Crown without soundboards

[Delwin D Fandrich]

Tim Keenan & Rebecca Counts wrote:

> .... Cracks in the soundboard just turn the system into several
> parallel stressed-skin panels, each of which will still remain curved.
> There would have to be an enormous number of cracks to reduce the overall
> curvature of the soundboard/rib system barring failure of the board/rib
> glue joint, I think....
>
>
> Tim Keenan
> Noteworthy Piano Service
> Terrace, BC

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If the implication here is that the soundboard with cracks is just as effective a transducer as is one without them, I must
conditionally disagree.

Soundboard cracks most commonly appear in soundboards that were originally compression-crowned. All compression-crowned
soundboard panels begin to undergo compression set virtually from the moment they are crowned. For numerous visible cracks to
appear in one of these panels there must certainly have been sufficient internal compression for a long enough period of time
to have caused permanent and irreparable wood fiber damage within the panel. While compression set is not visible to the eye,
it is there nonetheless. With sufficient compression set, the amount of stress differential available to form and hold crown
will have decreased to such an extent that the soundboard assembly is no longer able present an effective load to the
strings. That is, the spring component of the mechanical impedance relationship will have been reduced to such an extent that
the energy from the strings will be bled off more quickly than is desired and sustain will inevitably be decreased.

(Slots machined into a soundboard assembly designed for them from the beginning are another matter.)

For more detail, see the three-part series on the subject currently appearing in the Journal.

Del