GB2035651A

GB2035651A - String-tension adjusting mechanism

Info

Publication number: GB2035651A
Application number: GB7845809A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-11-23
Filing date: 1978-11-23
Publication date: 1980-06-18

Abstract

A string-tension adjusting mechanism for a pedal-steel guitar includes a bridge finger (6), pivotally mounted (9) at its upper end to which the string (4) is anchored, and resiliently biased (11, 12) against the string tension into a normal operative position. Two bell-crank levers (13, 14) are mounted adjacent the bridge finger and are pivotable by respective pull rods (18, 19), acting in the same direction, to engage respective cam surfaces (24, 25) with a roller bearing (26) at the lower end of the bridge finger to pivot the bridge finger in opposite respective directions from the normal operative position into engagement with a stop (28) and lever (13) acting as a stop respectively to lower or raise the pitch of the string by predetermined intervals during play. <IMAGE>

Description

SPECIFICATION String-tension adjusting mechanism The present invention relates to a string-tension adjusting mechanism for a stringed musical instrument, particularly a pedal steel guitar.

A steel guitar is similar to a classical guitar in that it has a number of strings which are attached at one end to the guitar body, are stretched over a bridge and along a fretboard and attached at the other end to respective tuning pegs, the strings being played by plucking with a fingerpick. Unlike the classical guitar however, the steel guitar is designed to be played with the fretboard substantially horizontal, the strings, which are of steel, being pressed against the fretboard during play by a bar, usually of polished steel, to vary the length of string which is free to vibrate and hence the note produced thereby.

Afurther difference between the classical and steel guitars is that the amplification of the sound produced by the latter is effected electronically.

As with a classical guitar, the strings of a steel guitar are tuned to desired notes by varying their tension, for example, by turning the respective tuning pegs before playing is commenced. In the classical guitar and in simple steel guitars these tensions, set up during tuning, remain substantially constant throughout the playing of the instrument, but the more complex, pedal steel guitars include mechanisms operable by pedals or levers to adjust the tension of one or more strings during play. The pedals of such a guitar are normally foot operated, the levers being knee operated, and each may control the tension of one or more strings; release of the pedal or lever allows the string or strings controlled thereby to return to its normal tension applied during the initial tuning stage.

The tension-adjustment mechanisms for adjusting the string tensions usually act on a respective bridge to which an individual string is anchored, the bridges, or rather bridge fingers, comprising levers, each pivotally mounted on the instrument body for pivotal movement about a common axis substantially perpendicular to the longitudinal axis of the fretboard and each having a rounded upper end over which the respective string is stretched. The tension adjusting mechanisms are connected to the lower ends of respective bridge fingers to pivot them out of their normal positions into secondiary positions to vary the tension in the respective strings, stops being provided to prevent pivoting beyond desired secondary positions.Release of each mechanism allows the respective finger to pivot back to its normal position which may be determined either by a stop or by resilient biasing means which counteract the pivotal force of the string on the finger.

Since it is normally desirable to adjust the tension of a string to alter its note by a given pitch, it is necessary to tune the string at its normal tension and at each of the one or more secondary tensions to which it can be adjusted by adjusting mechanisms.

For this purpose, different tuning means are provided for adjusting the secondary positions of the bridge finger to correspond to the desired tensions of the respective string, one such means being the tuning peg referred to above; other tuning mechanisms may comprise variabie stops which the finger abuts to determine respective secondary positions.

In simple pedal steel guitars, the bridge fingers are pivotable in only one sense, either to increase or decrease the tension in the respective string passing thereover to raise or lower the pitch of the plucked string respectively. In more complex guitars, however, one or more of the bridge fingers may be pivotable in either sense from the normal position such that the note of the string passing over the bridge may be raised or lowered as desired; in such guitars the bridge finger must be accurately returned to a central normal position in order to play the normal note of the string.

Many mechanisms have been proposed and, in fact, used for operating such bridge fingers. Some of these incorporate push rods which operate on the bridge fingers to push them in one direction but it is found that, due to bending of the rod and other factors, accuracy of the string tensioning and hence of the tuning cannot be maintained by this method.

