How do noise-canceling headphones actively block out ambient sound?

Noise-canceling headphones work by playing a special kind of sound that cancels out the annoying background noise you hear.

Imagine you're in a really loud room, like a party with music blasting and people shouting. It's hard to hear yourself think. Now imagine someone is playing a quiet, soft song just for you, and it’s exactly opposite of the loud sounds around you. The loud sound and the quiet sound meet up and cancel each other out, like they’re best friends who don’t want to fight.

Inside the headphones, there are little computers (called microphones) that listen to what's going on around you, like the hum of a plane engine or the chatter in a restaurant. These microphones tell another part of the headphone, called the speaker, what sound to play so it can cancel out the noise.

It’s like when you’re playing with blocks and you stack one block on top of another, if they match perfectly, they make a stronger tower together. But here, instead of making something stronger, they're making the annoying sounds disappear!

So now you can hear your favorite song or think clearly even in the loudest places. Pretty cool, right?