Building a Rubens' Tube

For her 5th grade science fair project, my daughter Samantha decided to do her report on "Visualizing Sound Waves." To do this, one of the things we built was a Rubens' Tube. A Rubens' Tube is a long tube, sealed at both ends, with closely-spaced holes drilled in a line down one side. One end of the tube is sealed with a sheet of latex rubber, and a speaker attached to the outside, so that sound sent through the speaker will enter the tube. Here's a picture of what ours looks like:

The tube is filled with a flammable gas (propane), and the gas escaping from the holes is lit. Then, by playing sounds of different frequencies through the tube, standing waves can be created. The standing waves will create areas of higher and lower pressure within the tube, and these areas will be visible outside the tube as flames of different heights. You can easily determine the wavelength of the source sounds (or the standing wave) by measuring with a ruler:

Our Rubens' Tube was built in a manner similar to the one described here by Nik Vaughn, with some modifications and parts substitutions. Here is the complete parts list. Our tube is 60 inches long with 101 1/16" holes drilled at 1/2" intervals, and five inches of "buffer" on each end. Gas is fed into tube via two inlets at the rear of the tube (spaced a third of the way in from either end) from a 20 lb. propane tank (the kind you use with a barbecue grill). Sound was delivered from an iPhone to a pair of computer speakers; one speaker was at the end of the tube, and the other was for the audience. We found that converting the MP3s to monaural (as opposed to stereo) helped, since only one channel was feeding the tube.

Samantha worked very hard to learn all the physics behind how the Rubens' Tube works, and she practiced her presentation several times. All her hard work paid off; she tied for First Place - 5th Grade at the school science fair.

The videos below were included on the DVD that we made as part of Samantha's project. Note that the music chosen here was selected because it created lots of standing waves within the tube. You can run other stuff through the tube as well, and make the flames "dance" and otherwise go crazy (Styx' Come Sail Away and Dire Traits' Sultans of Swing are good examples), but that was not the point of the project. With the exception of the signal generator video, I have remixed the stereo MP3s back onto the videos; this sounds much better than the monaural audio played through a crappy computer speaker and recorded by the camcorder microphone.

All videos are in MP4 format.

Using a signal generator to create standing waves at various frequencies in the Rubens' Tube. If you have an iPhone, the Generator app from Studio Six Digital is a nice $6 alternative to the actual test equipment versions that cost several hundred dollars.

Carrie Newcomer, singing an a cappella song she wrote while she was with the group Stone Soup in the 1980s (she is now a solo performer and was voted Folkwax magazine's Best Artist of 2009). Carrie has a beautiful voice, and the lack of musical background makes it especially easy to relate what you see the Rubens' Tube doing to what you're hearing.

Mike Oldfield has written a lot of interesting stuff over the years, most notably Tubular Bells (used as the them music for The Exorcist), and the score for the movie The Killing Fields. But in the early 1980s he collaborated with a wonderful Scottish singer named Maggie Reilly, and they created some terrific songs, including this one.

Anybody who grew up in the 1960s and 1970s is familiar with the instrumental song Popcorn. It was so cool way back then, when synthesizers were a new thing. Nowadays it's more nostalgic than cool, but the techno remix included here is still kinda fun. Anyway, the idea here was to provide a somewhat more "active" song, but keep something that produced lots of standing waves. Classical music would probably have been better here, but these kids nowadays, they just don't like that stuff. :-(

Loreena McKennitt is a Canadian Celtic singer who writes and performs some really neat music that you'll almost never hear on the radio. You may have heard the song The Mummers' Dance, which still shows up on adult contemporary radio once in a while (at least on the east coast of the United States). This song, The Highwayman, is a musical version of the narrative poem by Alfred Noyes, published in 1906.