7. Adjusting Tarhus with Sympathetic Strings
Peter Biffin October 2019
Much of this topic has already been discussed in Post #5. The main differences are in the adjustments around the bridge when sympathetic strings are involved. For adjustments around the bridge of longneck tarhu and shah kaman, use the information below in this post (it is assumed that shah kaman will be using a type 3 cone).
The cone adjustment section below only contains specific information for longneck tarhu which was not included in Post #5. So far as cone adjustment for shah kaman is concerned, just follow information for Kamancheh Tarhu cones in Post #5.
Around the Bridge
1. Adjust the length of the bridge stick carefully such that when the bridge is sitting on the bridge pin, the bottom of the bridge is parallel to the bottom of the bridge-well. This is necessary so that the bridge pin will be able to slide right along the bottom of the bridge without changing the bridge angle. If the bridge stick is too long, when the pin moves towards the centre of the bridge the pin will lose contact with the bridge and will rattle. If the bridge pin is too short, when the bridge pin is moved towards the centre the pin will raise the bridge and break the contact between bridge stick and cone, again resulting in a rattle.
2. If the bridge stick is inadvertently made too short, a small disc of wood can be glued on. Because this is always a possibility, it is best to leave the end of the bridge stick unrounded until all adjustments are complete.
3. Once the lower angle of the bridge is nicely adjusted, proceed to adjust the top of the bridge in relation to bridge height/string action and bridge curvature. While it is not always possible to set the final height at this stage, it is worth trying to get it as close as possible.
4. Adjust string height at the nut. While this doesn’t have any particular significance for tarhu making, this is a reasonable point to do it.
5. Make an initial adjustment to the string-angle block immediately behind the bridge so that each string has just enough downward angle where it passes over the bridge so that it won’t buzz. This angle is much smaller than you would think if you are comparing it to something like a violin – for tarhus the angle required is barely perceptible. This adjustment will usually be done by filing grooves of the required depth in the string-angle block. This adjustment is best done a little bit at a time with frequent checking.
6. Proceed to adjusting the sympathetic string height. The sympathetic string height-adjusting block behind the bridge can be screwed in or out to raise or lower the strings. Again, the angle required is very close to no angle at all. Usually you would be checking this angle looking from the bass side of the bridge. Experience has proven that when making these adjustments, it is worth also looking at the sympathetic block from the treble side of the bridge as well – the perspectives gained from only the bass side usually means the sympathetic strings on the bass side will have too much angle and will be pulling the bridge up more than is desirable.
7. Now fine tune the balance between upward pressure from the sympathetic strings and downward pressure from the playing strings. Start with the bass side of the bridge. Pluck the bass string and immediately push upwards on the bass edge of the bridge with your thumb, lifting it up away from the cone. If the sound of the bass string is cut off straight away (because the bridge stick has been lifted off the cone) then there is either too much upward pressure from the sympathetic strings or not enough downward pressure from the playing strings. If the thumb pressure continues to lift the bridge and the sound is not cut off, then the reverse situation applies. Look carefully at the string angles of both sets of strings and make a guess as to which set you are going to change. Because the sympathetic strings are easier to change (and the changes are more easily reversed) that is the usual starting point. Once an adjustment has been made, check by playing with the bow. If there is still too much down pressure, that won’t instantly show up in a sound test. If there is still too much up pressure, distortion in the bowed sound is the usual result (especially with firm bow strokes). While it can be tempting to just put plenty of downward force on the bass side so that rattles are avoided, this will place the cone itself under tension which is not desirable from a sound point of view.
8. Now check the balance of up/down pressure on the treble side of the bridge. If you have too much upward pressure it will lift the bridge away from the bridge pin and allow it to rattle. Too much down pressure on the treble side will make the bridge pin difficult to adjust. The usual approach is to move the bridge pin around a little whenever the height-adjusting block is being adjusted, making sure there is enough pressure to prevent rattles, but the pin can still be moved without excessive force.
9. A way of achieving minimal pressure on the cone without rattling is to use powerful neodymium magnets inlaid into the end of the bridge stick and the top of the cone. The ones I use are cylinders 3 mm diameter x 2 mm long. They weigh only 0.1 gms each, so in that location they have a minimal effect on the sound.
10. On instruments that have a truss rod in the neck, adjust as necessary to optimise playability
Adjusting the Cone (longneck tarhu)
Since its creation in 1995, the general concept behind longneck tarhu cone design has remained unchanged. The main areas of experimentation have been: variations in cone size (which mirrored changes in body size); changes in the width of the edge; changes in aspect ratio. Below is a short list covering the cone dimensions and their matching body sizes along with the average tap-tone for each cone size. The intention is that these may be helpful in working out a starting point for cone adjustments regardless of the cone size.
Something to bear in mind with longneck tarhu cone stiffness is that the target resonant frequencies presented below are for an instrument with a very particular function in mind: an instrument that can be used equally as a plucked and as a bowed instrument. Whenever I have made adjustments on a longneck tarhu cone, I have evaluated it from both points of view. BUT: I realise that most longneck tarhu players don’t see the instrument the same way that I do, with most players considering it to be purely a bowed instrument. If you are adjusting a longneck tarhu from the bowed-only point of view, I would suggest using my tap-tones as a guide for the upper end of the desired stiffness range - my findings have been that resonant frequencies for bowed cones are generally lower than for plucked cones.
The first group of measurements are for the earlier body sizes explored: the first spherical longneck tarhu (turned bodies); the laminated bodies used for many years; hand-beaten brass bodies. The second group are from more recent work.
The cone measurements appear in this order: apex width; height; width of the cone only; total width of cone plus edge.
Tap-tone: 295 Hz
Body: 280 x 210
Body: 290 x 210
Tap-tone: 290 – 300 Hz
Tap-tone: 245 - 255 Hz
Body: 330 x 225
These two both used an offset cone hence the apex of the cone is smaller - with the apex directly under the bridge stick it doesn’t need to be as big.
Cone offset 15 mm
Tap-tone: 250 Hz
Body: 340 x 220
NB. Even though this is the biggest body used, the cone is slightly smaller than the one used in brass tarhus. This is because of the reduction in width necessary for the cone offset
Cone offset 15 mm
Tap-tone: 290 - 300 Hz
Body: 310 x 220