Pull mechanisms, and particularly pull rods, have been found to be far more effective and therefore efforts have been concentrated on developing adjusting mechanisms in which the pivoting of a bridge finger in both senses is effected by respective pull mechanisms. Such mechanisms which have been made so far, however, have been very complex and/or ineffective in that the tuning of the instrument has not been maintained over prolonged periods.

The object of the present invention is to provide a simple tension-adjusting mechanism, particularly for a pedal steel guitar, which is relatively cheap to manufacture and allows the tuning of the guitar to be maintained over long periods.

According to the present invention there is provided a string-tension adjusting mechanism for a stringed musical instrument comprising a bridge finger pivotally mounted adjacent one end on a support and resiliently biased into a normal operative position to tension to a desired pitch a string anchored to the said one end in use of the mechanism, two levers, pivotally mounted about axes parallel to the pivot axis of the bridge finger, each having a cam surface for engaging a respective surface of the finger and respective pull members attached to each lever, such that on pulling of each respective puli member the corresponding cam surface engages a respective surface of the finger to pivot it from said normal position, the pull members pivoting the finger in opposite respective senses and the engagement being such that on release of each pull member, the corresponding lever allows pivoting of the finger from the normal position in the opposite sense to that which said lever causes.

Release of each pull member allows pivoting of the bridge finger back to its normal operative position under the combined action of the resilient biasing means and the tension of the string on the bridge finger, the corresponding lever being pivoted to a rest position possibly with the assistance of additional biasing means connected to the pull member.

The adjusting mechanism of the present invention is thus very simple, comprising two independently operating levers attached to respective pull members, each operating on the bridge finger to cause pivoting only in one sense and being disengaged to allow pivoting in the opposite sense. The normal operative position is thus determined solely by the string tension and the biasing means and the possibility of the string going out of tune with prolonged use is reduced compared with other, more complicated systems. Such a mechanism is particularly applicable to steel guitars but may be used in any other instrument in which it is desired to alter the note given by a string by changing its tension.

The pivoting of a bridge finger under the action of each lever of a mechanism according to the invention is preferably limited by respective stops which determine respective first and second secondary positions of the bridge finger corresponding to respective secondary tensions of the string carried thereby. At least one of the stops is preferably adjustable to allow adjustment of the corresponding secondary tension of the string and hence tuning of the string. If only one stop is adjustable, th resilient biasing means are preferably adjustable to allow adjustment of the normal position of the bridge finger and hence tuning of the normal pitch of the string; the secondary pitch of the string when the bridge finger abuts the fixed stop may then be tuned by adjusting the tuning peg to which the string is attached.

It is found in steel guitars that a small change in tension of a string results in a considerable change in pitch of its note. In order to provide greater sensitivity of the instrument to tuning, in preferred embodiments, each lever has two arms inclined to each other and interconnected at the pivot axis, the respective pull members being attached at or adjacent the free end of a longer arm of each lever and the cam surface being provided on the other arm.

The longer arm of each lever preferably extends substantially parallel tothe longitudinal axis of the bridge finger in its normal position, the pull members preferably comprising respective pull rods attached one to each lever and extending substantially perpendicular to the longitudinal axis of the bridge finger in its normal position. This allows the pull rods to move substantially axially in pivoting the lever, and hence the bridge finger, since a relatively small arc of movement suffices to alter the note of the string carried thereby by a desirable amount.

The respective surfaces of the bridge finfer which the cam surfaces of the levers engage are preferably spaced further from the pivot axis of the finger than the end carrying the string, again to improve the sensitivity of the mechanism according to the invention during tuning processes. The said surfaces of the bridge finger may be provided at the end of the bridge finger remote from the end carrying the string but these surfaces are preferably rounded surfaces of a projection which projects out of the plane of pivoting of the bridge finger. This allows the levers to be formed from plates which can be located in respective planes closely spaced from each other and the bridge finger, the cam surfaces comprising edges of the plates; the mechanism may thus be made very compact allowing such mechanisms to be associated with adjacent bridge fingers of an instrument.

