Creating Tension II--Mechanisms for Tensioning Chordophone Strings

The sound of a chordophone is shaped by several interacting variables: the material, thickness, mass, structure, and tautness of its strings; the shape, volume, and design of and the materials used for its resonator; how the strings are physically linked to the resonator; and how and with what the strings are activated. The presence of a sustained level of tension in a string is an essential condition for sound production on chordophones, albeit an invisible one. However, there are visible design features on any chordophone that can reveal just how tension is created and regulated in its strings. This essay concentrates only on the subject of tension creation and control in strings, the systems that have been devised and applied by stringed instrument makers the world over to create musically useful tension in strings.

String Tensioning

Strings possess a degree of elasticity, a characteristic that allows them to be made taut when stretched but which also programs them to return to their natural state of looseness when the energy used to stretch them is removed. For a string to be useful musically it must be stretched taut and held in that state of tension (measured in a unit called newtons), a silent and invisible condition that we will refer to as its ‘resting position’. A string in resting position has elasticity and the potential to be set into modes of vibration (by being plucked, hammered, or bowed) that in turn produce sound waves. We are interested here in instrument designs that have been devised to establish the resting position of strings on chordophones. These designs involve the attachment of string ends to immovable parts of chordophone bodies (‘string carriers’) called here ‘anchors’, and to moveable components of string carriers that we will refer to as ‘tension-control machines’. Two basic string-tensioning designs are found on the instruments in this collection--designs with no mechanical tensioning device and designs that include a tension-control machine. While on some instruments the segment of a tensioned string used for sound production is the total length between its anchors or its anchor and tension-control machine, most chordophones include further elements (nuts, bridge-pins, pressure bridges, and tension bridge saddles) to articulate a shorter segment of string for sound production. These secondary elements will not be covered in this essay but are discussed in the individual chordophone entries.

The remainder of this essay focuses on illustrating the various forms that anchors and tension-control machines take on the chordophones in this collection. But before launching into this task we need to briefly discuss and illustrate another, easily overlooked design component of string tensioning systems--string ends. The design of a string’s end needs to complement the design of the anchor or the tension-control machine to which it is coupled. A sting with a straight end can be threaded through and wound around a rotating machine shaft or tied into a hitch knot around a stationary component of a string carrier. A string with a catch end terminates with a closed knot, a ball, or a stick that keeps the end from passing through an opening in a string carrier. Or a string with a loop end can encircle a protruding and immobile feature of the string carrier. These various string-end forms are illustrated in image #1, from left to right: straight end (also referred to as ‘tie end’); knotted catch end; ball catch end; stick catch end; and loop end.

Anchor Designs

The primary purpose of anchors is to provide resistance against the stretching force that is being applied to a string. Anchors can be in the form of: 1) the string carrier itself, be it rigid or elastic (such as with musical bows) or an articulated part of it; or 2) an object that is attached to and made integral with the string carrier. How the end of the string is designed and linked to the anchor is also very important to the success of a design. Following are several examples of anchor - string-end designs divided into two groups:

         Direct anchoring

The surface contours of some instruments are shaped in such a way as to provide a secure tie down for a string end. Bow blades (image #2) or stubs carved into the tips of them (image #3), a row of holes drilled into an integral foot (image #4) or the protruding end of a spike lute neck at the base of the resonator (image #5), or catch holes drilled in soundboards (image #6) and catch slits carved into the edge of a string carrier (image #7) are several design features built right into the body of an instruments that can serve as string anchors. The string-end forms seen in these images include: straight ends (image #2), loop ends (images #3 and #5); and stick ends (images #6 and #7).

        Indirect anchoring

Indirect anchoring involves imbedding into or attaching to the surface of the string carrier body immobile, resistance-creating devices to which the string ends are connected. These include screws (image #8), nails (image #9), tension bars (image #10), and pins (image #11), referred to here collectively as ‘hitch pins’, torqued or pounded into the body of the string carrier. Posts sunk into blocks at the base of resonators, called here ‘buttons’ (images #12 and #13), can themselves serve as string anchors, but on many instruments they are paired up with a tailpiece--one end of the tailpiece is secured over the button while the ends of the strings are connected to its other end (images #14 and #15). Tailpieces are also used on some spike lutes, were the stub of the neck at the base of the resonator functions like a button (images #16 and #17). Attached devices include tension bridges glued onto the resonator soundboard (images #18, #19, and #20) and hook plates (image #21). The string-end forms seen in these images include: straight end (images #10 and #20), loop end (images #8, #9, #11, #12, #13, and #21); ball-catch end (images #15, and #17), and knot-catch end (image #18).

