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MMD > Archives > August 1996 > 1996.08.18 > 08Prev  Next

Duo-Art Expression Box Muffler Felt
By Craig Brougher

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.

(Message sent Sun 18 Aug 1996, 13:16:14 GMT, from time zone GMT.)

Key Words in Subject:  Box, Duo-Art, Expression, Felt, Muffler

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