Soundboards: Thickness and Area

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: October 21, 2003 3:07 AM
Subject: Re: Soundboards: Thickness and Area


>
> Chaladni patterns are created by exciting the panel to one of the
> reasonant frequencies found, and you dont do that by just taking out a
> plastic hammer and smacking the bridge with your hand. The lowest
> reasonant frequency is usually around 50 hz or above and you are going
> to have a good time hitting the panel with a hammer 50 times a second.

I am aware of how Chladni patterns are formed, having actually played
around with them some. It is not necessary to hit the soundboard 50 times a
second to generate vibrations within the panel under test at 50 Hz. This
frequency, along with a broad spectrum of other frequencies will be excited
with just one blow. It will also, of course, die out rather quickly.


>
> Aslo... The fundemental frequency mode pictures I have seen never follow
> the edge pattern of the soundboard /rim. And it would be a bad thing
> indeed if the fundemental mode was so large. I dont believe that
> Steingræbers sand gathering proceedure has anything at all to do with
> the fundemental reasonant mode... Lot of good a cutoff bar is if the
> vibrational modes dont get affected (limited) by it ... or what ?

Never, of course, is an awfully inclusive word. Unless, of course, you have
been privilaged view all of the photographs ever taken of these tests. But,
yes, there are fundamental modes this large. The common style of rib
feathering encourages this performance.

Del