Sound waves(The behavior of soundboards)

[Ron Nossaman]

> 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