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Holly,

This may not answer your question completely, but...

1) Definitely use metal for the tube.  Realize it will get hot.
2) If you really want to find out about creating standing wave patterns,
then http://www.instructables.com/id/S9QLGKXF5R8MTGP/ is a nice place to
start, but it's not 100% correct.  The fact that you are feeding a gas into
the tube and the gas itself is moving changes the equations a bit.  Rather
than adding flow gauges, etc. to do exact equations I would just start with
these equations and modify the frequency until you get a standing wave.
3) Anything can be your sound source - as long as you use a speaker to get
the sound source into the tube.  Some versions don't us e a speaker at all,
but rely on someone yelling into a latex diaphragm to create the sound
ripples - I've heard that works, but it's not convenient, you can't control
the sound source and the latex diaphragms are problematic.  With that being
said, it is cool that you don't need electronics to accomplish this!
4) I recommend make it relatively easy to change out the speaker.  You'll
probably have to do this at some point.  Most of us don't make it easy to
change it out because that takes more time and better engineering, but it
helps long-term.
5) For safety, I've always thought that we should build a Rubens tube with a
thermocouple that would shut off the gas supply if enough heat wasn't
present (like some gas fireplaces and heaters), but I don't know anybody who
has actually done it.
6) Amplitude matters!  If you have a sound source that changes amplitude
dramatically you can blow out the flame jets you are using (this is
particularly true if you are using a limited gas supply with low pressure).
7) All the obvious rules apply - don't get things near the tube, have fire
extinguishers on hand, make friends with the fire dept. so they don't want
to close you down, don't use materials that are very temperature sensitive.
8) Unless you have some way of cooling down the Rubens tube be carfeull
about running if for a long time because it will heat up and that can cause
all sorts of problems (from slowly burning the stand it's on to causing
problems with your speaker system (unless you've really designed the whole
apparatus to operate in a high heat environment).
9) Now think about why you are doing this...make sure the demo fulfills your
need.  Next experiment with songs and sounds so that the sounds help your
demo fulfill its purpose.
10) Ten is here because we tend to live in a base 10 oriented society so I
felt like I needed to round this out with a 10th point...  ;)

-William

William Katzman
Director of Exhibits         
Catawba Science Center
(828) 322-8169 x307
"The Magic of Learning, the Science of Fun" 
 
Now Renting Out
Dinosaurs! (3,000 sq. ft. only $25k)
Body Carnival (2250 sq. ft. only $15k)
Maze Mania (3,000 sq. ft. only $7.5k)
http://www.catawbascience.org/

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