4/17/12 edit: Broken link note - the "full-length K701 review" referred to several times in the review text below was an exact copy of this thread's review: http://www.head-fi.org/t/187240/akg-k701-after-1000-hours-final-review. The link was rendered broken after a Head-Fi software upgrade in which all "Featured Review" sections were deleted from the site database.
The timing of this review couldn't be more auspicious - my biggest, boldest review yet, and right on the eve of Christmas 2006. Merry Christmas to all here on Head-Fi, always 'tis the season for giving, and this is my present to you guys!
This is my promised review of these three premier AKG headphones, against each other. Ever since they came out, Head-Fiers have clamored for a three-way review from a soul brave enough to take them for the team - and unfortunately that victim became me. The questions have been posed - is the K601 worth the extra over the K501? Is the K701 better than the K601? Is the K501 worth finding used now that it's discontinued? I'll do my best to answer those questions and more in this unique three-way review!
- Arcam DiVA CD73 w/ Black Sand Violet Z1
- Cambridge Audio Azur 640C v2 w/ Iron Lung Jellyfish
- Signal Cable Silver Resolution Analog and Analog Two
- HeadAmp GS-1
- HeadAmp 2005 AE-1
- Portaphile V2^2 Maxxed w/ LT1210 & Black Gate caps, hours unknown but long past burn-in (on loan from Romanee)
- DIY Millett Hybrid
- Cayin HA-1A
The K501 and K601 were burned in for about 700 hours before listening for this review started (they were fed music nearly continuously 24/7 for over a month).
All ABX tests mentioned below were done via the GS-1, thanks to its dual headphone outputs. They were not done blind-folded, or swapped while plugged in.
This review also assumes that you the reader are familiar with the K701 through either personal experience or reading about it at length (due to the large number of K701 reviews here on Head-Fi - mine in the Featured Full Reviews being just one of them).
Disclaimer: the K501 model that I have is apparently the bass-light variation, one of two variations currently out in circulation.
Alison Krauss - Now That I've Found You
Azure Ray - Hold On Love
Eva Cassidy - Songbird
Howard Shore - The Lord of the Rings: The Return of the King [OST]
James Newton Howard - The Village [OST]
Jewel - This Way
Joshua Bell - Lalo/Saint-Saens: Violin Concertos
Kevin Kern - Imagination's Light
Massive Attack - Blue Lines, Mezzanine
Orbital - Middle of Nowhere
Peter Kater - Inner Works
Porcupine Tree - Deadwing
Portishead - Portishead
Radiohead - OK Computer
Renee Fleming - Thais (Massenet, 1894)
Secret Garden - White Stones
Snow Patrol - Eyes Open
Thievery Corporation - Sounds From The Verve Hi-Fi
The Crystal Method - Legion of Boom
Various Artists - Descent II (PC game soundtrack) (featured artists include Type O Negative and Skinny Puppy)
- K501 vs K601
The K501 and K601 turned out to be vastly different from each other in a variety of ways - most notably, in the bass and mid-range. The K501 has been said to have "anemic" bass by many, and in a way that's true, it doesn't have very present bass. However, I found its lack of bass response only really noticeable in electronica, which uses lots of synthesized bass lines. I'm just going to come out and say it: the K501 is not, and I do repeat, not suitable for electronica at all, even a little bit. It doesn't matter which sub-genre - ALL electronic music I tested it with suffered from the lack of bass presence so much that it neutered half of what made the music. It was like listening to music with a 2.0 speaker system.
