Instead of turning up the volume to block out external noise—which is never good for your hearing. Noise-cancelling headphones’ work is to isolate and "remove" those unwanted sounds while preserving the original audio signal. That means you can listen to music, movies, audiobooks, and podcasts at much lower volumes than you would have otherwise. But before picking a pair, it's important to understand what type of noise cancellation you're looking for.
Active Noise Cancellation
Noise-cancelling headphones use microphones that listen to outside noise and special circuitry that analyzes it and generates a counter-signal. This signal does more than simply block out noise, like thick earpads on headphones (that is called noise isolation); it actively cancels out the noise to generate a quiet that's unaffected by what's going on around you. The best noise-cancelling headphones work so well, many owners will put them on, turn on the power, and not listen to anything through them—just to enjoy the silence.
Noise Isolation (Passive Noise Cancellation)
Even without the electronics, good over-ear headphones can still block out most outside noise with the aforementioned noise isolation, which is sometimes referred to as passive noise-cancelling. You just need good-fitting earcups that form a strong seal around your ears.
Noise-Canceling Headphones vs. Earphones
Early noise-canceling headphones had to be big, over-ear cans to properly block out sound, but the technology has shrunk a lot in the last decade. Now in-canal earphones can hold the same microphones and circuitry needed to block out sound, providing even better noise cancellation than a good-fitting silicone or foam ear tip will provide. Bose is at the front of the pack, with both wired and wireless earphones that feature some of the best noise-cancellation technology we've experienced.
Wired vs. Wireless Noise Cancellation
Now that a number of popular phones have abandoned the headphone jack, you might want to think about going the wireless route. A few years ago, the idea of wireless noise-cancelling headphones was laughable due to technical constraints like battery life and miniaturizing circuity. Those problems have been solved, and now you can get wireless headphones that offer solid noise cancellation.
True wireless earphones (earpieces with no wire connecting them) are a fairly new category with several inconvenient aspects getting shaken out as headphone manufacturers develop them, but after two or three generations they've improved significantly from the first models we've seen. They too can hold noise cancellation circuitry, though so far it isn't as strong as more tradtional pair of headphones (or earphones)
Noise-Canceling vs. Standard Headphones
Though not always the case, noise-canceling headphones generally don't sound as good as same-price standard headphones. Manufacturers prioritize the noise-canceling algorithms, which can interfere with the quality of the remaining audio signal. Audiophiles will generally prefer headphones without noise cancellation, to ensure they get an accurate sound that's unaffected by audio processing.
Noise cancellation isn't cheap, so once you've found the right pair of headphones, make sure to take good care of them.