Orthotropic Soundboard (was Laminated Soundboard Ribs)

[Ron Nossaman]

>The fact that the bridge is most often oriented in the grain direction of the
>board is interesting to me.  As I've said, I'm unconvinced that the board
>itself needs to be orthotropic.  But if it is, which it necessarily is if 
>you use
>solid wood, is there something magical about the bridge being oriented along
>the grain?  

Since I've been pretty limited in where I can put the bridge, I'd have to
call that orienting the grain to the bridge, rather than the bridge to the
grain. And no, there's nothing magical about it that I'm aware of, but it
is handy mechanically.


>On the other hand, since the bridge is a (seemingly) predominate
>path for wave propogation is it really necessary that the grain follow the 
>bridge?

Since I can't see them, I'm not terribly concerned about what waves
propagate in which directions. I'm more interested in the simple more
predictable mechanical diaphragm response. The waves seem to take care of
themselves just fine. With the bridge and soundboard grain running roughly
parallel (I'm using 60°-70° grain angle from the belly rail), The stiffness
of the assembly along the bridge means that the diaphragm response is
primarily going to be by bending of the ribs, not the bridge. As long as
the stiffness along the grain is adequate (bridge tall and stiff enough),
that's good enough. I don't have to worry about it and can design the
response I want into the ribs with reasonable assurance of getting what I
expect. If the panel was stiffer cross grain than the "standard" spruce
panel, I'd have to make adjustments to the rib dimensions to accommodate
the stiffness and still get the diaphragm response I want. This stiffness
with the grain is, I think, what makes floating the bass of the board so
effective, because it takes away the restriction of the stiff  long panel
grain, and gives control of the ideally much bigger diaphragm movement to
the ribs where it belongs. The panel shouldn't have to flex any more than
necessary along the grain when the board is working. Grain angle can be
used to "steer" flexibility of the bass float to where it will most benefit
the bass without making the low tenor too flexible. Since the board
response requirements of the low bass and low tenor are so different, yet
they are pretty close together on the panel, I'll take whatever help I can
get. 


>As JD mentioned this stuff has been thought about (and probably experimented
>with) before.  It would be nice to have access to the data which was gathered.
>Too bad the PTG Journal didn't exist in the 1800s.  I'll have to check out
>Dolge's Mathusek reference that JD mentioned.
>
>Phil F

And as we have repeatedly seen right here on the list, it's very unlikely
that a half dozen technical professionals looking at the same thing will
see the same thing and understand what they see in the same way, if at all.
Many a good idea has been abandoned because it was unrecognized as a good
idea, or was different from the accepted expert opinion, while other much
less ideal approaches became entrenched gospel in spite of the long and
venerable history of problems associated with their continued acceptance as
a standard. How do we know by comparing sparse old notes of the very few
who wrote it down what is gold and what is straw? At a certain point, we're
going to have to quit relying on comparisons of our interpretations of what
a couple of experts past wrote a hundred years ago on what they thought
they knew, and find out for ourselves what they did know, didn't know, and
were utterly mistaken about. At the same time, we can hopefully learn how
much we ourselves know, don't know, and are utterly mistaken about. 

Ron N