The K501's mid-range might not sound very recessed on its own, but compared to the K601, it was immediately apparent. It was like the anti-thesis of the K601. It took away the otherworldly creepy vibe of Portishead's "Western Eyes," Horace Andy's deep intonations on Massive Attack's "Five Man Army," Eva Cassidy's inner soul on "Fields of Gold," Jewel's lung power on "The New Wild West," and Annie Lennox's raw power on "Into The West," just to name some of the songs that it severely affected. They weren't even subtle changes - these were all noticeable right away and definitely not in a good way. The lacking mid-range made the K501 sound top-heavy ("top" meaning the treble), and compared to the K601, thin and brittle. In my opinion, it took away too much of the mid-range, recessing it to the point where fullness and lushness was lost and unable to be retrieved, even with the help of a tube amp. Neither the Cayin or the Millett Hybrid did much to help balance back the mid-range - not to say that they tried (because they did), but ultimately neither ended up filling back in the mid-range to a very satisfactory level.
Also, it's worth mentioning that both the K501 and K601 had an unresolvable inability to recover fine details like tape hiss on analog recordings (Portishead's self-titled album, Massive Attack's Mezzanine, and various other CDs). This tended to be dependent on CD - sometimes tape hiss was audible, but it wasn't conveyed with detail and it wasn't apparent that it was tape hiss (I was only able to tell by comparing with the K701). On some other CDs, both these headphones completely missed the tape hiss - it wasn't anywhere near audible, and I was intentionally trying to strain to hear it too.
- K501 vs K701
There was no contest here. If this were like a real match-up, the K501 would be like Little Red Riding Hood scurrying away from the big bad K701 wolf. The K701 was simply better than the K501 in every single way possible - WAY better. There was no need to even critically listen for differences.
Oh that's not to say the K501 is miserable against the K701. It just sounds like a cheaper headphone against the might that is the K701. But when you take the K701 out of the equation, the K501's virtues are clear - a strong, defined treble that's slightly aggressive, with a very emphasized sparkle. And a forward lower treble.
For some reason the recessed mids were more noticeable in this match-up than in the previous one (despite the fact the K601 is warmer than the K701) - in a way it reminded me of the DT770 and ATH-A900. It just sounded thin and even hollow depending on the music. No backbone, no meat, nothing. I kept asking myself "where's the mid-range?" but alas it was scarcely there. Those here on Head-Fi who know my preferred sound signature know that above all else I prefer mid-range warmth and treble precision, but of those two the K501 only has the treble precision. Its mid-range makes it seem like a leaf being blown about in a wind.
This match-up proved to be the most disappointing - it really showed all the deficiencies of the K501 like a glaring spotlight. It couldn't hold up here - not in any stretch of the imagination. There was just so much more sound on the K701.
- K601 vs K701
Initially, the K601 sounded fairly different than the K701 - but then, it also didn't sound burned in. Bass was relatively light, and it sounded a bit dark, but the most noticeable aspect of its sound delivery was a honky, nasal quality. In other words, an emphasized lower treble. This made most music sound weird more than anything - not very pleasant to listen to and somewhat bothersome.
After the course of the burn-in process, it was evident that the K601 had more than just "slightly" changed - it had actually changed quite a bit. The honky/nasal quality was nearly gone (only a small trace still left), bass was actually fleshed out, and the mids had warmed up slightly. The part of the spectrum that seemed to change the least was the treble - the K601 started out slightly dark, and remains slightly dark.
In direct ABX tests against the K701, it was plainly obvious that the K601 has a colored sound. Whereas the K701 strives for balance (its "focal point" is the upper mids) and has a tonally neutral sound overall, the K601 is not only noticeably mid-range-centric, it's also clearly an outright "warm" signature. Granted it's not a K271/K240, but instruments have measurably more fullness and lushness than on the K701.
As a result of this extra warmth, the mid-bass on the K601 is also emphasized, to the point where it can sound like it's a tad "muddy" and not entirely clear. There's a good force to it though, better than the K701, and it's more energetic, with more PRAT. This actually is a good thing for those who prefer a colored, "groovalizer" type sound, and naturally not so good for those seeking neutrality. I found this to be particularly euphonic and synergistic with industrial (the Descent II soundtrack), metal (certain tracks on the Descent II soundtrack get pretty close), alt/prog rock (Porcupine Tree), and dark electronica (Massive Attack's 100th Window for example). IMO, you could go as far to say that the K601 is AKG's way of appealing to the Top 40-listening masses - it really is just a nice, pleasant listen with any kind of music that could conceivably be "mass market."
