Of course, we’ve all heard what someone sounds like when they inhale helium, but why does helium make your voice sound funny in the first place?
DISCLAIMER: We’ve said it many times and it’s especially relevant for this topic: You should never inhale helium. It’s incredibly dangerous and potentially lethal. Here’s why.
Why does helium make your voice sound funny?
Fact: Inhaling helium does not change the pitch of your voice.
It’s a common misconception that inhaling helium changes the pitch of a person’s voice, causing you to hear the squeaky, cartoonish sound. The sound is certainly different, but the pitch (the vocal cord vibrations that produce the sounds that we use for speaking) doesn’t actually change.
So why does helium make your voice sound funny?
The speed of sound
It’s all about speed baby. As a general rule—the denser something is, the more difficult it is to get through quickly. Makes sense, right?
For example, if you’re running through a cornfield that’s been plowed, you’ll be able to move pretty rapidly. If the field is filled with tall, green stalks, you’re going to be slowed down pretty significantly as you work your way through the obstacles.
Well, sound is no different. Sound travels slower through denser materials and faster through less dense materials.
And that brings us back to helium. We know that helium is less dense than air. Therefore, we can conclude that if sound is traveling through helium and through air, that it will move faster through the helium.
A helium environment
When helium is inhaled, the air that is normally in your vocal tract becomes displaced (and if this happens in your lungs, you’re in big trouble). So, what is normally an air-filled environment is now replaced by a less dense, helium-filled environment.
As we learned a minute ago, sound will travel faster through a less dense medium. (Remember? Good!)
When you inhale helium and then speak, the sounds coming up your throat move through much faster than normal because they’re now traveling through helium, not air.
When that happens, the resonances of your vocal tract become more responsive to the high-frequency sounds: helium voice. (The low-frequency sounds of your regular voice are still there as they always were, they’re just much quieter than the high-frequency sounds, so we don’t hear them.)
This harmonic relationship makes up the timbre of your voice, and the timbre (or tone)—not the pitch—is actually what changes when helium is inhaled.