strict temperature effects

[Dick Beaton]

James...
Normally when the temp goes up the pitch drops because the strings lenthen
(expands).  However, I recently had an experience with an old upright that
sat out overnight and got real cold..near freezing.  The piano was moved
into a theatre where I was waiting to tune.  I checked the pitch and it was
about 30 cents or so flat. I raised the pitch and decided to come back
later and tune it after the temp had equalized.  The plate was very cold! 
When I came back a couple hours later the piano had gone 25 cents or so
sharp!  I figure the plate was warming up (expanding) and stretching the
strings. So I lowered the pitch and had a fan blowing ion the piano for
awhile to get the temp down in the ball park, then I tuned it.  A jazz band
used that evening and from what I hear all went very well.  Haven't had a
chance to check it since.
Anyway that should give y ou something to think about...even experiment
with.
Dick Beaton RPT Helena, MT

----------
> From: james payne <jlpayne@netw.com>
> To: pianotech@ptg.org
> Subject: strict temperature effects
> Date: Wednesday, March 11, 1998 9:02 AM
> 
> Can anyone help me with a little research project I am pursuing? I am
> trying to figure out the effect of temperature changes on the pitch of a
> piano. We know that changing the temperature of the air will normally
> change its relative humidity, hence the moisture content of the
soundboard,
> and hence pitch. My question is, if relative humidity were kept constant
so
> that no soundboard changes occurred, what happens to the pitch of a piano
> when its temperature is raised? Does it go sharp, or flat, or not change?
> I’d be happy to hear about a) any speculations or theories; b) any
> empirical data or experiences; c) anything written on the subject.
Thanks.
> Jim Payne, RPT Sandpoint, Idaho: jlpayne@netw.com
>