NEWS FLASH! "Conover clobbers Steinway !"

[Ric Brekne]

Hi Mike...

You have to sort of put 6 and 6 together if you are just using the 
Wogram article to get to the equalized speed of sound.  Start off with 
the fact that sound moves  many times faster along the grain then across 
in an unribbed panel because moduli of elasticity in the two directions 
are in a ratio of approximately 20:1   (anisotropic) . We can discern 
from that that in general, adding stiffness will increase the speed of 
sound through wood regardless of orientation. (because /v/=root(Y/d) in 
solids)  Throw in the fact that by equalizing the stiffness of the board 
across the grain one also equalizes the speed sound propagates in either 
direction and that if you dont do the former (which consequents in the 
latter) then

    "effective vibrating area is reduced and the radiation efficiency is
    decreased over a broad frequency band."

And you arrive at the assumption that it is the need for a homogenous 
anisotropic relationship in general that is what is desired.  And that 
by definition includes the speed of sound. 

Seems kind of self evident elstwize that if sound is moving at highly 
reduced rate of speed in what is essentially half the board you are 
going to limit the boards ability to radiate sound efficiently.  You are 
effectively just letting it vibrate (significantly) in one direction yes 
??  over simplified but more or less correct I believe.

Otherwise.. this has been presented several times in several places 
before in the archives and other places. 

My point was that it seems possible that one can compensate for the 
panels anisotrophism independent of any structural requirements by 
laminating a panel much like crowned laminated ribs are constructed and 
running the grain of such a soundboard perpendicular to the bridge.  
Ribs in such a configuration could be used primarilly for such a 
compenation since the need for crown support would be much less then in 
a conventional board.

At least... thats where my musing on the idea has taken me at this point.

Cheers
RicB

*Michael Spalding writes:*

Ric,

I've never understood the importance of sound travelling through the
soundboard parallel to the grain and across the grain.  When we "hear" a
piano, we're sensing air pressure differences, which are created by the
diaphragmatic movements of the board.  Wogram states clearly in the
excerpts you provided, that the ribs are there to equalize the stiffness of
the board across and parallel to the grain, to optimise the diaphragmatic
response.  He says nothing about the speed of sound transmission throught
the wood, at least in the excerpts provided.  Where does this idea come
from?