Hi Perhaps in some pianos the pins move back and forth (pivot) as humidity swings? and longer length is the one that moves the most in pitch? This longer one is also the shortest one at the other end. I have seen but not actually measured the change in angle. Of course in these cases the piano has also been out of tune by a considerable amount. As to the pitch rise from a broken string--did you measure the bridge height before and after -- or just the pitch change. If you only measured pitch change you really can't point to the cause. I really believe plates and hitch pins in particular move a lot more than we give them credit for, and that both the plate and hitch pins are quite elastic. At 07:26 AM 8/18/00 -0700, you wrote: > Oh, and about the question of a string breaking, and what happens to the >pitch of the adjacent strings; They go sharp. The bridge has the same >tension on it, but with fewer strings the remaining strings have to absorb >that tension. When they do that, they go sharp. I've seen this, and measured >it, so on this one I know that it happens. >-----Original Message----- >From: Paul <tunenbww@clear.lakes.com> >To: pianotech@ptg.org <pianotech@ptg.org> >Date: Friday, August 18, 2000 6:17 AM >Subject: Re: Humidity Change and Unisons > > >>John >>What you suggest about the plate being affected infers that it is >>hygroscopic like wood. I've worked in machine trades around many kinds of >>metal including many types of cast-metal poured into a mold for shaping. I >>cannot recall ever hearing that any metal takes on moisture, or at least >>enough moisture to change its shape. Temperature is another matter. But >>metal moving temperatures are usually not in a home environment around a >>piano. I live in SE Minnesota where humidity changes of 30% and more can >>occur daily. Pianos here are always shifting. I figured the pitch >difference >>between the left, center, right string in a unison is the result of >>soundboard and bridge cap movement. When humidity rises, wood takes on more >>moisture and becomes bigger. This movement changes the tension of the >>strings. Consider the formula for calculating pitch. If you alter any >>element of the formula, the resulting pitch will also be altered. A tricord >>unison has three different lengths (beyond its speaking length). When the >>same amount of tension change is used in pitch calculation for each string, >>the shorter string will come out with a higher pitch. I verified this >"idea" >>in conversation with my math major daughter and physics major son. They >>concurred.( although most of the time they were way beyond my math >>abilities. They used words I can't even pronounce let alone spell here.) >>They helped me dust off my high school algebra and figure this out. This >>seems to bear out because the most amount of unison pitch deviation occurs >>where the sound board and bridge react the most to humidity fluctuations. >> >>I would like to hear from someone with some metallurgy experience and shed >>some light on the affects of moisture on metal shape. I don't know your >>backgrounds, so maybe one of you has this experience. >>Just my thoughts. >> >>Paul Chick >> >>Don wrote: >> >>> >Hi John, >>> > >>> >I agree that a broken string will cause the plate to move. But the same >>> >effect would happen without a soundboard/wooden support structure. How >>does >>> >humidity affect the plate? (Other than rust in extreme cases). >>> > >>> Don, >>> >>> I was tempted to say, "heavy metal" but........ >>> >>> Throw away the soundboard and bridge and just have your strings and >plate. >>If the plate doesn't swell with humidity, although I think it might, it >will >>at least be tilted somewhat through expansion of that upon which it rests. >>> >>> This may not be as extreme where you have those "adjustable" duplux >>doohickeys on some grands though. >>> >>> John Lillico, RPT >>> Oakville, Ontario >>> >>> >>> >> >> > > > 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
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