The levers may alternatively have projections which project out of the major plane of the lever and on which the cam surfaces are provided, preferably for engaging the end of the bridge finger. In such embodiments the pivot axes of the levers may be spaced further from the pivot axis of the bridge finger than the end of the bridge finger. In a preferred embodiment of the invention, however, the pivot axes of the levers are preferably located to one side of a plane through the pivot axis of the bridge finger and the longitudinal axis of the latter in its normal positions, the longer arms of the levers extending towards the pivot axis of the bridge finger, the shorter arms of the levers extending towards a projection on the bridge finger.One of the levers would thus be arranged to pivot the bridge finger away from its own pivot axis, while the other lever would be arranged to pivot the bridge finger towards its pivot axis.

The levers are preferably mounted for pivotal movement about a common pivot axis, preferably comprising a spindle on which levers of mechanisms acting on adjacent levers are also mounted.

According to a further aspect of the inventon there is provided a stringed musical instument, such as a pedal steel guitar, incorporating a tension-adjusting mechanism as described above.

One embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a purely diagrammatic, perspective view of a pedal steel guitar incorporating stringtension adjusting mechanisms according to the invention; Figure 2 is a diagrammatic perspective view on an enlarged scale of one of the string tension adjusting mechanisms incorporated in the guitar of Figure 1; Figure 3 is a plan view of the mechanism of Figure 2, showing a bridge finger of the mechanism in a normal position, and Figure 4 is a view similar to Figure 3 showing the bridge finger displaced from the normal posotion, Referring to Figure 1 of the drawings, a pedal steel guitar is shown having a fretboard 1 carried on a body generally indicated 2, mounted on legs 3 such that the fretboard is substantially horizontal. Ten steel strings 4 (not all shown) are stretched along the fretboard, being attached at one end to respective tuning pegs 45 and at their opposite ends to respective bridge fingers 6, forming part of respective string-tension adjusting mechanisms.

Referring to Figures 2 and 3 ofthe drawings, one of the string-tension adjusting mechanisms is shown in greater detail. The finger is formed from mild steel plate and is generally rectangular in form but for a rounded upper end 7 over which the string 4 passes, the string being anchored to the bridge finger by a pin 8. The finger is pivoted near its upper end 7 about a shaft 9 carried by the body 2, on which the other bridge fingers 6 of the guitar are also mounted and which extends substantially perpendicular to the length of the string 4.

The bridge finger 6 is resiliently biased to its normal operative position, shown in Figures 1 and 2 in which it extends substantially perpendicular to the plane of the fretboard 1, against the action of the tension in the spring 4 which tends to pivot the finger in an anticlockwise sense, as seen in the drawings, by means of an adjustable stop, generally indicated 10. The stop 10 comprises a screw threaded bolt 11, mounted for axial sliding movement substantially parallel to the length of the fretboard 1 in an aperture in a portion 2a of the guitar body 2 and is retained by a nut 1 1a. Acompression spring 12 surrounds the bolt shaft and urges the head against the bridge finger 6 to restrict its pivoting.The nut lia is adjustable from one end of the body 2 to adjust the distance between the bolt head and the body part 2a to adjust the said normal operative position of the bridge finger 6.

The string-tension adjusting mechanism of the present invention includes two levers 13,14 each cut from hard steel plate and pivotally mounted on a common spindle 15, which also serves as the pivot for similar levers 13, 14 operating on other bridge fingers 6 of the guitar. The levers 13, 14 are parallel to each other but spaced from each other by suitable spacing elements, such as washers. The spindle 15 extends parallel to the shaft 9, is adjacent a lower end of the bridge finger 6 and is spaced from the finger 6 on its opposite side from the stop 10.

The levers 13, 14 each have a longer arm 16, 17 respectively which extends from the spindle 15 substantially parallel to the longitudinal axis of the bridge finger, in its normal operative position, and towards the string 4. Pull rods 18, 19 are attached one adjacent the upper end of each arm 16, 17 respectively and extend beneath and substantially parallel to thefretboard 2, each rod being connected at its opposite end in known manner by a bell crank (not shown) to the upper end of one of several upright rods 20 (see Figure 1) supported between the rear legs 3 of the guitar. The lower end of each rod 20 is connected to a foot pedal 21 such that depression of the foot pedal pulls the pull rod 18 or 19 towards its bell crank end, rotating the respective lever 13 or 14 in an anticlockwise sense as seen in the drawings.

