Ian inquired about the "snakebite" holes in his Steck Duo-Art. I have
a Stroud foot-operated Duo-Art and had to figure these things out too.
The foot operated machines had only one expression box, which
controlled, automatically, the "Theme" part of the music. The
Duo-Arts with an electric pump had both "Theme" and "Accompaniment"
expression boxes and controlled the volume of both automatically. When
pumped by foot, the "Accompaniment" level was controlled by how much
foot-power the player provided. Thus the one expression box.
Like all Duo-Arts, the half version has a split stack: that is, the
keyboard's suction level can be controlled separately for both the
treble and bass half of the keyboard.
The "snake-bite" holes tell the machine which half of the stack is to be
controlled by the "Theme" expression box. So in theory, a "Theme" note
will be accompanied by a snakebite controlling its half of the stack.
In this manner the machine can determine which notes are to be played at
the "Theme" level with controlled vacuum and leave the other notes to be
played by full vacuum as it comes from the foot pump.
I hope this all makes sense...
Drop me a line if you have any questions.
Long Beach, NY