The so-called "expression box" of the Aeolian Company's Duo-Art
reproducing piano has gone through significant structural changes
during its production lifetime (circa 1914-1938 in the United
States).  Moreover, it is unclear exactly when and where the first
Duo-Art piano became available for sale to the public.  Estimates
based on the dating of extant Steinway Duo-Art piano serial numbers
span a two-year range from 1912 to 1914.

Because of the scarcity of reliable historical information (the
Duo-Art reproducing system was introduced about 100 years ago), the next
two sentences should be considered as conjectural in nature.  Though
I have not seen one first hand, an early (first?) implementation of the
expression box could have been in the form of two disjoint expression
regulators (accompaniment and theme) positioned under the soundboard of
a grand piano.  These would be pneumatically interconnected to other
island-like devices, which acting together, could translate piano roll
coding perforations to piano playing with human-like expression.

The next clearly discernible structural transition appears to be the
merging of the two separately mounted expression regulators into a more
unified box-like form.  The movable board of each expression regulator
faced the underside of the soundboard of the piano, not the floor.  The
box, with a contiguous end-mounted appendage was also coupled (with
large tubes) to a nearby device (theme and accompaniment switching
control).  Photos of such a configuration (1915 Steinway grand, XR
172139) were published in the AMICA Bulletin, March/April 1998, Vol.
35, No. 2, by H. Lindahl and S. Hoar.

A third variation of the expression box, and the one that most
likely experienced the greatest production volume (>10,000?), was more
compact, more symmetric, and probably a more effective expression box.
In contrast with its earlier incarnation, the movable boards of the two
regulators faced the floor, rather than the soundboard of the grand
piano.  Within one centralized, self-contained unit, it incorporated
the essential Accompaniment and Theme expression regulators as well as
the outboard devices mentioned above.  This version is most often
referred to as "the" Duo-Art expression box.

The fourth and last variation has come to be known as the fan-accordion
expression box.  The fan-accordion descriptor reflects the unusual
(Japanese) fan-shaped implementation of the two associated accordion
pneumatics (4 chambers each) that so characterized all previous
versions of Duo-Art expression boxes.  This configuration appears to
have been produced as early as 1927-1928 and was available until about
1938, the year that Aeolian ceased Duo-Art production in the United
States.

It is curious that the fan-accordion and conventional (third variation
above) Duo-Art expression boxes were produced concurrently for about
ten years.  Photos of these fan-accordion expression boxes (and their
variants) were published in the AMICA Bulletin, March/April 2009, Vol.
46, no. 2, by Tockhwock.

The four editions of the Duo-Art expression box cited above might
be viewed as major evolutionary steps in the development of a
sophisticated pneumatic device for the reproducing piano.  As with
so many other evolutionary processes, small changes (incremental
developments) to the overall system occurred along the way.  Where
practical and economically sensible, these changes were incorporated
within the previously established production process.

The description above may not be complete from a historical perspective
because all the evidence has not yet been "found".  Nevertheless,
one has to start somewhere.  Hopefully, others within the MMD community
will be able to contribute additional material to this archeologically
and technologically significant history.  Because the author of this
text has no experience with examples of Duo-Art instruments made in
Great Britain, he hopes that English Duo-Art enthusiasts will be
amenable to contributing their insights to this genealogically
challenging story.

Bill Koenigsberg