KRK KNS6400 Studio Headphones

General Information

Whether you are listening to some tracks, or tracking your next recording, the KNS6400 gives you the famous KRK sound independent of your monitors. KRK Headphones provide a precise listening experience that takes you from personal studio to commercial studio to on-the-go track evaluations -- and they allow you to evaluate and enjoy your music with the consistent voicing philosophy and honest reproduction top producers and engineers have come to trust. The KNS6400 headphones have a closed-back around-the-ear design that brings you closer to your music, and the highly isolated surround pads give you the freedom to immerse yourself in the sound without having your mix escape into open microphones -- and keeps live instruments out of what you are monitoring. Having One Voice that consistently gives you accurate reproduction of your music or mix will help you achieve just what the artist intended -- especially if the artist is you.

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Pros: Excellent detailing, very well rendered mids, surprisingly good sub-bass, responds well to EQ, comfortable headphones, high isolation
Cons: Even after EQ, lack of bass impact due to an overdamped bass response, very unmusical with stock settings
I'm going to level with you -- I bought these headphones for a reason that probably nobody in history has ever purchase the KRK KNS 6400s. I bought them because I thought I might be able to coax a good bass response out of them. I saw the graphs at HeadRoom and InnerFidelity and thought: "These things have the most extended bass response I've seen out of anything in its price range! Only a modded T50RP has that kind of extension under $100! They're underemphasized, but that can be equalized!" Their drivers looked to me like they had the potential to produce a strong bass, along side their excellent mids. It looked like a complete bargain. Thus, I put down the money to buy the KRK KNS 6400s.
Build Quality:
Simply put, these headphones are built very well. The whole frame feels strong and the headband has a strong piece of metal on it. The cable is detachable and feels like it isn't the type of cable that would break easily. Of every pair of headphones I own, these are the ones I would trust to last the longest physically. I'd feel very comfortable using these as portables due to both their decent size and durability.
I found the clamping force to be a bit high at first, but overall they're quite comfortable. They're a bit higher than I'm used to, but it's certainly not prohibitive. As far as the pads go, they're well filled out but still leatherette. I would have liked another option like velour pads, but, as far as pleather goes, they're quite nice and they don't heat up my ears. I can use these headphones for hours at a time and not feel uncomfortable.
Sound Quality:
Of course, the most important part of the headphone is how it actually sounds. I'll break this section up into the highs, the mids, and the lows. I tested these headphones with a Pro-Ject Head Box MK II amp and noticed no obvious differences between them being amped and not.
Overall, the sound staging felt above average for a closed pair of headphones.
tl;dr: The highs are well-defined with a few minor issues that were probably just me being use to overly bright headphones.
The mids are beautiful, but a little cold.
The bass is very recessed at stock, but improves significantly after EQ. It still lacks some impact, though.
Highs: The highs were crisp and quick. One thing I did notice was that the KRKs almost did seem to render the hi-hats with a lack of fullness or something of that sort. It sounded slightly off, but not necessarily bad, just a little different than I was used to hearing. Overall I found the highs to be well defined, but a little duller and laid-back than I am used to. There was no sibilance or any other major problems with the highs. Warning: I am coming to these after mostly using Grado SR80is and Superlux HD-681s, two notoriously bright headphones. It's entirely possible that my ears are just used to bright, fatiguing headphones.
Mids: The mids are very beautiful and neutral. The vocals come out more clear on these headphones than I've heard on any closed headphone under $200. Overall, I'd say they're slightly forward but overall very nice.  Switching to any of my lower-end cans makes me immediately miss the detailed mids that the KRKs are able to pull out of the music. In terms of musicality, I feel like these still hold very analytical studio monitor sound -- clear, but not necessarily "fun" or "musical." Regardless, I have almost nothing but praise for the mids on these headphones.
Lows: I first tried these headphones as stock and I felt like the music was just missing the basis that held it all together. Even though I enjoyed their overall clarity, their stock bass felt so shy and polite that it really made them one of my less favorite headphones. They certainly could hit low frequencies and noticeably rumble at frequencies even in the 25-30hz range during frequency sweeps, better than some of my other dynamic headphones, but they never really came out to play that much in actual music listening. When I was actually listening to music, the bass was there, but it didn't like to make itself known. Compared to the last headphone I had been using, the Grado SR80is, their bass impact was very lacking.
Now, these are not finalized EQ settings and I have only really been actively working on them for about 1-2 days, but I've gotten some pretty good returns on it. I increased the bass and sub-bass while adding a small mid-bass hump and receded the mids a bit. After I EQ'd up the frequencies around the 65hz region and some of the other bass and sub-bass regions I felt like the cans became much more musical. The music began much more full and less thin sounding. At the same time, it wasn't quite perfect. The bass impact had improved but was still a little lacking, even though the volume was there. Still, there was a definite improvement and made the quite musical.
Personally, I found the graphs at Inner Fidelity and HeadRoom to be accurate, but they were simply not showing one fact -- the KRK KNS 6400 sounds like it has overdamped bass. Overdamped bass just does not get the same impact that normal bass responses can and are more subdued overall, even at the same volume. This, combined with the already recessed bass tuning, resulted in a very bass-shy sounding headphone. This is also why I wasn't able to completely EQ away all of the bass shy factors.
