Dear MMDers, I have an issue with the action of my 1926 Steinway
upright Duo-Art.  On a few very, very quiet passages on some rolls,
it suffers from bobbling bass hammers.  It appears to me that the
pneumatic does not complete it follow through on the bass notes
when asked to play very quietly.  I can cure this by just upping
the suction levels until it does, but then it is too loud overall
on these quiet passages.

I can understand why it does fail.  I have measured the pneumatic
at its lowest playing level and it exerts its greatest push when the
pneumatic starts to collapse.  In this case about 6 ounces, but by
the time it is over half way collapsed, the push has dropped to about
2-1/2 ounces as the sides get sucked in, just when the hammer gets
to its heaviest with the damper being lifted.  On very light playing
the action stops here and the hammer goes on to strike the string and
bounces back and forth on the jack which has not cleared.  On light
hand playing the finger goes on to finish the key press and so there
is no problem.

I can imagine that early Duo-Art stacks with graduated pneumatics would
overcome this problem on the bass notes as the larger bass pneumatics
would have a greatest suction per square inch compared with the rest of
the stack and be more likely to complete their follow through.

Has anyone any hints on how to overcome this without just upping the
overall playing level?

Thanks,
James Black