NEWS FLASH! "Conover clobbers Steinway !"

[Ric Brekne]

Hi Steve:

Thanks for the post.  I wont pretend to know one way or the other for 
sure mind you.  But it does strike me that as a consequence of 
compensating for anisotropism that both the bending stiffness and speed 
of sound in both directions are evened out. Since it is sound (waves)  
traveling through that actually causes whatever vibrational motion 
soundboard displays.... its strikes me that speed of sound in all 
directions is an intregral part of that motion. 

Be that as it may... lets just agree on the exact quote from Wogram and 
get back to the main question I had.  He said

    "From the measurements it can be concluded that the two most
    important functions of the ribs are to stiffen the soundboard and to
    compensate for the differences in bending stiffness parallel to and
    across the grain (anisotropism). The bending stiffness exerts a
    greater influence than the mass. For this reason it is more
    advantageous to use narrow, high ribs than ribs with a low and wide
    section."

What I'm thinking about is that in principle achieving equal bending 
stiffness in both directions is in itself an independant objective from 
supporting crown. However  In boards that have the grain going in the 
same direction as the bridge these two requirements must be balanced 
against one another.... perhaps even to some degree are at odds with one 
another ?  On the other hand.. if you built a soundboard with grain 
going perpendicular to the bridge and were able to establish enough 
crown support along the grain by way of cauled laminants all going in 
the same direction,  then ribbing across grain could be used exclusivly 
to equalize bending stiffness.

It strikes me that the soundboard needs crown support more in the 
direction perpendicular to the bridge then paralell to it. The bridge 
itself is very stiff lengthwise to begin with. The need for support 
perpendicular to the bridge appears (to me at this point) to be one of 
the primary reasons todays soundboard construction uses ribs in that 
direction which in turn requires grain to go paralell to the bridge. 

There is much about all this I dont understand.... but I'd like to hear 
what problems this kind of configuration would have. 

Cheers
RicB



Ric,

I doubt Wogram is referring to the speed of sound within the mass of the
soundboard when  talking about "vibrating area" and "radiation efficiency".
Isn't the sound we hear primarily a result of the diaphragmatic motion of
the soundboard disturbing the air?

Imagine a square soundboard with the grain running parallel to two of the
sides.  If the soundboard bends easier across the grain than parallel to th=
e
grain, then the shape of the fundamental diaphragmatic deflection will be
more rectangular than square.

Then if you add stiffeners perpendicular to the grain to equalize the
stiffness, the shape of the deflection will be more square, and the
"effective vibrating area" will be maximized.

Respectfully,
Steve Fujan