RC vs CC again

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: October 01, 2003 8:04 AM
Subject: Re: RC vs CC again


> Secondly...we have this unclear bit about panels of same dimensions with
> ribs of same dimensions and with same crown... in two boards one CC and
> one RC.  Seems to me that the CC board here is bound to have more
> stiffness due to higher panel compression. Tho mass and dimensions be
> the same... in other words... one is able to achieve a higher stiffness
> to mass level in the compression board... all other things being
> equal....

Compression-crowned soundboard systems and rib-crowned soundboard systems
are two distinctly different designs. They do not use ribs of the same
dimensions and the same crown. That is the whole point.

The ribs used in a compression-crowned soundboard system must, by
definition, be somewhat flexible. They must be flexible enough for the
expanding soundboard panel to force them into a crown. Hence, they are
nearly always somewhat wider than they are tall. As well they are, again by
definition, flat when glued to the soundboard panel.

The ribs used in a rib-crowned system must act as structural beams. They
are nearly always taller than they are wide. And they must, also by
definition, be crowned in some way. All of the design crown comes from the
crown machined into the rib. Yes, there may be some additional crown
induced by the expansion of the soundboard panel under certain climactic
conditions, but this is incidental to the design.

Yes, the two technologies can be blended as is the practice of some. But
that is a whole different issue.

Del