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.

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.
<p>UAU! Awesome very good instructable! keep going, it is really enlightening . Thanks for your time and effort</p>
<p>Hello I'm trying to replicate this however I'm unsuccessful such as the flames dies out almost immediately after ignition and I've checked for leaks and there were none.Can someone please help me </p>
<p>I still have to make mine and I'm not an expert on the subject, but try using your propane to light a barbeque or something and see if that works, if it works check the size of the holes you drilled it might make a difference.</p>
<p>this is cool, great tutorial my first time to this site. I think I am going to like it here,</p><p>Thanks again,</p>
<p>Would this work without an amplifier because I cannot afford one.</p>
<p>I made this, and yes, the size of the tube dosent matter as long as you have equal gas pressure, and equalt spaced holes in the tube.</p>
<p>I have a few questions about this experiment:</p><p>1. Is teflon tape required for this and if we don't use teflon tape, can we use duct tape instead?</p><p>2. Would the ruben's tube work for a 2ft long tube?</p>
<p>isn't it compression rather than condensation?</p><p>i thought condensation was something that happened on cold windows...</p>
<p>It is somewhat the same thing. To condense is to compress. like compressing water as a gas to water as a liquid on cold windows. Or to compress gas molecules together to form a higher density of gas (instead of turning into liquid).</p>
<p><strong>Very Nice</strong>... great the way you included the parts source too.</p><p>Thanks!</p>
<p>Awesome Instructable. Reminds me of old talking gas lamps that I can not find a reference for at the moment from the late 1700's and 1800's. I did find London still has gas lamps in place too. Anyhow... I did find this more modern system that seems really interesting also: https://www.instructables.com/id/Build-A-Plasma-Speaker/</p>
Can i do this with 1&quot; copper pipe with 2m length by using natural gas as fuel???
<p>If I had to guess, I would say that copper will conduct the waste heat too well, and limit you to short burn times. I would stay away from copper and opt for steel. Also, copper is really expensive.</p>
Great instructable! I wanted to make a smaller version for a class project. Could I make it with a 1&quot; 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!
<p>My first prototype is 1&quot; metal tube with 2ft length and a small speaker. It works but doesn't seem quite good because the fire hardly react to the sound wave because the diaphragm are very small. I have improve it by change the small speaker to the normal speaker (with subwoofer), and enlarge the diaphragm by using funnel water and attached it to the tube. It works....but doesn't seem very nice. </p><p>Currently I am using 2&quot; tube (I want 3&quot; but couldn't find it anywhere) with 2ft ++ and a normal speaker (with subwoofer). It works perfectly fine.</p><p>Conclusion: Use bigger tube with enough length. You don't have to buy anything except the tuba (you have to drill it to make hole), but you can always borrow proper speaker from your friends to try it on your project. </p>
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.
<p>is it dangerous,,,if how can we prevent it !!<br> does it need high volume of sound??? any cause to speaker????</p>
<p>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. </p>
I am doing this for my science project at school.
<p>I wander why you use propane and not natural gas.</p>
<p>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.</p>
Looks Crazy...
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 :-) <br>
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?
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. <br><br>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.<br><br>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.<br><br>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)<br><br>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.
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<br>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.. <br>
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.<br />
I didn't do a great job cutting the tube to a good length, if i can cover the hole well will it matter?
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!
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?
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.
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
good call.
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.<br><br>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.<br><br>Strong, low piano notes or driving bass seemed to get the most effect, and higher notes had the least effect.<br><br>Managed to keep everyone entertained for 12 minutes!
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.<br><br>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.<br><br>Strong, low piano notes or driving bass seemed to get the most effect, and higher notes had the least effect.<br><br>Managed to keep everyone From 4 to 65 entertained for 12 minutes!
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?

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