Fire Pit Burns To The Beat With Bluetooth

Humans have several primal fascinations and perhaps two of the biggest ones are fire and music. While you can picture some cavemen and cavewomen sitting around a fire beating on sticks for rhythm, we think they’d be impressed if the fire danced along with the music. Through the power of Bluetooth, that’s exactly what [Random Tech DIY’s] new fire pit does.

Technically, this is called a Rubens tube, and while it’s an old technology, the Bluetooth is a certainly a modern touch. As you might expect, most of this project is workshop time, cutting MDF and plastic. The audio system is off-the-shelf and drives some car stereo speakers. The results looked good, and although it always makes us nervous building things that carry propane gas, it seems to work well enough from where we’re sitting.

We had to wonder what things you could change that would affect the display. Changing the number of holes, the diameter of the holes, or the gas pressure, for example, would certainly change how the flames look and react to the sound waves.

We have seen other Rubens tube projects, of course. However, we were really interested in the use of these as crude oscilloscopes before the availability of cathode ray tubes. We’ve seen a modern take on that, too.

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A Song Of Fog And Fire – Taking A Look Inside A Rubens’ Tube

The dark winter months are still a bit ahead of us, but with night returning even to the northernmost places, it might be a good time to get your next mood lighting project started. Despite the ubiquitousness of LED strips, cave-time nostalgia makes it hard to beat the coziness of an actual flame here — well, assuming it’s a controlled flame. While modern LED candles do a decent enough job to fool you from a distance, there’s one apparatus they’ll have a hard time to replicate though: the Rubens’ tube. Tired of their usual straight pipe construct, [RyanMake] added some twists and turns to the concept and created a flexible Ruben’s tube made from semi-rigid aluminum ducts.

If you’re not familiar with the Rubens’ tube, it’s a combination of science, fun, and danger to visualize standing waves with fire by attaching a loudspeaker to a pipe with equally spaced holes that’s filled with flammable gas, and light it up. As the resulting visual effect depends on the audio signal’s wavelength, and by that the length of the tube itself, [RyanMake]’s flexible duct approach adds some variety to the usual fixed-length pipe versions of it. But that’s not all he did. After seeing the flames in person, he got curious about what’s actually going on inside that tube and decided to build another one, this time using a clear plastic tube and a fog machine. While the fog escapes the tube rather unimpressively (and could hardly compete with fire anyway), it gives a nice insight of what’s going on inside those tubes. See for yourself in the videos after the break.

Of course, no experiment is truly conducted without failure, and after seeing his first tube go up in flames several times, you should probably hold on to building one as decorative item for indoors. On the other hand, if shooting fire is what you’re looking for, you might be interested in this vortex cannon. And for some more twists on a standard Rubens’ tube, check out the two-dimensional Pyro Board.

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My Oscilloscope Uses Fire

If you want to visualize sound waves, you reach for your oscilloscope, right? That wasn’t an option in 1905 so physicist [Heinrich Rubens] came up with another way involving flames. [Luke Guigliano] and [Will Peterson] built one of these tubes — known as a Rubens’ tube — and will show you how you can, too. You can see a video of their results, below. Just in case a flame oscilloscope isn’t enough to attract your interest, they are driving the thing with a theremin for extra nerd points.

The guys show a short flame run and one with tall flames. The results are surprising, especially with the short flames. Of course, the time base is the length of the tube, so that limits your measurements. The tube has many gas jets along the length and with a sound source, the height of the flames correspond to the air pressure from the sound inside the tube.

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The Pyro Board: A Two Dimensional Ruben’s Tube

Like visualizing music? Love fire? If so, you’re going to want to take a look at this Pyro Board.

What happens when you take a tube, put some holes along it, add a speaker on one end, pump some propane in, and then light it on fire? You get an awesome fire visual — also known as a Ruben’s Tube. It works because the sound pressure from the speakers causes the flow rate of gas leaving the holes to vary, which results in a visible “standing frequency” of flames, i.e. a flaming VU meter.

The folks over at [Fysikshow] decided to step it up a notch by building a 2-dimensional Ruben’s tube with 2500 holes. They have a steel box with the evenly spaced holes on the top, and two speakers attached to the sides. And it works amazingly well — see for yourself after the break.

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Single-column Rubens’ Tube

Here’s a fiery project which [Patrick] calls his Pyro Jam Can. It’s the simplest Rubens’ Tube build that we can think of. For the uninformed, a Rubens’ tube uses flammable gas to reveal wave forms passing through the supply vessel. In the past we’ve seen projects with multiple columns, which very clearly show a standing wave. But this version lacks the resolution for that, so the wave is seen as a modulated flame height.

You can see the propane feed tube coming into the can from the right. This keeps the gas flowing steadily, but a diaphram on the bottom of the can made of a latex balloon allows for modulations in flame height by pushing the gas through the aperture a bit faster than it is flowing. A speaker in the base bounces sound waves off of the diaphragm for the effect seen in the video clip after the break.

We wonder if the can will ever heat up enough to melt the balloon on the other end?

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