The Duo-Art expression box uses a wad of 1/4-inch thick muffler felt as
both a silencer and as a basis for the entire regulation of the box.
The original muffler felt was always skived a bit with a felt knife at
the edge which stuffs into the hole so that its leaker hole would have a
consistent diameter.  Half of the felt strip sticks out of the hole.
The other half was originally glued into the hole after its own hole was
carefully measured.

This is a very important beginning step for the Duo-Art expression
system!  It cannot be stressed strongly enough that unless you remove
the felt and reset it, wrapping it around a 1/4" drill and then
inserting gently back into its hole in the expression box, you will have
no chance of ever seeing that box perform as it is supposed to.

I have seen a number of D/A expression boxes which have been modified by
just lining that hole with a piece of name-board felt.  One owner had
about 3 or 4 of them, all done the same way, and complained about the
expression, compared to some he had heard later.  A musical ear will not
abide this modification for long.  Be sure that your expression box has
its muffler felt correct before trying to do anything else with the box.

The trick seems to soften the first 3 intensities, but actually it only
flattens the curve at the low end.  The zero intensity is sometimes as
high as the first, and the first three intensities are too close
together, so you have the appearance of a softer playing piano.  Chart
the box, though, and you can see that you really don't want it that way.

Duo-Art expression boxes are an art in themselves. The first step is in
the correct (and not always obvious) rebuilding of the box.  One of the
important considerations will always be repeatability, and with old and
tired felt bushings and such, that isn't an easy thing to achieve
regardless how long you've been doing it.

There are lots of tricks to an expression box, and it would take a
manual, some apprentice time, and several boxes of your own to know them
all and get them right.  But, to make a long story short, very few Duo-
Arts will chart the way they are supposed to.  A _lot_ of them bluff
their way through, except to the ear of a musician, and the "test roll"
isn't a big help, either.  If somebody actually cut a test roll that
would really check out a Duo-Art, it would be a very big help.  I might
have some helpful ideas along that thread, myself.

Craig B.