I've been reading with interest about the efforts some are making to
quiet the damper drop on PianoDiscs.  The problem may not be so much
that solenoid systems allow dampers to fall with no delay, thus making
an audible "thud".  If the lift of the damper tray is kept to a minimum,
the "thud" will be lessened to a tolerable level.  A small lift will
also benefit the solenoid.  Since it is lifting all the dampers, it
works much harder than any other solenoid in the system.  Letting it
work as little as possible will keep heat down and extend its life.

A small lift means that the damper tray at rest must be just below the
damper levers, with minimum lost motion.  All the dampers must lift
absolutely at the same time, with no late or early ones.  If you spend
the extra time to seek perfection here you can get away with a lift
from the solenoid of only an eighth of an inch, or a point where the
dampers are just above the potential vibration envelope of the strings.

Another tip, if you have replaced the damper felt, trim the wedge felt
points so that when they rest on the strings, the point extends just
below the strings.  Then, when the pedal is on, the points, or tips
won't have a chance to touch the vibrating strings.  Also, the dampers
will be less likely to fold over with age.

Jeff Davis, Seattle