The key aspects in which the K601 didn't measure up to the K701 were threefold: detail, soundstage, and frequency response. As already mentioned in its match-up against the K501, it's simply not detailed enough to catch tape hiss (and distinctly separate it from the mix) or other subtle background details. It'll get foreground sounds, but if something is intentionally placed back in the mix, chances are the K601 won't get it. As for soundstage, it's just a simple matter of being smaller - estimating, about 67% the size of the K701's. Keep in mind though that this may actually be a good thing for those who don't like the abnormally large soundstage of the K701, because the K701 does have a copiously large soundstage. The K601's soundstage is narrower, more focused, and more directed - almost like a spotlight that illuminates only what it wants to, unlike the field lights-type presentation of the K701. If the K701 is an ampitheatre, then the K601 is like a medium-sized auditorium. It's also worth noting here that the K601 has considerably less "air" than the K701 too - there's not as much of a sense of sound "hanging" in the soundstage and like it's floating off (can also be a good thing for those who don't like airiness). Finally in terms of the frequency response, the K701 is more extended in both directions - but not by all that much. The extra extension of the K701 isn't anything casual listeners would probably notice - audiophiles would of course, but there's nothing severely deficient with the K601, it's only really noticeable in comparison against higher-end cans. And as already mentioned, the K601 has warmer mids.
Despite those three perceptual flaws of the K601, it still manages to sound surprisingly like the K701, as if its frequency graph follows the same general shape (but marginally above or below at points). It has the same clean "separated" sound of the K701 too - layer separation on it is about 75%-85% of what the K701 offers. It has the upper-end AKG house sound, if you will - it's simply just not as refined and balanced and introspective as the K701.
The K501 starts losing signal strength fast (and I do mean fast) between 70 and 80 Hz, spiraling downwards to finally cut off above 40 Hz. In other words, the points at which it loses strength and finally cuts off are fairly far apart, leaving an overall impression of a "valley" or "sinkhole" in the low bass region. Most other headphones have these two points in the frequency spectrum much closer together - the K501 is the first headphone I've heard that has this kind of bass response. Needless to say, bass is probably the most deficient area of the K501. It's simply not enough extension for electronica, and the fast drop in the signal strength makes it unsuitable for acoustic music that relies on double-bass or other bass-specific instruments.
The K601 starts losing strength just above 50 Hz, and begins cutting off around 40 Hz. Significantly better than the K501, and it provides an enjoyable bass response, sufficient to enjoy industrial and metal, but still not quite enough for those who listen to primarily breakbeat electronica and absolutely need those low bass lines.
The K701 has the best bass of the three, which has already been described in my full-length K701 review. Not only does it have a lower point at which it loses strength, it also extends lower than the K601, that it's actually quite noticeable in electronica. However, as already pointed out in my K701 review, even the K701 doesn't extend low enough for electronica.
To put these bass responses in perspective though, the K501's bass is fine for most purposes, and probably won't even be noticed if you listen to older, 0%-electronic genres. It's only when you get into newer music that's been aided with the use of computers and synthesizers (i.e., 1980s and later) where its deficiencies start showing up. The K601 is an acceptable middle-ground, although it's still simply not enough that it can satisfy someone who's craving deep, defined bass. And while the K701 is a definite step up from the K601 in all aspects of the bass (definition, extension, and impact), even it's not enough for that deep, defined bass. So to summarize, none of these three headphones is going to be for someone who's looking for that kind of bass - look elsewhere. But they do all have a nice clear definition where they can hit and can at least give the listener a good sense of rhythm and impact.
In order of ranking, the K601 was the warmest here, followed by the K701, and then the K501 as a very distant third (it was not warm at all). However, while the K601 is the warmest, it was also the least detailed due to its relatively dark response, but I found it somewhat tolerable. Unlike the K701, the K601 isn't anywhere close to being a reference monitor sound - it's quite colored with a boosted mid-bass, warm mids, and a slight forwardness in the lower treble.
