humidity and DC on grands

[J Patrick Draine]

Don wrote:

>
>
> I had measured the pitch *before* plugging in the DC system and then just
> before I left measured again. The pitch had dropped by 1.3 cents in 2
> hours. I felt very vindicated for cancelling the tuning appointment and
> felt much better about charging for a service call.

Don:
Seeing all this detail, just makes me wish for more data.
Temperature wasn't mentioned, but it is an important factor. Presumably the
ambient temperature appeared to be constant (i.e. air conditioning wasn't
turned off). Then there's the question of the temperature at the soundboard --
while we know the plate and strings can react quickly to a temperature change
(i.e. air blast from an air conditioner will cause a rapid raise in pitch),
how much of your pitch drop was the temperature affect on the soundboard, and
how much a change in its humidity content (my slightly educated guess is it's
the temperature change).
Any comments or rulings from you or others (Del, Newton, Laoshi Liu Baoli?)?

Patrick Draine