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.
Conclusion:
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.
Retrospective:
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.
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.
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.
Conclusion:
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.
Retrospective:
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.
I don't believe anyone has tried it yet, but they make a perfect competitive gaming headphone for when a closed headphone is required.