Yes, you can make an organ pipe out of PVC or concrete or just about
anything.  You just have to have a way to lower or raise the languid
and manipulate the upper lip.

When he was researching new pipe tones, Robert Hope-Jones made organ
pipes out of every known substance .  He invented the Tibia pipe,
because it plays with a tone almost devoid of partials, being mostly
fundamental tone.  This is why the Tibia can be used so well to
construct tones by mixing the different pitches.  Since it has so
few overtones, nothing gets in the way of using the Tibia pipes as
you would a modern synthesizer.

Modern theater organs come with Tibias played at (resultant) 32', 16',
10-1/5', 8', 4', 2-2/3', 2', 1-3/5', 1-1/3', 1' and sometimes 1/2' or
a Septieme and I don't know what mutation that would be.  It plays
around a seventh to the pitch and way high up.

Hope-Jones single-handedly did more to advance pipe organ technology
than any person other than Dom Bedos de Celles.  Classical organists
sometimes look down their noses at Hope-Jones and his Tibia, but he
developed many other things found on most classical organs today.
These include springs on a reservoir, stop tabs of whale teeth,
solid-walled swell chambers (he made his out of concrete) and double-
shuttering swell chambers.

He was known to have made organ pipes out of concrete to prevent
sympathetic vibration of the pipe itself.  (Normally only the column
of air in the pipe vibrates.)  He also built mixtures of non-standard
pipes, including trumpet mixtures and Vox Humana mixtures.

D. L. Bullock    Piano World    St. Louis

 [ A short account about Robert Hope-Jones and the
 [ Wurlitzer Hope-Jones Unit Orchestra appears at
 [ http://www-personal.usyd.edu.au/~sgroves/tosa/thor.html
 [ -- Robbie