Crown without soundboards

[Delwin D Fandrich]

A440A wrote:

> Greetings all,
>      I read with interest the postings concerning crown and the rim influence
> on it.   I have often wondered if a bridge attached to the ribs, with no
> soundboard would be able to withstand the down pressure.  I am skeptical that the soundboard itself, what with soft thin
> wood, actually provides much
> support.

It depends on how the ribs were made. Ribs must be designed to be compatible with the type of crowning system designed into
the piano. If the soundboard is to be compression-crowned then they must be flexible enough for the expanding soundboard to
able to bend them into a curve. If the crown is built into the rib, this calls for another type of rib design.


>    That a board is still crowned with glue joint failure around the rim
> doesn't tell me much.  Would not the joints of the ribs to rim actually have a
> lot more bearing on  crown maintenance?

Not really. Again, see the sidebar accompanying my article in the December Journal.


>    From a structural standpoint,  the principle  of arches seem to describe
> the transfer  and containment of bearing pressure.  When you vector the
> downward force from an arch, you see that there is a transfer of pressure from
> straight down to a more lateral direction, where the pressure meets the case,
> ( and any centripedal apparatus that may be in the area.......(:)}}

Ditto.


>    So,  has anyone ever considered that the ribs alone might support a bridge,
> and the soundboard itself  does very little? Or to ask another way,  how long
> would a board remain crowned if there were no ribs?
> Regards,
> Ed Foote

With a "solid spruce" soundboard panel, there would be no crown without ribs. An 8 mm thick spruce panel is VERY flexible
across grain. It would simply buckle.

There are many different types of soundboard design. Although they all look the same from the top, there are some very
important, albeit subtle, differences in the way they are made. All to often we speak in generalizations; as if they were all
the same. The current three-part series of articles on soundboards attempts to describe these differences and explain the
pros and cons of each. I'm sure in the end I'll probably have raised more questions than I'll have answered, but at least
it's a start. Until the last article comes out in February, I'm going to try to not repeat myself too much.

Del