Regarding the "unloader Theme bleed" in late model Duo-Arts mentioned
in the AMICA Bulletin, one thing should be mentioned.
Aeolian apparently thought that, once round valves had become standard
even for the new Steinway M's being fitted with players, the overall
tightness of the new design 80-note stacks made an occasional slight
rise in rare portions of some rolls, in which a rise in dynamic
unaccompanied by valve travel losses created a very slight excess of
unwanted residual vacuum pressure for the next note to play on. While
this effect can be noted during test roll regulation when the roll is
stopped and then started again, it is compensated for by the roll when
It was said in the article, Duo-Art Piano Rolls, that "the wear and
tear in hardware make the fall-off method of achieving Theme expression
levels quite unreliable." For the record, and to be respectfully and
technically accurate, this is an exaggeration, and also questionable.
Duo-Art always used very thick, heavy suede valve facings with lots of
natural cushion which in turn have a combined small amount of leakage
usually sufficient to get rid of residual vacuum in a predetermined
amount of time, scaled to their own roll coding standards. Granted,
when restored with materials like patent leather substitutes, they can
turn into nightmares to regulate.
The natural ability of elastic, compressive valve facings to tighten
proportionally under greater vacuum and ease their seal under the
lowest vacuum pressure when the correct suede is used seems to have
been taken into account in Duo-Art recordings. When a fixed bleed to
air is placed in the theme supply line, this ideal variable is either
nullified or at least changed somewhat, modifying the ideal response of
the stack very slightly to all dynamics. This is equivalent to placing
a fixed leak right into the stack itself.
While the expressions will cascade linearly under a fixed load as they
are supposed to (and were initially adjusted with fixed bleed), the
codings were adopted to compensate for stack transient losses, and were
found experimentally, so every characteristic of the Duo-Art stack was
compensated for, initially.
Ideally then, the stack unloading requirements are dependent on vacuum
pressures. Possibly another reason that the in-line unloader bleed
was not found in all the newly designed Duo-Arts after 1927, either.
I have therefore suspicioned that this bleed was likely cut-and-try
on some late models, but did not seem to appear on the majority of
them, and I restore and regulate every expression box fully that comes
into my shop. Of all the 1927 and later Duo-Arts I have come across,
only one has had the bleed.
Therefore, I suspect that this innovation is similar to the rare cross-
valve stems which were found machine-pinched and whose top stem guides
then had been changed to a thin slotted hole instead of a round one,
conceivably to prevent the valve from rotating and becoming leaky.
This innovation appeared on a number of Duo-Arts, too, however, it was
ineffective because necessary minimum stem clearances did not allow
tight enough control of the poppet to actually prevent vacuum losses
due to the slight rotations usually experienced, anyway.
Aeolian also made Steinways without the usual expression levers, too.
I presently have one in my shop right now. It was originally owned by
the founder and former owner of the Jenkins Music Co. of Kansas City,
Missouri. It doesn't even have the expression cutout block, and the
Duo-Art on/off switch, while retained, still had its original gray
tubing with shellacked stoppers, indicating that it was not to be used,
apparently. Also, the Soft-Normal-Dance plate had been trimmed so that
Dance was removed, and the "dance" pallet valve had never been put on
that piano. The usual slots in the key slip board had also been filled
at the factory, and the other label plates had never been placed.
So whenever you hear that Aeolian always had hand expressions, or
always did this or that, and you've never seen one different, don't be
too surprised to discover sooner or later that it was done that way,
too. It may have been a special order, a design change that didn't
appear in other areas or countries, or experimental. But in regard
to Duo-Art expression, they all work the same in that that piano is
completely controlled by the roll, and all of its characteristics,
including expression recovery times, taken into account.