Abstract:
In one embodiment, a device includes: first, second, and third paired-strand levers each configured to receive a pair of tensile strands at locations spaced apart from one another along the paired-strand lever; first, second, and third fulcrums each supporting a corresponding one of the paired-strand levers between the tensile strand receiving locations; a fourth lever linked to the first and second paired-strand levers through the first and second fulcrums, respectively, at secondary lever link locations spaced apart from one another along the fourth lever; a fourth fulcrum supporting the fourth lever between the secondary lever link locations; a fifth lever linked to the third paired-string lever and the fourth lever through the third and fourth fulcrums, respectively, at primary lever link locations spaced apart from one another along the fifth lever; and a fifth fulcrum supporting the fifth lever between the primary lever link locations.

Description:
BACKGROUND 
       [0001]    Guitars and other stringed instruments are tuned by adjusting the tension in the strings. In the case of a guitar, for example, the tension in each string is adjusted individually by turning the tuning heads on the headstock of the guitar. The desired string tension is often obtained by comparing the tone of one string with the tone of another string. The strings get out of tune when the tension in one string changes relative to the tension in one or more of the other strings. One way to help keep a guitar or other stringed instrument in tune, therefore, is to maintain the same relative tension among the strings. 
     
    
     
       DRAWINGS 
         [0002]      FIG. 1  is a plan view illustrating an electric guitar that includes a tension equalizer, according to one embodiment of the invention. 
           [0003]      FIG. 2  is a perspective view of part of the guitar of  FIG. 1  with the cover over the tension equalizer removed. 
           [0004]      FIG. 3  is a partially cut-away perspective view of the tension equalizer on the guitar of  FIGS. 1 and 2 . 
           [0005]      FIGS. 4 and 5  are plan and elevation views, respectively, of the tension equalizer shown in  FIG. 3 . 
           [0006]      FIGS. 6 and 7  are detail partial section views showing a point groove bearing joining the strings and the paired string levers in the tension equalizer of  FIGS. 3-5 . 
           [0007]      FIGS. 8 and 9  are detail partial section views showing a point groove bearing joining the connecting rods and the primary and secondary levers in the tension equalizer of  FIGS. 3-5 . 
           [0008]      FIGS. 10-12  are detail plan, front elevation and side elevation views, respectively, showing an adjustable point groove bearing joining levers in the tension equalizer of  FIGS. 3-5 . 
           [0009]      FIGS. 13 and 14  are detail views illustrating a tension equalizing lever from the tension equalizer shown in  FIGS. 3-5  in different adjustment positions. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Embodiments of the new tension equalizer were developed in an effort to keep the strings on a guitar in tune. Embodiments, therefore, will be described with reference to a guitar. The new tension equalizer, however, is not limited to use with a guitar but may be used with other stringed instruments or with other devices in which it may be desirable to maintain the relative tension between strings. “String” as used in this document means a tensile strand of any kind. 
         [0011]      FIG. 1  is a plan view illustrating an electric guitar  10  that includes a tension equalizer  12  that is mostly hidden behind a cover  14 .  FIG. 2  is a perspective view of the body of guitar  10  with cover  14  removed so that tension equalizer  12  is more visible. Referring to  FIGS. 1 and 2 , guitar  10  includes a body  16 , a headstock  18 , and a neck  20  extending between body  16  and headstock  18 . Each string  22  extends from tension equalizer  12  over a bridge  24 , along body  16  and neck  22 , over a nut  26  to a tuning head  28 . Guitar  10  also includes electrical pick-ups  30 , an amplifier jack  32 , and adjustment/selection knobs  34 . 
         [0012]    Referring now also to  FIGS. 3-5 , which are close-up views of tension equalizer  12 , the end of each of the six strings  22  is secured to one of three paired-string levers  36 ,  38  and  40 . As used in this document, “lever” means a rigid bar that pivots about a point of support, called the fulcrum, located between the places at which counteracting forces act or will act on the bar. (A lever such as this, in which the fulcrum is located between the places where counteracting forces act or will act on the bar, is commonly referred to as a first class lever.) Strings  22  are referred to individually as the low E, A, D, G, B and high E strings. Two of the three paired-string levers, levers  36  and  40 , are linked to a secondary lever  42 . The third paired-string lever, lever  38 , and secondary lever  42  are linked to a primary lever  44 . Primary lever  44  is anchored to guitar body  16 . Paired-string levers  36  and  40  are linked to secondary lever  42  through connecting rods  46  and  50 , respectively, or another suitable link. Paired-string lever  38  and secondary lever  42  are linked to primary lever  44  through connecting rods  48  and  52 , respectively, or another suitable link. Primary lever  44  is anchored to guitar body  16  through a connecting rod  54 , or another suitable link, and an adjusting nut  56 . 
