>From bridge to plate, then how can you account for one string of a tri-chord being 100 cents sharper than the other side, (which goes to the other note?) -----Original Message----- From: John Lillico, RPT <staytuned@idirect.com> To: pianotech@ptg.org <pianotech@ptg.org> Date: Sunday, August 20, 2000 6:03 PM Subject: Re: Humidity Change and Unisons >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 > > >
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