Thanks Jim, This is a golden nugget to think on. Joe Goss RPT Mother Goose Tools imatunr at srvinet.com www.mothergoosetools.com ----- Original Message ----- From: "James Ellis" <claviers at nxs.net> To: <caut at ptg.org> Sent: Wednesday, March 08, 2006 9:00 AM Subject: [CAUT] Unison Drift and Humidity > There is an ongoing discussion about left-to-right-string unison drift > associated with changes in relative humidity. Fred Sturm and I have been > discussing this off list. I have observed this phenomenon for decades on > end. What I'm talking about is not due to tuning technique, and it's not > the same in all pianos. In some pianos, it's excessive. In other pianos, > it's almost nonexistent. > > Generally, I find it to be worse in pianos with solid bridges, and least in > pianos with thin hardwood laminated bridge caps. In typical cases, I think > it has to do with the expansion and contraction of the bridge due to > humidity changes, and the pattern of the bridge pins relative to the bridge > grometry. In one case I observe from tuning to tuning, I believe it comes > from shrinking and swelling of the pinblock, but this is an atypical case. > It's not what I usually find, and I think in most cases, this drift does > not come from the pinblock. In most cases, I think it comes from the > shrinking and swelling of the bridge. > > There are so many variations to this phenomenon that I can't say it's any > one certain geometric configuration, but I do believe in most cases it's > due to bridge swelling and shrinking due to changes in relateve humidity as > it relates to the pattern of the bridge pins. Due to the side bearing, the > slightest change in pin spacing will have a profound effect on the tension > of the string, and if that change in pin spacing is not exactly the same > for all three unison strings, they will go out of tune with each other. > > Jim Ellis > > _______________________________________________ > caut list info: https://www.moypiano.com/resources/#archives
This PTG archive page provided courtesy of Moy Piano Service, LLC