To continue the thread about using a pressurized spoolbox with a glass
door, rather than vacuum to read music rolls; this system was quite
common for both reed and pipe organ players.  I can only speak with
authority about the Aeolian Company, but since they made far more
player reed organs and player pipe organs than all other firms put
together, there must have been thousands of examples.

The earliest Aeolian 46-note reed organs, and some of the later,
cheaper models of their 58-note reed organs, used the standard
'American' system of vacuum actuated reeds in grooved boards on
the under-keybed wind chest.  The players in these instruments used a
player-piano-like action, using vacuum, to actuate the keys or valves.
(There is a good picture of an early 46-note instrument in eBay; search
'Aeolian'.)

The better grades of 58-note reed organs (Orchestrelles), and all of
their 116-note 'Solo Orchestrelle' reed organs, used pressure actuated
reeds.  These were not mounted on the 'box', but rather were arrayed in
separate, narrow chests, mounted above one another in the upper half of
the case.  Elaborately shaped wooden resonators were mounted in front
of each rank, to further shape that rank's tone, and differentiate the
sounds among the various stops.

Each individual reed had its own valve, pulled open by a pouch or small
pneumatic in the chest, which collapsed under the influence of the
chest pressure when vented.  All these 'pulldowns' for any given note
were channeled together through the 'backplane' of the case, to primary
valves.  These valves, when actuated by a pouch, closed off pressure to
the channel, and vented it to atmosphere, allowing the individual
reed's pulldown to collapse.  The reeds for that particular note would
then play, if the pressure in any individual chest was 'turned on' by
pulling the stop for that rank.

Since these organs had no vacuum supply (the pedals work opposite of
those in an ordinary reed organ), pressure was also used to read the
roll.  After the roll is mounted, a sliding glass door is pulled across
the front of the spoolbox, and the organ's wind is admitted to the box.

A channel from the tracker bar leads to a pouch and bleed, under the
primary valve.  A hole in the paper admits pressure to the pouch,
inflating it to play the note.  Being pressure actuated, these pouches
are right out in the open, where you can see them operate (and the mice
can eat them up!)

Interestingly, the manual keys are connected to tiny pallets in a small
wind chest, leading to the same primary pouch.  No mechanical key
linkage is used.  Of course, with the keys and the tracker bar always
connected in parallel, it was necessary to fit a leather cover that
could be swung down over the tracker bar during manual play.  Otherwise
either all the notes would play when no roll was in place, or the
system would not work at all if the spoolbox door were left open.
(Later 116-note systems had cut-out pouches in the tracker bar tubes,
required for the elaborate logic of that format, so the tracker bar
could be 'turned off'.)

When Aeolian introduced the player pipe organ, using the 116-note
format, the pressurized spoolbox system was retained.  Only now the
pouches worked an electrical contact instead of the organ's primary
valves.  The earliest models used a tiny primary valve and pulldown
action to close the contact; later sensitive pouch actuated contacts
were developed.

In all these organs, the roll drive motor was just like any other
6-stage, double acting Aeolian motor.  But it was inside a sealed box.
Pressure, through a regulator and tempo valve, was admitted to this
box, and the motor valves let the pressure out through the center
channel, the same place where the vacuum hose is normally connected.

Only with the introduction of the fully automatic 'Duo-Art' 176-note
player organ format in 1915, did Aeolian switch to a vacuum roll
reading system.  The elaborate sectional tracker bar, and all the
machinery necessary to adjust it to the width of the roll, would have
been hard to put in a sealed spoolbox.  Never mind where to stash a 20
inch wide glass door when it was slid open.  Then they had to furnish a
vacuum pump, or an eductor powered by organ wind, to supply the 'power'
to read the roll.

Richard Vance

 [ For many years Matthew Caulfield has helped maintain Wurlitzer band
 [ organs at dusty amusement parks.  He offers this view:
 [
 [ "Though I like the looks of the vacuum system, the pressure system
 [ has two advantages over it: it eliminates the need for two separate
 [ wind sources (pressure and vacuum) and, more importantly perhaps,
 [ it doesn't suck paper dust into the tracker bar and clog up the bleed
 [ holes with minute paper particles that still get past the tracker bar
 [ screen."
 [
 [ -- Robbie