[pianotech] pitch and temperature

[David Love]

You can do a very simple experiment.  Take a piece of felt (or a split
hammer shank) are rub a string vigorously enough to heat it up.  Measure the
pitch before and after and you'll find that it changes quite a bit depending
on how warm you get it.  If you wait for the string to cool again back to
the original temperature you'll find it goes back to where it started.
Temperature effects metal, humidity effects wood, simply put.  The change in
pitch coming from a change in temperature that is influencing the metal is
pretty instantaneous, the change in pitch that comes from the humidity
influencing the wood takes longer.  The change in pitch that accompanies
stage lighting for example, is due to a change in temperature on the strings
and happens pretty quickly, during the tuning.    

> 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
>
>