Soundboard crown

[Delwin D Fandrich]

----- Original Message -----
From: "Sarah Fox" <sarah@gendernet.org>
To: "Pianotech" <pianotech@ptg.org>
Sent: August 12, 2003 3:26 PM
Subject: Re: Soundboard crown


>
> Well, there's modal analysis, but I presume that assumes linearity in the
> system, which probably breaks down, especially at higher amplitudes.  I
can
> appreciate the complexities of this system.  I once did some preliminary
> research on an acoustically simpler system and couldn't land an NIH or
NSF
> grant to study it further, using something very similar to a modal
analysis.
> Some reviewers seemed to lack confidence that it could be understood via
the
> techniques I proposed.  I think they were being overly pessimistic;
however,
> I'll admit the acoustic complexities of the system were daunting at
times!

Well, I've done that too. Although it was late 1980s and I expect things
have progressed a bit since then.


> >
> > How are you mass loading the thing? Where, how and how much can make
quite
> > a difference.
>
> Well, as I said, it was "cursory" and "noninvasive" stuff -- hardly a
> satisfactory test.  I had a few moments before I had to scoot out of
town,
> so I rubber-banded a large (heavy) magnet to the top of the high-treble
> bridge (around C7), making firm, non-buzzy contact with the tops of the
> bridge pins.

Not good enough. Have you done any work with accelerometers? Check out the
coupling (the resultant frequency response) between the test object and the
accelerometer with the various mounting techniques. Non-rigid adhesive
bonding (bees wax, etc.) always loses out to solid mechanical bonding.
You'll need to get in there and physically and closely couple the mass(es)
and the spring(s) to the bridge. Usually by screwing and/or solidly bonding
the things to the bottom of the board directly opposite to the bridge. Best
with a screw going up through the mass, through the soundboard and into the
bridge.

Del