In terms of sonic character we found the KNS-8400 to be a mixed bag. On the plus side of the ledger, the headphone offers admirable and impressive levels of clarity and detail for its price. It also offers bass that is quite deeply extended and very well defined. On the downside of the ledger, there is the fact that the tonal balance of the headphone seems skewed in a midrange-forward direction with particular energy in what some might call the “presence” region; that is, the upper midrange band where mids transition into highs.
Another potential way of looking at this balancing scheme is to say that bass (and perhaps the lowest of lower midrange frequencies) are quite good sounding in their own right, but shelved downward in level relative to the broad middle of the midrange that the KNS-8400 provides. Either way you look at things, either as the KNS-8400 having forward-sounding mids or somewhat recessed bass, there are several practical implications of this balancing scheme.
First, midrange details in general, and upper midrange details in particular sound remarkably clear and easy to pick out from within the mix. Frankly, I have observed this same general characteristic in some of the monitoring loudspeakers I have heard in recording studio control rooms, so that it seems that KRK is right in making the claim that the KNS-8400 is balanced much like (some) other high quality monitoring devices.
Second, bass, when heard in isolation, sounds taut and, when the music calls for it, quite deeply extended. Low frequency pitch definition is quite good, too, especially in light of the headphone’s modest price. These qualities are all to the good.
The trouble, though, is that the KNS-8400 does not give an entirely accurate view of the overall tonal balance of good recordings (or if it does, then a great many high-end loudspeakers and headphones have got things wrong, which I doubt). Thus, mids and upper mids sound pressed forward, while bass—though capable of great depth—seems lacking, at least relative to the midrange, in weight, power, and punch. These points of emphasis (or de-emphasis, as the case may be) are subtle enough that the KNS-8400 can be and is enjoyable for music listening, assuming its voicing fits your musical tastes. But it also means that—if you are used to listening to familiar recordings through high-end transducers—the general shape and balance of mixes may seem a little bit “off.”
These qualities mean that while the KNS-8400 makes it easy to focus on potential sonic problems in the midrange and upper midrange, which is precisely the area where the most obvious problems in recordings are likely to crop up, it doesn’t really give you a clear picture of how mixes are balanced. In practice, I think this means the KNS-8400 might be more useful for monitoring the recording process—especially when capturing vocal or other midrange-centered tracks, but less reliable for mixing (where you really would want to know exactly how the mix is balanced from top to bottom).
For purposes of illustrating some of my comments above, let me draw two examples from Reference Recordings excellent Jazz Kaleidoscope compilation album. The first is the Mike Garson Quartet’s performance of “Nothin’ To Do Blues.” The track opens with just the sound of a piano, brushes on a snare drum, and Brian Bromberg’s bass. Through the KRK’s, the “swish” of the brushes on the snare sound crystal clear, the piano sounds beautifully articulate and expressive, but the bass sounds out of character, with less weight on mid-bass frequencies than it would normally have, and more emphasis on midrange accents, fingering noises and percussive (string-on-fingerboard) sounds than would usually be the case. Mike Garson’s piano solo sounds lovely, though a bit up-turned in the upper midrange, and thus prone to a slightly “pingy” sound. Later, when Brian Bromberg takes his solo, his bass manages to sound fascinating through the KRK’s, yet not quite right. Bromberg’s flashing fingering techniques and midrange accents are, to a degree, spotlighted by the KNS-8400, but middle and lower register of the bass lack their usual degree of weight and power (though their sheer depth is properly shown). Let me emphasize that there’s no problem with bass extension (it goes plenty deep); instead, the difficulty is that bass is pulled back in the mix relative to mids and upper mids.