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KRK KNS6400, a detailed monitor

A Review On: KRK KNS6400 Studio Headphones

KRK KNS6400 Studio Headphones

Rated # 470 in Over-Ear
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Price paid: $79.00
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Pros: Extreme detail, excellent mids, isolating, comfortable

Cons: Noise floor hiss, unforgiving, very bass shy

KRK KNS6400 A detailed monitor


So I had to give the KNS6400's a shot because they were recommended to me based on my love for the SRH940 and other headphones that are all about mids and details. The KNS6400 is only $80 from Amazon, but I was lucky enough to have Tdockweiler let me borrow his pair for a while to audition and get a feel for them, so a huge thanks to him for letting me borrow the cans. So the KNS6400's are supposed to be a very detailed, clear, studio monitor and I had to know because I've tried other studio monitors in the past, which are often passed as being a headphone for casual music listening, and felt they were nothing of the sort. So, let's put another one to the test or figure if it's something for casual use or if it's something for more professional uses (mixing, monitoring, producing, etc).




Here's a quick summary of what you'll read about in this review:


  • Closed back, isolating
  • Over-ear, full size
  • Details, details, details
  • Clear & accurate
  • Absolutely unforgiving of sources
  • Very shy on the bass


Since I borrowed this pair, I cannot comment on what came in the box or the package itself, so I'll have to skip to the rest of my typical approach to reviewing the headphone. I imagine it comes with an adapter to convert 1/8th" to 1/4th" plugs, and I don't think it came with a case or bag, but not many headphones do.


Construction, Materials & Comfort:


The overall appearance of the KNS6400 is very simple and built for use. They're clearly not made to look like something stylish or poppish, they're literally studio monitors. The materials are hard plastics, very sturdy and seemingly built to take a lot of rough abuse. Again, this just further shows that it's a real studio monitor and not just labeled one. For it's cost, $80, it's quite a tank.


The cable is pretty long, solid, rubbery and detachable which is a nice detail. It locks in with a twist, so if yanked, it doesn't give, so it's not there for protection. It's just there to be able to take it off and replace if damaged basically, and that, again is indicative of a professional product that is likely to take a lot of abuse from use.


The pads are pretty comfortable. It's a memory foam and it isolates pretty well as far as typical closed headphones go. That sort of material is not my particular favorite, simply because it can be sweaty and oily on your skin after hours of use, but that's my own personal preference, not a fault of the headphone. From my understanding, the pads are upgradable and swappable with other models of other brand headphones. They slid right off if needed.


Clamping force is good enough to secure and isolate, but not so much that it makes you feel like you're getting pinched and squeezed to discomfort.


Overall, comfortable to wear for hours on end.




Sound Characteristics:


The real meat & potatoes of this headphone is how it sounds. It's not much to look at, and it doesn't come with fancy stuff. It's not supposed to. But how it sounds is what matters here. This is a studio monitor, so let's see just how much it lives up to that or if it's just labeled that like so many.


Quick summary for the impatient:


  • Detailed mids & highs
  • Clear
  • Noise floor (hiss)
  • Isolates
  • Analytical/critical listening in nature
  • Absolutely unforgiving of source
  • Not for all genres (see Bass)
  • Bass shy (not adequate for some genres of music or some tastes)
  • Adequate soundstage (not congested)
  • Easy to drive


Music tested, from my trusty test-group that I tend to use on all headphones (all lossless), included: Ani Difranco (Acoustic, Female Vocals), Regina Spektor (Folk, Pop, Female Vocals), Sierra Hull (Folk, Blue Grass, Female Vocals), Euge Groove (Jazz, Bassy), Ludovico Einaudi (Classical, Piano), Keith Jarrett (Classical, Piano, Live Concert), Bach Cello Suites (Classical), The Cranberries (Pop, Female Vocals), Elton John (Classic Rock),  Avantasia (Metal, Fantasy), Buckethead (Alt. Metal), Rusko (Dubstep), JesusDied4DubStep (Dubstep), Robyn (EDM), BT (Trance, Techno), OceanLab (Trance, Techno).


Hardware used, Sansa Fuze, Vivid V1 Technologies DAC/AMP, Matrix Cube DAC/AMP, Schiit Lyr, Auzentech Forte Soundcard.


Noise Floor:


I noticed a noise floor on these headphones. A hiss, if you will. I tried them on several pieces of hardware to try and differentiate between my hardware and the headphones to ensure I wasn't indirectly adding the noise floor due to over amplification or simply putting the wrong impedance with the wrong outputs so to speak, so I removed all amplification beyond minimal from most devices and it was still present. This is actually normal for headphones that are extremely detail oriented in my experience. So this can be a negative or positive depending on your uses. For music, I personally did not like the noise floor and hiss, even though you do not hear it during most playback, it is there during quiet moments (I would notice it during acoustic sessions when there's no complex playback or some light vocals). Again, please understand, this may not be the headphone itself, but rather, a quality of it's impedance or sensitivity compared to the outputs of what you'll plug it into. I had a lot of hiss coming from my setup, which on all of my other headphones doesn't have that hiss, so I could only assume it was this particular headphone or something about it. I'm not a sound-science person, so take this with a grain of salt. I don't quite know why it was hissy.


