Impedance Matching

[Doug Richards]

Del,
I'd second the notion that soundboard characteristics change with load.
For SURE!

While I'd agree that a modal analysis is meaningless without the full system
(strings), it can be very valuable calibrating FEA models.  It's very simple
to add/remove components of a finite element model and is invaluable for
checking the accuracy of parts of a very complicated model (like a piano).

I know, "so what are you waiting for"?
I'll get back to it ;-)

doug richards
San Jose, CA

-----Original Message-----
From: Delwin D Fandrich [mailto:pianobuilders@olynet.com]
Sent: Friday, August 13, 1999 9:33 PM
To: pianotech@ptg.org
Subject: Re: Impedance Matching



----- Original Message -----
From: Richard Brekne <richardb@c2i.net>
To: <pianotech@ptg.org>
Sent: Friday, August 13, 1999 3:12 PM
Subject: Re: Impedance Matching


>
> Hmmm.. In the section of the Wogram article entitled "Influence of string
> tension" He seems to be saying that the condition of an uloaded soundboard
is
> not a problem. He says that the basic impedance curve and sound radiation
> curves remain basically the same and that only the lowest resonances are
> effected and that the effect is predictable enough to take into
consideration.
> Is this outdated ??

------------------------------------------------------

I don't know what the basis for this assumption is, but my own -- admitidly
limited -- tests have indicated otherwise.  Soundboard characteristics do
change as it is loaded.  Partly because of the increase in stiffness within
the panel, but also because the string plane affects the mobility of the
entire assembly.

One of the problems I have with most of the testing I have seen on the piano
soundboard is that it was done on an unloaded board and is, therefore,
largely meaningless.



> The article seems to point to some significant degree of potential for
> re-distributing resonance points for the different nodes by introducing
new
> stiffness and / or mass to different areas of the soundboard. Course one
would
> have to gain lots of experience to know just how, why and where to
introduce
> such changes on an existing board, but it seems like enough information
can be
> obtained by the modal analysys to accomplish this. Or is this just a sugar
> coated red herring ?? Opinions ??

I consider modal analysis of the working soundboard to be a good first step.
You know, like, "one small step for man...."

Del