The KRK KNS 6400s are a very clear, detailed headphone that I feel is really underrated at Head-Fi. I wouldn't agree fully with MalVeauX and call them "murderously detailed and unforgiving" but they are definitely analytical at heart. To be fair, they were very unmusical to my ears on first impression until I really started playing around with the EQ settings. Still, with a little bit of time working with them, I found them ultimately a surprisingly musical headphone that was less cold than my first impression. For me, they ultimately had no fatal sonic flaws -- I loved the mids, the highs seemed clear and detailed, and the lows were adequate, but not exceptional, after EQ. I give them a guarded recommendation for the detail lover if you're against EQing, but I give them a definite thumbs up at the $80 price point if you're willing to play around with the bass. 
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I returned to the KRK KNS 6400s which I so lovingly used as my main headphones for several months and eventually dropped when I received my T20RP -- amusingly enough, I did get a T50RP derivative to get the bass extension I wanted and noted in the introduction to this review. I've grown to adopt the more typical headphone roll-off of the 2khz upper mids/lower treble region. My original equalization made them sound very thin compared to what I was used to hearing now. 
Now that I actually have a better DAC than my original headphone out that I was using for the KRKs when I originally wrote the review, I also can appreciate that they were a click more detailed than I original gave them credit. 
As for the sound of the headphones, they still retain this level of coldness and a small veil on the highs. I called it "laid-back" in my original review, but I now am hearing it as more of a very slight veil. I said in the original review that it wasn't necessarily worse, but different -- I'd like to revise that to say that I do find it worse. It's not a huge knock against the sound, but it's one regardless.
Even playing around with the equalization, the KRK 6400's mids still remain analytic, cold, and removed to an extent. They are definitely bring more clarity than almost anything else in the price range, hands down. Detailed mids are one of the main calling cards of the KRK KNS series. Even with the de-emphasis of the upper mids, though, I still feel like the KRKs are a bit shouty because they jump out forward so much, but that is partially what brings the vocals forward to be analyzed.  
I still give the KRK KNS 6400 a thumbs up at its price point.
2015 Retrospective:
I've since sold the KRK KNS 6400s. I believe that the headphone world has moved on a bit since my first review -- we have much better budget options under $100. I've reduced the rating to 3.5 stars as a result.
Nice review! These are one of my old favorites that I'll never part with. They seem to really benefit from a warm amp and a good DAC. You can even upgrade the pads on these to the memory foam pads on the 8400.
I don't believe anyone has tried it yet, but they make a perfect competitive gaming headphone for when a closed headphone is required.
Just like most sub $100 headphones claiming to be best bang for buck i am very skeptical.
I'm just going to reiterate that the bass sounds overdamped, meaning that I'm not going to say that they're the best bang for the buck. For more descriptions on what an overdamped bass, like what I hear from the KRK KNS 6400 sounds like, look at reviews of the Beyerdynamic DT1350's bass. The DT1350 is another headphone with good bass extension and frequency response curves that make them look like they have full bass, but doesn't show up in actual reviews of the headphone. Although I have not listened to a DT1350, I do know they have overdamped bass and probably about the same bass quantity as my +6-8dB bass equalized KRK KNS 6400s. I found the reviews of the DT1350's bass to perfectly describe what I hear from the KNS 6400s.
Descriptions of the DT1350's bass include: "very clean, but no body to it," "what little bass produced by the 1350 to be very clean and totally unbiased with very little exaggeration" "bass lovers might want to skip this one" "lacking any sort of fake resonant punch."
at the same time while having/being:
"Tight and bottomless bass" "more finely controlled (but still deep and heady enough to feel positively seismic at times" "Bass is FLAT. Extended. Tight. Tuneful." "The bass is alive and deep.'
And these reviews were for the DT1350, which has about 5-8dB more bass than the KRK KNS 6400s without EQ. It's the combination of the recessed bass in combination with the damping of the housing that makes the KRK KNS 6400 sound like the most bass shy headphone ever. With a little EQ, we can bring it up to DT1350 levels of volume.
Pros: Extreme detail, excellent mids, isolating, comfortable
Cons: Noise floor hiss, unforgiving, very bass shy
[size=24.0pt]KRK KNS6400 [/size]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).
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Here's a quick summary of what you'll read about in this review:
  1. Closed back, isolating
  2. Over-ear, full size
  3. Details, details, details
  4. Clear & accurate
  5. Absolutely unforgiving of sources
  6. 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.
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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:
  1. Detailed mids & highs
  2. Clear
  3. Noise floor (hiss)
  4. Isolates
  5. Analytical/critical listening in nature
  6. Absolutely unforgiving of source
  7. Not for all genres (see Bass)
  8. Bass shy (not adequate for some genres of music or some tastes)
  9. Adequate soundstage (not congested)
  10. 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.
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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.
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Very best,
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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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