Soundboard grain angle

[Ron Nossaman]

>This is an interesting and seemingly inefficient way to gain this stiffness. 
> As I see it there
>are two ways for the board (neglecting the ribs) to resist the motion of the 
>bridge:
>1.  The bending stiffness of the board itself.
>2.  The compression in the board from it acting as an arch.

A comment here on something pertinent that may otherwise be overlooked, if
I may. Remember Dale Erwin pointing out that you have to force the right
front and left rear of the board down to glue it to the rim? That's because
of the board stiffness along the grain. The ribs are forcing a crown
(nominally) perpendicular to the grain, and wooden panels don't willingly
conform to the compound curve required of a soundboard installation. The
board is being bent the length of the grain against it's will by the rib
crown, and is more nearly at rest under string load than it was before the
strings were installed. The load from the bridge doesn't bend the panel
along the grain until the crown is concave. As long as there is positive
crown, the bridge load is aiding the long grain stiffness in trying to
overcome the ribs and cross grain compression, and force the board flat.

The treble end of the long bridge is very near the clamped edge of that
long "beam" of bridge and long grain. Set up an old yard stick, which is
probably made out of spruce that should have been held in reserve for
future soundboards in the first place, and support it under each end to use
as a beam. Put a stack of washers or whatever handy weight you have at
hand, at the 30" mark and note the deflection. Now move the weight to the
1" mark and again note the deflection. The board is effectively stiffer in
the treble, close to the edge, than it is in the low tenor and bass
considerably farther from the edge. 

 
Ron N