The recent rekindling of interest here on MMD in Duo-Art expression
box regulation, has once again shown how many opinions exist on one
component and its correct regulation.

Admittedly, there are several approaches to adjusting the Duo-Art
expression box.  Which approach is used is a matter of personal
preference.  I prefer to use a method of regulation that recognizes
the extreme propensity for error resident in the crude mechanical
linkage set-up in the Duo-Art.  Let me explain this last statement.

Duo-Art expression levels are set by accordion pneumatics collapsing
in a linear motion.  That motion is transmitted to the knife valve as
rotational motion.  In between the accordion and the knife valve are
two shafts which rotate in felt bushings, an additional felt bushed
connecting rod, a loose metal-to-metal bearing based on a shoulder
screw,  a metal to wood felted bearing for spring tension, and a felted
metal in wood bearing on the knife valve.  Whether or not you follow
that muddy description, suffice it to say, that the transmission of
motion within the Duo-Art is one potentially sloppy contraption.  No
two expression boxes will have the same lost motion, shaft wobble, or
other inaccuracies.  But it can be very accurately regulated.

Indeed, Larry Givens' advice about regulating the four accordion gaps
to perform the test roll is the answer.  It is this setting that makes
the linkage nightmare work.  The series of "play" and "don't play"
tests cancel all the induced errors within the linkage.  Additionally,
all the system leaks, operating valve losses, and spring irregularities
are "zeroed out" as well.  There are no short cuts.  After setting the
gaps and the test roll performs flawlessly, the springs may used to
tweak volume levels to suit personal preferences.

The Duo-Art system is very capable of rendering beautiful performances.
My opinion is that it should be regulated without regard to visual
cues.  Let your ears be your guide.

Bob Taylor