A. It depends. Noise-cancelling headphones use active technology to play unique frequencies that block outside noises, and depending on which model you buy, the battery can last anywhere from 15 to 40 hours. If you’re using a set of wireless headphones, the battery will be used for both noise cancellation and wireless connectivity, so expect the battery to deplete faster if you’re using both.

That depends on what you’re using them for and how much you’re willing to spend. At the high-end, over-ear and in-ear headphones can both perform fantastically. For those of us not willing to spend thousands on headphones, over-ear headphones typically offer better bass response and a bigger soundstage, but in-ear headphones are significantly more portable and convenient — especially wireless earbuds.

Total harmonic distortion: True, headphones with lower actual total harmonic distortion (THD) will sound better than those with higher THD. But the quoted THD numbers -- "less than 1 percent" -- aren't helpful in predicting sound quality. Listen to recordings of simply recorded acoustic guitar to assess the distortion of one set of headphones versus another. Some will sound appreciably cleaner than others.
However, most people won’t be able to hear the difference if they’re older than 24, have some form of noise-induced hearing loss, or are in the presence of outside noise. For this reason, we recommend wireless Bluetooth headphones for those commuting, or in noisy situations. If you’re listening primarily at home at the computer—get a set of wired headphones.
These headphones hush ambient noise by creating anti-noise that obviates the noise at your ear. They don't eliminate the outside world, but the better models significantly reduce the whoosh of airplanes' air-conditioning systems. Noise-canceling headphones come in all forms, from full-size to earbuds. Since you no longer have to crank up the volume to overcome background noise, this type of headphone lets you listen at lower levels, which leads to reduced ear fatigue. You'll also hear more low-level detail in your music.
Dale: The examples listed here are good general rules, but one thing to keep in mind is in the mid-to-lower price tiers, open-back headphones aren’t nearly as common as the closed types. The smaller list of choices, and the more limited reviews of those items, could make getting a perfect fit more difficult. Sound stage and openness are often given as the advantage of the open-back types, but it’s just a general rule and some closed-back headphones excel at those properties. An important thing to consider is the music itself, since sound stage and perspective varies widely in different recordings.
Every single Bluetooth codec has significant quality issues—despite many creative solutions employed to make the most of the limited bandwidth the standards employ. For those keeping score at home: not a single codec available can meet wired signal quality. Though Bluetooth audio has come a long way since its noisy beginnings, it’s still not ready to replace the headphone jack. Qualcomm’s aptx HD, and Sony’s LDAC 990kbps codecs come close, but everything else falls far short of the mark.
Earbuds have small speakers that rest on the ear canal of the wearer. These are usually much less expensive than on-ear and over-ear headphones and reproduce the sound well. However, outside sounds, such as traffic or power tools, can get past the earbuds and interfere with your enjoyment. Earbuds also don't stay in place very well if the wearer is moving much, such as exercising. These also are lower fidelity than on-ear and over-ear headphones.