Bob Taylor makes a number of excellent points regarding the design,
connection and regulation of the Duo-Art una corda (action shift)
and hammer lift (half blow) mechanisms.  However, I will add my own
observations on a few points.

First, Bob is entirely correct that in most Duo Art grands with both
mechanisms, the una corda pneumatic was originally triggered only by
the #95 hole, and that the hammer lift (usually with some compensation
boosting such as the #2 Accompaniment dynamic) was then used only for
the "soft" setting switch.  And he makes an excellent point that "the
owner should select an operating option and regulate the piano to sound
right with that option," considering the available options and perhaps
some personal preference.

He is also on firm ground dismissing concerns that the action shifting
during playing will somehow damage the poppets or key backs.  Similarly,
I am not convinced by concerns I've heard that the una corda will
somehow "shave" hammers against the strings, leading to premature
hammer wear.  The maximum amount of sideways hammer motion that could
ever occur during the very short time the hammer is in contact with the
strings is negligible.  If anything, regular use of the una corda may
slightly decrease hammer wear, spreading the impact across the hammer
heads and lessening the deep grooves that can develop on an instrument
played for a long time only by the player, with the una corda never
used.

I am also unconvinced by concerns that playing with the hammer lift
actuated for long periods of time by the "soft" switch will somehow
damage the keybacks or felts where the poppets strike with a bit of
lost motion.  First, in that option all of the playing will be
relatively soft because of the modulator reducing the vacuum force.
Also, the impact of the poppet will be pretty much the same regardless
of any lost motion, as the pneumatic leaves have little mass or
momentum, so the impact force is mostly set by the pneumatic force,
as it should be.

I have seen only one valid concern about using the una corda, in cases
where the Duo-Art stack rebuild and poppet alignment to the key backs
were sloppy enough that the action shift caused some individual poppets
to strike the keybacks of two adjacent notes.  In those cases, it may
be easier to disable the una corda and put everything on the hammer
lift than to do a full stack rebuild or repair to improve the poppet
alignment so that only the correct notes are played as the action shift
operates.

I don't entirely agree with Bob that the "soft" switch is "mostly
a gimmick", as I've seen many who find a Duo-Art grand in their living
room a little overwhelming at the "normal" setting, even with the lid
down, and are very happy to find a way to "turn the volume down" a bit
more.

In a properly adjusted Duo-Art with both mechanisms in the original
configuration, the zero-level accompaniment setting should just barely
play single notes as quietly as possible with dampers lifted and the
hammer rail not lifted.  So somehow asking it to become "quieter" by
lifting the rail is not musically or mechanically possible without some
or most notes failing to play at all.

As Bob points out, "turning on the #2 Accompaniment does mostly negate
the effects of the hammer rail lift."  And in my view, that is exactly
how it was designed to work, negating both the hammer lift and reduced
supply from the modulator so that quiet notes stay the same, while the
loudest notes are played with much less power.

While I don't know all of the history of Aeolian, I do question whether
the una corda only went into Duo-Arts after 1926.  I have recently
worked on both a 1920 Steinway model XR and a 1920 model OR with
pneumatic una corda mechanisms, including valves, original supply tees,
and the extended high-leverage pedal trapwork, etc., with no indication
that they were in any way retrofitted.  And I have seen many later
Duo-Art grands with only the hammer lift.

My guess has been that Aeolian introduced the una corda mechanism early
on, but installed it only as a more expensive option, more frequently
on larger pianos like the OR or AR models.  Certainly early Duo-Art
advertisement copy makes the point that it replicates the "artists
expression and pedaling," and I suspect it was used successfully as a
point of distinction to win over "exclusive Duo-Art classical artists,"
as the Ampico never had any way of using the una corda.

While Ampico coding apparently used the "half blow" as just another
tool for controlling volume, I strongly suspect Duo-Art coding, at
least in classical artist rolls, were coded from early on to reflect
actual use of the una corda pedal.

If only the hammer lift is present, the zero-level adjustment should be
increased so that single notes still reliably play when the hammer rail
is lifted, making the overall effect a little louder when hole #95
isn't triggered.  If anything, I have seen more later Duo-Art grands
missing the una corda than earlier ones, possibly as Aeolian followed
Ampico's lead and realized that many customers can't distinguish the
nuanced sound of the una corda, even as competition from the radio
appeared, the depression was looming, and the company became more cost
conscious.

Ralph Nielsen
McLean, Virginia
http://www.historicpianos.com/