When I first came to my present high school I found
one in a storage closet. No one had any recollection
of who made it or if it was every used. I have fired
it up every year for the past ten years.
Is is a thin-wall steel pipe about 9 feet long, 4
inches in diameter, and has holes space about 1/2
inch. It is driven from one end with a cheap four
inch speaker. The other end is closed with a steel
plate brazed across the end. Gas is fed into two
equally spaced ports along the length of the tube.
It works well. Resonant flame patterns are dramatic
from about 200 Hz up. It will quickly make the room
very hot. At the resonant frequencies the flames often
blow out resulting in a lot of unburned gas going into
the air. I open the windows first. The room gets very
smelly of the oderant in the natural gas. I use a
disposable lighter to quickly relight any flames that
go out. It is much faster than those flint things.
Speakers have caught fire. The speaker used to be
cemented on the end, but now I have springs which
secure it against the end of the pipe. This
facilitates quick speaker replacements when one burns.
I have found that if the speaker end leaks gas the
flame will quickly find its way to the leak. Some of
the failures resulted in large, memorable flames at
the speaker end. Make sure you are not directly under
a fire detections system, nothing combustible is
nearby, and be prepare to shut the gas off quick if
you have a problem. At one time I tried closing off
the driven end with a flexible plastic sheet but the
sound did not transmit well through it.
It certainly get students interested and helps them
understand resonate air columns. I always finish by
driving the speaker with some overly percussive music.
Matt Jusinski Morris Knolls HS, Rockaway, NJ
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