 

 

 

 

Tension-Control Machine Designs

A tension-control machine is a mechanism that works with the inherent elasticity of a string and against the resistance provided by the anchored end of a string. Such a mechanism allows the performer to stretch or slacken the end of a string that is attached to it, therefore increasing or decreasing the tension in the string and raising or lowering the pitch of the string when it is excited. Tension-control machines need to create friction in their workings so that once the desired degree of tension has been introduced into a string the machine can successfully resist the natural tendency of the string to recover its original, un-tensioned state. Several distinct tension-control machine designs are found amongst the chordophones in this collection, and these are enumerated, described, and illustrated in the following paragraphs.

        Sliding friction rings

Rings, usually of woven rawhide strips (image #22) or of tanned leather (image #23), tightly encircle the neck of a chordophone and provide a tie-down object for a string end. There is enough surface friction between such a ring and the neck it surrounds to resist the inherent force in its taut string to return to its relaxed state. The performer can tune the string (modify its degree of tautness) by sliding the ring up and down the neck. In both examples of sliding friction rings the straight end of a string is tied with a knot to its ring.

         Rotating friction rings

Rings, usually of entwined rawhide strips (image #24), tightly encircle the yoke of a chordophone and provide a tie-down object for a string end. There is enough surface friction between such a ring and the yoke it surrounds to resist the inherent force in its taut string to return to its relaxed state. The performer can tune the string (modify its degree of tautness) by rotating the ring around the yoke in one direction or the other.

         Rotating screw

A metal screw (image #25) partially imbedded in solid material and with a string end knotted around it can serve as a tension-control machine. The surface friction between the screw threading and the material into which it is imbedded is sufficient to resist the inherent force in the stretched string attached to it to return to its relaxed state. The performer can tune the string (modify its degree of tautness) by rotating the screw in one direction or the other.

        Rotating friction pin

A stocky metal pin imbedded in or passing entirely through a block of wood and to which a string end is connected can serve as a tension-control machine. Two basic designs of tuning pins are found on chordophones in this collection--one typically used for zithers (including Western keyboard instruments including the piano), the other for harps. Here we will refer to them as zither pins (see image #26) and harp pins, respectively. Both pin designs share a number of features in common: they are cylindrical for most of their length; their diameter will be slightly larger than that of the hole in the pin block into or through which they are pounded; they will have a small hole drilled through them through which a straight end of a string can be threaded; and one end will have beveled faces (usually four) filed on it over which a cranking device can fit. Zither pins are pounded into holes that are drilled into a block of solid or laminated wood called a ‘pin block’ that forms one side or end of the instrument’s string frame. The beveled end of the pin sticks out of the block, and the hole through which the string end is threated is located below the beveled end but above the surface of the pin block (see image #27). Harp pins (see image #28) are pounded through holes that are drilled through the solid wood neck (which functions as the pin block) of the instrument. The beveled end of the pin sticks out from one side of the neck, the end with the hole through which the string is threaded sticks out the other side. For both types of pins, the surface friction between the pin and hole into or through which it is forced is sufficient to resist the inherent force in the stretched string attached to it to return to its relaxed state. The performer can tune the string (modify its degree of tautness) by rotating the beveled end of the pin with a socket wrench in one direction or the other.

        Rotating friction peg

A friction peg (see image #29 below) with a head and a (usually, but not always) tapering shaft passes through a hole or holes drilled in the string carrier. A string end is connected to the peg by threading it through a hole in the shaft, which can be rotated to serve as a tension-control machine. The fit between the peg shaft and the hole/s in the string carrier through which it passes is snug and creates enough friction to overcome the inherent force in the stretched string attached to it to return to its relaxed state. Four different friction peg mountings are found amongst the chordophones in this collection--neck, pegblock, peghead, and pegbox. Neck-mounted friction pegs are typically found on open harps (see image #30) and on Asian spike fiddles (see image #31). The pegs typically pass entirely through the neck from side-to-side or from back-to-front. Some lutes have a thick wooden terminus to their neck that can serve as a pegblock; tapering holes are drilled through such a block to accept the tuning peg shafts (see image #32). Other lute necks terminate in a flat board referred to as a peghead (see image #33). Tapering holes are cut through a peghead from its bottom side, each hole accepting a friction peg. The peg knobs (or buttons) are therefore located on the bottom side of the peghead and the string ends are wound around the exposed ends of the peg shafts on the topside of the board. Yet other lutes have a box-like structure, called a pegbox, carved into the top end of their necks. Pegboxes can be entirely closed (see image #34) or have an open top wall (see image #35) or open top and bottom walls (image #36). Regardless of the design of the ‘box’, the tuning peg shafts it supports pass through two of its sidewalls and the string ends will be wound around the segment of the shafts between those two walls. The performer can tune a string (i.e., modify its degree of tautness) attached to a friction peg (often by threading a straight string end through a small hole drilled in the peg shaft and winding any excess string length around the shaft) by rotating the peg knob in one direction or the other.

