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Tonight, Mikix and I tried an experiment. This experiment was inspired by the widely known property of helium that if you breathe it in, it changes the tone of your voice as you breathe it out. The explanation for this phenomenon that I learned is that your vocal chords vibrate differently in the medium of helium than they do in normal air, causing the change in your voice as helium passes over them.

The experiment was to surround a computer speaker in helium and see if it vibrated differently. We took a ziploc bag and placed the speaker in it, then fastened the zipper most of the way, leaving only enough room for the speaker’s chord to come out, and a little more leeway for the nozzle of our helium tank. I pressed out all the excess air of the bag before pumping helium into it. Then, Mikix played a couple of songs and we listened to the left speaker (inside the bag) and the right speaker (in normal air). The result of the experiment is that the speakers sounded exactly the same.

Hopefully, someone with a better knowledge of physics than I have can explain this.

Update on 09/27/2006:
My friend Kate has helpfully pointed me to the following article which explains the results of my experiment.
http://en.wikipedia.org/wiki/Helium#Helium_Voice
From the article:

It is a common misconception that Helium’s effects on the voice are related to its density. The real explanation is slightly more complicated. Because Helium is monoatomic (earth’s atmosphere consists of over 95% diatomic molecules), its adiabatic index differs from that of air. This means that the speed of sound in helium is faster, and sound of the same frequency has a longer wavelength compared to in air. This difference results in the vibrational modes of the larynx corresponding to higher frequencies, and thus a higher pitched voice. An audio source which does not rely on a resonant air cavity (such as computer speaker) will not change pitch in a Helium atmosphere. If you took an orchestra to Jupiter (whose atmosphere is primarily Helium and Hydrogen), the winds would be out of tune but the strings would remain unchanged.

Today, my roommate Mikix and I headed down to Boston Common with a helium tank, a package of empty balloons, and a mission. That mission was to give away as many of the balloons as possible. Our estimate is that we gave away about 40 in total, which is not a bad chunk of the 55 or so we brought with us.

The very first balloon we inflated was given birth at our apartment, and we brought it with us on the T. Mikix named this one “Sir Balloonsalot” and we vowed that we would not give that one away. Unfortunately, a little girl was very insistant on getting a pink balloon and Sir Balloonsalot was the only inflated pink balloon we had at the time, so Mikix (begrudingly) gave it away.

Toward the end, business slowed down a bit so I started inhaling helium. The phrase “Hey kid, want a balloon?” sounds 10 times creepier than you think it does when said with a helium voice. I also discovered that Mikix doesn’t know how to breathe in helium from a balloon.

(Sir Balloonsalot is the pink one toward the bottom)

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