Crown without soundboards

[Jim Coleman, Sr.]

Hi Ed:

When one considers a piano soundboard with many splits and there is
still downbearing, one might think that indeed the ribs are supporting
the downward force of the string bearing. However, when one also
considers the fact that as humidity increases, the soundboard rises and
increases the tension on the strings, one might think that the board is
the crown supporting member. It is well known that the ribs do not
lengthen any to speak of when the humidity increases, but the soundboard
certainly does swell and rise with humidity increases. Perhaps we can
gain a little more insight from the harpsichord builders who have to
work with much fewer ribs and funny wavey things that go on with the
soundboards.

Jim Coleman, Sr.

On Mon, 29 Dec 1997, 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.  
>    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? 
>    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.......(:)}} 
>    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 
>