Hi Thump,
> David, begging your pardon, I think it would be
> helpful for purposes of conceptualization to see the
> vibrations as rippling across the board, as a stone
> causes ripples in the water, rather than the whole
> assembly pumping up and down. I am no expert on these
> matters, but I consider that more probable.
With all due respect, when you drop a small stone in the water, there is a
"splash," and there is some splatter of water around the area of impact. Do
you see *that* reflected in the ripples?
Vibrations have frequency components, and different things happen to those
frequency components. You may have the same fundamental periodicity, but
the spectral composition can be completely different. The fact that the
waves propagate is of less interest than the question of how they do so.
> Not stiff enough: the vibrations get wasted as
> heat energy within the board. Too stiff: they are
> transferred to the case and lost there ( after a quick
> initial "boom" )
Stiffness doesn't mean efficiency. Two different things. The spring in a
Bic pen isn't very stiff, but it's pretty efficient. As a spring, a
hardwood floor is much, much stiffer, but much less efficient. If you jump
on it, the vibrations won't last very long.
If the SB had very little stiffness to it, like a speaker cone, that would
be the condition under which the sound would go "bonk." If the SB were
incredibly stiff -- perhaps a thick plate of steel or a concrete slab --
then the strings would vibrate a veeeeeeery long time. This is the tradeoff
of amplitude vs. duration (loudness vs. sustain). Either way, there's a
certain amount of energy imparted into the system, and it is dispersed
either very quickly ("bonk") or slowly (with a long, soft whine).
> That is my "gut" feeling on the matter. A board's
> job is to create sound waves from as much of the
> vibrations as possible before they pass into the rim.
> Or are absorbed internally. How to create conditions
> conducive is our job. I suspect it has much to do with
> an interface of tensed and compressed molecules.
Inefficiencies are everywhere in the piano. When you play a note, the
entire piano vibrates, right down to the casters. The pianist vibrates.
The bench he/she is sitting on vibrates. The *Earth* vibrates. Where does
the sound energy get eaten up? Just about everywhere. I highly suspect
most of it gets dissipated into the damper felt on any damped strings, the
braid strung through backscales and front scales, hitch pin washers, etc.
Slightly shorter sustain is an accepted cost of cleaner sound.
Peace,
Sarah
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