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How do noise-cancelling headphones work?

What do noise-cancelling headphones do? How do they cancel noise? Why are they so expensive? Do I even need them? Read on...

Noise-cancelling headphones are, like sound-isolating earphones, an unconventional idea for the average consumer, and so I get asked many questions about them. What do they do? How do they cancel noise? Why are they so expensive? Do I even need them? If you've ever pondered one of these questions yourself, you're reading the right article.

What is noise cancellation?
Noise-cancelling headphones are battery-powered headphones that actively cancel out the ambient noise surrounding a listener. The most common use for them is during plane journeys. While sound-isolating earphones will block out chatter, it won't get rid of the noise of a jet engine. Noise-cancelling headphones will.

Put simply, they work by using tiny microphones that listen to the noise surrounding the listener. Then, in real time, they record and invert the frequencies of the noise, then play the inverted signal into the ear. This inverted signal directly 'cancels out' the ambient noise that enters the ear naturally, thereby eliminating it.

A typical noise-cancelling headphone

This makes for a much more enjoyable music-listening experience. Noise-cancelling headphones are also great for use on trains and the London Tube system, as well as in offices -- one of the most noticeable effects noise-cancelling headphones have in an office environment is the elimination of noise from loud air-conditioning systems.

Pros, meet the cons
There are a few downsides to this kind of headphone, however. Firstly, they all require batteries to operate. Some more expensive models -- such as Sennheiser's PXC 450s -- allow the headphones to be used as conventional passive headphones when batteries expire, but you'll have to carry replacement AAAs to ensure noise cancellation goes uninterrupted.

Secondly, you may find the battery compartment is integrated into the cabling of the headphone. This can be bulky and inconvenient. Some models do integrate the battery directly into the headphones themselves, however.

And of course these headphones aren't as convenient for outdoor use as lightweight earphones -- they're best suited to travelling as opposed to general listening. A notable exception are the Audio Technica ATH-ANC3s -- a pair of noise-cancelling earphones.

For an excellent first pair of noise-cancellers, check out the Audio Technica ATH-ANC7s. Or for the premium experience, look up the Sennheiser PXC 350 or PXC 450 models.