Noise-canceling means the headphones generate a sound that is out of phase with the ambient noise, to cancel out that noise. It works, to some degree, on steady lower-frequency rumbling noises like airplane engines. It does not work on transient sounds (gun shots being an example) or on human speech or wailing babies. Because by the time the microphone in the headphones picks up the sound, so have your ears. The headphone can generate the out-of-phase cancellation sound, but it is too late. For those noises, you need mechanical isolation, meaning over the ear headphones. Go to a Best Buy that has a display of working noise-cxl headphones and compare the on the ear models with the over the ear models, using human talking and wailing (bring a noisy friend). You'll see, and you won't waste $100.
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Review: Noise-canceling headphones Review | Default | Macworld