         [0013]    Each paired-string lever  36 ,  38  and  40  is attached to a connecting rod  46 ,  48  and  50  with a point groove bearing  58  or another suitable link so that each lever  36 ,  38  and  40  pivots in a plane formed through the two strings secured to the lever. Secondary lever  42  is attached to connecting rod  52  with a point groove bearing  58  or another suitable link so that lever  42  pivots in a plane through connecting rods  46  and  50 . Primary lever  44  is attached to connecting rod  54  with a point groove bearing  58  or another suitable link so that lever  44  pivots in a plane through connecting rods  48  and  52 . Each link in tension equalizer  12 , connecting rods  46 - 54  in the embodiment shown, is placed in tension when strings  22  are taut. Each lever  36 - 44 , therefore, is supported at its fulcrum by the tension force in each respective link, connecting rods  46 - 54 . That is to say, the levers are linked in tension when the strings are made taut. The links between the levers must be able to maintain tension but not compression. Hence, the links need not be rigid links. 
         [0014]    In the embodiment shown, each lever  36 ,  38 ,  40 ,  42  and  44  is constructed as a threaded pin  36 P,  38 P,  40 P,  42 P and  44 P that turns in a mating threaded receiver  36 R,  38 R,  40 R,  42 R and  44 R that pivots in a bearing  58 . Each threaded lever pin may be partially threaded (as shown) or fully threaded as necessary or desirable for the particular embodiment of the tension equalizer. While it is expected that a threaded pin/receiver may be used in many embodiments, any structural feature that allows the user to change the distance between the parts worked on by the lever and the fulcrum may be used for levers  36 - 44 . 
         [0015]    Preferably, each string  22  passes over bridge  24  on a ball bearing roller  60 , as shown, to help reduce resistance to the movement of a string  22  lengthwise over bridge  24 . The links between the strings and the levers, and between the levers and the connecting rods, are also configured to minimize friction in equalizer  12  to help ensure that the full measure of adjustment/equalization is delivered to the strings undiminished by friction forces. Any change in the tension force in one string used to overcome friction on its way to all of the other strings will detract from the tension equalizing function of equalizer  12 . Hence, equalizer  12  will perform best to maintain the same relative tension among all strings  22  when a change in the tension in one string is transmitted to all of the other strings unimpeded by friction. 
         [0016]    For example, the end of each string  22  is linked to a lever  36 ,  38  or  40 , and the rearward end of each connecting rod  46 ,  48 ,  50  and  52  is linked a lever  42 ,  44 , by what I have called a “point groove” bearing  62 , which is shown in detail in the partial section views of  FIGS. 6-7  (string to lever link) and  FIGS. 8-9  (rod to lever link). Referring to  FIGS. 6-9 , point groove bearing  62  includes an eye  64  on the end of each string  22  and each rod  46 - 52  and a groove  66  on each pin  36 P,  38 P,  40 P,  42 P and  44 P. Only pin  36 P is shown in  FIGS. 6 and 7 . Only rod  46  and pin  42 P are shown in  FIGS. 8 and 9 . The inside diameter  68  of eye  64  contacts groove  66  along an edge  70  formed on inside diameter  68 . When viewed in section, as in  FIGS. 6 and 8 , eye  64  contacts groove  66  at a single point. This contact point becomes a line, as seen in  FIGS. 7 and 9 , whose length is determined by the relative size of the outside diameter  72  of pin  36 P/ 42 P at groove  66  and inside diameter  68  of eye  64 . Similarly, the forward end of each connecting rod  46 - 54  is linked a lever  36 - 44  by a point groove bearing  58 , which is shown in detail in  FIGS. 10-12 . Referring to  FIGS. 10-12 , each point groove bearing  58  includes a clevis-like piece  74  on the end of each connecting rod  46 - 54  and sharp edges  76  on each lever receiver  36 R- 44 R. Only lever  36  and rod  46  are shown in  FIGS. 10-12 . The inside diameter  78  of each eye  80  on clevis piece  74  contacts an edge  76  on receiver  36 R. 
         [0017]    Each lever  36 - 44  supported on and pivoting at its respective fulcrum works to equalize the tension in the two parts on which the lever is working. As noted above, levers  36 - 44  will perform their equalizing work best when the tension forces in the strings are transmitted to the levers unimpeded by resistance at points of contact. As best seen in  FIGS. 3 and 4 , paired-string lever  36  equalizes the tension in the low E and D strings; paired-string lever  38  equalizes the tension in the A and B strings; paired-string lever  40  equalizes the tension in the G and high E strings; secondary lever  42  equalizes the tension in the low E/D string pair and the G/high E string pair (through connecting rods  46  and  50 ); and primary lever  44  equalizes the tension in low E/D and G/high E string quad and the A/B string pair (through connecting rods  48  and  52 ). If, for example, the tension in the low E string decreases, such as might be the case after a period of use, then the momentarily higher tension in the D string causes lever  36  to pivot counter-clockwise at its fulcrum until the tension in the two strings is again the same. The now momentarily higher tension in the G/high E string pair, in turn, causes secondary lever  42  to pivot counter-clockwise at its fulcrum until the tension in the low E/D and G/high E string pairs is again the same. The now momentarily higher tension in the A/B string pair, in turn, causes primary lever  44  to pivot counter-clockwise on its fulcrum until the tension in the low E/D and G/high E string quad and the A/B string pair is again the same. Of course, it is somewhat simplistic to describe the tension equalizing function of device  12  with respect to distinct, incremental changes in tension when, in fact, levers  36 - 44  are continually equalizing the tension among all the strings as the tension in any one of the strings changes. 
