Instructables

The Rubens' Tube: Soundwaves in Fire!

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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.)


Step 2: Nerdy stuff - a bit on waves.

Visualizing sound as a wave can be a bit misleading. Sound is often a often portrayed as a sine waveform because it's easier to illustrate than the longitudinal compression wave that it actually is.
The first image shows the typical way a sound wave, or just about any wave, is portrayed visually. Because sound is basically a vibration created by changes in air pressure, the peaks on the waveform correspond to the highest pressure and the troughs correspond to the lowest pressure. The wavelength is measured by the distance between two peaks, or two troughs.

The second image is more accurate way to visualize compressional waves, including sound waves. Each dot could represent a molecule of the matter (such as air) that the wave is traveling through. At the points where the pressure is highest you can see that the density of the material is relatively higher than the areas with lower pressure. These are called condensation and rarefaction, respectively.

The third image shows the previous two stacked, it's easy to see how the peaks of the wave correspond to condensation, and how the troughs correspond to rarefaction

Step 3: Nerdy stuff - the application.

wave.jpg
compression.jpg
In step two we were able to grasp some of the basics on sound waves, and although the concept isn't all that abstract, I thought it might be nice to take it from the theory level, to the application level as it applies to what's going on inside a Rubens' Tube. I've made a few diagrams to help illustrate the concept.

The first image represents a functioning Rubens' Tube under normal conditions. We can assume that in this image an arbitrary, constant tone is being played into one end of the tube. But what might we witness if we were able to peer inside the tube, and see the sound waves?

The next image, gives us an idea what's going on if we were able to see the sine wave of the tone. But what's critical to remember is that what's actually occurring is a change in pressure between different amplitudes of the waveform.

The final image illustrates these pressure changes as a compressional wave. Understanding sound in the way makes it clear as to why we have the varying flame height. The taller flames correspond directly with the higher pressure. This higher pressure in the compressional wave is what's pushing the gas out of the holes with more force than in the areas with lower pressure.

Step 4: Nerdy stuff - measuring sound.

The speed of sound is roughly 340 meters per second at sea level, but this is when air is the medium through which the sound waves travel. But because propane is of a different density than air, the velocity of sound is also different, and like all gases, the density changes with heat or pressure changes. For our purposes, we can work with the a velocity of 257 meters per  second.

As mentioned in the last step, sound is a vibration, we measure the frequency of this vibration in hertz (Hz), which is the number of cycles of the vibration per second. Wikipedia tells us that "The frequency (f )is equal to the speed (v) of the wave divided by the wavelength (lambda) of the wave".

So in other words - frequency = speed / wavelength or:
f = v / lambda

To find the wavelength, we use basic algebra - multiply by lambda and divide by f to get.
lambda = v / f

To test this we can take the sound wave used to demonstrate the device in the video as an example (360Hz), and use or rough speed of sound for v.

lambda = 257(m/s) / 360Hz
This gives us a value for lambda of about 0.71 meters. Which should be close to the distance between the peaks of the flames. Though the actual measured value may differ from what is calculated given the above mentioned scenarios.

Note - for some reason the lambda symbol keeps turning into this when I save "�»". So I've replaced the symbol with the word "lambda". I apologize for any confusion.


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Special thanks to user cposparks, who found an error on this page when it was originally published, I've since made best efforts to correct it.
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Step 5: Materials and Tools

Picture of Materials and Tools
The materials required to build this Rubens' Tube are fairly inexpensive, most of which can be found on Amazon.com, or your local hardware store. Note that some of the recommended are not identical to the parts that I've used, they will however, serve the same, or superior function to what I've used. That being said, the materials you use, and the build process is extremely flexible and forgiving.

Building Materials:
Ventilation Ducting Amazon
Ducting used for HVAC, though any thin-walled metal pipe should work. My tube uses 4 inch ducting, I'd imagine success using anything from 2, to 6 inch material.
Amazon has a number of other products that should work. Something to consider is that if you use a large tube (in both length and diameter), you'll be dealing with more volume, which will result in taking more time to "prime" your tube. See step 13 for details.

Brackets x2 Amazon
These are brackets used for the supporting the ducting. Obviously the same size as the above ducting. (I used brackets which were an inch larger in diameter for buffering, however, in retrospect, I do not believe this is necessary)

Propane Amazon
This is the fuel source. Anything with a valve so you can turn it off and on safely should work.

