soundwaves (the behavior of soundboards)

[Robin Hufford]

Ron,

     I have not maintained that the stem of the fork is not vibrating. Obviously
it is and can be felt to do so and this is refered to in the post. Vibration
being simply periodic motion both the tines, the base and the stem vibrate.
They vibrate in different ways as the result of the difference in stiffness.  A
continuum of effect  is demonstrated in  the fork, at the risk of sounding
repetitious I say once again that on the one hand we have  transverse visible
flexion; on the other molecular vibration, stress disturbance, etc.
     With regard to pressure -  in the interests of  accuracy  perhaps you
should have noted the sentence immediately following your quote:  ..."Obviously,
one could say that a pressure sufficient to destroy the system could easily be
generated; evidently these effects would be different then  and these kinds of
pressure are not what I am refering to."
     Also, a little earlier....".The visible flexion can easily be stopped by
the merest touch of a finger but no human hand can exert sufficient pressure to
eliminate the stress wave in the base and stem that is felt as a vibration. "
     Clamping a fork in a big, heavy, vise, as you say, or hitting it with a
sledgehammer and noting that its vibratory capabilities are altered should be no
suprise to anyone.  Similarly, putting a jack hammer above the bridge and
driving it downward would most definitely introduce motion in the bridge whether
the string was moving or not.  I doubt that anyone would be surprised by this.
The point of the comparison was  to indicate the different results obtained by
pressure at the two different points and that whereas  a very slight pressure
was sufficient eliminate the transverse vibration of the tines neither a similar
or a much greater pressure exerted by the hand could  have the same effect.
This, among others things plainly illustrates that the two vibrations are of a
different character which they are.
regards  Robin Hufford
Ron Koval wrote:

> Here goes, jumping in at the middle again!
>
> Robin Hufferd wrote:
> Had this been the case then even a relatively light pressure upon the
> bridge should immediately reduce the loudness of the sound emanating from
> the soundboard as it does with the flexing part of the fork and a variable
> pressure would introduce variable volumes in the sound.  This is plainly not
> the case. It is the case, however, that pressure upon the stem and base of
> the fork does not eliminate the sound; and this is  precisely what occurs
> when pressure is applied to the bridge.
>
> Just to test the theory, I took out my trusty fork and gave it a listen.
> Next, walked over to the big, heavy bench with the big, heavy vise.  Clamped
> it down good by the "non vibrating" end and struck it again.  Hmmmmm......
> very quiet this time.  Maybe no matter how tightly you clamp the fork in a
> fleshy, nonrigid finger, you can't hear a difference.  Yet clamped in a much
> more rigid system, there is an obvious difference.  In much the same way, a
> strung piano soudboard/bridge assembly SEEMS to be rigid, yet allows
> periodic motion (tone, as opposed to a hammer rap) to set the structure in
> motion.  Does it take a lot of energy?  Nope, that's why pianos work.
>
> Ron Koval
>
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