Helium whistling

Earlier today my son asked me a question I didn’t know the answer to. So I took to twitter:

A few people chimed in on twitter, but mostly they suggested I try the experiment. Being that son’s birthday today we happened to have some helium around. So we tried it. But before we did (and before I let you see the video . . . oh, you went down and watched the video and are now back up to this paragraph, I see how it goes) we thought about how we’d know if your whistle sounded different. So we tested each other to see if we could match pitches. We also used the piano to give random pitches. By the way, I’ve talked before about my ability to match a pitch while whistling.

So, here’s the experiment:

My take, especially at the end, is that it did affect my whistle.

So here’s my theory: The helium changes the speed of sound in my mouth cavity which raises the resonant frequency of the effective Helmholtz resonator. Really that’s the same thing that happens when you talk with helium. There the helium doesn’t affect the vibrations of your vocal folds/chords since that’s decided by the tension in them which is decided by you. However, those vibrations have lots of resonances and the helium in your oral chamber raises the resonances of the chamber so higher resonances of the vocal folds/chords are amplified making you sound higher. Since the resonances of the vocal folds/chords are roughly harmonic, you typically sound an octave higher.

When you whistle you aren’t choosing the tension of your vocal folds/chords. You are shaping your lips/mouth cavity from memory to be a shape that causes a Helmholtz resonance with a particular frequency. When you have helium in your mouth, the resonance goes up and so does the frequency you hear.

So what do you think? Here’s some starters for you:

  • Why do you keep saying vocal folds/chords?
  • What about the other kind of whistle where some people use their fingers?
  • How do we know you were trying just as hard to match the pitch when you claimed that it wasn’t right?
  • I don’t think you understand how sound is generated at all in both whistles and talking. Here’s a tutorial for you.
  • So you decided to pop your son’s balloon? On his birthday? What kind of monster are you?
  • Why are you too lazy to see if the heard frequency compared to the expected frequency matches the ratio of sound speeds in helium and air?
  • You wrote “raises you whistle” instead of “raises your whistle” in your tweet. How do you ever expect people to take you seriously?
  • You posted this before the youtube video was ready. What, you think I have the time to come back when it’s ready? Thanks for nothing, loser.

About Andy Rundquist

Professor of physics at Hamline University in St. Paul, MN
This entry was posted in fun, physics, teaching, twitter. Bookmark the permalink.

3 Responses to Helium whistling

  1. bretbenesh says:

    A great contribution to science!

  2. pa32r says:

    If you’re channeling the Mythbusters, it’s “myth confirmed,” not verified. Still that was fun to watch.

    • Andy "SuperFly" Rundquist says:

      it’s so funny that both my son and I had a brain fart right then. As soon as I hit stop we both said “confirmed.” Oh well.

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