Constructive Interference:

When two crests or two troughs combine together when they have the same relative amplitude and frequency as they move in the opposite direction towards each other creating a combined wave.

 

Destructive Interference:

When one crest and one trough combine together as they have the same relative amplitude and frequency as they move in the opposite direction towards each other which cancels out the wave momentarily.

 

Standing Wave:

When the waves have the same relative amplitude and frequency as they move towards each other to creating a “standing place” in the energy of the wave. It looks like that part of the wave is not moving calling it a node/nodal point.

 

How do Noise-Cancelling Headphones Work?

Noise-cancelling headphones use the properties of physics and waves to basically creating a constant destructive interference. This works by the headphones finding the surround noise waves and then creating the exact opposite type so they can line up troughs and crests together making the sound waves cancel out. The headphones also can help this cause out by having sound absorbing materials as well creating a higher noise-cancelling type of headphones.