"60' vs. 100' Radius Board"

[Delwin D Fandrich]

Dale,

Who said any of these were "standard?" I've never actually measured a soundboard
with a 60' crown radius. Has anybody? This is because the crown radius of the
piano soundboard is an ever changing quantity. Among other things, it varies
dramatically with changes in ambient humidity. This is especially true with
compression crowned boards, but the crown radius of all soundboards -- with the
notable exceptions of laminated panel construction -- is going to change as
humidity changes.

The actual design crown radius of a soundboard assembly depends on how the
soundboard is designed and built. If it is a pure compression-crowned soundboard,
then the crown radius is primarily dependent on the moisture content of the panel
when the ribs are pressed on, the stiffness of the ribs resisting the development
of the crown and the humidity level of the factory in which the soundboard is
being pressed. If the rib cauls are radiused, then this must be factored into the
equation. If the ribs themselves are crowned, then the results will, once again,
be quite different.

Depending on the type of sound we want to get from a particular instrument and
depending on the soundboard shape and the location of a particular rib on that
soundboard, we will use one of 5 different radii. None of them are as large as
either 50' or 60'.

I really don't care what the soundboard looks like after it is ribbed. I care a
lot more about what it sounds like once it's assembled into a piano and loaded
with a bunch of strings. I'm not building salad bowls, I'm building pianos.

Regards,

Del

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Daleboy@aol.com wrote:

> Dear List,
>      Just a lil' question about Soundboard radius configurations..........
> In the past the SB installers that I was associated with were using a radius
> of 100' on Steinways and a 60' radius on Mason & Hamlins........how come most
> everybody has gone to a "universal" 60' and in some cases a 50'...???
> A 50' radius board pre-installed must look like a salad bowl (chuckle).
> Curiously yours,
> Dale Whitehead, RPT
> Franklin Piano Restorations