Tubing Amazon
Nothing too insightful here, 1/4 inch inner diameter, or whatever fits your fuel source.

Hose T Connector Amazon
I used brass, but something like this would work fine.

Hose Splicers x2 Amazon
Used for fuel delivery. This will work much better than the small piece of copper tubing I used.

Latex Sheets Amazon
This will serve as our diaphragm. I used polyethylene sheeting, however, latex should perform much better as it's thinner and more pliable, but either will work and it just goes to demonstrate the flexibility of the build.

Scrap Wood

Tools and Supplies:
Drill Amazon
You'll also need a 1/4 inch bit and a bit between 1/16 and 1/32 Amazon

Hammer Amazon

Tape Measure Amazon

Knife or Scissors Amazon

Silicone Sealant Amazon

Epoxy Putty Amazon

Duct Tape Amazon

Masking Tape Amazon

Teflon Tape Amazon

Misc.
Various hardware for attaching the brackets to your wooden base. Simple wood screws should work fine. A nail or similar may be needed for pre-drilling. And finally some hot water for working with the tubing.

Step 6: A Note on the Sound Source

Picture of A Note on the Sound Source
For this project, any sound source should work. I used my iPod with the driver from old 3 computer speakers I got from Goodwill. But nearly anything should work, from a do-it-yourself setup, to an old radio, to a hi-fi sound system, to a boom-box. In keeping with the Amazon spirit - I'd imagine most of these would get the job done, provided they require an external power source.

I also, have three recommendations.
1 - Whatever speaker you use should be able to reach volumes to move the diaphragm.
2 - The speaker should be placed or mounted close enough to the diaphragm to easily move it, without making physical contact
3 - The speaker's diameter should be as close as possible to the tube's diameter to ensure maximum diaphragm movement.

We're even lucky enough here in the Instructables community to have projects that would work wonderfully as a source of sound with little to no modification.

If you're interested in getting your hands on sine wave audio tones, they can be had by Googling for "Audio Test CD" or "Audio Test Tones". The one I used for this project was found here.

The image below shows the basic components of the business end of my setup.

Obviously, depending upon what you use to push sound into your tube, your mounting methods will vary, if you use a speaker that's still in it's housing, in all likelihood, you should be able to simply move the speaker close to the diaphragm. I've attached an image of my setup for reference, clearly not the most elegant solution, but it got the job done.

Step 7: Construction 1 - marking and drilling

First - determine what will be the top side of the tube. If you're using ducting like I did, there's a seam on where the ends of the tube connect, this will be the bottom.

Second - Run a piece of masking tap along the top of the ducting. Using a tape measure mark off every half inch running down the center of the tape. I came 14 inches out from the center in both directions - this left 4 inches on each end of the tube without markings.

Third - Using a nail, or other object carefully tap a point in each marking with a hammer. The goal is to create a small depression at each location to facilitate drilling.

Fourth - Remove the tape and carefully drill through the ducting at each depression.

Step 8: Construction 2 - sealing and diaphragm

Obviously, in order to get this thing to function the way we want it to, we're going to have to seal up the tube and create a diaphragm.

First - Use duct tape to cover the potentially sharp edges of the tube - this will prevent the ducting from ripping through the diaphragm. You'll probably want to use more than one layer, but again, this is coming from my experience with the ventilation ducting. Depending upon the type of material you're using, it may not be necessary.

Second - Cut a latex sheet to serve as your diaphragm. You'll definitely want to cut it large enough to completely cover the end of the tube with enough extra to tape down and pull taut. You can see from the image that the size I selected was roughly 6 inches square. It's also worth noting that my picture reflects the use of polyethylene sheeting. This will work, however latex will provide additional flexibility. It's also worth noting that latex will slowly oxidize, and may need replacing over time.

Third - Start taping the sheeting down to create the diaphragm. The concept here is to basically emulate the head of a drum. It needs to be tight enough to allow it to easily vibrate, but not so tight that it will tear. Once satisfied tape down, or trim the excess, and tape around the circumference of the tube in order to create an airtight seal.