Treble (Highs):


The treble of the KNS6400 is detailed and clear. That literally sums it up.  Another way to describe them would be analytical or critical. Details crawled out of the walls into your ears on this thing. It's an absolute detail monster, which is a very good thing for some, but can also be a very bad thing for others because it's so detail oriented that it becomes completely unforgiving of source. Again, this can be great for some, while for others it may be very hard to cope with. I did not notice any out of control sibilance in particular at my listening levels, there was some on particular pitches, but overall did not come across as being too brilliant (in a good way). Definitely a crisp sound with good definition. It's a pretty fast headphone too,  I felt it could snap and keep up with things nicely. Overall the response is pretty flat sounding.




The mids are probably the most this headphone has to offer of all its attributes. It definitely just bubbles with mids as that's the primary frequency response of this headphone when I judge by ear. The mids are very detailed and clear as well. In some tracks, I could definitely hear the artist shuffling, breathing, moving parts on instruments being played, etc. Hearing the audience (silent audience mind you, not live rock albums, I'm talking about classical recordings here specifically) in the background of some live performances was pretty clear. Vocals came across nicely and very articulate. I felt the mids were less musical however compared to some other headphones, largely due to the mids not having a relatively equal bass component. Again, unforgiving to source. Anything low quality, or poorly recorded, or simply with subtle details recorded in the background will be pretty apparent. This again can be a good or bad thing depending on what you're after. Mids were not very warm sounding to me (again, like the comment on musical) largely again due to the shy bass. If a critical listening session to mostly mids is what you need, this would be the headphone for the job. This pretty much is in line with what a studio monitor is like in my experience. The sound is quite flat.


Bass (Lows):


The bass is probably the most apparent lacking section of the frequency range of the headphone, and a pretty start attribute for pleasure listening compared to professional/critical/analytical listening. Most analytical headphones are not going to have gobs of bass, so that detail and clarity can be as crisp and present as possible. That seems to be the roll here too, as a studio monitor. The bass is quite shy. Likely the most shy I've ever heard in a closed back headphone. The frequency response curves from HeadRoom and InnerFidelity are so completely off that it really doesn't represent this headphone at all. The flatness is gone, as it sounds like the roll off happens very early. This makes the headphone less neutral and more of something that has emphasis on mids/highs. The graphs display a very neutral/flat response from top to bottom nearly but this is not at all what I hear when I listen. Instead, it sounds like the bass response is absolutely vanished by the time you get to the 100hz stuff and below that just is so shy that you can't even tell it's happening sometimes unless you really listen for it. These are definitely not for someone who needs at least even neutral bass. These are for detail critics or someone who really doesn't like bass or prefers a very light bass. The idea of reverb is definitely not in this headphone. Accurate bass is there, it does have an impact and snap, it will let you know some bass just happened, but the lingering bassy reverb needed in some applications is not there and I think that easily makes or breaks this headphone in terms of who will want to use it and for what it will be used for. For me personally, this really shy bass makes it less of a musical headphone, it's not warm at all. Very apparently, just for reference, the SRH940 and Grados (SR60 and SR325) were quite a bit more bassy and musical (the SR325 being the bassiest of the bunch) when comparing other detailed mids oriented headphones.


A Special Note on Frequency Response Graphs:


Here are the two graphs from HeadRoom and InnerFidelity. Again, I just wanted to point out, that these graphs do not represent what you will hear. Sometimes, the graphs are very close to what you hear. Other times, they're so far off that it's quite unbelievable. Needless to say I was shocked by how shy the bass response was, especially after having seen these graphs because these graphs indicate that you will hear the same volume of some very low end bass as you will the mids essentially, and this is entirely false. I found that very interesting, and quite critical to know, if interested in these headphones for music-listening purposes.


Again, warning, these headphones do not sound like these graphs suggest at all.








Soundstage is pretty good for a closed headphone. It's not quite as expansive as some other headphones that have different methods of achieving larger soundstages, but it was not cramped or congested in a way that took away from the sound. They could probably be used as gaming headphones for competitive-foot-step-listening (FPS's) due to the detail and clarity and super shy bass, but don't expect a wide expansive sound stage unless you have some kind of emulation means (like the Mixamp, or Dolby Headphone, etc). Imaging is good.


Closing Thoughts:


The KNS6400's are definitely not for everyone. They're not a musical headphone to my ears. They're very shy on bass. But they're murderously detailed and unforgiving which makes them a very good critical or analytical headphone for that kind of listening. That pretty much says "real studio monitor" to me, instead of just a labeled monitor that has tons of bass (the M50 comes to mind, in a bad way). Detail monster definitely describes the KNS6400.


