Can I try to explain Doug Heckrotte's dilemma --

Firstly, I'm not sure what Doug was trying to demonstrate in his days
of youth.  I think he was probably trying to see if he could create
a time delay in the operation of playing a note.

Assuming that the operation delay was going to be the time taken for
a pressure wave to travel down the tube, the time delay would only be
of the order of 27 milliseconds.  How such a small time delay was to
be detected is not clear.  It is also possible that the Haas effect
had an influence on his detecting of what was happening.

When a hole is opened, there is instantaneously a pressure increase
at the open end, and a wave is progressed through the tube.  It is
the "rate of change of pressure" which, when it arrives at the pouch,
causes the pouch to lift.  The tube has a pressure gradient along its
length.  Once the pouch has lifted, the mechanism starts to close the
pneumatic.

It is not necessary to completely fill the tube with air before the
pouch will lift.  It is necessary to increase the pressure under
the pouch but this pressure is not necessarily the same at _every_
part of the tube.  There are "dynamic" conditions and "steady state"
conditions and the initial pulse propagation along the tube is part
of the dynamic conditions.  These conditions are changing with time,
but after a time, these conditions will become constant with time,
and then the "steady state" is reached.

Mostly, prediction of the dynamic conditions is a difficult subject,
and much discussion about "what is going on", ignores the dynamic
conditions and simply assumes the change from one steady state to the
next, occurs instantaneously.  It is the dynamic conditions, which
give rise to the "repetition speed" and every one knows what a mess
of noise it is when notes don't repeat rapidly enough.  This explains
Dr. Hickman's "variable bleed".

Similarly, when the port closes, the bleed extracts air from under
the pouch first, and can allow the pouch to collapse, even though there
could still be air along the length of the tube.

Generally, the smaller the tube diameter, the more responsive the
pouch will be to the port opening and closing.  Repetition, and ease
of pumping, is also to be considered by the size and length of tubes
and channels.  In my experience, the dynamic performance of the Simplex
unit valve, is way ahead of constructions like the Standard action,
as good as it may be.  The useless air volume above the valve poppet
connecting to the pneumatic, is unnecessary inertia for the exhauster
bellows.

Hope these comments help.

Paul Rumpf
Melbourne, Australia