Loud Duo-Arts are a pet peeve.  Phil Dayson (MMDer on this list) has
applied the controlled leak to his upright Steck Duo-Art with very good
results.  When I saw it, I was surprized to see how very small the
progressive leak is.  It seemed to be a simple and reversible solution.

Another factor, often overlooked in my opine, is the hardened hammers
that deliver a more percussive blow to the string.  The cushioned blow
of a soft hammer would have altogether different auditory responses to
weak vs. strong blows.  Since many expertly restored Duo-Arts still play
too loud, one is tempted to conclude that present day hammers are
either hardened from wear, or new hammers are manufactured with hard
surfaces.

$.02, please.

Bill Chapman