eli5 Noise cancelling headphones are magical but how does the technology work and does it drain the battery?

Question

eli5 Noise cancelling headphones are magical but how does the technology work and does it drain the battery?

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Answer 1

First off, there’s a big difference between noise cancelling and noise suppression. Suppression works by blocking the outside sound from getting in. This is a passive process. Noise cancelling is an active process, and runs the battery down quicker.

You can think of sound as the air wobbling up and down. (Really, it’s getting squashed and stretched, like thrusting one end of a slinky, but let’s keep it simple to visualise it.) There’s a tiny microphone on the outside of the earphones/headphones. It picks up the external noise that’s going into the ear and copies it, but with an important difference. When the air squiggles up, the speaker plays a down, and vice versa. Basically, it plays an upside-down version of the same noise. When this goes into your ear, the ups from outside cancel with the downs from the speakers, meaning there’s no overall motion.