Check out Piano Soundboard Movements

[paul bruesch]

This is all way beyond my current level of understanding and knowledge, but
I do want to mention something... and with this disclaimer... I don't know
if it's so much marketing hype or not, I realize that it might be... again,
it's way over my head at this point, but here goes....

I attended a presentation by Udo Steingraeber that was held at a dealer in
Rochester, MN just a couple days before the convention in KC.  In that
presentation, he discussed "voicing the soundboard" whereby they sprinkle
some iron filings or pixie dust or something and (sorry, forgetting exact
details here) pound on the board and look for areas where the sprinkled
substance does not collect. They shave those areas down and repeat until
they achieve uniform distribution.

Again, for all my skeptical mind knows it could be hype. I'll defer to those
on the list who know far better than I.  I would guess they gave the same
presentation at KC. Can any of you SB and/or voicing gurus speak to it?

Paul Bruesch
Stillwater, MN

On 12/16/07, Richard Brekne <ricb at pianostemmer.no> wrote:
>
>  The article is actually quite interesting, and tho I'll need a couple
> more reads to properly digest it there are a couple relevant points right
> off worth mentioning.  It turns out, according to these folks mind you, that
> the soundboard deflects under string bearing in patterns quite identical to
> the those of the lower modes of panel vibration.  They claim to be able to
> identify changes in mode shapes and resonant frequencies for changes in
> string bearing amounts. Further,  they claim they are able to measure
> driving point impedance of the assembled piano with relative ease and
> without an impedance head that simultaneously measures the applied force and
> the acceleration. They use a kind of electronic version of the Chladni
> method which does not require the soundboard in a perfectly horizontal
> orientation. I'll include the conclusions paragraphs for your edification:
> The whole article is definitely worth a read.
> Cheers
> RicB
>
> Conclusions:
>
> We have described a method of electronic speckle pattern
> interferometry that not only works with moderate decorrelation
> of the speckle pattern, but demands it. We have
> shown theoretically and experimentally that this arrangement
> can be used to determine the deflection shapes of an object
> that is normally too unstable to observe interferometrically,
> and applied it to the study of a piano soundboard in situ.
> Using this interferometer we have investigated the dynamics
> of the soundboard of a piano and have compared the
> results to a simple closed-form theory, as well as a finiteelement
> model. Comparison of the deflection shapes of the
> piano to those predicted by these models demonstrates that
> the pressure exerted by the strings on the soundboard can
> make significant changes in mode shapes and resonant frequencies.
> The presence of this pressure has a significant effect
> on the lowest modes, but appears not to be important in
> determining the shapes and frequencies of the higher modes.
> We have also shown that this interferometer can be used
> determine resonance curves and driving-point impedance.
> We have presented the resonance curves for the lowest three
> modes of a soundboard and shown that they do not overlap
> significantly.
> We close by noting that the applications of this interferometric
> technique are not restricted only to the investigation
> of piano soundboards. Harmonic vibrations of any unstable
> object that meets the requirements outlined in Sec. II can be
> observed using this technique. Additionally, the theory can
> be applied outside of the approximations if the value of  e in
> Eq. (10) is known.
>
>
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