Backscale design... Ron N. ?

[Ron Nossaman]

>Hi Ron,
>
>Thanks for the input.  Could you help me a little more with the above?  I'm
>not quite sure I know what you mean.   What's a "bridge cantilever"?  Is
>that another name for the apron?  When you say you moved the bridge 'down',
>is that toward the pinblock in the direction the strings are going?
>
>I just want to make sure I'm understanding what you're telling me.  (I'm not
>now, but I'm trying.)
>
>Thanks Ron.
>
>Brian


Yes, with the customers' approval, I remove the apron. That type of design
puts a lot of unnecessary leverage on the soundboard and forces that lovely
"s" curved crown you see in some of the old boards. Besides that, it's
heavy, and bass bridges are generally heavy enough without it. The idea of
the cantilevered bridge is, I think, to increase the flexibility of the
assembly to let the bridge move more freely for better energy transfer from
the bass strings. Then they design in a long speaking length that results in
a very short back scale that cancels any possible benefit of the cantilever.
Probably a committee decision. Del did a terrific series of articles on
soundboards in the Journal a while back, with pictures and arrows and such,
that explains in great detail why this type of construction isn't such a
good idea. Required reading if you can lay hands on them. Alternately, you
can get adequate flexibility without resorting to hanging the bridge out on
the end of an apron. You can design the rib scale and panel thickness so the
soundboard assembly in the bass will be flexible enough to let the bridge
move with the strings. Then you can move the new (sans apron) bass bridge up
(You're right, that was stated backward. "Down" would be toward the tail) to
increase the backscale length. You have to work with what the plate will let
you get away with here, since changing the rim contour and plate layout
might be a little bigger job than your estimate will cover. If you can't get
the bridge far enough from the rim to get the soundboard flexibility that
you need, you can always undercut the low end of the bass bridge a couple of
inches. If there is a Walter at the Convention in KC this year, check it out.

                                  So
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I read an article by Klaus Fenner once where he proposed that you should
keep the backscale as short as possible to limit soundboard movement as an
aid to tuning stability! That was a while back, and he may be of a different
mind now, but I personally think soundboards ought to be able to move. 

 Ron