        Rotating bushing peg

A bushing peg looks very much like a back-mounted friction peg and, like the latter, is mounted on a peghead. However, looks can be deceiving. Whereas a friction tuning peg is an integral piece of wood (or plastic) that fits snugly into and creates friction with the lining of a hole drilled into a peghead, a bushing peg is constructed from a number of pieces of different materials connected together. Additionally, there is no contact between the rotating shaft of the bushing peg and the lining of the peghead hole it passes through. Although today there are numerous bushing peg designs to choose from, the older style bushing pegs found on the instruments in this collection (‘ukulele, banjo ukulele, tenor banjo) have the following crucial components (image #37): a wood, ivory, metal, or manmade material (such as celluloid or plastic) peg button/knob; a metal shaft that is basically cylindrical but at one end has two flat sides and also an internal threaded hole, and at its other end two raised rings on either side of a hole drilled through it; a short length of metal tubing (called a ‘bushing’) with fluted sides and a rounded cap at one end; and a small but long metal screw (image #38 shows all these elements assembled). The bushing fits snuggly into the peg hole from the topside of the peghead, leaving only its rounded cap visible. The bevel-sided end of the shaft is then inserted through the bushing but is forced to stop when its first ring comes into contact with the bushing cap. The bevel-sided end of the shaft protrudes from the backside of the peghead and fits snuggly into a hole in the base of the peg button. The long screw passes through the peg button from its top and is threaded into the hole at the bevel-sided end of the shaft. The mechanical friction needed to hold a string in a tensioned state is generated between the base of the tuning button and backside face of the peghead (image #39); the pressure between these two surfaces can be adjusted with the screw inserted into the top of the peg knob. The performer can tune a string (i.e., modify its degree of tautness) attached to a bushing peg by rotating the peg button in one direction or the other, which rotates the peg shaft that in turn increases or decreases the tension on the string the end of which is threaded through the hole in and is wound around the shaft.

        Rotating vertical tension peg

A few East Asian long zithers make use of a particular variety of friction peg that stands vertically on the backboard of an instrument. The peg itself has two intersecting holes drilled through it, one running vertically from the peg’s flat base all the way through its rounded top, the other horizontally through the peg a short distant above its base. A rope-like extension to the string passes through the body of the instrument after crossing over the fixed bridge on the topside of the instrument (image #40). From where the rope emerges on the bottom side of the instrument it is then threaded into the base of the peg, out one of the side holes to run halfway around the peg before re-entering the peg through the other side hole, and then upwards through the remainder of the vertical shaft. The rope is then tied in a stop knot that keeps the rope from being pulled back through the peg. Basic tension is introduced into the string by pulling its other end while winding it around a knob protruding from the backboard at the other end of the instrument. This tension holds the base of the tuning peg tightly against the baseboard and in its vertical position (image #41). Fine-tuning adjustments to the string tension are made by rotating the peg; the friction necessary to hold a desired degree of tension is generated at the interface of the peg base with the backboard of the instrument.

        Rotating geared machine head

The mechanically most complicated string tension-control device is commonly referred to as the ‘machine head’. Unlike the above-described devices this one includes gears, and it is in the gearing that the friction necessary to hold a stretched string in tension is generated. The components of a machine head are (see image #42): a metal plate to which a worm gear is mounted horizontally, the shaft of this gear terminates in a peg button/knob; and a cylinder called a ‘roller’ with a pinion gear at one end, the roller passes through a hole in the plate but is stopped by the pinion gear. The pinion gear interlocks with the worm gear on the topside of the plate, which introduces a right angle and friction into the rotational motion of the machine. Two basic machine head designs can be distinguished by how the roller is situated in relation to the peghead to which it is attached: in one design the machine plate is mounted on the backside of the peghead (image #43), the roller passes vertically through a hole drilled in the peghead and its distal end is left unsupported (image #44)--this will be called here the ‘capstan’ design (vertical standing roller with unsupported end); the other design has the machine plate (often with a row of four or more machines) mounted on the side of a slotted peghead (two parallel longitudinal slots cut through the peghead), the rollers passing through holes drilled in the side of the peghead and the open slot before their distal ends fit into shallow depressions in the side of the dividing wall of the slotted peghead (image #45)-- this will be referred to here as the ‘slotted-peghead’ design (horizontal rollers with supported ends). The roller has a hole drilled through it to accept the end of a string; the excess length of the string is wound around the roller by rotating the machine head peg button, which is also used to make fine tuning adjustments. ‘Slotted-peghead’ machine heads are found on most varieties of modern classical guitars, some types of mandolins, the tres cubano and some charango. A variation of this side-mounted design is found on the double bass, which has a pegbox rather than a slotted peghead (see images #46 and #47). ‘Capstan’ machine heads are generally found on banjos, folk guitars (steel-strung and dobro), some mandolins, balalaikas, and electric guitars and electric basses.

Bibliography

Adkins, Cecil. 1984. “Machine head.” NGDMI v.2: 587-588.

Campbell, Murray, Clive Greated, and Arnold Meyers. 2004. Musical Instruments: History, Technology, and Performance of Instruments of Western Music. Oxford: Oxford University Press.

(by Roger Vetter)