Hi Don, Take a close look at the position of the ribs, wrt to the coupling effect and each note, Things tend to look less random. I have only measured the effects on two pianos, but I am starting to think that the mechanical reactance of the board may have some thing to do with the coupling effect. Roger At 12:43 PM 8/15/01 -0600, you wrote: >Hi, > >I read this with great interest. I wonder if the damping effect of the cast >iron and the resultant energy *bleed* is the cause of the lowering of the >pitch on three string unisons. It would certainly be variable from piano to >piano as plates are not really too consistent. > >>My thinking was that when a string is struck and vibrates then there must >>be an periodic increase in tension. When a string of fixed length is >>displaced then it seems to me that there must be an increase in tension. >>For the fundamental, as the string swings up the tension increases, comes >>back to nominal as the string comes back level, and increases again as >>the string swings down. This is happening several times a second. Also, >>this is happening for all of the partials, just at different frequencies. >This >>increase in tension must be sustained by the plate. Admittedly, the loads >>in question are low and the deflections must be small. But, cast iron has >>high damping (by metal standards) and the vibrations are occurring several >>times per second, so even a small amount of deflection could perhaps >>dissipate consequential amounts of energy. The amount of this deflection >>will depend on how stiff the plate and pinblock arrangement are. >--- > > >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 > >mailto:drose@dlcwest.com >http://donrose.xoasis.com/ > >3004 Grant Rd. >REGINA, SK >S4S 5G7 >306-352-3620 or 1-888-29t-uner >
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