– Noise canceling headphones use active circuitry that measures external noise (external to the headphones) and the noise that makes it through the headphone, and then constructs a counter-wave to cancel out the noise. It’s not 100% effective, but in some models, low-frequency noise can be reduced by as much as 20 decibels, making the background noise perceived as about 1/4 as loud as compared to no noise reduction. Not all noise canceling headphones are the same.
– Some headphones have very quiet electronics that do not create additional high frequency noise when active, but others are not so well-designed. Also, the sound quality of noise canceling headphones can be very different when the circuitry is switched on versus switched off. However, if you do a lot of travel, these types can be great on long flights or other high-noise environments.
– This is because they allow you to play the sound back (from your portable device, computer, in-flight entertainment system etc) at a lower level due to the noise reduction inherent in the headphones, the result is generally far less listening fatigue.