Abstract:
An electric pickup for stringed musical instruments for installation on a bridge that includes height-adjusting wheels for adjusting string height. The pickup includes three piezo-electric sensing elements symmetrically arranged around the adjuster stud, and the entire downward force generated by the strings and coupled to the instrument face through the bridge is borne by the piezo-electric elements.

Description:
RELATED APPLICATION 
     This application claims the benefit under 35 USC §119(e) of the filing date of U.S. Provisional Patent Application No. 61/848,003 entitled “The Lifeline”, filed Dec. 20, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     Electric pickups used in connection with “acoustic type” stringed musical instruments have been in use for many years. Indeed, the present inventors have previously co-invented and patented two different designs that are in common use today (U.S. Pat. No. 6,018,120, and U.S. Pat. No. 8,455,749). Others have also designed and patented various configurations. 
     SUMMARY OF THE INVENTION 
     The present invention is designed for use with instruments that use a bridge having a string height adjustment mechanism in each leg (i.e., height adjustment wheels). Generally, this means the larger stringed instruments, such as the upright bass. There is no actual limit on size of the present invention; the preceding comment arising merely because smaller instruments ordinarily do not use adjustment wheels. While the invention is expected to find its primary use as described above, it is not so limited, and the invented pickup can also be used in connection with other bridge types. Accordingly, the example shown herein with the invention installed on an upright bass bridge with adjuster wheels should be taken as illustrative, and not limiting. 
     Depending on the type of adjustment mechanism used (there are currently two general types in use, as will be explained below), the invented pickup fits and is clamped between the adjusting wheel and either (1) the bridge foot or (2) the bridge leg. The pickup can be installed on either the bass or treble side of the bridge, but is more commonly installed on the bass side. The pickup, which includes three piezo-electric elements connected in parallel, bears substantially the entire force that is transmitted from the strings, through the bridge, to the instrument face on the selected side. The term “piezo-electric element” as used herein refers to an element fabricated from any one of a number of materials that generates a voltage between its faces when subjected to compression. Such elements are common in the industry, and need not be further described. 
     The three piezo-electric elements, as installed on an instrument, are arranged at the apexes of an equilateral triangle, i.e., a substantially symmetrical disposition around the adjuster screw. The static loads on the elements are approximately equal. The “tripod” support configuration provides a very stable base for the forces transmitted downward through the bridge. Unintended asymmetries in installation and adjustment may create some differences, but such differences are not believed to be significant in terms of affecting performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a presently preferred embodiment of the invention, with the locations of the three piezo-electric elements indicated by dashed lines. 
         FIG. 2  is a schematic diagram showing the electrical circuit of the invention. 
         FIG. 3  is an exploded view of the presently preferred embodiment of the present invention (not including the cable). 
         FIG. 4  is a rear view of a musical instrument bridge (i.e., looking from the instrument tail) with an exemplar of the embodiment of the invention as shown in  FIG. 1  installed on the bass side. 
         FIG. 5  is a left side view of the bridge of  FIG. 4 . 
         FIG. 6  is a trimetric view of an adjusting wheel such as is commonly used on bridges suitable for use with the present invention. 
         FIG. 7A  is a partial cross section of the bridge shown in  FIG. 4 , taken at  7 - 7  of  FIG. 4 . 
         FIG. 7B  is a view similar to  FIG. 7A  but depicting a bridge using a second type of adjusting wheel for string height adjustment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a top view of a presently preferred embodiment of the invention, designated by the numeral  10 . The invented pickup  10  includes three piezo-electric compression sensors  12  arranged symmetrically around an opening  13  that extends through the pickup. Slot  15  allows the pickup to be installed on the bridge adjusters without having to completely remove the bridge from the instrument. The three sensors are shown as dashed lines in  FIG. 1  since they are not actually visible from the outside of the pickup. In the presently preferred embodiment of the invention, the sensors  12  are about 0.180 inches in diameter, and about 0.030 inches thick. Different sized sensors may, of course, be used if desired. As seen in the connection diagram of  FIG. 2 , the three sensors  12  are connected in parallel to cable  14 , which carries the combined signal to amplifying and reproducing means, not shown, located elsewhere. While  FIG. 2  is a schematic diagram, hot foil  23  and ground foil  20  are identified thereon for clarity.  FIG. 2  shows a two wire shielded cable, but persons of skill in the art will understand that a single conductor shielded cable could be used as well, with the shield connected to the ground foil  20 . The connections between the cable conductors and the ground and hot foils may be made by soldering, welding, or other means as is convenient. 
