[CAUT] temperature and pitch

[Fred Sturm]

On Dec 11, 2009, at 4:07 PM, David Love wrote:

> Can't comment on the amount of change per unit of temperature but  
> the speed
> with which it happens is fairly quick.  Started tuning a piano in a  
> church
> this morning with the temperature about 50 degrees at the start.   
> Pitch was
> about 2-3 cents sharp in the tenor section.  Tuning up from there by  
> the
> time I got to C5 (20 minutes or so) the temperature had risen to 70  
> with the
> heat on and a remeasure of the tenor section showed that the pitch  
> was about
> 2 cents flat--pretty uniformly.  Steinway D.  It does show that  
> there are
> clearly two aspects to pitch swings.  Temperature in which probably  
> the
> metal parts are affected, and humidity in which the wooden parts are
> affected.


What I think my example shows is the whole thing, strings and plate,  
getting to the new temp and stabilizing there. Strings themselves move  
pretty fast, especially if there is a bit of air movement with either  
hot or cold air moving, or radiant heat (sun, stage lights). Some of  
that is bound to be happening if the temp is rising in a room by 20  
degrees over 20 minutes. That is one thing. But another thing is the  
plate catching up with the temperature change, and possibly/probably  
counteracting the initial pitch change a bit. I am assuming that  
happened thoroughly overnight in my example, that plate and strings  
had plenty of time to come to a stable new temp.
	Not that this is some kind of definitive proof of anything. I just  
had the opportunity to take data from an experiment that happened  
without my needing to go to any effort. So I did so and documented it  
"for the record." One Steinway A under the conditions I described did  
what I described.
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu