Abstract:
The invention is directed at a piezoelectric transducer for a stringed musical instrument which reproduces the real acoustic tonal qualities and resonances of an acoustic instrument. Also, due to its design, the transducer provides improved feedback control and feedback rejection over prior art devices. The transducer comprising a base unit; a piezoelectric unit, including a piezoelectric element housed within a shielding enclosure; and a multi-conductor cable connected to said piezoelectric element for transmitting signals produced by said piezoelectric element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/605,523, filed Aug. 31, 2004, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to musical instrument transducers and specifically to a piezoelectric transducer for stringed musical instruments.  
         [0004]     2. Description of the Prior Art  
         [0005]     At present, piezoelectric transducers for guitars can be broken down into two prominent types:  
         [0006]     1) Transducers that are located in the bridge saddle slot of the guitar with the saddle of the instrument situated on top of the transducer, and a subgroup of that design where the transducer is integrated within the saddle itself. These transducers receive vibration from string actuation acting almost entirely upon the bridge saddle and do not pick up the actual tonal qualities, vibrations or resonances, or the acoustic instrument body structure. The transducers in this group are also generally complex to manufacture, can be complicated to install in an instrument, and can be fragile in structure. Furthermore, the sound quality produced by these transducers does not accurately reproduce the acoustic nature of the instrument that the transducer is installed within. Transducers of these types are described in U.S. Pat. No. 4,491,051 to Barcus, U.S. Pat. No. 4,727,634 to Fishman, U.S. Pat. No. 4,774,867 to Fishman and U.S. Pat. No. 5,155,285 to Fishman.  
         [0007]     2) Transducers that are attached to the soundboard or bridge plate of the musical instrument. Transducers in this second group are generally better in being able to more accurately reproduce the acoustic tonal qualities of the instrument but are usually not able to provide quality feedback rejection. These soundboard transducers that seek to overcome the low feedback threshold are often very complex, difficult and costly to manufacture, and difficult to install into an instrument or to retrofit into an existing instrument. A transducer to this type is described in U.S. Pat. No. 6,605,771 to Baggs.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an aspect of the present invention to provide an improved piezoelectric transducer, preferably for use with a stringed musical instrument such as a steel string or classical guitar. Another aspect of the present invention is to provide an improved transducer which provides the conversion of string vibrations into electrical signals that substantially exactly correspond with the character of such string vibrations.  
         [0009]     A further aspect of the present invention is to provide an improved musical instrument transducer which is simple in construction and may be easily and inexpensively fabricated.  
         [0010]     Another aspect of the present invention is to provide an improved musical instrument transducer that is readily useable for retrofitting to existing stringed instruments without requiring major modification thereto.  
         [0011]     A further aspect of the present invention is to provide an improved musical instrument transducer that does not interfere with the normal sound characteristics, adjustments or playing action of the instrument during instrument string actuation when it is installed.  
         [0012]     In another aspect of the invention, a means for more accurate sound reproduction is provided. Although the present invention is adapted for use with a steel string guitar or nylon string guitar, it may be used in association with other stringed musical instruments such as a banjo, mandolin, arch-top guitar, violin, bass or other musical instrument having a vibrating and/or moving soundboard or other resonating surface.  
         [0013]     In yet a further aspect, the invention provides a transducer that attaches or adheres to the bridge plate or soundboard of an instrument generally in the area directly under the saddle. Due to its design, the transducer preferably reproduces the real acoustic tonal qualities and resonances of an acoustic instrument. Also, due to its design, the transducer provides improved feedback control and feedback rejection over prior art devices.  
         [0014]     In another aspect, there is provided a piezoelectric transducer comprising a base unit; a piezoelectric unit, including a piezoelectric element housed within a shielding enclosure; and a multi-conductor cable connected to said piezoelectric element for transmitting signals produced by said piezoelectric element.  
         [0015]     In another aspect, there is provided A piezoelectric transducer for a stringed musical instrument, securable to a resonating surface of said instrument, comprising a piezoelectric unit raised above said resonating surface by a supporting lower base unit, said piezoelectric unit having a piezoelectric element surrounded by and attached on one surface to a suitable RF shielding medium.  