The substantially perpendicular connection of each rod 18,19 to its respective arm 16,17 allows the rod to travel susbstantially axially over the permitted range of movement of the levers 13, 14 which will be described below.

Ashorter arm 22,23 of each lever 13, 14 respectively extends towards the bridge finger 6, the upper edges 24,25 of the arms 22, 23 respectively being formed as cam surfaces which abut, or are closely spaced from, respective surfaces of a roller bearing 26 mounted on the bridge finger 6. The bearing 26 is mounted on a pivot pin 27 for rotation about an axis parallel to the pivot axes of the levers 13, and of the bridge finger 6, the bearing being located substantially further from the shaft 9 than the upper end 7 ofthe finger 6.

The cam surfaces 24, 25 are specially adapted to act on the respective surfaces of the bearing 26 on pivoting ofthefingers 13, l4bythe rods 18, 19to pivot the bridge finger 6 in opposite senses. For this purpose the cam surface 24 is convexly curved towards the bearing 26 and is so located that the reactive force between the surfaces has a component acting in an anticlockwise sense on the finger 6 about the shaft 9. On pivoting of the lever 13 in the anticlockwise sense under the action of the pull rod 18, the bridge finger is therefore also pivoted in an anticlockwise sense. The cam surace 25 is so located and shaped that it allows this anticlockwise pivoting.

The surface 25 which engages the roller bearing 26 is substantially straight but inclined at an acute angle to the arm 17 of the lever 14, the reactive forces between the surfaces being such that the force on the bearing 26 has a component in a clockwise sense about the shaft 9. Pivoting of the lever 14 under the action of the pull rod 19 thus pivots the bridge finger 6 in a clockwise sense about the shaft 9. The lever 13 allows this clockwise pivoting through a small arc of movement, but in the position shown in Figure 4, further pivoting is prevented by the engagement of the roller between opposing surfaces of the arms 16 and 22 of the lever 13. The lever 13 thus acts as a fixed stop, preventing clockwise pivoting of the bridge finger 6 beyond this predetermined secondary position.

Pivoting of the bridge finger 6 in the anticlockwise sense is restricted by an adjustable stop 28 comprising the end of a screw 28 which extends parallel to the bolt 11 and is located in a cooperatingly screwthreaded bore in a portion 2b of the guitar body 2.

The screw can be rotated by means of its head to adjust the spacing of the end from the bridge finger 6 to regulate the secondary position of the finger 6 at which ft is stopped on rotation in an anticlockwise sense.

In use ofthe guitar of Figure 1, the string 4 is first tuned by rotating the respective tuning peg 5 to tighten or loosen the string. The pull rod 19 is then operated by means of the corresponding pedal 21 to pivot the bridge finger 6 into its secondary position in which it abuts the lever 13. The string 4 is then retuned to a desired secondary note by rotation of the respective peg and pedal released to allow pivoting of the bridge finger back to its normal position, the lever 14 also being pivoted to its inoperative position.

The string 4 will now be out of tune with the other strings 4 and must be retuned by adjustment of the stop lotto adjust the normal position ofthe bridge finger 6. The bridge finger is then pivoted in the anticlockwise sense under the action of the lever 13 until itabutsthe stop 28 and the string 4 is again tuned to a further secondary note by adjusting the position of the bridge finger 6 by means of adjustment of the stop 28.

The string 4 will now give three different notes according to the position of the bridge finger 6, that is, a normal note in the normal operative position of the bridge,and two secondary notes, one while each of the two pedals operating the levers 13, 14, are depressed, the bridge finger returning to its normal position on release of the pedals.