The K701's mid-range is mostly tonally neutral, very fluid and vivid, but falls short of being truly engaging and immersive. A better description of its mid-range is in my full-length K701 review.
The K501's mid-range is somewhat of a valley or sinkhole, starting from the lower treble. There's just not enough signal strength here to provide a feeling of fully hearing the instruments, it's almost as if the instruments are there but not really there. General clarity over the mid-range is good but there's no real "attachment" to core instrument sounds as there just isn't the necessary body. Despite this, the K501 seems to do a decent job with guitar acoustics and plucking, helping them jump out from the soundtrack a bit.
The K501 has the most emphasized treble and even has a peak over the "tsss" region. Not the sibilance region, but slightly below it. It doesn't quite have the "tzzz" or splashiness of a Grado, nor is it harsh, but it's still somewhat on the aggressive side, as it's almost immediately noticeable whenever cymbals or other high-pitched percussion enter the mix. There's a good energy here, more than the K701, as it brings out the aforementioned "tsss" sounds more. A very good attack too, it doesn't sound sluggish at all (it's more like the very anti-thesis). Overall a very defined treble, with razor-like precision but it manages to not be crisp or edgy. Extremely able to give a blackness between fast notes. A special note on the K501 here though - it's not recommended for use with a typical silver IC or most solid-state amps.
The K701 follows behind with a similarly precise treble, only not as razor-like or as jabby. Compared to the K501, it's almost a calm treble. Of course it too has a treble sparkle though, it's just not as brash as the K501. More controlled, and an equally swift attack (but not as tight around the edges).
Following suit, the K601 doesn't have as much treble energy as the other two and lacks sparkle. It's more of a recessed response, as the mid-range is much more noticeable in comparison. Despite any high-frequency sounds that might try, it never sounds tipsy - always mid-range centric, never offensive to the ears. It is rolled off at the extreme though, fairly noticeable with any music that runs up harmonics anywhere near 16 kHz. It could barely squeak out a 17 kHz test tone, and a 10 kHz test tone didn't carry as much signal strength compared to the K701 or K501. Still, despite the recessed treble, the K601 has a decent level of refinement, just enough to merit its class in the >$100 category of headphones and certifiably audiophile-grade.
- Amplification & Volume Levels
All three headphones came to life with the right amplification - the K501 and K701 matched up better with tubes while the K601 was better on solid-states. Both the K501 and K601 were more difficult to drive than the K701, which was expected due to their higher impedance, requiring an extra notch on the volume pot to achieve the same volume of the K701.
While the tubes were a better match for the K501 and K701, both opened up particularly well with the GS-1 - deeper, more defined soundstage, greater dynamic range, and clearer overall sound.
And speaking of the GS-1, a volume comparison was completed on it. A difference in volume could not be discerned between the K501 and K601 at any given setting. Not unexpected, as the two headphones are both rated at the same impedance (120 Ohms). However, because volume is partially dependent on the presentation of the entire frequency spectrum, the K601 has a tendency to sound a tad louder than the K501 due to more-present bass, mid-bass, and mids.
The K701 sounded marginally louder than the K601 at any given volume setting, and significantly louder than the K501.
- Genre Matching
Because of the K501's lack of mid-range and bass, I personally found it to be unacceptable for almost every CD in my main listening genres of electronic, trip-hop, and alternative. However, it did fare much better on music that relied exclusively on fully-acoustic instruments, like classical, jazz, and solo piano.
The K601 was very versatile and handled every genre I threw at it, but it was especially adept with the metal, industrial, and alt/prog rock, giving them excellent energy and drive. Not entirely ideal for classical/orchestral though, as it doesn't have treble sparkle and falls short of being extended there. In its favor though, it does sound appropriately lush and full, quite vivid, with a good sense of vitality, especially compared to the K701, which doesn't have as much.
