>>>I have always considered sound board rise (or fall) to be the biggest >>>factor in seasonal pitch changes >> >>Everyone always has, as far as I know. But then we've thought the pitch >>drop during a pitch raise was from soundboard deflection too until fairly >>recently. > >And we still dont really know for sure that this is not the case.... or what >?? I seriously doubt that we'll ever know anything for sure, but my spreadsheet figures show some interesting things - if I did it right. A 410.5mm A4 speaking length with a 75mm back duplex and the bridge top at 0.025" above the plane between agraffe and aliquot will have a 0.514° bearing angle. Raise the bridge 0.025" to 0.050" above level and the bearing goes up to 1.148°, making the string path between agraffe and aliquot 0.00001866 longer. Putting the bridge height back down where it was and figure what happens if the bridge swells and pushes the string 0.001" up the pins. The pin size is 0.086", wire dia 0.035", stagger angle 10°, pin angle 20°, and row spacing 19mm. A 0.001" rise in the bridge top will, by my questionable math, increase the string path length by 0.00003369", which is nearly twice what a 0.025" soundboard rise did. My experiment showed that my sample bridge changed dimension 0.009" from very dry to very humid, which is a broader humidity abuse than they would normally get in the field. Still, even at half that, it indicates to me that the string path increase/decrease between pin rows with humidity swings ought to be at least suspected as being a factor. Now I need someone else to eventually work this out too so I can do a reality cross check on my attempt. Ron N
This PTG archive page provided courtesy of Moy Piano Service, LLC