[CAUT] pre-stretching new string?

[Fred Sturm]

On Jun 7, 2007, at 2:21 PM, Fred Sturm wrote:

> One of the Fandrich's (I forget which, but think Darrell) wrote  
> about pitch change due to elongation of the bridge toward the tenor  
> end about ten years ago, citing speaking length change as a major  
> factor.

	I looked up that article, (7/96, by Darrell), and confess I am more  
confused reading it today than I was then. Very interesting article,  
filled with calculations and observations. I _think_ the point he was  
making was about treble bridge expansion "along the grain" causing  
greater pitch change at the bottom of that bridge, based on the  
bridge pins "pulling" (elongating) the wire (ie, friction between  
pins and string allowing the bridge to pull the string away from the  
front termination, thereby raising tension). He writes of creating  
greater physical stability in that area of the soundboard assembly  
(adding wood and screws), and that this had a noticeable and dramatic  
impact on stability of the bottom of the treble bridge. But I guess I  
don't really follow all his explanations. DIdn't at the time, to the  
point of writing a long and rather pompous letter to the editor  
finding fault with his calculations. [It can be rather embarrassing  
to look back at oneself from a perspective of ten years later <G>.]
	Anyhow, there are a few articles by Del, mixed with a couple by  
Darrell, and a few letters by yours truly in that period of a few  
months before and after, speculating about wood and moisture and  
pitch. Perhaps we are a little farther along in our knowledge of  
these things now. Sometimes I wonder <G>. I promised to do a whole  
lot of research in a couple of those letters. Never found the time to  
do it right (documenting). Just kept observing and puzzling. I feel a  
lot more puzzled now than I did then. I think I know a good bit more  
about how things behave (as in what pitch change is observed  
following humidity change, what patterns occur, and what variants),  
but the mechanism and the theory behind it are more clouded than ever  
- much more complicated.
	I will say that Ron's observations about bridges and bridge pins are  
definitely an enormously valuable contribution to the mix. I'm  
curious about what data is out there physically and accurately  
measuring soundboard rise and fall on strung pianos in response to  
humidity change. Have there been such measurements? One reads a lot  
of assertions about seasonal increase/decrease in bearing and crown  
and its affect on tone quality. Is that just fertile imagination, or  
are there physical measurements to back it up?
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu



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