Thursday, May 19, 2011

How to see sounds with a Ruben's tube (Sound and Fire!)

DISCLAIMER: Nothing in this post is software/code related.

But who cares it's really cool none-the-less.

A bit of background first. I've been working on demonstrating the science of waves at my kids elementary school for the past 3 years now. At about 2 weeks out I start asking myself this question:

What experiment/trick can I perform to help the kids visualize a pressure wave?

We use a slinkys, use a spectrum analyizers, watch a video of the tacoma narrows bridge, etc.But what can I do that really is an attention grabber and helps cement the concept for these grade school kids? And can it rate high on the coolness factor?

So, the idea of building a Ruben's Tube looked light it might fit the bill here. A Ruben's tube basically is an experiement where sound affects fire--how cool is that? Pretty damn cool that's what I say. I asked my cohort (Ross) and wife (who helps to organize the whole affair) if this would fly... And to my complete surprise no one said NO.

So we went off and built us a Ruben's tube...

What exactly is a Ruben's tube? A Ruben's Tube is a length of tube filled with flammable gas (propane) with small regularly spaced holes. The tube is sealed at one end and capped at the other end with a speaker. The gas has nowhere to escape but through these little holes. And the sound (via the speaker) creates a standing wave (at the right frequency that is) that affects the gas pressure along the length of tube. This results is varying flame height based on the location of the hole and the degree of particle motion due to the standing wave. This would be a sine wave of flames along the length of the tube.

When a resonant frequency is pumped into the tube a standing wave will disturb the gas at the points where the motion in the p-wave is the greatest and suppress the gas leaving the tube at holes located at these points. Likewise holes near where the p-wave motion is less will then to escape at a greater velocity.

That mostly makes sense to me (having a bit of a background with acoustics myself).

This required a trip to a local scrapyard (for the tube), the nearby Lowes, and then expropriating a small speaker from Brian's speaker system. And a big ole tank of propane gas. After much drilling, and fitting and drilling we ended up with a 72 hole ruben's tube, about 4 feet in length.

Below we are in the middle of drilling the 72 hole array (that's Ross doing the work with Brian supervising).

The mostly assembled tube is here (sans propane tank connector):

With a closeup of the speaker end of the tube (tube and speaker are 2 inches in diameter):

So, the darn thing worked, but really really wants a sheltered place. Given that no such place exists anywhere in windscape of San Francisco, below video of the contraption working (briefly before the wind gets the better of it). I apologize for the wonky orientation of the video--next time I'll get that straight (the tube really is stationary in a horizontal position). The amplitude modulation of the waves shows up in the last few seconds of the video.

What we discovered what the tube could be shorted (i.e. fewer holes), or we need more pressure and we have to do this in an enclosed space (i.e. NO WIND).

Next up (when I get around to it) will be video of the Ruben's tube playing to "When the levee breaks".

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