Dave Goggin wrote to the MMD Pipes Forum:

> I am no fan of reed pipes, mainly because I don't understand them.
> (Well at least I'm honest.)  So I guess the deal is that you tune
> the reed to exactly the note you want, you find a resonator (sawed
> off a flue pipe?) of the same frequency and pop it on the end of
> your reed ("boot" in the pipe lingo) and presto, you get a reed
> that is out of tune with the note it is supposed to be and out of
> tune with the resonator you popped on there.  So then apparently
> you have to fiddle randomly with the resonator until it
> (hopefully) comes back into tune and at which time the reed tongue
> still vibrates, who knows?  So I think I'll stick with flue pipes
> for now.

A few weeks ago Dave sent me recorded sounds from some of his
experimental pipes.  On analyzing the sounds I suddenly saw why Dave
dislikes them and said I would a try to give a little lesson later on
about the scant things I have picked up.

From a systematical point of view there are three kinds of reeds:

1.  Free reeds.  Used in harmonica, accordion, reed organ.  The reed
is mounted on one side of a support plate and moves freely through a
rather close fitting hole in the plate.  The oscillating frequency is
close to the natural frequency of the reed; normally no resonator is
connected.  Extant but unpopular with resonating organ pipes because of
fabrication complexity and lack of tonal distinction.

2.  Outward beating reeds.  Used in brass wind instruments and human
speech.  The wind supply tends to _open_ the reed passage.  The
frequency is complexly related to the natural frequency and is also
much dependent on pressure, and very difficult to control.  Outward
beating reeds are used with a resonator, but coupling of the resonance
to the downwind side of the reed is normally _weak_, and is almost
negligible in speech.  Resonance coupling is augmented in brass wind
instruments by using a narrow bore at the reed to ensure a very high
acoustical impedance.  The reed is dominantly a mass; the fundamental
frequency of the tone is slightly _higher_ than natural for the reed,
and the resonator gives a stiffness contribution.

3.  Inward beating reeds, as found in the oboe, bassoon, clarinet,
saxophone, and organ reed pipe.  The wind supply tends to _close_ the
reed passage.  The frequency is complexly related to the natural
frequency and is also much dependent on pressure.  Inward beating reeds
are used with a resonator, and the coupling of the resonance to the
downwind side of the reed is _strong_ because of the large exposed reed
area.  The reed is dominantly a _stiffness_; the tone fundamental
frequency is slightly _lower_ than the natural for the reed, it is
dragged down by an additional air mass in the resonator.

Hopefully these distinctive features tell why inward beating reeds are
the ones used for pipe organs.  Basically low pressure is needed, and
high feedback (high coupling) from the resonator.  A discussion about
about this reed type only will follow.

Johan Liljencrants

 [ Professor Liljencrants teaches speech communication and
 [ electroacoustics at the Royal Institute of Technology, Stockholm,
 [ Sweden.  Born in 1936 in Uppsala, his first training was in
 [ electronic engineering and he worked in industry for 10 years.
 [ He holds a Doctorate in Technology and has published many scientific
 [ articles on topics from loudspeaker enclosures to sound production
 [ in the human throat.  See his professional home page at
 [ http://www.speech.kth.se/~johan/index.html
 [
 [ Johan is a skilled handiworker, too, and enjoys several hobbies
 [ including pipe organ building.  He is moderator of the MMD Pipes
 [ Forum, an e-mail (list-server) technical discussion group concerned
 [ with the theory and practice of small player pipe organs.  Send an
 [ e-mail note to Jody <rollreq@foxtail.com> if you wish to participate
 [ in the discussion group.  -- Robbie