And as already mentioned in my K701 review, that headphone is akin to a jack of all trades, master of none, but still ranks as royalty compared to the K601's scribe or errand runner. Not completely realistic with classical but it certainly tries and does a commendable job. Not rich enough for the metal or industrial attitude but if you're listening to those, get a Grado or Sennheiser. Just balanced enough to handle pop/rock, alternative/trip-hop, folk/country, and most jazz, with an excellent clarity and fluid mids.
- System Synergy
A silver & copper cable test was done with the Arcam and GS-1 (the Arcam has two pairs of analog outputs and the GS-1 has two pairs of analog inputs). Note: this should not be taken as a serious test between silver and copper cables in general, as the Signal Cable products don't sound as different from each other as might be expected of much more traditional copper and silver cables - the silver IC doesn't have even an inkling of harshness or edginess. That said, only the K701 was noticeably sensitive to the cable swap - neither the K601 or the K501 changed much, though the K601 did give slightly better imaging with the silver-core IC. However, in a test against a Radio Shack-grade cable, both headphones were able to resolve the difference that the Signal Cable ICs made.
Aside from the interconnects, all three headphones were appropriately sensitive to changes in source and amplifier - equipment with warm mid-ranges recommended for the K501 and K701, but higher-precision ones recommended for the K601.
The K501 had the largest soundstage on display in this round-up, around maybe 120% the size of the K701's. You thought the K701 sounded spacious? Wait 'til you hear a K501! It was so large it was like sitting in an ampitheatre with concert-hall acoustics - a large projection of sound coming at you from a good distance away. Very airy too, as it lets sound hang and float even more than the K701.
The K701, as most know, has its own large soundstage, which I prefer to liken to an ampitheatre. Excellent projection, with a large, epic, and truly soaring sound.
And finally the K601 has the smallest soundstage, but even its stage is larger than what you'll find in other headphone brands like Grado and Sennheiser. Very focused, directed, and intent on what it's trying to do. It doesn't really have an epic/soaring quality but it sounds appropriately intimate yet relatively distant at the same time.
The relative comparisons aside, one thing was consistently clear with these headphones - each one is absolutely designed and engineered for its purpose. While I was disappointed with the K501, even that one is an audio machine. These headphones are squarely in the mid-fi market of open dynamic headphones, yet together, all three form a deadly trio that's worthy of an audiophile calling. Pick your poison:
The quirkiest headphone of the trio. Top-heavy, with a highly noticeable angled shape on the frequency graph as you go down. Like most other AKG headphones though, there's an emphasis in the female vocal range that works decently for female singers. But if there are any genres that really shine on the K501, they're classical and jazz (and anything else that's 100% acoustic and on the simplistic side).
At $184 shipped from Northern Sound & Light (www.northernsound.net), there is absolutely no reason to not own the K601 if you can't afford to step up to the K701 ($244 shipped from NSL). Not only does it sound a lot like the K701, sharing the same basic sound, it easily offers about 75% of the performance and is a fantastic "sampler" of the high-end AKG sound. It's not as technically proficient as the K701, but I'm betting most people won't care - this headphone really is a solid, all-around performer guaranteed to work well with any music or gear. I recommend this over the K701 if you just want to groove to the muzak! And let's not forget its sleek black color either, in contrast to the garish white of the K701!
I've already said everything I need to about the K701 in its full-length review. It's definitely worth seeking if you're after a refined, accurate sound or need a headphone to act as a reference monitor. Pay no more than $350 (before shipping) for it though, as IMO it fails to provide sound worthy of more than that, considering its $450 MSRP. Still a premium headphone though!
Ultimately, the K701 ended up beating the others here based on purely technical merit, but in actuality, all three ended up being winners, no losers here! The K501 can revel in its expansive soundstage and precision (and EXTREME VALUE FOR THE PRICE if you can find one for $100!), while the K601 can pride itself on being an excellent gateway to the high-end headphone world. It all comes down to what YOU want!
Edited by Asr - 4/17/12 at 1:51pm