US 3291887 A
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Description (OCR text may contain errors)
F. c. CARMAN ETAL 3,291,887 PIEZOELEGTRIC MUSICAL PICKUP ARRANGEMENT Dec. 13, 1966 2 Sheets-Sheet l .F'iled Jan. 50, 1964 ATTORNEYS F. c. CARMAN ETAL 3,291,887
PI'EZOELECTRIC MUSICAL PICKUP ARRANGEMENT Filed Jan. 30, 1964 I Dec. 13, 1966 2 Sheets-Sheet 2 INVENTOR5 IWM/(C. (HF/44M LYN/V JO/IAGOM sW/u #WGZA United States Patent 3,291,887 PIEZOELECTRIC MUSICAL PICKUP ARRANGEMENT Frank C. Carman and Lynn Johnson, both of 165 Social Hall Ave., Salt Lake City, Utah- Filed Jan. 30, 1964, Ser. No. 341,243 9 Claims. (Cl. 841.16)
This invention relates generally to a musical pickup arrangement for the conversion of mechanical vibrations into electrical oscillations, and more specifically, to a musical pickup arrangement incorporating a piezoelectric transducer for converting mechanical vibrations generated in a musical instrument into electric signals that may be supplied to a loudspeaker system.
A typical system for electrifying a musical instrument includes a pick-up for conversion of the mechanical vibrations into electrical oscillations, means for amplifying the electrical oscillations, and loudspeaker apparatus for converting the amplified electrical signals into acoustical energy. Such systems have been used extensively in the past, especially in connection with stringed instruments such as guitars and ukuleles.
The present invention is concerned with the pickup portion of such a system. It will be convenient to describe the invention in detail as a part of an electrified stringed instrument, such as a bass violin.
According to the invention, a stringed instrument having a bridge member is provided with an elongated, narrow opening or gap defined by spaced-apart walls and a piezoelectric transducer is mounted within this opening in contact with the walls thereof. The transducer has a signal-carrying lead attached thereto for conducting electrical oscillations generated in the transducer to suitable amplifier and loudspeaker components.
Upon plucking or bowing the strings of the musical instrument, vibrations are set up within the bridge member, causing relative movement between the opposed walls of the gap in the bridge member. Being in contact with such walls, the piezoelectric transducer is stressed upon vibration of the bridge and electrical oscillations corresponding to the mechanical vibrations are generated. These electrical signals can be amplified and converted into acoustical energy in a loudspeaker system.
The pickup of stray radiation by devices of this type is frequently a problem since it produces an objectional humming signal. The present invention minimizes this problem by surrounding the transducer with electrical conductive shielding means. The walls of the opening or gap, along With the face of the bridge surrounding the opening, are coated with electrically conductive silver paint. An electrically conducting cap covers the opening and contacts the electrically conductive paint on the face of the bridge. The ground lead from the transducer is in electrical connection with both the cap and the silver paint.
A more complete understanding of the invention will be gained from a consideration of the following description of certain embodiments illustrated in the accompanying drawings, in which:
FIGURE 1 is a perspective view of a bass violin assembly embodying a bridge fitted with a pickup arrangement of this invention;
FIGURE 2 is an enlarged elevational view of a bridge of the type shown in FIGURE 1 disclosing the details of the present invention;
FIGURE 3 is a partial vertical cross-sectional view of the bridge shown in FIGURE 2; and
FIGURE 4, 5, 6 and 7 are partial elevational views of a bridge showing various modifications of the pickup assembly.
The music system depicted in FIGURE 1 includes a bass violin 2 having a body portion 4, a fingerboard 6, a bridge 8, and a plurality of strings 10 passing over the bridge 8. Mechanical vibrations generated upon plunking or bowing the strings are converted into electric oscillations by a pickup assembly incorporated in the bridge 8. The oscillations pass through a signal carrying cable 12 to a loudspeaker enclosure 14 where they are amplified and converted into acoustical energy.
FIGURES 2 and 3 show, in detail, the pickup assembly incorporated in the bridge of the bass violin in FIGURE 1. A conventional bridge 8, fabricated from a nonmetallic material such as wood, has notches 16 which receive the strings 10. At a point below the notches 16 an elongated, relatively narrow, opening or gap 18 is provided which extends substantially vertically when the bridge is in an upright position. It is to be understood that this opening 18 may extend completely through the bridge, although FIGURE 3 shows the opening extending only a portion of the way therethrough. The opening is defined, basically, by opposing side walls 20 and 22, end portions 24 and 26, and a bottom face 28.
At a portion midway of the length of the opening 18, its width may be enlarged by providing a bore having the same depth as the opening. This results in concave side wall portions 29 and 30. A channel extending a portion of the way into the bridge is provided in each of the side wall portions 29 and 30, as shown at 32 and 34.
A piezoelectric transducer 36 is mounted within the opening 18 at the enlarged central portion in contact with the opposed side wall portions 29 and 30. As shown in FIGURES 2 and 3, the transducer 36 has a rectangular cross section with its ends 38 and 40 positioned within the channels 32 and 34, respectively. The transducer may be held in place by suitable means 42 such as an epoxy resin adhesive applied over the ends of the transducer and in contact with the side walls.
With the provision of the bore, the width of the remainder of the opening 18 may be relatively small while a transducer of a reasonable length may be conveniently mounted therein. However, the width of the groove 18 cannot be so small that the opposing sides will touch during the vibration of the strings. This would result in a distorted signal. In a standard bass violin bridge fabricated from wood, good results have been obtained using an opening 18 having a main portion of a width of & of an inch and a bore portion of a diameter of of an inch. The length of the opening 18 determines the amount of vibrational stress that is applied on the transducer 36. With a conventional bass bridge and present-day commercial transducers, a length of one inch has been found sufiicient.
The provision of the bore defined by concave faces 29 and 30 facilitates the attachment of a signal carrying lead 44 and a ground lead 46 to the transducer 36. As shown in FIGURE 3, the leads are connected to the top and bottom faces of the transducer by liquid solder 48. However, any convenient means of attachment may be used.
It is very important in devices of this type to minimize the probability of stray radiation being picked up and transmitted along with the desired electrical oscillations due to the vibration of the strings. This is accomplished by substantially surrounding the transducer 36 with electrically conductive shielding means. Such means comprise a layer of electrically conductive silver paint 50 applied to the walls 20 and 22, end portions 24 and 26, and bottom face 28 of the opening 18. As shown in FIG. 3, this layer of paint is continued over a portion 52 of the face of the bridge surrounding the opening. An elec- .3 trically conductive cap 54, preferably made from metal,- covers the entire opening 18 with flange portions 56 of the cap contacting the layer of silver paint 52 that is on the face of the bridge 8. A screw 58 is provided to hold the cap in place.
To complete the shielding of the transducer, the electrically conductive shileding means is grounded by connection to the ground lead 46. The ground lead is con- 1 nected to the ground wire of the signal carrying cable 12 in the manner shown in FIG. 3-. The signal carrying cable 12 contains a signal carrying wire 59 having a coating of insulation 60 surrounding it. Concentrically disposed around the insulation is the ground wire 62. The ground lead 46, which is attached at one end to the transducer 36, is connected to the ground wire 62 at a point within the opening 18 adjacent the end portion 26. The two wires are connected by solder 64 which in turn is in contact with the layer of silver paint 50 at that portion of the opening.
The connection between the signal carrying lead 44 and the signal carrying wire 58 may be accomplished in any convenient manner. FIG. 3 shows the two wires merely being twisted together. This connection should then be covered with a suitable insulation so it will not come in contact with the metallic cap 54 or the exposed parts of the ground connection. The signal carrying cable 12 should be attached to the bridge to prevent the connection from being pulled apart. An epoxy resin adhesive may be used to secure the cable to the bridge at a point 66 near the opening 18.
The above arrangement provides an effective shield that surrounds the transducer 36. The metallic cap 54 is electrically connected to the layer of silver paint 52 by the contacting thereof of flange portion 56. The silver paint is electrically connected to the ground lead 46 and the ground wire 62 through the provision of the solder 64. It is to be understood that if the opening 18 extends completely through the bridge, a second metallic cap would cover the other end of the opening.
When the strings are vibrated either by plucking or bowing, porportional vibrations will pass through the structure of the bridge, thereby narrowing and expanding the width of the opening. The piezoelectric transducer will respond to the variations in the width of the groove and produce electrical oscillations which are proportional to the frequency and amplitude of the vibrations. These signals are sent to the amplifier through the signal-carrying cable.
FIGURE 4 discloses a modified arrangement in which the transducer is more responsive to vibrations in certain directions. As can be seen, the transducer 36 is mounted in the opening at an angle of 45 with respect to the elongated axis of the opening. In all other respects, the modification is the same as the former one although the details of the opening and shielding means have been omitted for the sake of clarity.
If it is desirable to have additional gain over that produced by the embodiments already described, it is possible to utilize a transducer 68 having the configuration shown in FIGURE 5. As shown, the transducer 68 is omega-shaped. It is defined by a body portion 70 which is in the form of an inverted U and two legs 72 and 74 which are mounted in the channels in the opposing side walls of the opening or gap 18 as in the previous modifications. The increase in gain results from a greater bending moment about point 76 of the transducer for a given movement of the walls of the groove 18.
FIGURE 6 respresents a feature which can be applied to all the preceding modifications. The opening 18 is shown filled with a pliable or semi-pliable damping material 78. This material should be non-conductive and may be an appropriate synthetic resin. By providing such a material, it is possible to minimize undesirable transients set up by the vibrations of other parts of the 4- musical instrument as well as those due to high frequencies.
