Hi,  I am pretty embarrassed to post this question here, but I have
thought and thought about it and simply can't figure it out.  Can
somebody please explain to me the pneumatic physics of a hand-cranked
monkey organ which plays real pipes from holes in paper rolls?

I understand the paper holes allow air through the holes in the tracker
bar.  I understand that each tracker bar hole is attached via tubing to
a pipe.  What I do not understand is that this seems like a closed
system to me (tracker bar hole to pipe), and I can't figure out how the
pressure in the wind chest causes the rush of air which makes the pipe
sound.  I know there are valves involved in some organs, but I am
referring to a valve-less, direct-action organ such as the John Smith
Busker organ.

I'm sure I'm just missing something about the construction, since
I can't see how a continuous air passage from a hole to a pipe can be
affected by the conditions in the surrounding wind chest.  What causes
the suck of air, if there is no air flow between the wind chest and the
tracker hole-tubing-pipe line?  If there is air flow, where does it
come from?

Thanks for bearing with this stupid question,

Manda Clair Jost


 [ 'Tain't stupid, Manda, you just need to know one more crucial fact:
 [ the wind chest is the pressurized closed compartment with the
 [ music roll !
 [
 [ A large door over the compartment (often of transparent plastic)
 [ allows the roll to be changed.  Then close the door, start the
 [ blower and paper transport, and when a hole goes by the tracker bar
 [ the air flows through the tracker bar and a hose to the pipe.
 [
 [ One big problem is that the hole in the music roll slowly uncovers
 [ the port to the pipe.  This yields a very mushy attack and decay
 [ of the sound, unless the paper moves very fast.  That's one reason
 [ why valves are employed: to change a mushy control signal into a
 [ snappy on-and-off flow of air, with sufficient flow to assure that
 [ the largest pipe speaks proudly!  -- Robbie