Regarding comments and questions that are arising from the recent Duplex Tuning classes I gave in Valley Forge and at Burlington there are a few points that might be worthwhile to mention here. I was delighted that at both these conventions we were fortunate to have excellent specimen instruments to work on in the seminars. Having instruments that are in fine condition in terms of board, block, strings, hammers and tuning to work on makes the effect of placement of the duplex scale contiguous harmonic bridges more effective. In Valley Forge I had an S & S rebuilt by Webb Phillips, with Abel Hammers and voiced by Wally Brooks, and at NEECSO I had an S & S rebuilt by Alan Day with new stuff, also voiced by Wally. In both these cases the increase in sustain by fine placement of the duplexes was dramatic. One question that I appear to have slighted in one class concerned the use of measurements to place the duplexes. I distinctly recall using the Duplex Equation posterboard in a few classes, but I may have missed one. The Duplex Equation is simply the algebraic representation of the acoustic relationship of the two string lengths, the speaking length and the duplex length with the third factor being the number of the partial of the speaking length that is the fundamental of the duplex portion. The equation is D x P = X. Where D is the duplex length, P the partial, and X the speaking length. The reason i don't dwell on this theoretical relationship is in my experience that the numbers don't come out perfectly most of the time. There is always a margin of error, slight though it may be. I find it more practical and useful to tune the duplexes by ear, tap tuning the bridges till I get the segments in tune. The second point I'd like to mention was an experiment i did on the NEECSO A in response to Shawn Hoar's grave concern about weakening the pinblock by turning the tuning pins down about a quarter turn, 80 degrees, which I find necessary in order to move the duplexes with accuracy and ease. Shawn is a notable rebuilder and his concern deserved my serious concern so I borrowed a torque wrench and took sample unison readings from five notes from the section I was working on. Lowell Wakker was present and helped me read some of the numbers. I was a bit more than surprised to find that there was zero average variation of torque readings before and after the procedure. In a few pins the reading lowered from 138 to 137 and in a few others the reading actually went up to 140, probably from the resetting of the pin. Out of 15 pins the torque on 11 or 12 was exactly the same. Hope these comments are helpful. If there are any more, fire away. Dan Franklin
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