Sound waves(The behavior of soundboards)

[Robin Hufford]

Ron,
     A longitudinal wave experiences reflection from a free end just a does a
transverse wave.  In a transverse wave reflection from a clamped end results in
a phase reversal, that from a free end does not.  Longitudinal waves are the
reverse.  Reflection from a free end results in a phase reversal, now expressed
in terms of a rarefaction and compression.  The compressive phase reaches the
end of the medium where it is not longer opposed by the physical
characteristics of the medium as had been the case prior to reaching the
boundary.  The force of the compressive oscillation causes the medium itself to
bend outward at the boundary resulting in a phase reversal in which a
rarefaction then proceeds back through the medium.  There is no need to posit
any kind of physical, substantial motion to account for the bouncing of the
fork.  In fact, such an idea is thoroughly erroneous.   The reflection from the
end of the fork causes the stress wave which is, in fact, what we are talking
about here, to demonstrate itself as a kind o displacement of the end.  This is
strain and does not require the fork to be moving to occur.  Such an idea is at
odds with every analysis of this subject.
     Now I find you using the very same models to demonstrate longitudinal
behavior which last month you claimed could not occur, practically did not
exist, and if extant, was of no consequence, including taking into account the
effect of stress on longitudinal wave behavior in a tuning fork.
Regards, Robin Hufford .


Ron Nossaman wrote:

> >After all this, you can tell me how blindingly obvious it is that the
> >fork moves the wire and the wire moves the bridge.
> >
> >JD
>
> Run about 10 meters of music wire through your straightener. Make it #13,
> or #22, as you wish. Lay an unstrung piano down on a skid on it's side and
> lay the wire out on the floor so one end is propped up to touch the
> soundboard. Apply the fork to the other end. An internal compression wave
> in the wire shouldn't care at all what the wire sides are touching
> (embedded in concrete, I believe was your description), so the fork sound
> should come through loud and clear from the soundboard. If it is required
> that the wire be moved by the fork to transmit "sound", nothing will be
> heard from the soundboard.
>
> Recreate two sets your childhood cocoa tin phones, one with a 3 meter
> length of light wire or strong sewing thread between and one with a 3 meter
> length of 20mm diameter steel rod. A compression wave entering one end of
> the steel rod from the cocoa tin bottom diaphragm should come out the other
> end with the same volume as that produced by the string connected tins. If
> the connection between tins must move to activate the "receiver", then you
> won't hear much.
>
> Simple tests actually making an attempt to separate the two transmission
> methods.
>
> Yes, blindingly obvious.
>
> PS: If the fork handle merely vibrates, but doesn't move, you shouldn't be
> able to feel it bounce if you slowly touch the handle end of a ringing fork
> to your front teeth, should you? And a fork clamped in a vise should pass
> that compression wave right through the vise and sound from the bench top
> as loudly as it does pressed directly to the top. Does it?
>
> Blindingly obvious.
>
> Ron N