By "treble break" I assume you mean the break between the bass and the tenor, not the break about an octave an a half above middle C. The tenor break is where I find the most pitch variation. I find it on the lowest tenor notes, sometimes extending up to about A4, usually not much farther. The highest notes in the bass will vary some too, with the changing seasons, but not as much as the low tenor area. I've been telling clients for years that it's because of the soundboard absorbing and losing moisture and thus rising up and down (increasing and decreasing crown) because its edges are restrained, not because I've observed and measured it, but because that's what I've heard from other techs and books on pianos over the last 30 years. I think that phenomenon probably does happen, but apparently the math shows it does not happen to a large enough degree to cause the pitch changes we observe. >> This tells me that: 1. This can't possible have to do with >> soundboard rise/fall. 2. There is some sort of twist >> happening in the structure, with the pivot being at the >> treble strut. How else could flat notes be right next to >> sharp notes? << You mean the low tenor is flat and the upper bass is sharp? And that it's vice versa roughly six months later? What would the pivot be? What actually twists -- the whole wooden frame (of an upright)? Then you'd think two diagonally opposing casters would come off the floor. Or that the plate would crack from the strain, in an upright or a grand. Or that the top and bottom panels would rub and not fit properly at certain times of the year. By "structure" do you mean the wooden back (top beam, bottom beam, backposts); or in a grand, the rim, belly rail, and radiating beams? Or are you including both the rim and the plate? How much can the plate twist without cracking? Not challenging anything here, since I'm not a designer/rebuilder -- just trying to understand so I can tell clients what's really happening. There also was an article years ago about bridge elongation down in the low tenor, by Fandrich, I believe, but I never understood how the bridge could elongate when it's glued to the soundboard, unless they elongated equally (unlikely, with one being maple and the other spruce). Confused, --David Nereson, RPT
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