Wave interference

How do noise cancelling headphones use wave interference to eliminate unwanted sound?

Active noise control uses sound wave interference to reduce sounds . Outside noises are captured  through a microphone where a sound wave is emitted with the same amplitude but inverted. This cancels the wave out removing the noise.

 

1. Constructive interference: the crest or trough meets with another pairing crest or trough where the energies combine. The energies combine to create one big trough or crest by passing through one another and only have an affect where they meet.

 

2. Destructive interference: when an opposing crest or trough meets with the opposite wave, the energies combine by canceling each other out. The energies pass through each other and only have an affect where they meet

3. Standing wave: When passing waves have the same amplitude and wavelength resulting in the interference pattern becoming stationary.