Flame Tube (Ruben's Tube)

PIRA 3D30.50

The Ruben's tube is a length of perforated irrigation pipe, with each end covered by a dental dam. Because the latex oxidizes, the dental dams will periodically need to be replaced. On each end of the tube is a stand to hold the tube with a speaker mounted such that the speaker is directly in front of the membrane. These speakers are stored in a separate location than the flame tube. The two speakers are connected to each other in phase, which are then connected to the output of the switch box with alligator clips. The inputs for the switch box come from the sine wave signal generator and a boom box. The switch box also has 1/4" signal out and signal in connections. These are for connecting to the amplifier. Pictures showing the details of these connections can be found below.

This experiment is best done in a darkened classroom. When there is no signal, the gas jets are fairly uniform in height, with variations mainly due to air currents. Once the signal generator is turned on, however, the heights of the flames will show a wave pattern when the frequency is adjusted to form a standing wave in the tube. The frequency can be adjusted to show many different standing wave patterns. Music can also be played into the tube. The switch box is used to determine which source, music or pure tones, are played into the tube.

Close ups of connections:
Signal generator and switch box.

Connections for speakers.

Switch box and amplifier.

Output wire for boom box.