Introduction: How to Make a Ruben's Tube

About: I am an A-Levels Student at Karachi Grammar School, Pakistan. My passion is physics and mechanics and I want to be a Mechanical Engineer in the future. Actually anything in the field of engineering would do. :P
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Made By Manish Kumar, Murtaza Tunio and Minaam Abbas

The Ruben's Tube is a physics experiment demonstrating a standing wave. It demonstrates the link between sound pressure and sound waves.

A length of pipe is perforated along the top and sealed at both ends - one seal is attached to a small speaker or frequency generator, the other to a supply of a flammable gas (propane tank). The pipe is filled with the gas, and the gas leaking from the perforations is lit. If a suitable constant frequency is used, a standing wave can form within the tube. When the speaker is turned on, the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube. Where there is oscillating pressure due to the sound waves, less gas will escape from the perforations in the tube, and the flames will be lower at those points. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed. It is possible to determine the wavelength from the flame minima and maxima by simply measuring with a ruler.

Since the time averaged pressure is equal at all points of the tube, it is not straightforward to explain the different flame heights. The flame height is proportional to the gas flow as shown in the figure. Based on Bernoulli's principle, the gas flow is proportional to the square root of the pressure difference between the inside and outside of the tube. This is shown in the figure for a tube without standing sound wave. Based on this argument, the flame height depends non-linearly on the local, time-dependent pressure. The time average of the flow is reduced at the points with oscillating pressure and thus flames are lower.

Step 1: What You Need


Drilling Machine
A Long Metal Tube
Gas Pipe
Gas Cylinder
Speaker Wire
Guitar Amplifier
Crocodile Clips
Stands for the Ruben's Tube
Wire Strippers
Screw Drivers
Amplifier Wire (PC to Amplifier)

Step 2: Dismantling the Amplifier

Disconnect the wire connected to the speaker. Next Unscrew the back lid and the speaker itself from the amplifier. 

Step 3: Drilling Holes Into the Tube

Purchase a hollow metal tube from a scrap yard. Use the drill machine to drill holes in the tube approximately 1 inch apart.  From one side attach a gas pipe and cover the other side by using a balloon or cardboard. My metal tube was approximately 5 ft long and consisted of 50 holes. This way the tube will act as a closed system except for the holes on the top.

Step 4: Creating Crocodile Clip Wires

Cut approximately a foot of speaker wire and strip the insulation off from each end. Solder the crocodile clip to the speaker wire. Make two of these wires. Strip off some insulation from the wire attached to amplifier. Use the crocodile clip wire to now attach the wire to the speaker itself. 

Step 5: Closing the Tube

Cut a hole of the same diameter as the tube in cardboard using the paper cutter and stick it to the end with the balloon on it using super glue. 

Step 6: Stands

Place the tube on the stands. I got them made separately from a factory. 

Step 7: NCH Tone Generator

Download a tone generator of the internet. I downloaded NCH Tone Generator. It was a 14 day free trial but it was worth it. :)

Step 8: Attaching the Gas Cylinder

Attach the Gas Cylinder to the Gas Pipe. Make sure it is fastened tightly. 

Step 9: Attaching the Speaker

Super Glue the speaker to the cardboard piece attached to the Ruben's Tube. I Didn't do this step, instead I simply held the speaker near the cardboard during the experiment. It works perfectly fine both ways. 

Step 10: Last Minute Adjustments

Plug in the amplifier wire into the PC and the amplifier. You can see the settings I used for the experiment.

Drive Gain : 10
Drive Volume: 10
Clean Volume: 10
Treble: 0.5
Middle: 1
Bass 1: 

PS: The higher the frequency, the greater the amplitude needed.

Step 11:

Switch on the gas supply, plug in the amplifier in a power supply, light the gas and enjoy :) I used a 480 Hz frequency to generate a sine wave as seen in the pictures. Enjoy watching the Ruben's Tube with music too. :) Fire dancing to music can be an amazing scene.

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