         [0016]     Further details of the invention will be described or will become apparent in the course of the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will now be described with reference to the accompanying drawings of preferred and alternative embodiment(s), by way of example only. In the drawings:  
         [0018]      FIG. 1  is a front view of a first embodiment of the invention.  
         [0019]      FIG. 2  is a cut-away view taken along line  2 - 2  of  FIG. 1 .  
         [0020]      FIG. 3  is a perspective view of an underside of a stringed instrument top having a transducer mounted.  
         [0021]      FIG. 4  is a broken-away front view of the transducer of  FIG. 1 .  
         [0022]      FIG. 5  is a front view of a second embodiment of the invention mounted to a stringed instrument.  
         [0023]      FIG. 6  is a cut-away view of a piezoelectric unit.  
         [0024]      FIG. 7  is a front view of yet another embodiment of the invention mounted to a stringed instrument. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The invention is directed at a piezoelectric transducer for stringed musical instruments. Turning to FIGS.  1  to  4 , a first embodiment of a piezoelectric transducer in accordance with the invention is shown.  
         [0026]     Turning to  FIG. 1 , a front view of the transducer is shown. The transducer  10  comprises a piezoelectric unit  12  (comprising a piezoelectric element  13 , preferably a piezoelectric crystal, in an enclosure  14 ). The enclosure  14  provides radio frequency (RF) shielding and is preferably manufactured out of brass but other suitable materials such aluminum or a conductive plastic may be used. The piezoelectric unit  12  rests atop a base unit  16  which comprises, in this embodiment, three (3) legs  17  which contact the stringed instrument, as will be described below. The base unit  16  provides support to the piezoelectric unit  12  and the design (based on the location of cutouts  15 ) of the base unit  16 , (having a pair of arches and the three legs) allow for proper vibration transmission, structural integrity, and clearances necessary to avoid contact with areas of the vibrating top surface of the instrument or its supporting structures and bracing.  
         [0027]     A shielded multi-conductor cable  18  connects electrically to both top  20  and bottom  22  surfaces of the piezoelectric element  13  within the upper piezoelectric unit  12 .  
         [0028]      FIG. 2  shows a cut-away view taken along line  2 - 2  of  FIG. 1 . In this view, the details for the piezoelectric unit  12  and the base unit  16  are more clearly shown. The piezoelectric element  13  is preferably attached to an inner surface of the enclosure  14  via a soldering process  23 , however, it will be understood that other methods of adhesion such as conductive glue are also contemplated. In the preferred embodiment, the piezoelectric unit  12  is attached to the base unit  16  via a double-sided adhesive  24  (shown in exaggerated thickness for clarity). The enclosure  14  is also preferably filled with an epoxy  26  thus encapsulating the piezoelectric element  13  to support the piezoelectric element  13  so that the element is firmly located in the enclosure  14 . The epoxy  26  is selected to have necessary sound transmission properties as understood by one skilled in the art.  
         [0029]      FIG. 3  is a perspective view of the transducer installed on a stringed instrument  28 , such as a guitar. In this figure, the transducer  10  is installed on an underside of the guitar. The transducer  10  is preferably located on a bridge plate  30  (but may be located on any other vibrating surface) and attached to the bridge plate  30  via a pressure sensitive adhesive tape, a mastic putty, an epoxy, pressure sensitive tapes or any other adhesive which provides the necessary vibration transmission qualities. The bridge plate  30  is a slightly raised surface providing extra strength in the area under a guitar bridge for the top  32  of the instrument  28 . Bracing  34  are also located in the underside of the guitar to provide further structural support. It will be understood that the type of material with which the transducer is attached to the vibrating surface of the instrument may vary in order to lessen or increase the amount of vibration being fed through the base unit  16 .  
