An Introduction to Active Noise Cancelling technology
Active noise reducing technology uses 'opposite noise' to cancel out the undesirable sounds around you. Sound is made by a series of pressure waves traveling through the air. A sound is made up by equal numbers of high and low pressure waves that travel from where the sound is made to your ear where it is heard. With very low frequency sounds, you can even feel these pressure waves in your stomach.
Normally, the only way to quieten the sound of something is to put something that would block the passage of these waves to your ear. Ear plugs are the simplest form of achieving this; big heavy bulky ear muffs are another method. Active noise cancelling headphones use a different approach. They have tiny microphones alongside each earphone, and a very fast reacting amplifier.
The amplifier takes each sound's high pressure wave and creates an equal but opposite low pressure wave (what they call 'anti-noise', and vice versa for the low pressure waves. The two pressure waves simply cancel each other out. The net result is a reduction in background noise.
