[CAUT] temperature and pitch

[Jeff Tanner]

I was once tuning in the SC recital hall when an obvious malfunction 
occurred with the humidity control.  I noticed it happen immediately, when I 
felt the cool humidity falling from overhead and smelled the odor of stale 
water that was released by the system. My hygrometer, laying on the plate of 
the piano started up from somewhere in the mid 40% range and within 15 
minutes read over 70%.  I checked the tuning I had already accomplished up 
to that point and realized it had begun changing so fast that continuing to 
tune was a waste of energy. I just quit where I was, packed up my tools and 
left because I knew it would change back as soon as the system reset and 
restabilized.
Jeff

----- Original Message ----- 
From: "David Love" <davidlovepianos at comcast.net>
To: <caut at ptg.org>
Sent: Saturday, December 12, 2009 11:40 AM
Subject: Re: [CAUT] temperature and pitch


Are you suggesting that the moisture content of the wood of the piano
changes in 20 minutes enough to influence the tuning?  I don't think so.
Otherwise the piano in my house would go out of tune every time I boil a pot
of spaghetti.  Very simple experiment.  Take a wooden dowel and rub it along
the string with just enough force and speed to heat up the string.  See what
happens to the pitch and then see what happens when it cools.  Then, bring
your hot plate into the room with the piano and boil a pot of water watching
your hygrometer for a change in humidity.  After one hour measure the pitch.


David Love
www.davidlovepianos.com


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