surface of the body  52 . For purposes of the description of a presently preferred embodiment, the feet  59 ,  61  are considered to be portions of the lower leg sections  64 ,  66 , respectively.  
         [0025]     Each of the legs is divided into an upper and a lower section by a process of making two cuts to remove an intermediate section of each leg, the section having a thickness slightly greater than the thickness of an enclosure  22  of the transducer  60  or the main body of the height adjuster  58  (not including the upper and lower vertical projections). Holes are drilled into both remaining sections and one of the holes in each leg is threaded. The force sensing transducer  60  and the height adjuster  58  are then installed into the leg section pairs prior to re-installing the bridge on the instrument.  
         [0026]      FIG. 4 , in which the vertical scale has been exaggerated for better clarity, and  FIG. 5  show the enclosure  22  formed from the cover  10  and the base  20 . The lower leg sections  64 ,  66  are threaded, and the enclosure  22  shape of the force sensing transducer  60  is identical to the shape of the height adjuster  58 . With component detail shown in  FIG. 4  and  FIG. 5 , this allows the threaded post  24  of the base  20  and its counterpart on the height adjuster  58  to selectively regulate the height of the bridge  54 . Likewise, the cover  10  has a cylindrical member  14  inserted into the bottom of the upper bass leg section  63 , and a disk  12  typically of thickness approximately in the range of 0.020″ to 0.060″ bearing against the bottom of the upper bass leg section  63 , establishing a pathway for the vibration of the strings  51  to travel through the bridge  54  and into the force sensing transducer  60 .  
         [0027]     It is preferred that the hole formed in the upper bass leg section  63  be deep enough such that the entire cylindrical member  14  of the cover  10  fits inside. It is also preferable that, once the cylindrical member  14  of the cover  10  is installed in the upper bass leg section  63 , the area of contact between the exposed end of the upper bass leg section  63  and the disk  12  of the cover  10  be maximized. Such an arrangement maximizes the vibrational force coupled into the transducer  60  through the disk  12  of the cover  10 .  
         [0028]     The disk  12  of the cover  10 , in turn, bears on a plurality of circularly-disposed transducer elements  35  within the enclosure  22 . Forces resulting from vibrations in the instrument cause the disk  12  of the cover  10  to act as a diaphragm, whereby mechanical deflection of the disk  12  results in a change in the compression to which the transducer disks are subjected. Ultimately, it is the electrical response of the passive transducers  35  to the dynamically changing compression which is used as an instrument-characterizing signal.  
         [0029]     The transducer cover  10  and base  20 , preferably made of a metal such as aluminum, are bonded together with a conductive adhesive  13  such as a silver-filled epoxy deposited within an internal cylindrical recess  26  therebetween. This allows the enclosure  22  formed by the assembled combination of base  20  and cover  10  to act as an environmental and electromagnetic shield for the transducer elements  35  within.  
         [0030]     Vibration-induced flexure of the disk  12  is limited by a rigid spacer  36 , here disposed between the plurality of transducer elements  35 , typically lower in height than the transducer elements  35  by an amount in the range of 0.002″ to 0.015″. This flexure limiting controls the range of mechanical bias placed upon the transducer elements  35 , and thus aids in controlling the quality of the output signal from them.  
         [0031]     A printed circuit (PC) board assembly  30  as shown in  FIG. 5  comprises the plurality of transducer elements  35 , the rigid spacer  36 , a conductive adhesive film  34 , and a disk preferably made of copper-clad circuit board  37 . The disk of copper-clad circuit board  37  is preferably comprised of an electrically insulating disk  31  with a lamination of copper  32  on one side, and an insulating border  33  by which the diameter of the lamination  32  is smaller than the diameter of the insulating disk  31  by at least 0.010″. The PC board assembly  30  is positioned upon a resilient support  29  within the enclosure  22 . In the embodiment shown, there is a first slot  38  in the PC board assembly  30  and a second slot  39  in the resilient support  29  for providing mechanical clearance for the coaxial cable  40  including both the signal wire  41  and the shield  42  contained within it. Furthermore, the enclosure  22  contains a wire groove  28  in a bottom surface thereof for clearance of the coaxial cable  40 . The coaxial cable  40  enters the wire groove of the enclosure  22  through an eyelet  16  which is pressed into a hole  27 . Once inserted, the shield  42  is soldered or otherwise electrically attached to the case, typically the eyelet  16 , to establish a ground connection, and the signal wire  41  is soldered to the lamination of copper  32  to make electrical contact with the plurality of transducer elements  35  through the conductive adhesive film  34 . Mechanical engagement (not shown) of the cable  40  within the enclosure  22  is also provided. The upper faces of the transducer elements  35  are grounded by contact with the underside of the disk  12 .  
