What are Noise-cancelling Headphones?

Noise-cancelling Headphones are headphones that cancel out unwanted external noise. Noise is all around us, in the form of loud buses passing by, the loud engines of airplanes, people talking, birds chirping, loud music...it goes on and on. Wouldn't it be nice to be able to block out this noise and just listen to the sound coming out of your headphones? This is the goal, or purpose, of noise-cancelling headphones. They block out the unwanted, external noise and allow you to hear just what you want to from your headphones.

There are two ways in which noise-cancelling headsets achieve this. The first way is passive noise cancellation. This is the cancellation that occurs from the physical design of the earcup of the headphone. Depending on how the earcup is designed determines the amount of outside noise that a headphone can block. The headset earcup is designed to have a coutoured shape that fits completely around the person's ear and not allow any sound to leak in and none to leak out either; it fully encloses the person's ear with no crack or hole for acoustic escape. This type of headphones that completely surrounds a person's ear is called circumaural headphones. This is how passive noise cancellation is achieved.

The second way that a noise-cancelling headset cancels noise is through active noise cancellation. This is cancellation that is done in powered electronic circuitry. The active cancellation works in the circuitry by detecting the unwanted outside noise signal and generating the exact same noise signal but the inverse of it. Since the two signals are equal and opposite, they cancel each other out. This is how noise-cancelling headsets achieve active cancellation. Since the circuitry requires power to work, noise-cancelling headsets must have power from batteries to operate.