Fourth - On the other end, repeating the processes will allow for later experiments using a "stereo" Rubens' Tube. However, simply sealing it off with duct tape to create a good seal is a perfectly acceptable method to create a functioning device. In either case, be careful what you set the opposite end on to make sure you preserve airtight seal.

Fifth - Finally, if you're using ventilation ducting like I am, it's worth while to run a bead silicone sealant down the seam of the tube. I pressed it into the joint using my finger, and then cleaned up the excess. Now we have our tube completely sealed where we want it to be.

Step 9: Construction 3 - fuel holes.

Now it's time to build the fuel delivery system. The basic idea is to evenly distribute the fuel within the tube.

First - Determine the location(s) where fuel will enter the ducting. I recommend using what will be the "back" of the tube - this is simply a right angle from the line of holes on the top. Additionally, depending upon whether or not you choose to have fuel delivered at more than one location, a bit of advance planning should go into where these locations are.
In my case, I chose two locations - at distances half way out from the center hole and the first and last hole. It's also worth noting, again in retrospect, that one point for fuel delivery would probably work equally as well, so long as this location is centered.

Second - As in the prior step, tap your marked location with a nail, and drill a hole large enough for your hose splicer to fit. In my first attempt, I didn't use hose splicers, but rather 1/4 copper tubing. Using hose splicers will make hooking everything up much easier, and I highly recommend it.

Third - Using a utility knife, nail, or other sharp object, lightly score the ducting around the hole, or holes. This should allow for the epoxy to create a more secure bond.

Fourth - Install the hose splicer(s) in the hole(s). Mix up some epoxy putty, and apply liberally. You'll want to create both an airtight and secure bond.

Step 10: Construction 4 - fuel supply

This step's all about hooking up the propane to the tube.

First - Teflon tape on the areas where you'll be attaching the tubing is a good idea to make sure you won't have propane leaking. This includes the propane nozzle, the tee connector (if you're using multiple delivery points for fuel), and end of the hose splicer(s) that will connect to the tubing.

Second - Hooking up the fuel is a pretty straight forward process. Simply cut and attach the hose. To do this, you'll want a cup of very hot water close by to soak the ends of the tubing in, this will warm and soften it up so you can easily get it over the connections.
If you're using one entry point for fuel, you'll only have one connection to make right now, if you're using a tee connector for two entry points, connect both ends to connector, and to the Rubens' Tube.

Step 11: Construction 5 - mouting

Considering the Rubens' Tube is round, it's a good idea to mount it on something so it won't roll around.

First - Attach the brackets to the base using screws. (I used a piece of scrap wood, I think it was part of a shelving unit once).

Second - This step may or may not be required depending upon how your tube fits in the brackets. During construction I found that the brackets were slightly larger than the ducting. To aid this, I used some scrap hosing and zip ties to put around the ducting, thus adding to the circumference.

Third - Finally, mount your Rubens' Tube inside the brackets. Tighten up the brackets and you should be left with a fairly stable setup.

At last! - Your Rubens' Tube is ready for action! Please read the safety notes before hooking up the propane and continuing.

Step 12: Safety First!

Picture of Safety First!
As with anything dealing with fire and flammable gas, there's some important, although fairly obvious things to consider. And although I am fairly confident that this is a sound design, just as with a propane grill, heater or lantern, I must urge on the side of caution, and cannot take any responsibility for any accidents or mishaps that may occur. In order to minimize the possibilities of an accident, do not operate the device without keeping in mind all of the following.

First - As alluded to above, propane is flammable! When using your Rubens' Tube, make sure you're in a well ventilated area or outside. In addition to the potential fire hazard, there is also a very real danger of carbon monoxide exposure from propane being less than completely burned. Carbon monoxide is DEADLY.

Second - Take note of the way you orient the propane tank. If the tank is not right side up, the propane may flow in unpredictable ways. Even a regular propane tank, used for a lantern or torch, turned on it's side, is likely to start spurting liquid after it's been turned on for some time - this can be extremely dangerous. Also allow for a safe distance between the Rubens' Tube and the fuel source.

Third - Even after the propane is shut off, the tube and hosing will still contain fuel. After turning off the fuel, you'll see the flames slowly start to lower. However, even after they're no longer visible, it's possible that they're still burning within the pipe itself. After shutting off the gas, remove the propane tank from the hose and allow plenty of time for the remaining fuel to burn off - there's more fuel than one would expect inside the tube itself!

