Ron N,
When I first posted on this subject a few days ago, I used an
analysis of
the mosquito hitting the aircraft carrier, something you derided at the
time
with what seemed to me quibling over paltry details, to indicate a
conceptual
answer to the question you now pose. "How much motion qualifies as
this
non-movement you keep refering to?" The answer lies, once again, in
the nature
of motion and energy transfer of objects undergoing contact. Just as
energy can
be tranfered through an object as heat, yet at the same the the object
itself be
still, so can mechanical strain or deformation. One could try the test
I
described of attaching a copper wire to a soundboard and the base of a
tuning
fork and ponder the results. Ultimately, of course, all deformation
or
stress waves are motion just as is heat, but this motion on a
molecular
level. Energy can easily be transferred .
Consider a bridge on a soundboard in which the strings are not
vibrating.
and is sitting still. Simplifying and ignoring things such as the
rotation of
the earth, fluctuations in air pressure, etc., is it moving? The
general answer
would be no. Yet on a molecular level there is a vigorous motion which
we
perceive as temperature, as you know. On the one hand we can say that
the piano
is sensibly still, while on the other it can be considered to be in
motion. For
the sense of the piano itself or part of it to be in motion we must be
able to
detect it through some kind of instrument or our senses, although in
point of
fact I care little in the context of this discussion whether such be
detectible. What I do argue with, however, is the idea that the
transfer of
energy from string to bridge significantly introduces flexion in the
bridge/soundboard. .
At the risk of beating a dead horse, but to contine. When
contact
forces are exerted by one body on another energy is transfered by
mutually
induced strain, that is deformation. Of course, one could say that
deformation
is motion, as it is motion at the molecular and macrosopic level, that
is: the
shape, volume and energy level of the objects may change.
Depending upon
the ratio of the masses and forces and time of application involved
this mutual
strain can result in the objects being accelerated, acquiring vibration,
or
merely experiencing a stress wave. That was the purpose of the
mosquito -
aircraft carrier model.
Ron Nossaman wrote:
> > If I take a 2" x 2" x 12" steel
> >bar, lay it on a surface and tap the end with a light hammer, the bar
> >will not move because the applied force is less than the limiting
> >friction. If I hit it with a larger hammer, the bar will move. In
> >both cases the whole bar will vibrate and the sound wave will spread
> >throughout the bar.
>
> And this is precisely why I asked what hitting a tuning pin with a tack
> hammer had to do with soundboards. This example is similarly unrelated.
> We're obviously not talking about sliding one object against another. We're
> talking about flexing. Bridges don't slide on soundboards, at least I do my
> best to insure they don't. If your bar is vibrating, it's flexing. If it
> will carry a compression wave, it will carry a transverse wave. One
> vibrating string will rock a bridge, flexing the soundboard, not sliding on
> it. You say you can't rock the strung bridge with a crowbar, which should
> to anyone be pretty obviously a false assumption. So what is your threshold
> definition of movement in this rocking bridge? Is it 1", or
> 0.00000000000000001"? How minute a movement qualifies as this non movement
> you keep referring to? I say that just touching a string will move the
> bridge a measurable amount (detectable with decent equipment). You say you
> can't move it with a crowbar, so please define "move" within the context of
> soundboards and bridges. Sines and cosines are acceptable if that's what it
> takes.
>
> >>2. Why doesn't touching the fork to the edge of the soundboard not produce
> >>the same tone as touching it to the top if it's compression wave driven?
> >
> >Well, apart from the extreme difficulty I have in picturing how you
> >would set up a valid test for this, it is no doubt possible to test.
> >One would need to make sure that the impedance at each test point was
> >identical to start with and that would mean dressing the edge with
> >something.
>
> Why? How tough is this? No such stringent controls were placed on your
> proposed definitive demonstration with the tuning fork and tack hammer.
> Just press the handle of the fork against the edge of the board at the
> belly rail, then on the top surface and listen to the difference.
>
> You've obviously made such an experiment so how did you
> >set it up and what did you discover?
>
> A somewhat more than obvious difference. Try it.
>
> >But I think you are missing
> >something. The vibration or compression wave that I claim in my
> >theory to pass from the string termination through the bridge to the
> >soundboard reaches the soundboard in such a direction as to induce
> >transverse vibrations in the soundboard. That has never been at
> >issue.
>
> That is precisely what is at issue. What else are we discussing?
> And if you are referring to this,
>
> >>The vibrations cause by the transverse movements of the taut string
> >>are passed into the bridge at a point equivalent to the point of the
> >>tuning fork pressed against the bridge, and this point in both cases
> >>is static and not mobile. From this point the vibration, or
> >>molecular disturbance, radiates into the elastic medium that is the
> >>beech or box or maple + the steel of the pin and travels as
> >>compression waves in all directions as fast as the medium, the grain
> >>direction etc. allow. Virtually every molecule of the wood or steel
> >>will be displaced and oscillate in response to the kicks and shoves
> >>from its neigbours. It is the oscillation of the molecules next to
> >>the glue line, excited by kicks and shoves from all directions within
> >>the bridge, that will now raise a rumpus in the soundboard. The
> >>bridge so far remains unmoved, its internal tranquility severely
> >>disturbed but outwardly unmoved, unrippled, unfurrowed.
>
> then I have indeed missed something. I hadn't realized that "in all
> directions" meant strictly vertically. My mistake, obviously. There seems
> to be a language as well as a conceptual barrier.
>
> >The difference between us is that I see the movement of the
> >soundboard as the result of vibrations passing through the bridge to
> >"hit" it at a right angle and shake it up and down, whereas you see
> >the whole bridge as moving and rocking and what not and shaking the
> >board. The bridge certainly does move bodily once the soundboard has
> >received the energy to cause it to vibrate, but according to your
> >theory it is the bodily movement of the bridge that pushes and pulls
> >the soundboard up and down. The more arguments you and the others
> >give in support of this theory, the more incredible it seems to me.
> >
> >JD
>
> Then we have a common ground after all. It seems incredible to me that
> anyone could imagine a soundboard moving before the bridge does.
>
> Ron N
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