Philip Dayson mentioned the lost motion of upright Duo-Arts when the
soft pedal is on being responsible for missing notes. This is also
true in the grand, of course. Any piano with a hammer lift rail will
generate some lost motion between the stack strikers and the action.
But Duo-Art was agreeing with Philip 80 years ago, since they switched
on the #2 int. every time they operated the soft pedal, for the express
purpose of canceling out the lost motion effect.
I am also gratified that Philip has verified my findings in regard to
the throttling effect of Duo-Art valves at about .035. Granted, suede
texture plays a big role in this measurement too, the heavier texture
requiring a bit more gap. But the point I want to make is that you
can, without fancy test equipment like Phil uses, get the same relative
results I did with just your breath.
The human senses are absolutely amazing, when you come to think about
it! The differences between a valve with and without a .0025" thick
paper under it is easily discerned! Like everything else in pneumatic
reproducers -- maybe one reason they are so lifelike is because, like
ourselves, they too breathe air! (chuckle)