Humidity Change and Unisons

[John Lillico, RPT]

Such a long post I usually never read for I thought it was billbrpt! So, what's the answer to Don's observation about the right string being sharp on both grands and upright tri-chords? I still say it's the angle of the plate. On the other hand, vote for me! I'll find the answer!!!

John L.
Oakville

>>The sharpness of the tri-chord's right string at this time of year has to be 
>>on account of the shorter distance from bridge to plate. If there's a tail 
>>end duplex and the right string is sharper than the left, I think I'll go 
>>into politics.
>>
>>John Lillico, RPT
>
>
>Everything in a piano moves all the time, so anything you could name will
>be contributory in some direction in some infinitesimal manner. The bulk of
>this stuff happens because the string friction at the bridge is so much
>higher than at the aliquots, V bar, and counterbearing bar. The bridge is
>the dividing point. With any bridge height change relative to the plate,
>the total string length behind the bridge (rear bridge pin to hitch) is
>shorter, and changes in tension more than the total string length (front
>bridge pin to tuning pin) in front of the bridge. In a unison, the shortest
>of the three lengths behind the bridge changes most among those lengths
>behind the bridge, and the same happens among the lengths in front. When
>the tension differences in a single string are far enough apart on either
>side of the bridge, the friction across the bridge will be overcome
>somewhat and enough string will render through to get those tension
>differences close enough that the bridge friction will again hold them. The
>shorter the back scale, the more the front tension will change with a given
>bridge height displacement. Also, with identical back scale lengths within
>a unison, the string with the shorter total front length will change
>tension in that front length more than the string with the longer front
>length. It's quite possible, depending on where in the humidity cycle the
>piano was last tuned, how nearly equalized the tensions were between front
>and back scales when the tuning was done (which you can't know), where in
>the cycle it is now, and where in the cycle(s) it has BEEN since it was
>last tuned, for the unison to be in tune, right string flat of center flat
>of left, right string sharp of center sharp of left, or anywhere from here
>to there.
>
>There is absolutely no way to make any sort of reasonable assessment of
>what's happening in any specific instance with nothing more to go on than
>pitch, temperature and humidity records. Just as well vote for the guy with
>the coolest looking suit - as long as you're going into politics. Another
>little tip from your Uncle Wookie.
>
>Or maybe it IS the casters or fallboard knobs. I'll leave it to Jim B to
>soak us up some knobs and report back later.
>
>Ron N