Unison coupling

[Richard Brekne]

Ron Nossaman wrote:

>

Hmmm I begin to catch a glimpse of what you are after here Ron.. at least I
think I do. Ok tho.... say you can establish through measurements that the so
called killer octave is most susceptible to this.. how can you tell if its got
anything to do with soundboard impedance with these measurements.. wouldnt you
have to actually check the soundboard for each case ??

In anycase.. will be making my first stab at measurements tommorrow.. will send
them along and you can let me know if the format is useable.

Richard Brekne
I.C.P.T.G.  N.P.T.F.
Bergen, Norway

> In a piano, the bridge and soundboard are, VERY roughly, the horizontal
> string in the above experiment. As the compliance of the bridge and board
> assembly act as the intermediary for two or more strings trying to pull one
> another into phase with each other. The closer the strings are to being in
> tune with each other, the more organized and efficient the energy
> transfers, and the shorter the attack pitch lingers. I agree that this
> probably happens throughout the piano, but why is it most obvious in the
> killer octave area? I think it's because the soundboard impedance is
> usually too low in that area (compressing the envelope by allowing too high
> an energy transfer rate back and forth between strings and soundboard
> assembly), and there are usually plenty of tuned duplexes and short
> backscales in that area bleeding energy from the speaking lengths and
> further compressing the attack phase of the envelope. It probably happens
> just as much in the upper treble, but there usually isn't a discernable
> attack phase in a "dink", so no one much notices. In the lowest bichords,
> The envelope is expanded so much that it's hard to tell if the phenomenon
> exists.
>
> I hope this is at least marginally comprehensible. I can mentally picture a
> lot of what I think I know about piano physics connecting here very easily
> and naturally, but I'm not even sure how to explain it all (which the above
> failed miserably to do), much less attempting to prove anything. One thing
> I'm pretty sure about though, there's no magic varnish involved. I believe
> you're thinking in the right direction though, FWIW.
>
> Ron N