Instructables
Picture of The Rubens' Tube: Soundwaves in Fire!
What could be more entertaining than fire and good music? How about fire that will dance to that music? The following will not only cause flames to pulse to a beat, but it will also allow you to see different wavelengths of audio frequency. The following is my first Instructable, and my entry to the Instructables Science Fair contest.

In addition to documenting the build steps to create something called a Rubens' Tube, I'll also go over some of the basic concepts and science involved with sound waves.

From the moment I discovered what a Ruben's Tube was, I wanted to build one... and considering I was in a physics class at the time, there couldn't have been a better excuse than extra credit.

Update: I'm thrilled to see that this Instructable's become popular, and I'm more than happy to have people build on the project, but please respect the Creative Commons BY-NC-SA license. 
 
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Step 1: What is a Rubens' Tube?

Heinrich Rubens was a German physicists born in 1865. Though he allegedly worked with better remembered physicists such as Max Planck at the University of Berlin on some of the ground work for quantum physicists, he is best known for his flame tube, which was demonstrated in 1905.

This original Rubens' Tube was a four meter section of pipe with 200 holes spaced evenly along its length. When the the ends are sealed and a flammable gas is pumped into the device the building pressure will have only one route to equalize. The escaping gas can be lit to form a row of roughly even flames. Upon introduction of a loud speaker to one of the sealed ends, standing waveforms can be seen in the flames.

Within the Rubens' tube, as soon as gas is ignited generally uniform flames will be seen. This is because there is very little pressure differential between any given area of the space inside the tube. Once sound is applied from one end, pressure will change within the tube. Should the sound be an easily measurable frequency, the wavelength will be visible in the series of flames, with the highest flames being where condensation is occurring and the lowest where rarefaction is occurring.



They can also be used as an incredible visualizer for music.
(Note that I've muted that audio intentionally, as I don't own the copyrights to the music being used in the clip, and I'm not sure what the Instructables policy on "fair use" is. Searching on Youtube or Metacafe for "Rubens Tube" will show you several videos with music.)


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is it dangerous,,,if how can we prevent it !!
does it need high volume of sound??? any cause to speaker????

ahayes134 months ago

I did this for a physics project this year. It's a very fun project that I highly recommend trying. However, when you do, save yourself some grief and don't try to use PVC pipe. I thought it would be easier to work with, and I was very wrong. The first time I lit it, it went south so fast I had to use a hose to put it out. We tried to use foil tape to stop the melting, but it promptly burned off due to the heat. Metal HVAC duct works much better.

rbalderrama6 months ago
I am doing this for my science project at school.
aschmidt136 months ago

I wander why you use propane and not natural gas.

arpoky8 months ago

Another warning, DON'T LET LIQUID PROPANE TOUCH YOU. I learned the hard way. The stuff boils at -66 degrees Fahrenheit when not in a cylinder, and it WILL give you a cryogenic burn, which immediately freezes the skin SOLID (it also causes a GIANT). Wear gloves designed to withstand the extreme cold. I was burned a few months, and it kept me from working for an entire week.

Jmoney12141 year ago
Looks Crazy...
azharz2 years ago
I saw this Ruben's Tube on an Show called FAQ, and I am from India you can also see the videos of Ruben's Tube from Faq on You Tube. And this Instrucatbles is just Awesome.
sulphur67642 years ago
to pennyroyal69 , i think the problem is with the size of the holes in your ruben's tube !! Not the size ! You see larger holes mean lower pressur and the fire gets into the tube but make the holes smaller and te length of the flames will increase. Hope it workes :-)
razvanlost2 years ago
I have built a tube just like yours with a colleague, you can see it in action here: http://www.youtube.com/user/rubenstube101
Hey i just built one of these out of metal ducting but cant seem to get the pressure high enough. I was wondering what size your holes were and the diameter/fittings used in your fuel delivery system. It seems my regulator wont work without enough backpressure. any ideas or tips would be appreciated.
is it possible to do this rubens tube by using lpg...pls send me wetr it can b done by using lpg to my email id shahrukhextreme@gmail.com
Just remember, propane goes down (heavier than air) and it fills the tube first. This is important so you don't get a fuel-air mixture INSIDE the tube before you light it. It's the only reason it doesn't explode.
my rubens tube doesnt light up on the top, but instead lights up inside the tube, and i have to turn off the propane supply immediately to stop the fire. do u know why that happens, and for how long should i allow the propane to build up inside the tube?
yourtvlies (author)  Pennyroyal692 years ago
Based on what frollard notes above, my guess would be that there's too much oxygen inside the tube. I may try the following: w/o the holes covered, allow the gas to run for a bit to push the O2 out of the tube, cover the holes to allow some pressure to build up, then uncover the holes and light the tube.

