[CAUT] Wire Stretch

[Leslie Bartlett]

Is there some source or "relatively easy" formula for calculating how much a
string must move through a termination point to produce pitch change?    I'd
like to have some tiny bit of basic information so that in describing pitch
corrections of significant distance I can use the information to explain the
likelihood that the piano will need a retuning in the near future.
thanks
les bartlett
 

-----Original Message-----
From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of John
Delacour
Sent: Sunday, April 29, 2007 3:31 AM
To: College and University Technicians
Subject: Re: [CAUT] Wire Stretch

At 9:57 pm -0500 28/4/07, Tim Coates wrote:

>I think Jeff Tanner asked a question that was interesting.  There was a 
>lot of discussion about crushed bridge surface causing the pitch to 
>drop, but then the thread changed to wire stretch causing
>the pitch to drop.  I thought his question was: which is it?   I 
>don't believe I've seen anyone answer his question yet.

It's easy enough to calculate.  If you have C76 of length 100mm at pitch
when lying on the surface of the bridge and then lower the wire 0.5mm into
the top of the bridge (some indentation!) then, all else, being equal, the
frequency of the string will drop about 0.026 Hz. 
producing one beat per 40 seconds against the proper frequency.  The
difference will be even slighter as the strings get longer.

JD

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