Downbearing / crown support question. Stéphane

[Ric Brekne]

Hi Stéphane

I tend to agree, tho that goes against the grain of the modernist who 
support the RC&S philosophy.  Wograms article provides a very good 
justification for this I believe.  In that article ribs are looked at 
from a perspective that has nothing to do with crown or down bearing 
support. The influence of rib numbers and dimensions on the acoustics of 
the soundboard is the only concern of his article.

It is interesting to note that he sites 2 primary acoustic functions of 
the ribs.  One is to increase soundboard stiffness as a whole. It is 
this bit that is interesting with regard to the RC& C vs CC discussions 
to my mind.  It is clear that placing the panel under compression cross 
grain will increase its stiffness to a significant degree.  This is 
especially valuable because the increase comes about without any 
additional mass.  That is to say, one adds mass when one adds ribs,  but 
if one figures panel compression into the equation one gets extra 
stiffness for the same amount of total mass.  I.e.  a compression 
soundboard with the same set of ribs will have more stiffness compared 
to a non CC board all other things being equal.

The other function he sites is the the need to compensate for the 
anisotropy of wood.  The reason he gives should be unquestioned at this 
point I think.  You basically reduce the effective vibrating area of the 
soundboard in half if you do not compensate for this, and that says 
nothing about the impedance problems one would most likely create in the 
bargain.

Cheers
RicB


Hi Ric.

I believe that the panel (soundboard) must be under some
compression to sound well.....

Best regards.

Stéphane Collin.