Darrel Clark is having problems with bass notes dropping out on his Duo Art

>    How serious is this problem in general and why isn't it more noticeable
>    in other players?
>    Is it more of a problem with grands where the motion of the hammers
>    is working directly against gravity?
>    Does it imply that the friction losses on my action are too high or
>    am I expecting it to play too softly?
>    Is there any simple solution to the problem? (the graduated pneumatics
>    must have been too complex and voicing will only work when the note is
>    struck fully and will likely alter loud playing too).
> The accompaniment suction is the same for both sides of the stack so it
> can't be done with the roll coding and any base side throttling would
> soften loud playing, not soft playing.
>
> Does anyone have any suggestions please?

I think your problem will be drastically improved if you have the piano
action regulated by someone who can keep a good classical concert pianist
happy.  If you cannot find such a person, you can regulate your own if you
get the book by Danny Boone called "Regulating Grand Piano Touch and Tone."
 He is the man who taught me to regulate and book describes the VERY
involved method of making the grand action extremely sensitive to pianist
control.

If you watch your hammers while you slowly push down each key and see how
far from the string the hammer lets off, you will find that your hammers
let off unevenly from note to note.  They should, in the bass, all let off
1/8" from hitting the string and they should drop only 1/16" thereafter
from the let off point.  The treble let off is 1/16"   The Duo Art may be
pushing each key the same pressure (IF the valves are all sealing and
regulated the same) but the piano plays differently because the regulation
is  way off.  There is a list of about 20 things to do to each note to
correctly regulate a grand piano of which the let off and drop are only
two.  If your knuckles are flat on the bottom then it is time to replace
the piano action parts, as well.

I once had a customer who had an Ampico and a Welte both of which played
quite well by local AMICA club standards.  He did his own player rebuilds.
He decided he needed new hammers on the Ampico and had me do it and I also
did a complete regulation.  He originally complained that the piano was too
loud and it solved that problem.  He also found that once the piano was
well regulated, he had to crank the stack pressure way down, as it played
way too loud on player only.  He had previously had it down as low as all
the notes would still play, but like yours it was uneven.  He also fell in
love with the piano all over again because of the refined tone the new
hammers gave it and the ease of control of the action when he played
himself.  Of course, the Welte also got the same thing later that year.

D.L:Bullock Piano World St. Louis