[CAUT] pre-stretching new string?

[Richard Brekne]

Hi again


    There are two separate issues both influencing string length,
    ultimately:
    1) a change in the moisture content of the wood in the piano which
    influences the speaking length due to expansion and contraction 2) a
    change
    in temperature which changes the length of the string directly. 

Ok enough.


    The issue is how a change in speaking length affects a change in
    pitch and
    which factors contribute to the degree to which there is a change.

I've been saying this for quite a while now, and posted a very easy to 
follow algorithm for how do calculate just this.


    It's not that difficult, if you want to take the time, to algebraically
    alter the formula for string tension, diameter, length and pitch to
    isolate
    pitch as the dependent variable.  Set up two notes of equal pitch but
    different tensions/BPP etc.  Notice what must be different in order to
    achieve equal pitch.  Find out what happens to pitch with an equal
    change in
    speaking length of each. 

You can not solve for change in pitch directly by re-writting / 
re-arranging the formula for string tension. You can not because any 
given change in length automatically carries with it a change in tension 
i.e. you have two unknowns.... tension and length.  Length change is 
easy to calculate with the simple trig talked about. But that leaves you 
with an unknown change in  tension still. You could measure pitch of 
course and calculate the new tension that the new length resulted 
in...... but aside from being the long way around... we are solving for 
pitch.  Its easy enough to do... just calculate the change in length, 
and then the resultant change in tension.  Then you have all the 
variables you need to calculate for resultant pitch.

Thats.... for a string whose vibration period is truly reflected by the 
soundboard... and not altered significantly due to any stiffness 
issues... which just came up and of course sheds a different perspective 
on everything to the degree that thought ends up being significant itself.

Cheers
RicB



    David Love
    davidlovepianos at comcast.net
    www.davidlovepianos.com

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