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MMD > Archives > June 2014 > 2014.06.24 > 04Prev  Next

Duo-Art Fan Accordion Enables Loudness Reduction
By Bill Koenigsberg

Why is the Duo-Art so loud?  My guess is that almost everyone has
asked this question, after listening to a restored Duo-Art reproducing
piano.  Now that I am almost done rebuilding my Steinway Model L
279076 "Duo-Art with a Drawer" from 1935, I suspect that the Aeolian
Corporation had listened to its customers when the "fan system"
expression box was introduced, probably as early as 1928, maybe 1927.
The fan system expression box appears to have a built-in "loud
reducing" mechanism.

The fan accordion is aptly named because its structure resembles that
of a collapsible Japanese fan.  It occupies about one-third the volume
of a "conventional" Aeolian box accordion (for lack of a better term)
pneumatic assembly.  The drawer-type Duo-Art incorporates the fan
accordion expression box.  The drawer itself is an Aeolian-modified
Ampico B drawer that accepts jumbo Duo-Art rolls.

Other Steinway pianos exist (without the drawer) that also incorporate
the fan-accordion system.  For example, collectors have found the single
roll and 10-roll carousel-type Concertola, and those few special-order
instruments with the fan-accordion assembly mounted above the keybed.
There may also be others.

Close inspection of the fan accordions from L 279076 revealed a small
but noticeable difference between its pneumatic fan-chamber "stop
screws" (delightfully, only one per chamber) and those (three per
chamber) found on a conventional, box-type Duo-Art expression box
(pre-1928, and some later).  That is, the fan accordion stop screws are
longer, by 1/16 inch (1/2" vs. 7/16").

This may be incidental, but it also may be that Aeolian wanted its
"latest" Duo-Art to be adjustable so that it could play less loudly
(without dropping notes) at peak intensity, possibly accounting for the
wishes expressed by some of its customers.  With longer stop screws,
each fan chamber, when vacuum activated, may be adjusted so that it
does not collapse as far, compared with a conventional box accordion
chamber from earlier instruments.

Fortunately, it is relatively easy to "update" earlier instruments
by substituting "slightly" longer stop screws (three of them) for each
chamber (four of them) of the Theme and Accompaniment box accordions
(two of them).  Several AMICA members have already done this, with
satisfying intensity-reducing results.

This geometric difference (stop screw length) appears to be consistent
with the confusingly high absence of a "crash valve" in many (but not
all) Duo-Art systems that utilized the fan accordion expression box.
The crash valve, even when properly adjusted, can make almost any
Duo-Art piano play excessively loud.  It may be that Aeolian offered
the crash valve in the fan-accordion system as an option, to accommodate
the tastes of those customers who hungered for that extra dose of
musical intensity.

At this point, one could consider the above supposition conjectural,
because there are some mitigating circumstances.  That is, the nominal
quiescent operating conditions for the conventional Duo-Art (box-type
accordions) are well known and well documented.  This is not the case
for the fan accordion system, which incorporates only two decks of
smaller striker pneumatics (7/8" wide), variable lengths (4" to 4.5"
long), and two curtain valves (one each) in the Theme and Accompaniment
zero pneumatics of the expression box.  By contrast, the conventional
expression box with box-type accordions utilized the usual Aeolian knife
valves, and the stack contained striker pneumatics that were 1-3/8" wide.

Because the fan-accordion striker pneumatics are significantly smaller
than their "conventional" (pre-1928, and some later) counterparts, the
zero level for the vacuum supply at the stack must(?) be greater, in
order to realize the same force to strike each note.  In addition, each
curtain valve operates with a geometry that differs from the knife
valve, i.e., the maximum flow-through area is smaller.

It may be that these two factors account for why Aeolian used slightly
longer stop screws on their fan accordion systems.  Then again, the
longer screws may have been less (more?) expensive, and fewer of them
were needed (fan accordion 8 vs. box accordion 24).

Comments regarding the above "fan accordion conjecture" would be
gratefully appreciated!  I am still working on the "Duo-Art with a
Drawer" -- why does it always seem to take longer than it should take?

Bill Koenigsberg
Concord, Massachusetts

(Message sent Tue 24 Jun 2014, 19:01:51 GMT, from time zone GMT-0700.)

Key Words in Subject:  Accordion, Duo-Art, Enables, Fan, Loudness, Reduction

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