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MMD > Archives > July 1997 > 1997.07.12 > 02Prev  Next


Modern Band Organ Design
By Craig Brougher

Regarding the blowing of pipes with a short toe directly from an electric
valve, D. L. Bullock mentioned the "pop" from the turning on of a pipe
too quickly.  I have noticed that certain kinds of pipes tend to do that,
whereas other designs do not. 

For example, if your pipe is not buffered with an off chest or flue
between the valve and the mouth of the pipe to straighten out the initial
airflow, you will tend to get this effect on pipes which are "straight
through" without a convoluted path to the languid,  and usually only on
the largest pipes, which tend to have large, direct windways and are
slower to speak anyway.

Metal pipes are possibly more susceptible because of their direct design.
However, they can be helped by little adjustments, such as lowering the
languid and straightening the lower lip.  Lower lips that bow outward in
a hollow fashion tend to be slow to speak (tip).  When you hit such a
pipe with a burst of air, it will momentarily overblow.  Different kinds
of pipes react differently.

Any pipe that tends to give you problems that way can usually be fixed
(for example) with _just a little_ coarse cheesecloth wadding stuffed
into the windway somewhere between the toe and the mouth.  Not much, of
course.  What you are trying to do is to diffuse a direct, momentary
turbulent blast of wind which otherwise overrules the desired wind
curtain. 

When the valve opens too abruptly below the pipe, you'll tend to get this
direct blast across the upper leaf momentarily before the resonance of
the pipe has a chance to add impedance.  That causes the wind to be
directed more on the outside of the upper leaf and the difference becomes
a honky, flutey tone instead of the full intended resonance from the wind
curtain stabilizing a moment later and equalizing on both sides of the
leaf.

There is lots of ways of doing it, but it really doesn't have to be a
problem.  What you are doing is getting better control of a resonant
circuit at start-up by preventing overshoot.  That can be done a number
of ways, other than making the system larger.  For example, the resistor-
capacitor suppression circuits mentioned by Bob Billings (snubbers) which
dampens transients can also slow down a magnet or solenoid by weakening
its initial pull until the capacitor charges up.  You might find that is
all you need.  It is really a minor annoyance, once you understand the
principle to fix it.

Craig Brougher


(Message sent Sat 12 Jul 1997, 15:36:13 GMT, from time zone GMT.)

Key Words in Subject:  Band, Design, Modern, Organ

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