Everything you need to know about noise cancelling
Noise cancelling filters outside noise to leave you with what you really want to hear. How it does this is by the use of Active Noise Control (ANC). Basically, when you place a headphone around your ear, the electronic circuit in a noise-cancelling headphone transmits an anti-noise signal. This signal makes the speaker driver in your headphone release a destructive interference, which cancels all the noise around, making it possible to enjoy music without blasting your ears.
This technology was first used in airplanes to prevent the pilots from going deaf due to aviation noises.