THE FLAME TUBE
Visualize Waveforms with Fire
By William Gurstelle
Fiery devices have always fascinated me. From Jam Jar Jets
(MAKE Volume 05) to Fire Pistons (Volume 19) to Faux Flames
(Volume 25), I’ve built all sorts of fire-related projects. So when a
friend told me about a device that lets you visualize sounds using
fire, I knew I had to make one. I found it described in several old
physics demonstration manuals, then I adapted those directions
to make it less expensive and easier to build.
When you play a constant-frequency tone into
the Flame Tube, it displays a perfect sine wave
of fire. Play music, and the flames make a wild
display caused by big, air-moving bass beats,
standing waves from resonant frequencies,
and other acoustic phenomena. It’s inspiring,
fun to watch, and good for heating up your
garage or workshop on a cold day.
Some thought it was the periodic evaporation
and condensation of water, but later scientists
showed that the sound was caused by waves
of air, set in recurring motion by the fire’s heat.
Hot air, being less dense, moved upward while
cool air sank. This vibrating air resonated at
the natural frequency of the tube.
In 1860, Dutch physics professor Pieter
Years after Rijke’s work, German scientist
Heinrich Rubens turned the idea on its head.
Rijke was investigating the relationship
between sounds, gases, and fire. He stuffed a
piece of iron mesh inside a large glass tube,
then held it over a gas flame until the mesh
was red-hot. Suddenly, the contraption emitted a sustained musical tone so loud that
workers several rooms away complained.
He knew fire could produce resonating sound
waves. Was it was possible to use fire to make
sound waves visible for the first time? In his
laboratory at the University of Berlin he
developed the standing wave flame tube —
also called the Rubens tube in his honor.
Intrigued, Rijke’s colleagues set out to
discover the reason for “the singing flames.”
SET UP: p. 75 MAKE IT: p. 76 USE IT: p. 79
Photograph by Garry McLeod
William Gurstelle is a contributing editor to MAKE. His new
book, The Practical Pyromaniac, is available beginning in early
72 Make: makezine.com/26