[pianotech] vibration stuff

[Ron Nossaman]

On 2/3/2013 4:03 AM, Euphonious Thumpe wrote:
>
> P.S. "Seems to me" that the bridge on a piano works as a crank: as the
> string oscillates, its effective length shortens and grows, and the
> elasticity within it yanks and releases the bridge top laterally,

Yes, it does.


>with
> that motion being transferred to the board in a "bell-crank", pumping
> motion contributing to "board collapse" and "bridge roll" on the
> speaking-length side.

This, however, doesn't follow.


> But restricted somewhat by the "waste" end of the
> string which would tend to transmiute* some of this "cranking" into a
> true up-and-down wagging of the bridge, and "funnel" some into a
> "shock-wave" through the material via its rsistance to stretching.

There is some of all of this.


> But
> if the fundamental tone is thus sent to the board via this "cranking",
> what of the partials?

Same things, at a mix of frequencies.


> Would perhaps the oscillations required by the
> bridge cranking in the fundamental vibration preclude the smaller ones
> from being effective (cancel them out) UNLESS transmitted via the
> "shock-wave" medium??? (And, no, I am NOT maliciously trying to explode
> your head! Honest!!!)

I have no doubt it happens to some degree, but that's one of the 
infinite number of details that has nothing to do with the discussion or 
understanding of the basic mechanism.


> P.P.S Thank you, in your last post on this thread, for saying that the
> PRIMARY mode of transmission is gross
> (physically, externally measurable) movement of the board by the string.
> Had I known that that was your contention (not that it was the SOLE
> mode, as I thought) we might have avpoided much tiff. (And a great, big,
> Kum-Bay-Yah to you too!)

The board's reaction is affected by temperature and humidity too, but 
that's not the fundamental explanation of how it works. I've never 
claimed that any of my brief and incomplete explanations is a complete 
and infinitely detailed description, though people seem to believe 
that's what they read in spite of what I write. No amount of explanation 
so far has been able to avoid this, and I doubt it ever will. So instead 
of learning, there will always be thousands of words wasted in arguing 
something I didn't claim, say, or even hint at.

Ron N