The Tarhu System
The tarhu family uses a unique system where an extremely light-weight wooden cone is suspended in a spherical body. The strings are connected to the cone, which functions in a similar way to a soundboard except that it is much lighter for the same area - compared to a violin soundboard, a tarhu cone is roughly the same area but 1/10th the weight. This gives the instruments an unprecedented level of sensitivity and an increased breadth in tone-colour variations.
One of the most striking visual features of the tarhu is the carving in the upper half of the body. This carved dome both protects the delicate cone suspended inside and provides a rigid support for the edges of the cone. The inspiration for the designs comes largely from Mughal architecture and the shell of the sea urchin.
Sometimes the aesthetic choices in tarhu design tend towards the use of timbers with contrasting colours, sometimes towards an emphasis on form, with the timber choices focusing more on lustre and a homogenous colour.
Unlike almost all other acoustic stringed instruments, the tarhu system does not subject the sound-producing components to the destructive forces of string tension. This allows the cone to be constructed on acoustic considerations only. This situation is achieved by two means: 1. The neck forms a continuous structural beam right across the top of the dome, with the strings being attached to the neck at the head and behind the bridge. All longitudinal string tension is thereby taken by the neck
2. The angles formed by the strings passing over the bridge are carefully adjusted so that the downward pressure exerted by the strings on each side of the bridge is in a state of balance – the downward pressure on the cone is only just enough to prevent rattling and no more.
This structural design has other benefits; there are no glue joints in a tarhu that are under stress; any repairs necessary due to impact damage are facilitated by the fact that a tarhu can be dismantled into it’s component parts with comparative ease in minutes, require no refinishing after reassembly, and can be carried out without de-tuning the strings.
The design of the bridge greatly affects the final sound of a tarhu, and after many years work it has now become possible to make some of the most significant parameters adjustable. The bridge has two feet: one is active, and is connected directly to the cone; the other is passive, resting on the neck of the instrument where it passes over the body. The passive foot acts as a pivot in a similar way to a soundpost in the violin family.
The way in which the bridge affects the sound of the instrument is determined by a network of proportional relationships, which are all interrelated.
Some of these are:
The distance between the feet in relation to the spacing of the strings;
the height of the bridge in relation to both string spacing and spread of feet;
all the above in relation to the amount of down pressure applied by the strings on each side of the bridge.
Adjustable Bridge Pin
With recent changes to the bridge and the whole region surrounding it, the passive foot is now adjustable in two ways:
1. The bridge rests on a piece of spring-steel wire that can be moved either towards the edge or the middle of the bridge, changing the location of the pivot point
2. The effective length of the spring-steel wire can be changed by moving the supports on each end of the wire in or out, changing the degree of flexibility at the pivot point.
While many hours are spent adjusting the final sound of each tarhu for optimum performance, the bridge pin allows each musician a significant amount of personalised tonal adjustment.