Sony claims the MDR-NC500Ds are the world's first digital noise-cancelling headphones. By this, Sony means they're the first to have an on-board digital signal processor that intelligently works out which background noises are the most annoying and then works to get rid of them. All this electronic jiggery-pokery comes at a price, however, as the cans will set you back a not-inconsiderable sum of around £260. That's more expensive than a new 16GB iPod touch.
As these headphones have an over-the-ear design, they're relatively large. Despite their size, however, they actually feel very light -- Sony has managed to keep the weight down by using magnesium and aluminium alloys in their construction. Unlike most over-the-ear models, the ear pieces don't actually sit on your ears, but rather completely envelop them and, as a result, they are much more comfortable during prolonged use.
The standard method for noise cancellation is simply to use small microphones on the outside of the ear pieces to capture external sound. This is then inverted and fed into the headphone drivers. The system used here, however, is more complex. The external sound is still captured using microphones on the ear pieces, but it's then analysed by a digital signal processor which intelligently works out which are the most annoying noises and removes them accordingly. It's clever stuff, but how well does it work?
Switching on the noise cancellation in a normal room is rather disconcerting, as it so severely cuts out background sound that you're left feeling isolated from the world. The effect isn't so startling in a much noisier environment. For example, on London Underground, although the headphones cut out a lot of background noise, some was still audible when we were listening to music at a low volume. We have to say, however, that the noise-cancelling system is still probably the best we've experienced.
Because the headphones use an intelligent system for cancelling noise, they can also adapt themselves to different environments. If you feel that the system isn't working as well as it should when you move from, say, a plane to a train, you can just press the 'mode' button and the headphones will update the noise profile to improve the cancelling process. In use this system really does work remarkably well.
The 'monitor' button provides another good feature. When you press it, the headphones cut the music and feed noise from outside directly into the ear pieces. This is ideal for ordering another gin and tonic when the air hostess arrives with the drinks trolley on a transatlantic flight.
The headphones are powered by a lithium-ion battery that takes around 3 hours to fully charge. Once charged, it has enough juice to keep them running for around 15 hours. This may seem impressive, but it's actually quite poor -- many rival noise-cancelling headphones can run for around 40 hours on a single charge. Sony seems to be aware of this issue, as it provides an external battery pack that takes two AA batteries and offers a further 10 hours of listening time.
The sound quality from the headphones is generally good, but one thing we did notice was that they never produce really punishing bass levels, even when you EQ the bass right up. We can only presume this is a side effect of the noise-cancelling technology.
Also, because the headphones are quite large, you may feel that you look like you've been time warped out of a 1970s hi-fi magazine advert when you're wearing them.
In terms of sound quality, the Sony MDR-NC500Ds aren't really up there with the likes of the Denon AH-D7000s, mainly because the bass response isn't as good as it could be, especially considering the high asking price. However, if you travel a lot, we think their excellent noise-cancelling abilities and comfort will make them worth the significant outlay.
Edited by Charles Kloet