Soundboard crown

[Calin Tantareanu]

Thanks to everybody for answering my questions. This list is a wonderful
learning place!

> With all this in mind, if we are to deviate from the established pattern
we
> must come up with a soundboard construction having a mass that falls
within
> certain limits combined with an amount of stiffness that will control the
> rate of energy transfer from the vibrating string(s) to the soundboard
> panel. One can argue that what the soundboard needs is stiffness, not
> crown. If the requisite amount of stiffness can be obtained sans crown a
> workable soundboard can readily be built without it. Certainly this was
> accomplished by Rippen with their laminated soundboards. These boards had
> no crown as built, though they did end up with "negative" crown through
> string loading.

By the way, how do laminated soundboards behave when exposed to humidity?
Do they expand less than solid wood ones?

>From the replies, i understood that crown is, basically, a means of
controlling the expansion of the board (that is, making it to move in
predictable ways). Another function of the crown seems to be that of adding
stiffness. For that to happen (and leaving the ribs out of discussion for
now) the board forms sort of a very wide arch that is supposed to counter
the pressure of the strings too, besides the ribs.
How significant is the stiffness added by the crown?
In other words, in a rib-crowned board, how much stiffness is provided by
the ribs (beams) and how much by the board (arch).
I suspect that most of the stiffness is provided by the ribs (no evidence
though) so please share your experiences.

My conclusion, so far (and please correct me if I'm wrong) is that:
1. Stiffness is directly inflencing a soundboard's function, while the crown
does it indirectly.
2. If a soundboard would be kept in a (hypotetical) environment without
humidity fluctuations and no subsequent wood expansion/contraction then a
flat board with flat ribs should work very well.
3. Crown is a way for dealing with the expansion/contraction of the wooden
panel in a predictable way.

More questions:

1. What are the thicknesses of the sounbooards of pianos produced nowadays?

2. What is the difference between making a board (for the same piano) with:
 a. Thick board with thin ribs,
 b. Thin board with thicker ribs.
For both cases, let's assume that the boards are designed to withstand the
same pressure from strings and to provide the same stiffness.

Regards,


 Calin Tantareanu
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