Depends on your reference point, and I really don't want to sound too negative, but basically they lack some body and heft in how they portray the sound, especially low/mid-departmentwise. The general sound is a bit on the thinner side of cans. The slam isn't there, although it's often missing from planars. Impact isn't the same as dynamic drivers, but I guess that's kind of out the question tech-wise, but then again punchiness is enhanced due to the almost unnatural impulse response, and the 400i is certainly snappy. It's a fine can for the money, and just superb for some genres, it does a lot of things well. The bass response is closer to neutral, it extends very deep without significant roll-off, the bass doesn't bleed into the mids and the areas don't feel unnaturally separated. There's a lot of detail there, and they resolve well. In whole, the 400i are exciting, albeit rather analytical, but not in a dry, clinical sense. It doesn't make much sense to compare them to my LCD-X, but that's one other reference point of mine; where the slam has these face-melting qualities. Probably the first thing you think after A/Bing them, is that the 400i sounds anemic in comparison. That's what I kind of mean.