Well-Tuned Duplexes (was!Re: Songwriters, ect.)

[Duplexdan@AOL.COM]

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