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.
[youtube http://www.youtube.com/watch?v=c2PmkXkBQ-4?wmode=opaque]
In 1860, Dutch physics professor Pieter 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.
Intrigued, Rijke’s colleagues set out to discover the reason for “the singing flames.” 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.
Years after Rijke’s work, German scientist Heinrich Rubens turned the idea on its head. He knew fire could produce resonating sound waves. Was it 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.
[youtube http://www.youtube.com/watch?v=WRWdpam_2to?wmode=opaque]
The flame tube (aka Rubens tube) is a waveform visualizer. It works because sound is a pressure wave. As sound moves through a gas like propane, the wave alternately compresses and expands the gas in different regions. When you use a frequency generator to produce a constant tone of, say, 440Hz (the musical note A), the speaker pushes this sound through the gas, and a stationary wave is set up.
The stationary wave causes areas of high pressure to appear at fixed points along the pipe, spaced half-wavelengths apart. Where the pressure is high, the propane is driven more strongly out of the pipe, resulting in a tall flame. Between these high-pressure points will be low pressure points that create lower flames.
When music is played instead of the frequency generator output, the clean curves of the sine wave are replaced by much more chaotic and perhaps even more intriguing patterns. Strong vibration from drums and low-frequency sounds from bass guitars, tubas, and string basses cause the flame tube to send fire pulses out of the holes nearest the loudspeaker. Overlaying that are sine waves that are visible whenever the musical pitches being played coincide with the tube’s resonant frequencies. This layering of resonant frequencies and bass beats produces a dazzling display of musical pyrotechnics.
Hi Rusty,
I don’t think the contest has been announced yet. Here’s the original post mentioning the upcoming contest: http://blog.makezine.com/archive/2011/07/the-flame-tube-project-and-contest-coming-soon.html
Keep an eye out on Makezine for a future post from Bill Gurstelle:
http://blog.makezine.com/archive/author/bill_gurstelle
Yep, I made this and about 20 minutes after it running, the couplers that were screwed into the tube started to melt, one enough that some propane flame was leaking out of it, at which point I immediately shut it off. I’ll have to find some metal couplers that won’t melt.
Contest?!?! Where…
http://www.youtube.com/watch?v=1AHYHdN3Gdk
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Hello,
I have constructed a Rubens tube for use in a classroom demonstration. I have one end sealed with a latex balloon and the other end is sealed with aluminum tape.
I got it to light properly once this morning, but since then every time I attempt to light it it explodes the balloon off the end with a loud bang.
I am giving it time to ventilate, so I don’t think its an issue with residual propane. Every time it happens the balloon end it open. Could it be an air/propane mixing side effect?
I would really appreciate an answer as I am going to attempt this with a class on Monday.
Thank you,
Nicole Baldwin
As a complete guess, without making one. I would assume you need to wait longer before lighting it. Propane is heavier than air, so it should displace all the air in the tube if you wait long enough. However if the rate of propane entering the tube is less than the amount consumed, I could see the oxygen entering the tube. You might be able to test this by taping all but one of the holes shut, waiting a while for the air to vacate, then lighting the one hole. You should then be able to peel back the tape (while being careful not to get burned) and see how many holes you can have going at once. Like I said, I haven’t made one yet, but talking to a couple people around the physics department, that might be what’s going on.
Hi,
Im planning on making a Rubens Tube for my final creative project for university. I’m trying to find the best material to use for the pipe, what did you use for your pipe?
Thanks,
Sara
Hi,
I am doing this for a middle school science fair and your instructions were a great help but I need more info on the history.
Thank you so much,
Kaleb
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