tdockweiler already wrote a review of these, but I've been so blown away by them that I had to sing their praises, as well. A shout-out thanks to him for pointing me in this direction.
I was in the market for some closed cans with good isolation, clarity and durability. I was looking at the Shure SRH 940s, the Fischer FA-003s, and the Beyerdynamic DT 250-80s. In the process of looking, I was recommended the KNS series by KRK. I had heard of them, but remained hesitant, since judging by the pictures the earcups looked fairly shallow (like the Sony MDR-V6), and comfort is a very big deal for me, so I ignored them. I decided to give them a try based on the suggestion, though. I first tried the KNS-6400s, and the comfort and sound quality were okay, but the 6400s had this perceived aggression in the mids and highs, and over the long term were a bit fatiguing. After wearing them for about an hour, they started to be uncomfortable, as well. So I returned them and got the KNS-8400s, instead. What a difference! All the issues with the 6400s were resolved, and much more besides.
The 8400s are far more comfortable over the long term. I've had them on my head for over four hours today, and the headband cushion sometimes needs some adjusting, but the ear cushions are very comfortable, and my ears don't contact the insides of the earcups; or, if they do, it's not enough to bother me.
When I hear about a pair of headphones designed to be used as monitors, I have a preconceived notion of that pair being perhaps a bit thin and lifeless. The 8400s are far from it. They are very rich and full. And when I hear that description, I'm inclined to think that pair is bassy and warm, and poorly extended in the upper registers. The 8400s do not match this perception, either. It is true that they are perhaps slightly warm, and they have excellent bass impact and depth (if they had more, I'd call them bass heavy; if they had less, I'd be dissatisfied), but do not think that the highs are left out in the cold. They are very present, and I think I can say that the highs on the 8400s are perhaps the best extended out of the 40+ pairs of headphones I've tried in the last several years. Perhaps not the best when isolated, but best when considering how well they fit in with the rest of the sound spectrum when comparing each individual model. What makes the highs so great is that they're very well extended, but not fatiguing or offensive. These headphones are extremely competent across the whole spectrum. Each part has its place. They are very clean and crisp, while remaining rich and full. In my experience, that is a rare combination, especially for models in my price range. If you had told me these cost $250, I would have not been surprised. I would gladly pay retail. They are that good. For prices seen online (~$130), they're a steal.
In my search, I believe I have found a great combination of my criteria. They are closed, they provide excellent isolation (the memory foam cushions produce a great seal), they are very clean and detailed, and they are presumably quite durable (spring steel headband, replaceable cushions and cable). I was planning on using them for a job requiring critical listening, but I'm very happy to say I can use them for enjoyable music listening, as well. If I had to criticize them, sometimes the treble can be a little hot on some songs, and the soundstage is not immense. But I've only put a few hours on them so far, and a smaller soundstage is to be expected for closed headphones. I firmly believe that everyone should give these a try. At these prices, I don't think you can afford *not* to. With their low impedance, portability, comfort, and excellent sound quality, I think they'd be a fantastic first headphone. Unfortunately, it took me a lot of money and time to find them:P. All in all, very highly recommended.
Edited by Marximus - 9/6/11 at 4:23pm