"Fish"....my best guess...

[V T]

Hi Terry,

I think everyone on this list (who hasn't already)
should try to see a high speed film that Don Mannino
shows at his presentations.  Don, do you make this
clip available for downloading?

It's a view of the first pulse as it propagates from
the hammer to the bridge, then  reflects and comes
back to the bridge, etc.  The film clip stops after a
few bounces, which is only a few milliseconds.  After
a few seconds (not seen in the film), the pulse
resolves and you see the typical sine wave that is
characteristic of the fundamental frequency with
little higher partial content.  The string acts as a
filter if you wish.  When the hammer hits the string,
it imparts a broad continuous spectrum of "noise" on
to the string (that is the sharp pulse that deforms
the string when the hammer hits it).  The string has
only certain frequencies at which it naturally
resonates.  After a few bounces of the pulse, this
filtering process reduces that broad spectrum to a
fundamental with some partials, and as the string
rings, the balance of the various partials changes
(they diminish).  All the other frequencies that re
not at the few natural resonances of the string die
out.  The rate at which they get filtered off is one
of the things  we perceive  when we describe the sound
of a piano.

So, you are right in saying that "it vibrates", but
there are some very important events that take place
before the string settles into its slowly decaying
vibration.  I would even say that we react to those
initial moments with much more interest.

Incidentally, from a mathematical standpoint, it
doesn't matter if the we are observing a pulse or a
half cycle of a sine wave on the string.  They both
"reflect" at the rim and follow the same laws!  If the
rim is soft, the pulse/wave will partially be
transmitted into the rim and the rest will reflect
back into the soundboard.

Vladan


Terry wrote:

Nawwwwwwwwwww. Your skipping rope is just like the
speaking length of a
piano string. You pluck it or whack it and it
vibrates. Period. It vibrates.
The length of time it vibrates will vary directly with
the
solidity/immobility of the speaking length
terminations (a cast iron capo
bar works better than a hunk of loose rubber). Similar
with the soundboard.
It vibrates. The more solid/immobile/massive the rim,
the less the
soundboard can vibrate the rim, and the less energy is
lost at the rim. I
really don't think there are things zipping back and
forth and bouncing off
this or that. I do know that it makes for great
graphics in four-color
brochures. That kind of thinking is consistent with
the thinking that bridge
wood/laminations need to have the grain oriented a
certain way so the sound
energy can pass through the bridge from the strings to
the soundboard. Don't
think so.

Terry Farrell



		
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