Check out Piano Soundboard Movements

[John Delacour]

At 23:37 -0500 15/12/07, Erwinspiano at aol.com wrote:

><http://vanadium.rollins.edu/~tmoore/piano_soundboard.htm>Piano 
>Soundboard page
>   Hi Guys
>   A friend sent this to me interesting stuff.
>   Any body see this before. Actual sound board movement pictures of sorts

Yes. Chladni <http://en.wikipedia.org/wiki/Ernst_Chladni> did all 
this 200 years ago.

Look up Chladni on Google and you'll get tons of pictures.  Here's 
just one movie demo:

<http://www.youtube.com/watch?v=Zkox6niJ1Wc&eurl=http://rogerbourland.com/blog/2006/05/30/chladni-patterns-video/>


The problem with using Chladni's method is that the plate 
(soundboard) must be horizontal and flat (no crown), so the method 
used by these people at Rollins is a lot more convenient and 
flexible, allowing the patterns to be created in the fully strung 
piano.

Chladni's work was most significant in the early development of the 
science that began with Galileo, of which acoustics is a branch that 
developed later with the work of Lord Rayleigh etc.

The most significant modern worker in this fascinating science is 
Timoshenko, and much of his "History of Strength of Materials" (where 
Chladni is mentioned) is online with Google Books:

<http://books.google.co.uk/books?id=c02ca_umoEIC&printsec=frontcover&dq=timoshenko&sig=DQsvyHyMPAYRME2Sl9NQB8SmcfQ>

The problem with all these University projects is that they may be 
very instructive in giving students a glimpse of a known phenomenon, 
but it is always but a tiny part of their curriculum and is never 
taken very deep.  The science of elasticity and the history of its 
development I find extraordinarily fascinating, but to get beyond the 
first steps of understanding these phenomena requires the most 
difficult of mathematics.

The point of these investigations, however, is to show how plates and 
shells (our soundboard) behave when subjected to _forced_ vibrations 
over an infinite range of frequencies, which is what happens with a 
piano.  It is one thing to force a plate to vibrate by imposing a 
pure sine wave vibration at a single frequency and to observe the 
pretty pattern, and it is quite another thing to investigate the 
behaviour of the plate when it is forced to vibrate at 10,000 
different superimposed frequencies and to quantify this behaviour in 
a useful way.

JD