Sound waves(The behavior of soundboards)

[Ron Nossaman]

>     A stretched piano string when struck by a hammer acquires a momentary 
>deflection
>upward which is dependent upon the hammer, the wire, the striking point, 
>etc. When a
>rock is dropped into a pond a similar momentary disturbance exists and can 
>be seen at
>the point of impact as a series of depressions of the surface with consequent
>rebounding and  decreasing amplitudes which disturbs the water and results 
>on the
>surface in a visible wavetrain departing from the region of impact.  The 
>analogous
>event on a string in a piano is invisible, but nevertheless a momentary 
>disturbance
>comprised, due to the elasticity of the material and its tension, of among 
>other
>things,  a local deformation and local tension occurs. 

Correct, initially caused in both cases by a physical displacement at the
point of origin. The rock physically displaces (moves) water, the moving
string physically displaces (moves) the bridge.



>  In both cases, in 
>string and
>water,  subsequently a series of pulses will now propagate away from the 
>disturbed and
>flexing  point of impact and can, of course, be seen as ripples radiating 
>outward in
>every increasing circles on the surface of the pond.   In the case of the 
>water, this
>is, of course, familiar enough; neglecting complications of the hammer and 
>shank,  a
>similar event happens locally at the point of interaction between string and 
>hammer,
>although not visible to the eye as are the ripples on the surface of the pond.

None of this has ever been disputed. This is what I initially said that
started this discussion.


>     Richard has clearly illustrated the three dimensional, compressional 
>aspect of the
>wave in the pond and  accounted for its appearance on the surface as a 
>ripple due to
>the absence of reflection.  

What he has shown is a progressive transverse wave on the surface, as in
the blanket analogy. Since the soundboard doesn't have the depth of a pond,
and the bottom side tends to follow the top side at any given point, the
internal compression waves are a much smaller part of the overall motion
than the transverse, and are of considerably less consequence as a result. 


 He has emphasized the fact that the wave 
>is, in
>fact, what it is,  that is the energy of motion on a molecular level,  
>moving through
>the medium,  not the medium itself, and that the particles of the medium 
>itself have an
>oscillatory motion, which is to say they oscillate around their neutral 
>positions.

That's what a compression wave is, but the progressive transverse waves in
the pond, the blanket, and the soundboard that you are talking about are
many orders of magnitude greater than molecular motion, and most surely do
move the medium itself. It's vibration. Remember vibration?

>2. Physics. a. A rapid linear motion of a particle or of an elastic solid
>about an equilibrium position. b. A periodic process. 

These are elastic solids we're talking about here.


> In
>so doing they transmit the motion of the wave itself, while they themselves, 
>return for
>the most part, to their neutral position.

Of course they return to their neutral position. So do salmon. Does that
mean they haven't moved in the interim?

>    In the case of the piano string, with the obvious caveat that a string 
>is not three
>dimensional as is the pond, similar, analogous events occur to a point. 

Etc, etc... Yes, we know.


>As to the capability of a longitudinal compression wave to 
>transport energy
>in equal measure with that of a transverse wave there should be no doubt.   

That, I can't say. It depends on the configuration, mass, stiffness, and
energy input of the systems, doesn't it? In pianos, for instance, the
longitudinal energy of a piano string is considerably less than the
transverse in a conventionally excited string.


>The
>transverse structure of the standing waves pulses, at the terminations 
>compression
>waves, as I have said before, into the bridge and thence they travel to the
>soundboard.  

Yes, you have said this repeatedly. What you haven't explained is how this
compression wave moves the board rather than the periodic forces (cyclic
load) of the transverse string vibrations moving the bridge, which moves
the board. I say the vibrating string pushing and pulling on the bridge
moves it and the board just like anything is moved by applied force, you
say it does not, but the compression wave resulting from the pushing and
pulling passes through the unmoved bridge and moves the soundboard. This is
the original point of contention. How is this possible? 

Ron N