Why Does Helium Make Your Voice Squeaky?

Step 1 of 5

Your voice has two separate parts.

Vocal cords make a buzz, and the tube above them emphasises certain pitches. The buzz sets your note; the tube sets the character.

Step 2 of 5

Sound moves nearly three times faster in helium.

Helium atoms are far lighter than air molecules, so they pass a push along much more quickly. Roughly 970 metres per second instead of 340.

Step 3 of 5

A faster wave in the same tube resonates higher.

The tube's length has not changed, but the wave crosses it more quickly, so the frequencies it reinforces shift a long way upward.

Step 4 of 5

Your actual note barely moves.

The cords still vibrate at nearly the same rate, so if you sing a note it stays that note. Only the tone colour changes — hence a cartoon voice, not a whistle.

Step 5 of 5

Heavy gases do the opposite.

Breathing a dense gas slows sound down and drops the resonances into a growl. Both effects come from the same rule.

Helium is not poisonous but it does displace oxygen, which is why more than a token breath from a balloon is genuinely dangerous.