[CAUT] pre-stretching new string?

[Don]

Hi,

The numbers don't support soundboard rise and fall (this also elimates ribs
as a factor). However it *is* clear that wood is somehow
involved--otherwise Damppchasers would not have significant effects.

We are left with bridges, the main wooden frame, and the pin block.

In uprights the main wooden frame is outside the influence of a DC
system--but adding a back cover does improve response. Typically on large
uprights without back covers pitch change in one year is 6 to 10 cents at
A4. With a plastic back cover that drops to 2 to 3 cents (sometimes 1 cent
or less).

In small quality uprights (say Yamaha P22) pitch change at A4 varies about
4 cents for every 5% change in humidity.

In grands the pin block is usually not well controlled by a DC system
unless the lid is kept fully closed or a full cover or an Edwards string
cover is in use. I know at least one technician who insists that the lid be
fully closed except when the instrument is being played (he, oddly enough,
hasn't installed any bottom covers). With a bottom cover response with a DC
system is typically 6 to 10 cents pitch change at A4. I don't have any data
for Edward's string covers. Without a bottom cover DC systems are (at least
where I live) almost futile.

I think that brings the focus of pitch change directly to the bridge and
bridge pins. That #2 is possibly the main frame, and #3 is the pin block.

If I had to guess at distribution numbers for a 20 cent pitch change at A4
I'd distribute the numbers as 9 cents for the bridge/pins, 7 for the main
frame, and 5 for the pin block.

Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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