The headphones shown in the movie below use active noise control to limit the amount of external noise that reaches the ear of the listener. They use the effects of interference. A sound wave is generated inside the headphones that is the opposite of the sound outside. These cancel each other out and reduce the amount of noise heard.
The movie shows you:
- The original sound that would reach the ear without headphones.
- The sound the headphone produces that is used to cancel the original sound.
- The combination of the original and cancelling sound.
The zone of cancellation‘ is pretty small. This works OK for headphones, but does not work well if we attempt to generate anti-sound for large areas, like cancelling the sound of your neighbour’s hi-fi, in your own house.