Each of the strings having associated stringtensioning mechanisms as described above must be tuned in this way. One or more of the bridge fingers 6 may be connected to be operated by a knee lever 29 rather than a foot pedal and a knee lever or foot pedal may be connected to operate more than one lever 13 or more than one lever 14.

Although the mechanism described includes only two levers, 13,14, for operating a bridge finger 6 to give two secondary notes of the string 4, the mechanism may incorporate further levers for pivoting the bridge into other secondary positions against corresponding adjustable stops to provide further secondary notes.

Claims

1. Astring-tension adjusting mechanism for a stringed musical instrument, comprising a bridge finger pivotally mounted adjacent one end on a support and resiliently biased into a normal operative position to tension to a desired pitch a string anchored to the said one end in use of the mechanism, two levers pivotally mounted about axes parallel to the pivot axis of the bridge finger, each having a cam surface for engaging a respective surface of the finger and respective pull members attached to each lever, such that on pulling of each respective pull member the corresponding cam surface engages a respective surface of the finger to pivot it from said normal position, the full members pivoting the finger in opposite respective senses and the engagement being such that on release of each pull member, the corresponding lever allows pivoting of the finger from the normal position in the opposite sense to that which said lever causes.

2. Astring-tension adjusting mechanism as claimed in Claim 1, in which each lever has two arms inclined to each other and interconnected at the pivot axis, the respective pull members being attached at or adjacent the free end of a longer arm of each lever and the cam surface being provided on the other arm.

3. A string-tension adjusting mechanism as claimed in Claim 2, in which the longer arm of each lever extends substantially parallel to the longitudinal axis of the bridge finger in its normal position, the pull members comprising respective pull rods attached one to each lever and extending substantially perpendicular to the longitudinal axis of the bridge finger in its normal position.

4. Astring-tension adjusting mechanism as claimed in Claim 3, in which each pull rod is connected to a foot operable pedal or a knee operable lever to be operated thereby.

5. A string-tension adjusting mechanism as claimed in any of Claims 1 to 4, in which the respective surfaces of the bridge finger which the cam surfaces of the levers engage are rounded surfaces of a projection which projects out of the plane of pivoting of the bridge finger at a point spaced further from the bridge finger pivot axis than the said one end to which the string is anchored.

6. A string-tension adjusting mechanism as claimed in Claim 5, in which the projection comprises a roller bearing rotatably mounted on the bridg,e finger about an axis parallel to the pivot axis of the bridge finger.

7. A string-tension adjusting mechanism as claimed in Claim 5 or Claim 6, in which the levers comprise plates which lie in respective planes closely spaced from each other and from the plane of the bridge finger.

8. A string-tension adjusting mechanism as claimed in Claim 7, in which the levers are pivoted about a common axis to one side of a plane through pivot axis of the bridge finger and the longitudinal axis of the latter in its normal position, the longer arms of the levers extending from the said common axis towards the pivot axis of the bridge finger.

9. A string-tension adjusting mechanism as claimed in any preceding claim, in which one of the levers acts as a stop to restrict the pivotal movement of the bridge finger caused by the other lever.

10. Astring-tension adjusting mechanism as claimed in Claim 9, in which pivotal movement of the bridge finger caused by the said one lever is restricted by an adjustable stop.

11. A pedal steel guitar incorporating a stringtension adjusting mechanism according to Claim 4.

12. A stringed musical instrument incorporating a string-tension adjusting mechanism comprising a bridge finger pivotally mounted adjacent one end on the instrument body and resiliently biased into a normal operative position to tension to a desired pitch a string anchored to the said one end in use, two levers pivotally mounted on the instrument body about axes parallel to the pivot axis of the bridge finger, each having a cam surface for engaging a respective surface of the finger, and respective pull members attached to each lever, such that on pulling of each respective pull member the corresponding cam surface engages a respective surface of the finger to pivot it from said normal position, the pull members pivoting the finger in opposite respective senses and the engagement being such that, on release of each pull member, the corresponding lever allows pivoting of the finger from the normal position in the opposite sense to that which said lever causes.

13. A pedal steel guitar and a string-tension adjusting mechanism substantially as herein described with reference to, and as shown in the accompanying drawings.