We've never been big fans of headphones that use active noise cancellation, chiefly because they mask the sound of aircraft engines, HVAC systems, computers, and other sources of ambient noise by generating noise of their own. A far better strategy, in our opinion, is to sufficiently isolate your ears so those sounds don't reach your eardrums in the first place.
The best way to do that is to plug your ears with miniature headphones fit inside your ear canal. But some folks just aren't comfortable sticking bits of foam rubber or silicone in their ears, which brings us back to active noise cancellation such as Sony is using in its new MDR-NC200D headphones. These particular headphones are equipped with a pair of tiny microphones that monitor ambient sound and adjust the frequency of noise they generate to cancel ambient noise.
Sony estimates the single AAA battery that powers its MDR-NC200D will last approximately 22 hours.
Sony claims the headphones automatically switch between three noise-cancellation modes—A, B, and C—but you can't choose these modes manually. According to Sony, NC Mode A is tuned to the noise you'll encounter in an aircraft, NC Mode B is tuned to the frequency of ambient noise in buses and trains, and NC Mode C is tuned to the sound of computers and other machines typically found in an office environment. We evaluated the headphones in an automobile, at home, and in the office and were impressed with their ability to cancel noise in each of these locations. The active noise cancellation—a constant sssssshhhhhh—was just barely perceptible in the absence of an input signal from a computer of digital media player, but it was detectable. We couldn't hear this hiss while music was playing, though, even in the brief moments of silence between notes. But we have to wonder if that noise is canceling out frequencies that we do want to hear.
Active noise cancellation isn't the only electronic trickery that Sony uses with the MDR-NC200D. These headphones use a digital equalizer to massage the source audio, resulting in a much brighter performance than the drivers are capable of delivering on their own. When you defeat the EQ—and the noise cancellation—by turning the headphones off and using them passively, the MDR-NC200D sound muddy and lifeless. We plugged the headphones into an iPod Touch and listened to a number of tracks ripped from CD and encoded in Apple Lossless. Even with the EQ turned on, the MDR-NC200D had difficulty rendering the boomy bass drum that sets the pace for the dirge-like "Polly Come Home," from the Robert Plant, Alison Krauss collaboration Raising Sand. The attack and decay of each strike of the mallet sounded ragged and sloppy on Sony's phones, but tight and well-defined on the Bowers & Wilkins P5 portable—and passive—headphones we used for comparison (B&W fights noise by designing their phones to form a tight seal over your outer ear). We encountered the same issue with higher frequencies, such as what you'll find in the incredibly tight horns on Tower of Power's funk ditty "It's Not the Crime," from the band's What is Hip? album (but to be fair, the B&Ws are $100 more expensive).
In terms of comfort, the closed-back MDR-NC200D fit on the ear, rather than around it. We found the thick and generously padded ear cups comfortable to wear for extended listening sessions, as long as we positioned the left muff so that it wasn't pressing against our earring. The left cup hosts the single AAA battery that powers the headphones, as well as the on/off switch, a noise-cancellation button (pushing this causes the active noise cancellation to recalibrate), and a "monitor" button that turns off the noise cancellation but that also mutes your source (so you don't need to remove the headphones or pause your source to hear someone speaking to you).
The MDR-NC200D fold up and inside the headband to fit inside a padded hard-shell carry case that has an interior pocket for the removable cable and the provided airline adapter plug. (iPod and iPhone users should note that the cable does not have an in-line control for those devices.) Sony's case is about the same width as B&W's P5 case and is about half as tall but it's easily twice as thick. Unless your carry-on bag has a lot of room inside, the P5s will make a much better traveling companion. Sony's active noise cancellation technology is very effective, and the MDR-NC200D delivers good value for the money, but these phones are not Kick Ass material.