Humidity Change and Unisons

[Larry J. Messerly]

Thanks All,

I wanted to think that it was a function of the soundboard crown
increasing more on one side of the unison than the other.  If it did then
the pattern would reverse on the more trebble (Down hill) side.  It
didn't seem to do so to as large a degree, though it may play a small
part. 
 
I really like the explanation of the plate moving.  It seems more
plausible to me, especially after reflecting on how the strings are
connected to the plate.

I find it hard to believe that the cast iron is affected by humidity, but
it is in direct, clamped contact with the rim and the beams, and the
belly rail.  It seems likely that these put strain, torque, or tension or
a combination, on the plate.

Thanks for the mental workout.

Larry Messerly, RPT