You've got quite a lot of choice these days if you're looking for a pair of headphones with active noise cancellation, in all types of shapes, sizes and price classes. We're discussing eight of them in this review.
Sometimes you just want to listen to your music without being disturbed or you might just want to have some silence around you, even though this is quite hard to achieve in practice. Think of busy environments such as public transport or the inside of an airplane. A normal pair of headphones does of course somewhat reduce the noise around you, but they never completely cancel out all noise around you. In cases like this you need a pair with active noise cancellation or noise reduction.
This technology allows you to suppress most of the noise around you. It's all about anti-noise. Sound waves have a phase and amplitude based on its frequency. A noise-cancelling headphone analyses the noise around you and produces anti-noise, with the same amplitude and wavelength as the noise around you, but with a completely inverted phase. In other words, the nodes are the same, but the anti-nodes are mirrored. The two sound waves form a single new sound wave, with nearly no 'sound' left since the two waves basically cancel each other out.