Fourth - While the entire Ruben's Tube isn't likely to reach very high temperatures while being operated for reasonable lengths of time, the top part of the tube will become hot, even after short runs. Be very careful to allow adequate cooling time before handling the device.

Fifth - In case of emergency, be sure a fire extinguisher is close by at all times. Finally, if you're a minor, never operate your Rubens' Tube without the supervision of a responsible adult.

Finally - Use common sense! As dire as the above warnings may sound, assuming you use common sense and play it safe, your Rubens' Tube will serve as an amazing scientific toy!
Let's move on to how to use the device.

Step 13: Using your Rubens' Tube

Assuming you've already gone over the safety notes, the first step in using the Rubens' tube is to "prime" the tube.

First - Attach the fuel source. Again, make sure there's a safe length of hose between the propane tank and the tube itself.

Second - We're going to want to create some positive pressure inside the Rubens' Tube. Because the flow of propane is fairly slow, and there's a lot of volume within the tube, we need to seal it up temporarily. To do this, use a strip of masking tape to cover all the holes on top of the ducting. Then turn on the gas.
Wait about two minutes, by this time enough propane should be in the tube to create a decent pressure differential. Depending upon the size of your tube, and the pressure of your fuel source, it may necessary to wait a greater, or lesser time.

Third - Remove the tape covering the holes. Then, using a long match or fireplace lighter, try lighting the gas by one of the holes. Assuming there's enough pressure, each hole should ignite down the tube. However, it may be necessary to light the tube in several places.
If the flame is very small, it may be indicative of lack of pressure within the tube, so you'll want to wait a bit longer the next time around before removing the tape.

The tube's ready for prime time when each flame is roughly an inch in height.

Fourth - Introduce an audio source near the diaphragm. You should be able to excite the flames by lightly tapping on the diaphragm, or even snapping next to it. However, for the most fun, and scientific pursuit, you'll want to use a speaker. See step 5 for notes on the sound source. Refer to the safety notes for turning it off.

You should be able to literally see the wavelengths of various audio sources. Head back and take another look at steps 2, and 3 to get a better understanding of exactly what's happening. As entertaining as dancing fire can be, there's a lot of science behind it too.

Notes
1 - I'd imagine one could complete this project in no more than an afternoon assuming all the supplies were on hand. I obviously worked with a bit of trial and error, so it took me some extra time.

2 - My average run times range from about 5-10 minutes. I'd imagine one could run the tube for longer than that, however, I'd err on the side of safety and keep the times limited.

3 - Keep an eye on the diaphragm. It's completely possible that the diaphragm may exhibit signs of wear over time. Although this has not yet been an issue for me, I could foresee possible diaphragm maintenance being needed one day.

And finally - Be safe, learn, and have fun.

Step 14: Further information.

Beyond Wikipedia, I was able to find some interesting articles relating to the Rubens' Tube, and its creator.

ScienceWeek - An article mentioning Heinrich Rubens' work with Max Planck on early quantum physics and their correspondence with Albert Einstein.

FYSIKbasen The English translation of a Rubens' Tube design on a Danish website for physics demonstrations. There's a number of other interesting demonstrations here as well.

ISU Physics Department Another Rubens' Tube design. This one uses a signal generator for its audio source.

Also-
Thank you for all the feedback thus far. I've updated the Instructable in several places to address the questions that have come via the comments and messages.
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ahayes131 month 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.

rbalderrama2 months ago
I am doing this for my science project at school.
aschmidt132 months ago

I wander why you use propane and not natural gas.

arpoky5 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...
azharz1 year 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.
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!
wolfmanofTX5 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)  wolfmanofTX5 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 tables5 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)  diskfurnace5 years ago
good call.
justjimAZ3 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
justjimAZ3 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
vonkeswick3 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)  vonkeswick3 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.
cposparks3 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)  cposparks3 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.
sci54 years ago
Thanks for all the info you have put up.  It helped me a lot with my tube.  My only problem was I put the propane injector and speaker at opposite ends.  Making the gas not evenly disperse throughout the tube.  The best way to install your injector is in the middle or to have multiple injectors.

JaketheSnake
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