         [0018]    The tension in all strings  22  may be adjusted by turning adjusting nut  56  to make connecting rod  54  longer or shorter and, correspondingly, to make all strings  22  longer and increase tension or to make all strings  22  shorter and decrease tension. In either case, the relative tension among strings  22  will not change. Tension equalizer  12  may be positioned in a recess  66  in guitar body  16 , as shown in  FIGS. 2-5 , so that it will not obstruct playing the guitar and so that it is more easily hidden from view. As best seen in  FIGS. 4 and 5 , paired-string levers  36  and  40  and secondary lever  42 , and their connecting rods  46 ,  50  and  52 , may be lined up with one another in one plane and stacked laterally adjacent to paired-string lever  38  and its connecting rod  48  in another plane. The lengthwise axes of levers  36 - 42  are substantially parallel to one another. The lengthwise axis of primary lever  44  is then oriented substantially perpendicular to the other levers  36 - 42 . (The axes of levers  36 - 42  may not be exactly parallel to one another because the axis of each lever  36 - 42  may not always be at the same angle relative to its respective connecting rod  46 - 52 . Also, the axis of primary lever  44  may not be exactly perpendicular to the axes of the other levers  36 - 42  because it may not always be at the same angle relative to its connecting rod  54  and because strings  22  diverge at different angles from bridge  24 .) This configuration allows the adjustment, relative to one another, of two strings not positioned on guitar  10  immediately next to each other. Also, in this configuration, strings  22  are held in the desired lateral spacing, congruous with the spacing of strings  22  from body  16  along neck  20  to headstock  18 . 
         [0019]    Strings  22  on guitar  10  may be tuned relative to one another by adjusting the position of the fulcrum of each lever  36 - 44  relative to the position of each part on which the lever works—that is to say, by changing the length of the moment arm through which the tension force in each part acts on the lever. In the embodiment shown, the position of the fulcrum on the lever is movable while the position of each part on the lever is fixed. In this embodiment, therefore, the position of the fulcrum is adjusted by moving the lever relative to the fulcrum, rather than by moving the strings (or other part on which the lever works) relative to the lever.  FIGS. 13 and 14  are detail views illustrating paired string lever  40  in two different positions. Referring to  FIGS. 13 and 14 , the range of travel of lever  40  is determined by the length of threads  82  on lever pin  40 P. In  FIG. 13 , lever  40  is positioned at the middle of its range of travel so that the lever arms LA G  and LA E  for strings G and high E are the same length. In  FIG. 14 , lever  40  is positioned at one end of its range of travel towards the high E string so that the lever arm LA G  for the G string is longer than the lever arm LA E  for the high E string. 
         [0020]    In adjusting the G and high E strings from the position shown in  FIG. 6  to the position shown in  FIG. 7 , in which the fulcrum for lever  40  is more toward the high E string, the tension in the G string will decrease and the tension in the high E string will increase, thereby lowering the tone of the G string relative to the tone of the high E string (i.e., raising the tone of the high E string relative to the tone of the G string). If it is desired to tune the G string higher relative to the high E string, then lever pin  40 P is turned to move the fulcrum for lever  40  more towards the G string, thereby increasing the tension in the G string relative to the high E string. 
         [0021]    Tuning strings  22  on guitar  10  proceeds by first adjusting the position of the fulcrum for each paired-string lever  36 ,  38  and  40  to achieve the desired tone for the low E and D strings, the A and B strings, and the G and high E strings; then adjusting the position of the fulcrum for secondary lever  42  to achieve the desired tone for the low E/D string pair and the G/high E string pair; and then adjusting the position of the fulcrum for the primary lever  44  to achieve the desired tone for the low E/D and G/high E string quad and the A/B string pair. When adjusting the position of the fulcrum for the secondary lever  42  or the primary lever  44 , the desired tone may be determined by comparing just one string in each of the two parts on which the lever works. For example, for primary lever  44 , turning lever pin  44 P in receiver  44 R until any one of the strings in the low E/D and G/high E string quad and any one of the strings in A/B string pair are in tune relative to one another will place all of the strings in tune relative to one another. 
         [0022]    Changing the length of connecting rod  54  by turning adjusting nut  56  will adjust the overall tone of all strings  22  simultaneously higher or lower. Once strings  22  are in tune relative to one another, however, the tension equalizing effect of device  12  will tend to keep strings  22  in tune indefinitely, regardless of the overall tension in, and the corresponding overall tone of, strings  22 . Tuning newly installed strings may be facilitated if, before proceeding with the tuning procedure described above, each lever pin  36 P- 44 P is positioned at the middle of its range of travel in the corresponding receiver  36 R- 44 R and the new strings are tightened using tuning heads  28  until each lever  36 - 44  is perpendicular to the corresponding connecting rod  46 - 54  (the position shown in  FIG. 13 ). 
         [0023]    The present invention has been shown and described with reference to the foregoing exemplary embodiments. It is to be understood, however, that other forms, details and embodiments may be made without departing from the spirit and scope of the invention which is defined in the following claims.