[CAUT] temperature and pitch

[Elwood Doss]

Fred, et al.,
It is my observation that it is the soundboard swelling and contracting with the change of humidity that takes place with the change of temperature that causes the pitch change.  As the soundboard swells, pressing up on the bridge, the strings tighten and the pitch goes sharp.  The opposite takes place when the soundboard contracts as the humidity level decreases in the air around it.  I should think wood will respond to humidity/temp changes much more quickly that metal.  After all its the humidity change with the rise/drop in temp that has such a profound effect on the tuning of a piano.

I would suggest that the change in metal, whether the plate or strings, with a 10° temp change would be negligible, especially compared with the response of the wood board.

I work in the Mississippi valley and, as with other parts of the country, we have wide swings of humidity.  In the buildings at UTM, there is a wide swing of temp and humidity changes...from 30%/78° in the dead of winter with the heat on, and 80%/72° in the middle of summer with the air conditioning on.  In fact, my rule of thumb is pianos like cool, rather than warm, interior temperatures.

I recall tuning a Baldwin Studio upright at a small Methodist church in mid-December.  They turn the heat/air off during the week.  I asked them to have the heat set at the same temperature that they worship which they did.  It was cool but comfortable.  In mid-January I received a call from the mother of the pianist who said the piano sounded horrible the Sunday before.  I made an appointment to meet the pianist at the church.  As I entered he was playing and the piano sounded quite in tune.  I noted the temperature was about what it was when I tuned it. As I walked down the aisle, the pianist noticed my presence and exclaimed the piano sounded great.  I asked him if this was the normal temperature and he said; then added a caveat..."when the little old ladies come in they jack the thermostat way up." 

I tune the piano at the small church where I serve and more than once I've thought to myself during the morning worship service that I need to get over here and tune that piano, a Baldwin spinet.  During the evening service on the same day I'd think, "the piano sounds great."  The difference...the heat/air was left on all day and the piano had an opportunity to acclimate to the temp/humidity level which was the same as when I tuned it.

I feel these two examples are due to humidity changes that corresponds to the temperature changes, rather than changes in the strings/plate.  Certainly the strings and plate can be affected by temperature changes but I don't see that as a primary reason we see such a change in tuning stability with a 5° to 10° change in temperature.

Joy!
Elwood


Elwood Doss, Jr., M.Mus.Ed., RPT
Piano Technician/Technical Director
Department of Music
355 Clement Hall
The University of Tennessee at Martin
Martin, TN  38238
731/881-1852
FAX: 731/881-7415
HOME: 731/587-5700
-----Original Message-----
From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of Fred Sturm
Sent: Friday, December 11, 2009 10:50 PM
To: caut at ptg.org
Subject: Re: [CAUT] temperature and pitch

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