     The invented pickup is a sandwich of parts, as can be seen in the exploded view of  FIG. 3 , held together between top cap  16  and bottom cap  17  by screws  18 . The terms “top” and “bottom”, as used herein, are used for descriptive convenience only inasmuch as the invented pickup can be installed with either side “up”, with no difference in performance. The caps are preferably fabricated from aluminum, but other materials can be used if desired. The parts may be finished (or not) as desired, such as by paint or anodizing or using other finishes. 
     Adjacent bottom cap  17 , is bottom plate  19 , which is preferably fabricated from stainless steel, but other materials may also be used, if desired. Bottom plate  19  (and the top plate  25 , which will be described below) may be used to provide stiffness to the assembly and therefore, in such case, should be relatively heavy. The plates, particularly top plate  25 , also provide electrical shielding for the pickup. The plate parts in the preferred embodiment are about 0.030 inches thick. If mechanical stiffness is not deemed important, thinner plates may be used. Also, it is preferred that the plates be bent slightly inward before assembly to keep the assembly from “opening up”. 
     Ground foil  20 , preferably made of copper or brass, rests on bottom plate  19 . The term “foil” is used herein for convenience, since the preferred embodiment of the invention uses metal a few thousandths thick, however, the actual conductor thickness used can be whatever is convenient. Pliant spacer  21 A rests on the ground foil, and has three openings  22  to position and retain the piezo-electric elements  12 . Pliant spacer  21 A is preferably fabricated from plastic foam sheet having about the same thickness as the sensors, i.e., in the preferred embodiment about 0.030 inches. Rigid spacer  21 B is placed adjacent to the pliant spacer  21 A (between the caps  16  and  17 ). Rigid spacer  21 B is preferably made of fiberboard or the like, and also has a thickness about the same as the sensors. The sensors rest on ground foil  20 , in the openings  22 . 
     Hot foil  22  lays on top of spacer  21 , and makes contact with the upper surfaces of the sensors  12 . Paper insulating sheet  24  covers hot foil  23 , and insulates it from top plate  25 . 
     Top plate  25  and top cap  16  complete the sandwich, which, as previously noted, is held together by screws  18  threaded into bottom cap  17 . Depending on how the caps are finished, it may be necessary to remove the finish in some area(s) so that electrical contact (for shielding purposes) can be maintained between top cap  16 , top plate  25 , bottom plate  19 , and bottom cap  17 . Bottom and top plates  19  and  25  are preferably unfinished stainless steel. 
       FIGS. 4 and 5  are a rear and left side view of a typical bridge  30 , as might be used on an upright bass, with an exemplar of the present invention  10  installed on the bass side. The bridge includes a body  31  that has two legs  32  and two feet  33 . The bridge also includes two adjusters that are each comprised of an adjuster wheel  34  and a threaded stud  35 . The top ends of the studs (which are not ordinarily threaded) are typically pressed or glued into holes in the bridge legs, which keeps the studs from turning when the wheels are adjusted. The adjuster wheels, which are threaded onto the studs, are used to adjust the height of the bridge to its desired height. The studs extend into clearance holes in the feet  33 . As can be seen in  FIG. 5 , the left adjuster wheel presses against the pickup such that the downward force generated by the strings is exerted on the pickup that is resting on foot  33 . 
     There is another type of adjusting mechanism in common use wherein the adjusting wheel and the stud are combined as one piece, and the threads on the stud mate with internal threads in the bridge foot, with the top portion of the stud being a slip fit into the bridge leg.  FIG. 7B  is a sectioned view similar to  FIG. 7A  except that the second type of adjusting mechanism, just described, is installed. In this type of adjusting mechanism, the wheel and the stud (including the threaded and unthreaded portions) are one piece, as indicated in the  FIG. 7B  by having all three portions numbered the same ( 34 ′). The unthreaded top part of the stud is a slip fit into a hole in the leg  32 ′, and the lower threaded portion is threaded into a tapped hole in the foot  33 ′. When using this second type of adjustment mechanism, the pickup is installed above the adjustment wheel instead of below it, but otherwise the operation is the same. 
     Since the piezo-electric elements  12  are symmetrically disposed about opening  13 , they form a very stable support for the bridge leg. The use of three equally spaced transducers makes it easy to locate the array such that the forces on all three are substantially equal whereby all three contribute substantially equal portions of the total pickup output. Equalizing transducer loading is important both from transducer life and performance points of view. Using three transducers, as opposed to two or four, makes equalization easier. 
     Placing the pickup in the bridge leg, relatively close to the strings, results in a more percussive, articulated sound output from the amplifier. This effect is highly desirable, especially when amplifying an instrument during a “live” presentation. Placing the pickup in the bridge leg, relatively close to the strings also helps to get a “cleaner”, less “fluffy”, or a more articulated tone. It has been found, also, that when the total load is substantially evenly shared, there is a significant reduction of the possibility of an intermittent popping” sound.