Bill Mintz commented on the "Silent Piano".

The "silent piano" is simply the keyboard of the instrument mounted
on a supporting tray, easily portable.  It is also sometimes called
a "dumb piano."  The most famous reference to its use is the story of
Sergei Rachmaninoff practicing his newly-composed Third Piano Concerto
on the way to this country in 1910.

When co-founder Greg Benko and I visited W. Creary Woods, one-time
editor of the Aeolian Co., in the mid-'60's to purchase his collection
of master rolls for the newly-founded International Piano Library (now
IPAM at the University of Maryland), there was the very instrument
Rachmaninoff used.  It had been given to Mrs. Woods, the former Edna
Bentz, by the composer.

So that is the _true_ "silent piano."

Albert M. Petrak