Why a string goes out of tune.

Ron Nossaman rnossaman@cox.net
Tue, 13 Apr 2004 11:06:24 -0500


>So does this mean I should pound to equalize the string? If I don't pound, 
>and the string doesn't equalize across the bridge, then when the pianist 
>plays hard and does move the string, then the piano will be out of tune.

Wim,
What's the difference between a lot of medium hard blows and a lot of hard 
blows? Mostly, it's string tension in the speaking length. If you're 
expecting to pull back scale through the bridge to equalize segment 
tensions, what are you accomplishing when the back scale tensions are 
already higher than the speaking length tension? In an attempt to balance 
tensions, you can just as easily introduce imbalances. By all means, whack 
'em hard once or twice to see if they are going to move, but take the 
pounding down a couple of notches and see what that does for your control. 
I'm not saying tune softly. I still make a heck of a racket tuning, but I 
don't pound. If I do pound, I find just the problems you describe. Or more 
of them, in any case. The problem here is that we can't directly measure 
friction, torque, and tension levels at the pin and throughout the string. 
We're looking at a complex system through a pinhole, with our only 
indications of the condition of the string tensions being what we hear, 
what we feel through a lever that we brought with us (that's not even part 
of the system), and our mental visualization of what we think it is we're 
doing when we're guessing about most of the conditions of the system. We 
have control of our lever, and we know how to hear the beats. That's the 
tuning part. What we don't have is an accurate measure of the physical 
state of the string and pin. That's the stability part.


>The other thing you're saying is that a little change in temperature or 
>humidity will cause a string to go out of tune. I can accept that to some 
>degree. I saw your demonstration of that at one of the conventions. But 
>you were taking a hair drier to a string on a mini back. On the concert 
>stage, most of the time a piano is not going to be subjected to that kind 
>of extreme changes. I would think that having the string equalized would 
>prevent most microscopic differences.

A string reacting to stage lights doesn't care if the segment tensions are 
equal on both sides of the bridge. The tension changes from the lights 
won't be anywhere nearly enough to pull a string across a bridge unless the 
segment tensions already weren't even close to the same and it was about to 
move anyway.

Ron N


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