Humidity Change and Unisons

[Don]

Hi Ron,

Think of the plate as a lever. a very small change in angle at the point of
contact with the rim makes a large difference in pitch at the string. Any
easy experiment (or mistake LOL) that many of us made when we were starting
out was to do a pitch correction and then tighten the plate.

As for bridge *twist* affecting smearing of unisons the treble side string
is the shortest tail length so *if* (and goodness knows I don't know the
answer) there is a counter clockwise *twist* then the bridge pins would
cause a greater pitch change on the shorter string. Next time I encounter
this...I may try to do something with the front duplex area. I envisage
measuring the treble side string and then giving the capo bar a *tap* with
a hammer to release friction and then remeasure the right string.

Could you Ron make a list (or add to) in point form of the various factors
that *may* be changing as humidity rises.

soundboard *curl*
bridge *roll*
bridge *twist* (if there is any)

rim and frame shape change causing plate distortion:
plate angle
plate position
nose bolt rise


At 07:08 AM 08/22/2000 -0500, you wrote:
>>Hi Ron,
>>My hunch is that the plate is moving *more* than the soundboard...in the
>>area of c7 for example. 
>
>Ok, I'll bite. Explain why the plate would move more than the soundboard,
>and why that would more reasonably account for this unison smear.
>
>
>
>>Another hunch is that the upwards movment of the
>>sound board (which is an actually arching) causes a vector of force to
>>twist the bridge counter clockwise.
>
>The bridge does tilt forward and backward as it rises and falls because
>it's curved, and the center will move farther than the low end, and much
>farther than the treble. It's not just in one direction, and I don't see
>how this could have any effect on your smear.
>
>
>
>>Lets try to consider each possible factor and with a *thought* experiment
>>decide whether it would cause pitch to rise or fall. Then if we add all
>>theses compenents perhaps some cause and effect could be seen for the
>>smearing of the unisions--other than the broad brush of humidity.
>
>Go for it. I've told you what I think, and why.
>
>Ron N
>
>
Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.M.T., R.P.T.

Tuner for the Saskatchewan Centre of the Arts

drose@dlcwest.com
http://donrose.htmlplanet.com/

3004 Grant Rd.
REGINA, SK
S4S 5G7
306-352-3620 or 1-888-29t-uner