Why a string goes out of tune.

[David Ilvedson]

Jim,

So wouldn't a slippery bridge pin be advantageous in helping to eliminate this "set".   I would think a graphited bridge cap should be slippery enough?   
I understand we can't equalize the tension in all the segments because why?  They are different lengths?  

David I.



----- Original message ---------------------------------------->
From: James Ellis <claviers@nxs.net>
To: <caut@ptg.org>
Received: Mon, 12 Apr 2004 22:20:24 -0400
Subject: Why a string goes out of tune.

>Wim,

>If you didn't understand what I was saying, I feel sure there are others
>who didn't as well.  I'll try again.  You say you can't believe that the
>pitch of the speaking length can be changed as much as 50 to 100 cents
>before the string will move at the bridge.  Well, I can, because that's
>what I measured.  It will depend upon how much of a "set" the string has
>taken at the bridge.  I would expect it to be more in some cases, and less
>in others.  I'll admit I did not take many measurements.  I plan to make
>more measurements in the future, and I expect to find a very wide range of
>values, for the very reason I just mentioned.

>No, Wim, I am NOT saying playing the note softly will equalize the tension
>across the bridge.  You know that.  I said pounding will cause it to move
>if it is about ready to move anyway.  If the tension is not equalized
>across the bridge, but the string is about ready to move, but you play
>softly, nothing will happen.  But if you do pound, or if the pianist
>pounds, then it will move, and the pitch of the speaking length will change.

>Now consider the fact that you have a whole bunch of strings whose tensions
>are only partially equalized across the bridge, because there is no way you
>can completely equalize it.  All it takes is for the relative humidity to
>change, the bridge to swell or shrink, or the temperature to change so that
>the difference in expansion coefficient between wood and steel will cause
>the string to slip a microscopic amount at the bridge, or someone to pound
>the key; the string will move at the bridge, and your perfect unison tuning
>will be spoiled.  I think this makes lots of sense.

>Sincerely, Jim Ellis


>_______________________________________________
>caut list info: https://www.moypiano.com/resources/#archives