[CAUT] temperature and pitch

[Ron Nossaman]

Fred Sturm wrote:
>     When you say "covered" you mean with a relatively waterproof cover? 
> So it is trapping heat and moisture, not allowing much exchange with the 
> air in the room?

Yes. I said warm moist air. If you're trying to make a case 
for humidity change here, be advised that the pitch goes sharp 
as the strings cool from the slightly elevated temperature 
from the heater bars under the cover. This is backward from 
the expected effect of a piano drying down very suddenly from 
elevated humidity levels, also under the cover. In my world, 
pianos go sharp with MC increases, and flat with MC decreases. 
Even for the sake of argument, do pianos react differently in 
yours?

To recap: Lowering MC lowers pitch, as does raising 
temperature (short term). Raising MC raises pitch, as does 
lowering temperature (short term). The short term condition 
means that the plate will eventually catch up with the strings 
and nearly cancel the early string pitch change. So, exposing 
a higher humidity and higher temperature piano interior to a 
lower humidity and lower temperature will, if the immediate 
reaction is to humidity, result in a lower pitch. If the 
immediate reaction is to temperature, the strings will chill 
slightly and go up in pitch (short term). Eventually, the 
plate will cool and the the pitch will drop some. Meanwhile, 
some time after the plate cools, the wood MC will drop 
(assuming less humid room), and the pitch will fall.

So my available evidence, and the timing thereof, indicates 
that these pianos are changing as a result of temperature 
change (short term), rather than humidity. They are long back 
under their covers before humidity changes become apparent, so 
they don't - at least not to me.
Ron N