Pete, (and others interested) I was glad to see your posting 8-96-15 on
Duo-Art dynamics.

I too have been through this phenomena with the Duo-Art.  All musical
values were lost with exaggerated dynamics even though I used factory
settings for the accordions.  Ugh!  I ended up rebuilding the stack and
setting the valves precisely to .032 inches--well almost precisely.  The
piano then picked up soft notes which enabled me to reduce the zero
level to 4.5"in turn starting the dynamic curve lower.  Still the
dynamics were unrealistic so I altered the settings on the accordions
and got rid of that ridiculous jump in loudness.  It took lots of trial
and error to find something satisfactory.  Self-adhesive felt stops
were used in the accordions to save turning the screws on each trial.

Incidentally, with factory settings on the accordions, the test roll
played fairly well except for the progression of chords that are
repeated with increasing loudness.  I used the chords as a reference
for narrowing the throw on the accordions until they sounded smooth in
increase of loudness.  Incidentally,  I noticed that the most convincing
DAs I've heard sound only mezzo-forte while playing with only #4
collapsed.

I believe much of the answer lies in the hammers.  IMHO the felt
hardens over time and the hammer becomes incapable of delivering a
moderate force to the string.  Instead of the felt compressing on
impact with the string, the hammer hits with its full momentum
delivered to the string all at once--not moderated by the cushion of
soft outer felt.  Maybe the characteristics of hardened hammers is such
it accounts for the exponential jump in dynamics--it would be
interesting to explore this but quite complicated.  I have the
oscilloscope but not the patience.  Steinways tend to get "crashy" as
they age, maybe okay in the concert hall, but not useful at home.  New
Steinways do not sound crashy at the factory.

I'm just about to tackle the hammers with emphasis on softer felt.  A
few people I've talked to in England believe that pianos were voiced
softer in earlier days--that would explain a lot.  I hope there will be
more postings on DA dynamics.