Temperature Change affecting pitch

[John R Fortiner]

I don't know this for fact, but the odds are that cast iron doesn't
expand or contract at the same rate that piano wire does.  If piano wire
is "more active" with thermal changes that would explain, at least in
part, why the piano may go sharp with AC.  Reasoning:  Both metals
contract, but the piano wire is contracting at a greater rate of "x"
therefore its tension is increasing - causing a raise in pitch.  All of
this, as I stated above is assuming that the two metals do not expand or
contract at the same rate.

John R. Fortiner
Billings, MT.

On Wed, 29 Mar 2000 16:43:00 -0500 "Farrell" <mfarrel2@tampabay.rr.com>
writes:
> Now why would turning on the AC make a piano go sharp? The cooler 
> temp.
> would make the plate and case contract (albeit very slightly), thus 
> lowering
> pitch, and the lower humidity (because any properly operating AC 
> unit will
> remove water from the air, thus lowering relative humidity) would 
> tend to
> make the soundboard contract, again lowering the pitch. Why in the 
> world
> would it go sharp?
> 
> Terry Farrell
> Piano Tuning & Service
> Tampa, Florida
> mfarrel2@tampabay.rr.com
> 
> ----- Original Message -----
> From: "pryan2" <pryan2@the-beach.net>
> To: <pianotech@ptg.org>
> Sent: Tuesday, March 28, 2000 11:02 PM
> Subject: Re: Temperature Change affecting pitch
> 
> 
> > I learned the hard way that temperature has a immediate effect on 
> pitch.
> > When I go into one of the showrooms to tune a piano, I click on 
> the air
> > conditioning (I'm in South Florida), proceed to strip mute a piano 
> and
> begin
> > tuning middle strings with the SAT.  After getting half way 
> through the
> > piano, I go back to where I started and re-check my work. All the 
> red
> lights
> > are spinning sharp now. What do I do now? Start over or let them 
> go?
> What
> > I do now is turn the AC on in advance and let the showroom and 
> pianos to
> > cool down before starting.
> >
> > Phil Ryan
> > Miami Beach
> > -----------------------------------------------------
> >
> > ----- Original Message -----
> > From: "Larry J Messerly" <prescottpiano@juno.com>
> > To: <pianotech@ptg.org>
> > Sent: Sunday, March 26, 2000 7:15 PM
> > Subject: Temperature Change affecting pitch
> >
> >
> > > Just for my own information, when I came into my store this 
> morning I
> > > took pitch readings on two grands at 61degrees F. then turned on 
> the
> > > heating system and raised the temperature to 68 degrees.
> > >
> > > The 6' Kranich and Bach dropped pitch 3.2 cents initially and 
> then when
> > > (I presume) the plate temperature rose ended up 1.6 cents flat 
> of where
> > > it had begun the morning.
> > >
> > > The 5'3" George Steck initially dropped 0.4 cents then continued 
> to fall
> > > to 1.2 cents from where it had been.
> > >
> > > They have not changed any more over the last hour.
> > >
> > > No real problem or question here, just thought it was 
> interesting.
> > >
> > > Larry Messerly, RPT
> > > Phoenix/Prescott
> > >
> >
> >
> 

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