         [0030]      FIG. 4  shows a view of the first embodiment of the invention which further illustrates the contact between the piezoelectric element  13  and the cable  18 . The multi-conductor cable  18  comprises a first, insulated, lead wire  36  which is preferably soldered to the top surface  20  of the piezoelectric element  13  and a second lead wire  38 , which is preferably soldered to the bottom surface  22  of the piezoelectric element  13 . Both the first and second lead wires  36  and  38 , respectively, are contained within the shielded cable  18 . The other ends of the lead wires  36  and  38  (or cable  18 ) are preferably connected to a means for amplifying the vibrations experienced by the transducer. Examples of means for amplifying include an amplifier or a public address system.  
         [0031]     In use, as a musician, plucks, strums or bows the strings of the musical instrument, the movement of the strings imparts a vibration through the bridge or other string supporting structure of the instrument to the soundboard and the transducer. The movement of the strings causes the bridge (or whatever vibrating support structure the transducer is mounted to) to vibrate which is then translated to the transducer. The transducer then generates a voltage as a result of the vibrations received from the interaction between the transducer and the bridge (or whatever vibrating support structure the transducer is mounted to), the vibration of the soundboard and/or the vibrations of the musical instrument bracing.  
         [0032]     The vibration of the piezoelectric element  13  in the transducer  10  (which is somewhat regulated by the vibration transmission qualities of the adhesive attaching the transducer to the musical instrument  28 ) generates a voltage in response to the mechanical vibrations. This voltage is then transmitted through the lead wires  36  and  38  to the amplifying means in order to amplify the sound produced by the musical instrument  28 . Due to the design of the transducer, the sounds which are produced by the transudcer are of better quality than prior art transudcers.  
         [0033]     Turning to  FIGS. 5 , a second embodiment of a piezoelectric transducer is shown.  FIG. 5  is a front view of the transducer mounted to a musical instrument. The transducer  50  comprises a piezoelectric unit  52  (comprising a piezoelectric element  53  in an enclosure  54 ) and a base unit  56  for supporting the piezoelectric unit  52 . The base unit  56  includes a number of cutouts  58  which are important to the vibration transmission quality of the transducer  50 . As with the previous embodiment, a conducting cable  60  is connected to the piezoelectric element  52  within the enclosure  54 . The shape and position of the cutouts  58  are selected/designed so that the base unit  56  does not contact the surface of the musical instrument.  
         [0034]     The base unit  56  is mounted to bracing  62  of a musical instrument  64 , in t he present embodiment via a pair of cutouts  58 . The mounting is assisted by a mounting material  66  such as mastic putty.  
         [0035]     Turning to  FIG. 6 , a schematic view of a second embodiment of a piezoelectric unit is shown. In this embodiment, the piezoelectric unit  100  comprises a piezoelectric element  102  mounted to a brass strip  104  which is in physical contact with an inner surface of an enclosure  106 . The piezoelectric element  102  is preferably surrounded by a potting medium or epoxy  108  within the enclosure  106 .  
         [0036]     In the present embodiment, a conducting cable  110 , comprising a pair of lead wires  112  and  114 , is connected to the brass strip  104  and the piezoelectric element  102  via the lead wires  112  and  114 , respectively to transmit voltages produced by the piezoelectric element  102  when the musical instrument is being used. As shown, the lead wires  112  and  114  are preferably soldered  116  to the brass strip  104  and the piezoelectric element  102 .  
         [0037]      FIG. 7  displays another method of mounting a transducer on a musical instrument. In  FIG. 7 , the transducer  120  comprises a piezoelectric unit  102  (as shown in  FIG. 6 ) attached to a base unit  122  having a first part  124 and a second part  126  connected via an adjustable rod  128  (or spring). In this embodiment, the piezoelectric unit  102  is placed up against a vibrating surface  130  of a musical instrument while the second part  126  of the base unit  122  is placed against a second vibrating surface  132  of the musical instrument. An example of the first and second vibrating surfaces  130  and  132  is the two legs of a double bass bridge over an opening of the double bass. In this embodiment, more physical energy is imparted to the transducer which, in turn, produces a higher voltage for amplification. Alternatively, a second piezoelectric unit  134  may be mounted directly to one of the vibrating surfaces  130 .  
