Date: Fri Mar 13 20:12:37 2009 Back to Contents ------------------------------------------------------------------------

Author: Paul Nord

Subject: Re: Ruben's tube and propane



Interesting point. I built mine with a cone and speaker on one end.
My speaker is about twice the diameter of the pipe. This makes many
of the longer-wavelength modes quarter wave resonances with an anti-
node at the speaker end of the pipe. It seems that this also draws
all of the propane toward the speaker and pulls air in from the other
end. After running at one of these resonances, it takes a bit of time
for the far end of the tube to re-light.

But also, as you start into one of these resonances, you can watch the
frequency shift because the density of the gas in the tube changes.
Propane is getting pumped out and air is getting pumped in. You can
tune it right to a quarter wave resonance and watch as it shifts just
a bit out of resonance. You can retune it as this goes along until
you reach a balance point between the gas inflow and outflow.

Can any of the acoustic experts out there comment on better ways to
attach a speaker to a pipe? Should I redesign it with a small hole in
the side?


On Mar 13, 2009, at 2:11 PM, Gary Karshner wrote:

> One small comment on Propane. It is heaver than air, unlike natural
> gas and can collect in closed containers. Your tube is relatively
> small and this should not be a problem. It is not as dramatic a
> difference as using sulfur hexafloride for sound demonstrations.
> Gary
> At 11:58 AM 3/13/2009 -0400, you wrote:
>> Hi Cliff,
>> Dale is correct in his description of how well propane works in the
>> Reuben's tube.
>> I actually don't know how many places I've used the Reuben's tube.
>> In bars, libraries, schools, gyms, and outside (!) demo shows, all
>> with many different air currents and winds. If you are really
>> worried about the air movement, just make a sturdy plexi shield to
>> stand one foot back and around the sides of the tube. I made one
>> when I first built the tube 20 years ago, but I never actually need
>> it so I don't use it. You sometimes need to finely regulate the
>> gas flow yourself to make the wave forms visible, and this will
>> vary as you go from low frequency to higher frequency standing
>> waves, but you quickly learn how to do that when you are using it.
>> McMaster-Carr is a great place to purchase a 5 lb propane tank to
>> use in shows and in classrooms. Since so many schools are taking
>> natural gas out of the classroom for insurance and safety purposes,
>> having your own tank guarantees you can perform the demo where and
>> whenever you want and need to.
>> BTW, my tube has size .04" holes, or 1.016mm, spaced every half
>> inch for 72". This seems to work pretty well.
>> Happy gas tubing,
>> Dave/RU
>> Dale E. Stille wrote:
>>> Cliff,
>>> Zig and Dave Maiullo both run their tubes off propane using small
>>> 7 to 10 lb tanks with the standard pressure regulators. While you
>>> need different orfices for things like stoves and water heaters
>>> for the different gasses, I think you will find that the Rueben's
>>> tube is pretty forgiving in this regard. So, you should be able
>>> to use it with either gas. I would suggest getting the quick
>>> couplers for ease of attaching the tank to the tube. ( They look
>>> and act the same as the couplers for high pressure air hoses).
>>> Later,
>>> Dale
>>> wrote:
>>>> One of our faculty wants to use my Ruben's tube as part of a road
>>>> show to a high school. The school does not have a natural gas
>>>> source for him so he wants to rent a propane tank to fuel the
>>>> tube. I am concerned about: how well this will work, as I seem to
>>>> remember that propane requires different sized orifices for flame
>>>> jets than natural gas, safety (a tank of gas under pressure near
>>>> an open flame in front of a large audience) and finally, in our
>>>> lecture hall use, I find I have to turn off our air handlers to
>>>> reduce air currents in the room so the flames are stable.
>>>> So I was wondering if any of you had experience using the Ruben's
>>>> tube on the road in such circumstances and had any advice for me
>>>> to pass along.
>>>> Cliff

From Fri Mar 13 20:12:37 2009