         [0032]     As the strings  51  are plucked or bowed, they transmit time-varying mechanical energy into the bridge  54  and thus down into the legs  55 ,  57 . The treble leg  57  is limited in its mechanical response by the sound post  68 , while the bass leg  55  has much more freedom of mechanical response. The vibrations in the upper bass leg section  63  are transmitted through the disk  12  of the cover  10  into the transducer elements  35 , with the overall mechanical excursion of the disk  12  being limited by the rigid spacer  36 . The electrical outputs of the transducer elements  35  are transmitted through the conductive adhesive film  34  and summed through the lamination of copper  32 , which acts as a common terminal for them. Under the PC board assembly, the resilient support  29  serves to distribute pressure evenly across the transducers and to prevent over-clamping.  
         [0033]     Rotating the force sensing transducer  60  relative to the bridge  54  causes the orientation of the transducer elements  35  to change relative to the transmitted modes of vibration in the bridge  54  and the upper bass leg section  63 , thus giving the player the ability to optimize the sound of the instrument for a particular style of playing and tonal preferences. Rotation of the force sensing transducer also enables bridge height adjustment as in the case of the standard height adjusting member  58  in the treble leg  57 .  
         [0034]     In another embodiment of the invention, the instrument that the presently disclosed transducer is mounted on may have fewer or more than the four strings illustrated here.  
         [0035]     Having described the above illustrative embodiments, other alternative embodiments or variations may be made. For example, such alternative embodiments of the force sensing transducer may include having the mechanism installed without threading on the cylindrical member  14  and without an adjuster in the other leg, thus retaining all of the sensing functionality but without any height adjustment.  
         [0036]     Another alternate embodiment has the transducer built as an integral part of the leg of the bridge. Such a fixed embodiment sacrifices the rotational tone adjustment capability and height adjustment capability to gain mechanical simplicity. In this embodiment, the transducer may be disposed within a leg of the bridge, or provided as a foot of a bridge leg.  
         [0037]     Alternative embodiments have fewer or more than four transducer elements, such elements being arranged circularly as described above or in a different pattern inside the enclosure, depending upon the application, thus yielding different sound characteristics and different sound adjustment capabilities.  
         [0038]     A further embodiment of the presently disclosed invention substitutes a fluid for the piezoelectric transducers  35  disclosed above. In this embodiment, shown in  FIG. 6 , the enclosure  22  is formed by securing the base  20  and cover  10  together to form a fluid-tight seal. To provide such a seal, adhesive, a resilient seal or O-ring, or other sealing means  72  may be employed. Inside the container, a chamber  76  for the fluid takes the place of the circuit board  37 , the piezoelectric transducer elements  35 , the spacer  36 , and the resilient support  29 . The chamber  76  is formed by the interior surfaces of the disk  12  and the enclosure  22  in one simple embodiment, and by a fluid-bearing bladder in another. Gas or liquid may be employed as the fluid. Instead of the coaxial cable  40 , a fluid-tight conduit  74  is in communication with the interior of the fluid chamber  76  within the enclosure  22  and interfaces to an external pressure transducer  70  which converts instantaneous pressure or time-varying pressure differentials to electrical signals. Preferably, the fluid-tight conduit  74  interfaces to the enclosure  22  through a conduit seal  73 , which may be an adhesive, a resilient ring, or threads formed on the conduit  74  end and in the enclosure. The conduit length is minimized to avoid damping effects resulting from conduit wall resiliency. Alternatively, a pressure transducer could be disposed in conjunction with the enclosure  22  to avoid such signal losses, with appropriate cabling extending from the instrument.  
         [0039]     In a further embodiment of the fluid-based transducer of  FIG. 6 , the movement of the diaphragm or cover  12  may be limited in a controlled fashion by a rigid spacer, such as the rigid spacer  36  shown in  FIG. 5 , positioned within the chamber, serving to prevent over-extension of the diaphragm and possible operation of the pressure transducer outside of an optimal range. Further diaphragm movement control may be gained by combining the rigid spacer with a resilient support material, such as the support  29  shown in  FIG. 5 , thus allowing the movement of the diaphragm to encounter a more gradual limit.  
         [0040]     It will further be appreciated by those of ordinary skill in the art that modifications to and variations of the above-described musical instrument transducer may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited except as by the scope and spirit of the appended claims.