[CAUT] Bridges, humidity, pitch (was Re: calculating change in pitch for change in lengths)

[Fred Sturm]

On 8/10/07 11:38 AM, "Alan McCoy" <amccoy at mail.ewu.edu> wrote:

> Hi Fred,
> 
> Assuming constant tension (which may or may not be a good assumption), if
> the speaking length is shortened, why would the pitch become lower?
> 
> Alan
    You're right, that doesn't make sense, does it? In isolation, that would
mean higher pitch. My intuitive reasoning was trying to include tension in
that theoretical movement of wood, and I wasn't catching the contradiction.
Thanks for pointing it out. I guess I need to rethink the whole model.
    In practical, observational terms, I just tuned a Steinway D, #151100 or
so, with that section of mid treble bridge that is almost not notched. (It's
an example of that experimental period where they were trying to improve the
killer octave by having those unisons be "untunable" - each string lightly
different length).  A possibly good experimental setup to see whether
notching might have something to do with unisons movement in response to
humidity change (although the difference in length of the strings of each
unison throws another variable into the mix). One might theorize that if
normal notching was a major cause of the effect, it would be absent in that
section. And, sure enough, in the tenor and in the high treble, the right
(treblemost) string of nearly every unison was significantly sharp of the
left, while in that section, there was no pattern. Interesting grist for the
mill. (The piano is at a private school I have serviced regularly for many
years, and it was last tuned during the spring, at an RH about 40% lower).
Regards,
Fred Sturm
University of New Mexico