[pianotech] pitch and temperature

[Tony Caught]

Hi Ron,

The land I take it is in the middle of the swamp with a few gators for
company.

My Take.
"a loaner sat on the moving van in freezing weather overnight"
Drives the moisture out of the soundboard. 

"brought on stage indoors in a warm theatre"
Soon as the piano hits the air it starts to absorb moisture at a (scientific
word) fantastic rate.
Soon as you open the piano to tune it the moisture absorbsion rate
increases.

I found out a long time ago that removing a piano from indoors at 21 degrees
C and 40%RH to outdoors at 32 degrees C and 80% HR and then tuning it to be
to say the least, challenging. The temp does not change that much but the
piano keeps changing whilst you are tuning.

Now you say that the strings change 1/2 way through the tuning. The question
is is this caused by the soundboard expanding or shrinking or the strings
expanding or shrinking.

Or, my head just shrinking so the sound is expanding.

Tony



Tony Caught
acaught at internode.on.net

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Monday, 10 January 2011 3:33 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] pitch and temperature

On 1/9/2011 8:57 PM, Gene Nelson wrote:
> Thanks everyone,
> I was trying to come up with a chapter technical on the subject.
> Possibly an approach from co-efficient of expansion for steel piano
> wire, isolating for the one thing that moves the fastest and possibly
> the most? The math is beyond me.

The math is pretty simple, and I'm math deaf. The expansion coefficient 
of music wire and gray iron are pretty close. The difference is in the 
cross section of the parts. It takes little time for a temperature 
change to migrate through 0.040" diameter wire compared to 0.5" iron. 
That's it.


> My challenge was a couple years ago in the winter, a loaner sat on the
> moving van in freezing weather overnight, brought on stage indoors in a
> warm theater and I had about an hour to work with it.
> Gene

There's the problem. The strings changed fairly quickly, maybe up to 
half way through the tuning, where the plate caught up about four hours 
later. This is an impossible situation, and any tech who hopes to 
anticipate the changes and accommodate them to all come together in a 
good tuning at a specific time is eligible for a really good land deal I 
have available in Florida.
Ron N