The Rubens Tube



We built the Rubens tube using the following model: Josh the Engineer blog

Essentially, the idea is to create a visual representation of a sound wave. This is possible using the idea of Harmonics and Resonance as discussed in the earlier post.

The soft membrane at one end of the tube will vibrate at the frequency of the speaker against it creating a longitudinal wave with the gas filling the tube. The wave travels down the tube and reflects off the end, and at the right frequency (again, harmonics!) the returning waves will perfectly align with the waves coming from the membrane and a standing wave is formed. Once this is achieved, there will be points of nodes and antinodes that are now stationary. This is visualized by the flames on top, with the higher flames coming at the nodes, and the lower flames at the antinodes.

The first 4 harmonics displayed

We were also able to find the fundamental frequency, which was 122 Hertz. This created a single wave standing on top of the tube (1 node, 2 antinodes). We were then able to produce 2, 3, 4 and more standing waves by using the higher harmonic frequencies (244 Hz, 366 Hz, 488 Hz, etc.)

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