Timings will vary based on the volume of the tube and the gas output, and this is a potentially dangerous situation. Without knowing more specifics of your construction, I hesitate to say give the above a shot. But again, that's where I'd likely start to troubleshoot the issue. Please take every precaution possible.
The rubens tube in question is a 5 foot PVC tube, 2.5 inch in diameter, with 3/32 inch holes half an inch apart starting one foot from the beginning of the tube and ending one foot from the end of the tube. Instead of attaching the other end of he tube directly to a speaker, i taped a diaphragm onto it. The gas enters the tube through two tubes each drilled into the tube at the non-diaphragm end of the tube, placed on each side of the tube.

So far i have taped the holes and then allowed the propane to build up for two min then four min. At two min, the propane lit up inside the tube, but at four min, i did have flames on the top, but they were very small, and i had to ignite every hole individually. i havent tried allowing the propane to push out of the tube yet, as i ignite it as soon as i pull of the tape.
You need to cover most of the holes and fill the gas VERY slowly so it fills and displaces the lighter air -- as soon as you smell gas coming out you should be good. You never need to 'build up pressure' inside the tube. covering all the holes will just result in a fuel-air mixture and stressing the diaphragm. Imagine if you will that you have a tube filled with oil and you want to displace it with water...go slowly and all the oil should be pushed out before any water hits the holes -- same buoyancy/stratification effect here, just with different fluids.

Again, turn on gas long enough to displace air, so that only gas is coming out of the holes. Don't hurry the priming process because it will cause turbulence in the tube and that will MIX the fuel and air, a VERY dangerous combination. (read: explosive)

You describe the fuel entry as 'far from the diaphragm. It should be as evenly spaced as possible to make the gas input equal across the tube.
Great instructable! I wanted to make a smaller version for a class project. Could I make it with a 1" dia copper tube and a small speaker? Also does it have to be really long? Could I make it less than 2 ft, or will the sound waves not form correctly? Thanks!
yourtvlies (author)  BeerBellyJoe2 years ago
I've not tried this so I don't know for sure. My guess would be that it might be okay if you were working on a smaller scale with everything (including higher frequencies) The a small pip like that is going to have a drastically reduced internal volume, so I don't think you'd be able to expect the unit to produce very tall flames at all. I think it would be interesting to try, though.
anjaliv2 years ago
i am really thank full to you...........it helps me a lot....
If I will prefer to use one location for gas source (the other end of the tube) will it work? and what is the best material that I can use to ensure airtight seal?
I saw a video on youtube of a guy that did it like you want it. http://www.youtube.com/watch?v=HpovwbPGEoo
He mentions that he made holes with half inch increment (i think thats the difference between the first hole and the last one (?)) to get an even sized flame..
Using the either end of the tube for fuel delivery would probably produce an unevenly filled chamber. If you use just one source, it should be closer to the center of the tube, as suggested.
I didn't do a great job cutting the tube to a good length, if i can cover the hole well will it matter?
sundet3 years ago
Does anybody have some good resources on modelling a Rubens tube? I have a pretty good background in mathematics. I'd like to make a tube and use it for many hours at a time. I also do not want to get blown up. What have you all tried for getting good seals on the ends and where the gas goes in? Has anybody tried attaching fins to the tube or a fan to dissapate heat? My guess is that the diaphram would be less likely to break if it were exposed to less heat.
You know what would be neat? To separate a musical piece into its component instruments, and then play each instrument through a separate Ruben's tube. That way each tube will be showing the music cleanly. Of course, getting them all to start simultaneously might be an issue. So maybe a better idea would be to have live musicians play their music like they do on stage. It'd be a poor man's Trans Siberian Orchestra show!
wolfmanofTX6 years ago
Would it be possible to attach some sort of heat resistant nozzle to each hole, and do you think this would allow extended run times?
yourtvlies (author)  wolfmanofTX6 years ago
I suppose thta would be possible, though it may allow for pressure to equalize and thus degrade performance. The number one consideration with projects like this should always be safety. The with longer run times, it may be possible for the ducting to get so warm that it starts to melt attached tubing or the diaphragm. Using longer copper tubing to to feed gas into the unit would get around the first concern. Limiting heat to the diaphragm though would be slightly more tricky. I'm almost tempted to think that using a thick walled steel pipe would be a step in the right direction. Although it would retain the heat longer, it would also take more energy to raise the temperature of the surrounding material. These are just ideas off the top of my head, so take them with a grain of salt.
you could add 2 circular heat sinks used for capacitors to cool the ends by the ducting and then for the holes, somehow adding a graphite ring like an eye hook around each hole. Graphite has a very hight melting point.
Would this work with a curved tube? Like a circle or a like a horizontal wave? That would look really awesome if you could really perfect this.
yourtvlies (author)  instructing tables6 years ago
That's an interesting question - though I don't think I can provide a solid answer. I'm trying to visualize what would occur, and my guess would be that something other than a straight segment would work, but the effect would be reduced, due to the wave being distorted by the curve in the tube. But then again, I'm thinking about how a stethoscope works - sound doesn't seem to have any trouble moving from one end to the other, regardless of how a doctor is holding it. Maybe someone with a better understanding of physics and acoustics can clarify?
I don't think a curved one would work well if at all because of all the waves bouncing off the walls. And it wouldn't be like a stethoscope because a stethoscope transports the waves through rubber, whereas this set up transports the waves through air thats in a tube. So they are very different concepts
yourtvlies (author)  diskfurnace6 years ago
good call.
justjimAZ4 years ago
Thanks so much for this! I made one for my Halloween party and everyone loved it. Don't know if the videos will load, but a friend recorded some with a cell phone.

