[pianotech] rescaled bass string "error"- formula & explaination

[David Renaud]

Hello

    I have always allowed my string making to make all calculations
and rescale so have not myself learned and digested the science of it.

   Now am am faced with the need to explain to a technician why something
is wrong and does not work......or admit to being wrong. I would appreciate
help from someone well versed in the science of rescaling.

   I have observed bass string unisions throughout a piano with windings that vary about 5mm left to right consistently across the bi cords. The string lengths on a big piano may be identical left to right, but on a smaller grand do  vary left to right. Somebody has made it a priority to match the winding lengths even though the string lengths are 5mm different left to right. This leaves the same winding lengths but very different bare wire lengths  near the termination points.

   Measuring harmonics with tunelab I get at least a 2 cent spread 
at the 6th or 8th partial with the windings like this. I have been 
measuring differentials in grands I like and get .2 -.3 spread.
I find these odd bi cord unisions difficult to tune. Also I have never
seen Bi cords that visually look like a zig-zag at the winding termination
points by design. Somebody is convinced this is best and making it a common practise. I hope to prove that it is indeed wrong, or understand the choice.

   My hypothesis is that the in-harmonic result perhaps varies linearly with string length but exponentially with stiffness and therefore a big variations in bare wire near termination points is messing with the strings overall stiffness in a much more profound way then any other consideration.

   Can somebody in the know address this and shed some light on the 
dos and donts, hows and whys here......

   I have let others do rescaling for me specifically for fear of
messing something up like I think this is messed up. 


                                    Much appreciated
                                    Dave Renaud
  




   



 




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