Flames, Music, Danger & Physics - $11 - Bargain

Recently Ramdaq, Dicey & I were chatting about various ways to visualise music. The conversation passed through lasers and smoke and finally settled upon flames. I suggested a classic physics experiment and sensory overload all rolled into one... the Rubens' Tube.

The basic idea is that you have a length of pipe with hole drilled along the top. The ends are sealed, at one end there is a speaker and at the other end there is a gas source. Once the pipe is flooded with gas you light the vapour flowing out of the hole, crank some tunes into the speaker and stand back. The speaker creates waves of sound pressure through the length of the tube, and these variations in pressure cause the flow of gas through each hole to vary... resulting in a visualisation of the sound wave painted in flames.

If you want a proper explanation then Wikipedia has the goods.

WARNING - This page documents our experiment. Do NOT attempt to do any of this yourself, do not treat these notes as instructions or as a guide. This is not a "how to" -Danger lies here, Doom and Death etc.

Project undertaken by Tinla, Ramdaq, Dicey.

The materials required are simple and inexpensive. We bought a length of 40mm waste pipe and some other small plumbing supplies from a local hardware store. Total cost was about £7 ($11). The other parts required, which we already had lying around, are an old speaker, lots of tape, some scrap wood and some kitchen foil. An amplifier, cables, music source and BBQ-type gas bottle will also be needed when the device is in use.

We had some very old bookshelf speakers that had seen better days and could be sacrificed for the project. In theory there is a benefit from using a good speaker because better defined (and stronger) waves could be formed in the tube. But in practice this was unlikely to be a problem in the prototype. Another option is to use a very cheap active PC speaker, these can be bought for next to nothing and have the advantage of a built in amp. The key thing to remember is that the speaker is in contact with the gas chamber, and as such we had to use something we didn't mind burning.

Due to cost we had used a plastic waste pipe. A large bore metal pipe would have been preferable, as the heat from the flames could deform or melt our plastic pipe. To compensate for this several layers of kitchen foil were taped onto the pipe prior to drilling. The foil acts as a very primitive heat shield/spreader, and while the clothe tape (Duct tape) will burn from the areas immediately surrounding the flames the majority will remain and hold everything tight and in place.

Once the foil and tape layers are in place marks are made at regular intervals along the pipe. The spacing of the marks, and the diameter of the holes to be drilled at the marks, was something we had to compromise on. We didn't expect to have the gas pressure to supply more than approx 30 holes and we had to drill them a little large to allow for some softening of the pipe and blocking by foil/tape. A metal pipe could be drilled more precisely. Our marks were made at 5cm spaces along the center approx 1.5m of our 2m pipe.

A frame was built around one of the speakers using offcuts of scrap wood. The picture above shows the speaker with three sides fitted. Once completed the wood covers 5 sides, with the speaker cabinet becoming the sixth side. A "port" is then drilled into the front face (directly in front of the speaker's woofer) and connected to the main pipe.

The speaker unit must be gas tight and joints are filled with an expanding sealant/adhesive.

At the other end of the pipe a pressure release cap is fitted, with a hole drilled through the centre to allow the gas supply line to be fitted to a narrow pipe connector. In the event of the gas within the pipe igniting the pressure cap will pop off, but there remains a risk of explosion and extreme care must be taken.

The butane BBQ gas bottle is connected to the pipe. A propane supply could also be used, but it is critical that a correct regulator is fitted between the gas bottle and the connection to the Rubens Tube. Once connected up paint all the joints with household detergent and run the gas, any leaks will show as soap bubbles.

The speaker box is connected to the other end of the tube. The golden cable running from the back of the speaker is connected to a normal household amplifier.

Once lit the flames should be of roughly equal height when no music is playing. We picked a slightly windy day for out build so the flames are being blown around a little in this shot, but overall we were pleased with the consistency of the burn. Despite the annoyance of the wind it is absolutely critical that the tube only ever be used outside, as there is likely to be a large amount of unburnt gas leaking from it. Even a well ventilated room or garage would be a very dangerous place to test such equipment.

Overall we consider the prototype to be a huge success. It was very cheap to build, very simple to build and yeilded a very rewarding result. With additional precision during construction, and by higher quality parts, a very impressive VU-Meter type device could be made. Fire holds a primeval appeal and fascination, everyone that has seen the tube running has stood silent and captivated by it... a compelling success for the prototype and a strong argument for a much much more ambitious build in the future.

Timelapse video, covering the approx 2 hour construction process:

Music - "Girl, Let Herself Go" by Ramdaq ft. Claude Boogie

Selection of video from the testing stage:

Article by Tinla.