With all this talk about loud Duo-Arts, I haven't heard anyone here
mention a simple solution.  If you want to compress the dynamic range of
one, why not just set the lever-whose-name-I-can't-recall-at-this-moment to
"Dance"...   which, according to some literature I have, compresses the
dynamic range.  Anyway...  I've never noticed mine being too loud, probably
because it is an earlier model without the crash valve (its a 1914 model FF
Weber by the way).  There might be a way to disable this in a newer Duo-Art...

-roc