I had trouble with the flame height at first, but giving enough time for the propane to build up helped. It also helped to raise the propane source higher than the tube - though far behind the flames, of course.

Strong, low piano notes or driving bass seemed to get the most effect, and higher notes had the least effect.

Managed to keep everyone entertained for 12 minutes!
Rubens Tube A Pic.jpg
justjimAZ4 years ago
Thanks so much for this! I made one for my Halloween party and everyone loved it. Don't know if the videos will load, but a friend recorded some with a cell phone.

I had trouble with the flame height at first, but giving enough time for the propane to build up helped. It also helped to raise the propane source higher than the tube - though far behind the flames, of course.

Strong, low piano notes or driving bass seemed to get the most effect, and higher notes had the least effect.

Managed to keep everyone From 4 to 65 entertained for 12 minutes!
67519_157923144246377_100000860775981_263792_474207_n.jpg
vonkeswick4 years ago
We tried constructing one of these (almost exactly as described) but couldn't get the flames to hold. It seems that the gas pressure from the standard propane + nozzle kit simply isn't high enough. Everything is fully sealed, and I tried doing it with very few holes (maybe ten) and it still couldn't keep them all ignited, let alone steady. Any suggestions?
yourtvlies (author)  vonkeswick4 years ago
It's hard to say exactly what's occurring to cause the problem you're experiencing. Though my first guess is that there's not enough pressure being built up before attempting ignition. I make a note of this on step 13 - I suggest looking over it again, paying particular attention to parts two and three.

Let me know if this doesn't resolve the issue - I'd be glad to troubleshoot with you in attempts to get your tube functioning as it should.
cposparks4 years ago
Were your experimental measurements similar to your theoretical measurements? I ask this because the speed of sound is 340 m/s in air but the sound waves are being created in a medium that is composed of propane. The speed of sound in propane is ~247 m/s. This would significantly change the theoretical wavelength for an arbitrary frequency.
yourtvlies (author)  cposparks4 years ago
I recall things being pretty close -- though now that you mention it, considering the peaks and troughs are fairly subtle, particularly at the longer wavelengths where the discrepancies would be more noticeable, I very well may have been off in my measurements. There's also the possibility of an air/propane mixture in the tube, which would put the density of the medium somewhere between propane and air.

It's been three years (to the day!) since this Instructable was published, and unfortunately, I no longer have the device, so am unable to go back and check for confirmation, one way or the other. However, your observation's very astute, and I've started to do some research on the issue, though have found conflicting reports. As soon as I've got things figured out one way or another, I'll update the Instructable to reflect that - though until then I'll put a disclaimer on the top of this page.
sci54 years ago
We have thoroughly enjoyed this project!  I have found some things work and others need improvement. We used a thicker pipe than we wanted. We found it in the fencing area of our local hardware store. It was a fence post. I recommend using the thinest pipe you can find. We drilled our holes 1/2 inches apart. I recommend drilling them 3/4 in to 1 inch apart. We sealed every other hole up. One end can be sealed with a pvc pipe-cap. Make sure to use Teflon tape on the pipe before sliding the cap onto your pipe. It can also serve as the fuel source by drilling a hole for the propane fitting. The other end can be sealed with any latex rubber you can find and some ordinary rubber bands. It is better to make sure to leave 6 to 10 inches on both sides to not allow your ends to get to hot. We used 7/64 drill bits. A few might break. I recommend using a smaller drill bit if possible. The 7/64 will work though.
sci5 is our physics teacher.
sm and bj the hallmonitor
yourtvlies (author)  sci54 years ago
I'm thrilled to find out that the project's being used in the classroom. Good luck, and keep us updated.
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