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Ruben's Tube


A 1.5m long aluminum tube with approximately 80 holes drilled in the top at regular intervals. One end of the tube has a fitting for attachment to a standard barbecue propane tank, while the other end has a brass membrane (to seal it) with a speaker mounted.


The Ruben's tube provides an exciting, flaming representation of a standing wave. There are about 80 holes along this tube, which are ignited once the tube is filled with gas. A speaker is fitted on one end and frequencies that create standing waves are played into the tube. The standing wave sets up areas where the static pressure is higher, increasing the flow rate and therefore the height of the flame at different points along the tube.



  1. Attach the function generator output to the input at the back of the stereo labeled “Phono Right” and ensure the stereo is set to play the Phono input
  2. Attach the two cables from the back of the stereo to the receiver/amplifier and then to the speaker on the Ruben's Tube.
  3. Select a frequency on the function generator, set the amplifier volume to the minimum, and turn the function generator on. Then slowly turn the amplifier volume up to test that the speaker is connected properly.
  4. Attach the propane tank to the flame tube using the tube and fitting on the end.
  5. Open the valve on the propane tank all the way, then open the valve on the flame tube.
  6. After a few seconds, begin trying to light the propane coming out of the holes. It'll take some time for the air inside the flame tube to be evacuated and replaced with propane.
  7. Once all the holes have lit flames above them, adjust the height of the flame using the valve on the tube. Setting the height of the flames so that just a little bit of the yellow part of the flame is visible seems to produce the best contrast. You may have to adjust the flames later in the demo.
  8. Finally, use the speaker and the amplifier as before to set up standing waves in the tube. A listing of some frequencies that work well is provided below.


If the volume is too low, you'll find that it's hard to see much of an effect. If the volume is set too high, the flames in the troughs of the standing wave may go out. The volume needed to achieve a good effect may also vary depending on the mode of the standing wave.

Music can be played into the tube for dramatic effect. Classical music or music with a lot of bass works best. As well, any piece of music with a lot of pure tones has good visual effect. Music can be provided.

Due to the flammable nature of this demo, please request assistance. Frequencies of standing waves are recorded on the function generator. Significant volume is required to reach a visible amplitude.

Please provide notice when requesting this demo as some set up is required as well acquiring propane.

Suitable Frequencies: f5: 286 Hz f7: 400 Hz f9: 514.5 Hz

Demo room information

Location S2
Maker Unknown
Current State Working
demonstrations/3_oscillations_and_waves/sound_waves/rubens_tube/start.txt · Last modified: 2020/02/14 17:17 by demoroom