high humidity (was tapping strings)

[Fred Sturm]

For my part, I am pretty well convinced that soundboard
movement/swelling is the major dimensional change affecting tuning.
Large area, hygroscopically active wood, constrained around the rim. A
small dimensional change gets magnified by the rim constraint to
generate a large push upward (assuming crown). Cross sectional swelling
by the bridge comes nowhere close. (Take an 8 1/2 x 11 sheet of paper.
Hold down one end and push the other 1/4" toward the constrained end.
Watch how high the middle goes up. You'll be amazed.)
	But it's very complex, as the push upward is countered by various
twisting pressures exerted by strings (especially considering variations
in waste lengths toward the hitch pins). How pitch is affected is partly
determined by relative tensions (if you want some of my take on why the
tenor area is often affected the most, go back about 8 years or so in
the PTJ to a series of letters back and forth). 
Fred Sturm
University of New Mexico

Michael Jorgensen wrote:
> 
> Ron,
>     If the bridge were most of the cause,  why does the low tenor go so far
> sharp?  It seems to me that if the bridge uniformly grew taller, the
> shorter/higher strings should change most?
> -Mike