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Eric,
You make an important point about standing waves and the difficulty of
understanding exactly what we are seeing in Rubens' Tubes, Kunst Tubes
( the ones with styrofoam or kerosine) and perhaps with YouTubes and
the intertubes in general! I have noticed similar confusion in the
explanations offered for the popular "air cannon" exhibits, by people
I would have hoped knew better, that they demonstrate sound waves.
(The cannons that use mist so you can see the rings slowly propagate
are less susceptible to such a misunderstanding.)
I am intrigued by William Katzman's mention of Rubens' tubes that use
an acoustic diaphragm instead of a loudspeaker as the sound source.
Turn of the century (I mean that other, older century of course) books
on acoustics are filled with ingenious mechanical apparatus to study
sound: a tuning fork with a stylus attached to draw waves on soot-
coated plates; harmonographs to study musical intervals, Chladni
plates (bowed, please, not shaken or stirred!); and strobe wheels. It
fascinates me how many of these antique devices survive today as
staples of a good sound and music exhibition. Not that our modern
instruments are not great and powerful tools, but there is something
so direct about those earlier experiments which still appeals.
I, for one, fondly remember the "light organs" you mention -- they
were one of the first projects I tackled back when I was learning
electronics. Always a bit disappointing that they only respond to
music in a vague, approximate way. Most schemes for sound
visualization fail in the same way -- eyes and ears process
information in quite different ways. My own favorite approach to
"seeing sound" uses an oscilloscope modified to have a circular
display instead of the usual straight line (think "lissajous figures",
but with an important twist). I made various exhibits based on this
idea over many years, but just recently thought of the --
retrospectively obvious -- idea to "tune" the display to the key in
which the music is performed: Eureka! You may be interested to see a
video I posted to explore the possibilities of this method:
http://www.youtube.com/watch?v=t0xLzml9HC8
all the best,
Tom Nielsen
The Exhibit Guys
On Mar 12, 2009, at 7:54 AM, Eric Siegel wrote:
> ISEN-ASTC-L is a service of the Association of Science-Technology
> Centers
> Incorporated, a worldwide network of science museums and related
> institutions.
> *****************************************************************************
>
> In watching the demos on youtube, I realized that there are two
> different things that you are showing that shouldn't be confused.
> When you are using a pure sine tone, you are showing standing waves
> and the resulting different pressure in different areas, not unlike
> the classic explo exhibition done with styrofoam bits in a tube.
> When you are showing a full band playing rock or any music into the
> tubes, you are still seeing different pressure at different points
> of the tube, bt I guess that the areas of greater pressure indicate
> frequencies in the recording that have greater amplitude at any
> given moment. It is much easier to use the pure sine tones for
> teaching the physics of waves, but arguably more fun to use the tube
> as kind of flame "light organ," if you remember those.
>
>
> Eric Siegel
> esiegel at nyscience dot org
>
>
>
> On Mar 12, 2009, at 9:37 AM, Willam Katzman wrote:
>
>> ISEN-ASTC-L is a service of the Association of Science-Technology
>> Centers
>> Incorporated, a worldwide network of science museums and related
>> institutions.
>> *****************************************************************************
>>
>> 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"
>>
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>> Dinosaurs! (3,000 sq. ft. only $25k)
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>>
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