         [0038]     Although described as a piezoelectric crystal, the piezoelectric element may also be a piezo-polymer film, or sensor material, or any other material that may provide the electrical output and signal qualities necessary for differing uses and applications of the transducer.  
         [0039]     Although the attachment of the piezoelectric element to the enclosure and the two lead wires is preferably performed via a soldering process, it will be understood that other means of attaching the piezoelectric element to these parts such as a conducting adhesive are contemplated. A conducting adhesive is simply an adhesive which not only adheres two surfaces but allows for the transmission of signals between the two surfaces, namely the piezoelectric element and the lead wires or enclosure.  
         [0040]     In an alternative embodiment, the lead wires may be connected to a preamplifier prior to being connected to the means for amplifying the signals.  
         [0041]     Although the base unit  16  is preferably made of wood, in other embodiments, the base unit  16  may be made of any medium such as plastic, aluminum, or fiber as necessary to provide proper vibration transmission properties and support for the piezoelectric unit  12 .  
         [0042]     As described above, the base unit is preferably attached to the piezoelectric unit  12  via a double-sided adhesive. However, the base unit may also be attached to the piezoelectric unit  12  with cyanoacrylate adhesive, epoxy or any other form of adhesive, adhesive sheet or means of mechanical fastening as may be necessary which provides vibration transmissions from the base unit  16  to the piezoelectric unit  12 .  
         [0043]     Although shown in  FIG. 1  as having three legs sandwiching a pair of arches, the design of the base unit may be altered so that the transducer may be used with all different shaped stringed instruments. The design (location of cutouts) of the base unit is selected so that the integrity of the sound provided by the transducer is not compromised.  
         [0044]     Although described as two separate parts, the piezoelectric unit  12  and the base unit  16  may be a single unit combining the base and piezoelectric unit into one integrated structure containing all elements of the invention conferring all required vibration transmission properties and RF shielding. Furthermore, although the piezoelectric unit and the base unit are shown to be of similar length/width, it will be understood that the sizes of the piezoelectric unit and the base unit need not be the same.  
         [0045]     Further, other embodiments may have multiple or differing base units and multiple piezoelectric units with the base units set in various arrays such as a “T” shape or any other shape. In the multiple piezoelectric unit embodiments, the units may be mounted to separate transverse bracing of the musical instrument in order to sample the vibrations from multiple locations when the instrument is being played. It will also be understood that multiple single piezoelectric unit transducers may be mounted to the same bracing while not affecting the sound transmission quality.  
         [0046]     The present invention comprises a piezoelectric unit that is raised above the mounting surface by a supporting lower base unit. The preferred embodiment of the piezoelectric unit has a piezoelectric element that is surrounded by and attached on one surface to an RF shielding medium of brass. In other embodiments the RF shielding medium may be of conductive plastic or other such materials that may provide suitable sound transmission characteristics and shielding properties to the contained piezoelectric element. Furthermore, in other embodiments, the transducer may not include the RF shielding medium, or enclosure.  
         [0047]     An advantage of the invention is that it is much less complex, more economical to produce and is easily retrofitted to existing instruments.  
         [0048]     Another advantage of the invention is the design of the base unit (such as the arches) which allows the base unit to move freely and to act in a spring-like fashion than a solid base unit without cutouts. A further advantage is that the mounting of the transducer to the bridge plate is seen as a “soft” mounting which isolates the transducer from the vibrating surface in a controlled manner and allows the transducer to move relatively freely in relation to the instrument.  
         [0049]     Another advantage of the invention is that the cutouts of the base unit impart more focused vibrational energy to the piezoelectric unit than would a solid base unit (although a solid base may be contemplated). Other embodiments of the invention may vary the shape of the cut outs in the base unit to allow for the increase or decrease in vibration transmission as might be required. Still other embodiments of the invention may vary the amount of spring action imparted by the base unit to the piezoelectric unit depending upon the requirements of the application.  
         [0050]     Another advantage is that the adhesive used to attach the base unit to the piezoelectric unit contributes to the vibration control and transmission properties from the lower base unit to the piezoelectric unit.  
         [0051]     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.