Why Does the Voice Change with Helium?

The sound of your voice starts in your voice box. Within the voice box, vocal cords vibrate against each other creating sound whenever you talk. On its own, it is just a simple buzzing sound. But, when it reaches your vocal tract, the sound waves start bouncing around. Those reflections interfere with each other which creates a mix of other frequencies resulting in your very own unique voice. So even though your voice starts out as one frequency, it ends up as a mix of multiple ones.

This is where helium comes into play. Helium is lighter than air, which means sound moves faster through helium than through air. Nearly three times faster, in fact. So the sound waves bounce around faster in your vocal tract, which amplifies the higher frequencies in your voice.

Instead of helium, if somebody sucks in sulphur hexafluoride which is six times heavier than air, the sound waves would move slower through it amplifying the lower frequencies in your voice.

Learn more about how the voice works:

Helium (0:56)
Sulphur Hexafluoride (1:19)

This video produced by Dr. Chris Chang:

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