Pitch raise and Stability

[Baoli Liu]

Hello Les and list,

After pitch raising,the shape-change of soundboard and other wood
parts is one of the main factors to influnce stablity.

Wood is a kind of "non-whole-elastic"material,or "sticky-
elastic"material,it's diffrent from steel and many other materials.

If you add force to a steel spring,the spring will change its shape
imediatly and then keep the shape or length for ever,
if you add force to a wood parts,the wood parts will change  it's
shape imeddiatly(but partly) and then keep it's shape changing for
a long time.

So,a "quick pitch raise" is diffrent from a "slower pitch raise".I
usually spent a definate time to finish a pitch raise,no break.

The structure of piano  is diffrent from piano to piano,so pitch
raise (or overpull) should be diffrent. one-fourth is only an
average  overpull for most pianos,some time it's not enough, some 
time it  may be too much.

Here  is some of my experince,hope it's a little help to a few
colleages. (assuming the piano is flat)

new string,more overpull;
new pinblock,more overpull;
new soundbord,more overpull;
loose pin,more overpull;
the lower bass strings,less overpull;(why? see the location of
bridge)
the lower tenor string,less overpull;
the higer bass string,more overpull;
above c4 or so,more overpull;


Thank you for your attention!

Baoli Liu

(summer) technician at the Interlochen Arts Center
visiting scholar at the College-Conservatory of Music,University of
Cincinnati