FIGURE 7 illustrates another embodiment of the invention in which two separate transducer elements are utilized. As in the previously described embodiments, it is shown applied to a bass bridge. Two elongated openings and 82, having their axes of elongation in the same horizontal plane, are formed in the bridge below the string contact points. Each of these openings is formed in the same manner as the previous modifications to include the spaced side walls 20 and 22 with opposing concave portions 29 and 30. A transducer 84 is mounted in each of the grooves and is inclined at an angle of 45 with respect to the axis of elongation of the opening. The ground lead 86 from each of the transducers is connected to the ground wire of the single carrying cable 12. The single carrying lead 88 from each transducer is connected to the signal carrying lead of cable 12. A cap 90 is provided, which along with the silver coating around the walls of the opening and on the face of the bridge, provides shielding from stray radiation in the manner previously described.
It will be noted that in all the modifications, the opening for the transducer lies below the point of string contact. This arrangement permits the arc of the bridge to be filed to match the arc of the fingerboard of the particular instrument to which it will be fitted. An additional feature of the invention resides in the fact that it is possible to vary the thickness of the bridge around the string contact point. This is a feature which many bridge fitters consider desirable since by doing so it will change the overall sound of the instrument and provide a distinctive touch.
Moreover, if the opening does not extend completely through the bridge, one side of the bridge will remain completely unaltered. This is a desirable feature to many artists since they prefer to have their instrument as natural as possible during the times when they are not utilizing the amplifier system.
While this invention has been described with reference to a bass violin bridge, it may be included in any musical instrument having a vibrating member of suflicient size to accommodate the gap without seriously weakening the structure or changing the tone of the instrument.
Various other modifications and alterations will suggest themselves readily to persons skilled in the art. It is intended, therefore, that the foregoing be considered as exemplary only and that the scope of the invention be ascertained from the following claims.
1. A musical instrument of the type having vibratable strings comprising a bridge member of nonmetallic material, said bridge member having an upper string-contacting portion and having an elongated opening therein at a location below and spaced from said upper string-contacting portion, said opening having spaced apart side walls concave for at least part of their extent to form an enlarged central portion of said opening, an elongated piezoelectric transducer mounted in said opening with its opposite ends in contact with the concave portions of said side walls, and signal-carrying conductors attached to said transducer.
2. The stringed instrument of claim 1 further comprising electrically conductive shielding means substantially surrounding said transducer.
3. The stringed instrument of claim 2 wherein said shielding means includes a layer of electrically conductive paint on said side walls, and electrically conductive cap covering said opening and in electrical contact with said paint, and a ground lead connected to said transducer and electrically connected to said paint.
4. The stringed instrument of claim 1 wherein said transducer is omega-shaped, defined by an inverted U shaped body portion and two legs extending therefrom into contact with said side walls of said openings.
5. In a bass violin having vibratable strings, a wood bridge member having an upper string-contacting portion and having an elongated opening disposed below said string-contacting portion, said opening extending substantially vertically when the bridge is in an upright position and defined by spaced apart side walls, a transducer mounted within said opening in contact with said side walls, signal-carrying conductors attached to said transducer, electrically conductive shielding means substantially surrounding said transducer, said shielding means including a layer of electrically conductive paint on said walls and an electrically conductive cap covering said opening and in contact with said paint, and a ground lead connected to said transducer and electrically connected to said silver paint.
6. A stringed musical instrument comprising a bridge, at least two openings in said bridge each being defined by spaced apart side walls and extending horizontally of said bridge when it is in an upright position, a piezoelectric transducer mounted within each opening and contacting said side walls, signal-carrying conductors attached to each transducer, and electrically conductive shielding means surrounding said transducers.
7. A musical instrument comprising a member mechanically vibratable at the tone producing frequencies of the instrument and having therein at least one elongated narrow opening the opposing side walls of which vibrate with respect to each other in response to vibration of said member, a pickup element responsive to mechanical vibrations for providing electrical signals representative of said vibrations, and said pickup element being mounted in said opening in contacting relation to said side walls to respond to the vibrations of said side wall relative to each other, and signal-carrying conductor means attached to said pickup element for transmitting the electrical signals provided when said member is vibrated.
8. The musical instrument of claim 7 wherein the configuration of said member is such that said opening therein is spaced from the location where the vibration imparting forces are applied to said member.
9. The musical instrument of claim 8 further comprising electrically conductive shielding means substantially surrounding said pickup element, said shielding means including a cap covering said opening in said member.
References Cited by the Examiner UNITED STATES PATENTS 3,073,203 1/1963 Evans 841.15
ARTHUR GAUSS, Primary Examiner. J. BUSCH, Assistant Examiner.