Again, not for everyone. It was fun to audition them and listen to music in a very different way, basically, critically. But not quite my cup of tea for pleasure listening as I like to have some warmth and musical properties in my pleasure listening.


I directly compared them to the SRH940 and found them to be very similar in detail levels, but I didn't have the noise floor on the SRH940 that I had on the KNS6400. Also, I found the SRH940 to have truer bass response and able to really give those low tones without becoming a boomy or bassy headphone, instead, staying neutral to bass lite even, but still being warmer and more musical than the KNS6400. Likewise, I found my Grados to have much more impact and bass than the KNS6400, but the KNS6400 was more clear and detailed.


Overall, an excellent detail headphone, but I wouldn't recommend it to someone for pleasure listening in general who didn't already express an interest in analytical sound with very shy bass response.






Very best,


Thanks for the well written review. Basically spot on with most things. I do disagree with a few tiny parts. I think based on your review, some will know from all this information if it's a headphone they will love or HATE. I personally love everything about them and am happy with it's bass and don't feel they're too bass light. They do lack some bass impact.
I think for those that love it's signature, the value rating would be more like a 5/5 and not a 3. I guess I'm one of the strange people here who consider this kind of studio monitor fun (and somewhat musical) to listen to. I guess most won't feel the same way. Lately a few people on here seem to prefer the 8400 more than the 6400.
One thing I should point out is that the memory foam pads are a $20-$30 upgrade. Pleather pads come stock. The headphones come with a good manual. With the 8400 you also get a volume control cable and memory foam pads and headband.
Heya, again thanks for letting me borrow them, was fun.
As for the value rating, that's difficult to truly rate, but really anyone who really likes a specific product will rate it highly, not necessarily fairly. Because this headphone is definitely not like another studio headphone, it's going to have a limited audience of people who really want to try it out, which makes it's cost for it's popularity hard to nail. So if you think about it numerically, giving a 3 is putting it above average for value (to give perspective, I would rate the D2000 a 4 star and the HE-500 a 4 star; not that they do not make 5 star, due to cost and build as a ratio for value). Anyways, rating systems with low counts are always hard to put down as folk tend to see a 3 stars and think it's not good, when it's actually better than average, and a 5 should be very hard to obtain.
They do have a lack of "body" in the bass on crappy laptop and DAP jacks and a total complete lack of damping on the Emu 0204.
Volume control cables are bad, so you shouldn't miss it on the 6400.
Noise is not created by headphones but by sources.
What is the impedance of the jacks on these two headphone amps you're using?
This headphone's almost as insensitive as the Fostex planar, current hungry, and needs a jack under 4 ohms. It *may* have a phasing issue in the low end, but I'm unable to test it. This could also be the fact the frequency response is so flat and they are a low impedance headphone sharing a common ground on the TRS headphone cable. That does weird crossfeed stuff.
My biggest annoyance with it is the very microphonic plastic-like cable. Weird choice.
I'll admit that it's impressive to read that an $80 headphone can compete with the $275 940's in terms of detail.
Detail is not the only aspect though. When listening to music, there needs to be more than detail. And that's the big difference between the two headphones. Also, build quality and comfort. I would put a lot of favor to the SRH940 for comfort and build, and quite more musical for casual listening of music for pleasure. I also preferred the sound stage of the SRH940, which I rate as better than average for a closed headphone. I think the KNS6400 has the edge, and it's very slight, in detail, but I think it's likely due to how cold and unmusical the KNS6400 is (to me), because you're not hearing anything but the mids & treble, so you can't help but notice every scratchy detail that might be possible (or in other words, a positive caused by a negative in my ears).
Ah I see, yes I would agree with the musical listening vs. detail only statement. And yes, I find the 940's to be very comfortable as a full-sized closed headphone.
I don't find the 6400 cold or unmusical fed the Emu 0204 as the DAC and Fiio E7 as the amp. They sound like their response curve looks, which is pretty close in measured response to the ER4S, Q701, and HD25-1. Neutral and not dependent on the genre.
Very helpful review. I'm considering the KRK KNS8400; have you tried it? I'm curious to know whether you think the 8400 fixes the problems (mainly missing bass) in the 6400. I've read some reviews claiming that the 8400 can have a bright, annoying treble. But if this depends on the recording, then maybe it's just a brutally honest transducer, faithfully revealing the source. Got an opinion?
6400 sounds even better from the E6.
How does this compare with the Sony V6?
The Sony V6 and 7506 have flatter mids and upper & mid bass, but the KRK has more extended bass & highs and better bass sustain & bass distortion figures. The Sony will sound more "crisp" and "glassy", but it may be too much for some.
how do they compare with senn's hd439s?
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