The noise that is around the wearer of noise cancellation headphones is referred to as the “ambient noise.” This noise can be anything depending on where the wearer is located; it can be the roar of a jet plane taking off or simply day to day background noise such as traffic and children playing outdoors. The objective of the headphones is to reduce this ambient noise so that music can be enjoyed at a lower volume than otherwise necessary, they can also be placed over the ears for quiet relaxation with no music, just solitude. There are two types of noise cancellation headphones; passive and active, both remove noises that compete for the wearer’s attention.
There are two frequencies; high and low. High frequency ambient noise can be blocked quite simply by using dense material in the ear cup. This is quite effective for headphones that have large ear cups. This passive noise canceling, PNC, although effective for large cups does not lend itself to lightweight headphones or the in-ear buds that rest in the ear opening, although the ear buds that actually slide into the ear canal are quite effective in blocking the high frequency noise.
Noise canceling headphones block out low frequency noise by using on-board electronics. The ambient noise is constantly sampled; the electronics generate a noise which is inverse; thus canceling the ambient noise. There is a microphone which is imbedded in the ear cup, this microphone picks up the surrounding noise and sends a sample to the electronics which then generates a wave form which is opposite to the ambient. Whereas high frequency noise is canceled mechanically, hence passive, the cancellation of low frequency noise is active and the headphone must have a power source, usually a rechargeable battery.
The best headphones are those that cancel both high and low frequency, however, as with many things, there are limitations as to how well these work under various conditions. Active noise cancellation is best at canceling consistent noises; it is not as effective if the noise constantly changes, such as background chatter. Although there may be a small limitation, when everything is taken into account, these headphones are ideal when the user is in ideal conditions.
