These are everything you'd expect from a flagship headphone, only MORE, because some flagships have come to disappoint me, even from the more expensive brands. In a lot of markets, I find there is often one brand that stands out as cheaper yet better, and in headphones, I think it's Audio-Technica. I should say I've not heard any planar-magnetic headphones, so I'm not comparing with the BEST. But comfort, sound, and price wise, you can't go past the ATH-AD range, and this is the top of the lot.
Compared them also to W5000's, W3000ANV's, W1000X, ESW11LTD's
Tracks used for testing:
Artur Rubinstein - Chopin Nocturnes (16/44 FLAC)
The Doors - The Doors - Break on Through (24/96 FLAC)
Extrawelt - Schöne Neue Extrawelt - Messy Machinery (16/44 FLAC)
Goldfrapp - Supernature - Ooh La La (16/44 ALAC)
Fischerspooner - #1 - Emerge (16/44 APE)
Flying Lotus - Cosmogramma - Do the Astral Plane (16/44 ALAC)
The Avalanches - Since I Left You - Live at Dominoes (16/44 FLAC)
Richard Galliano & Michel Portal - Blow Up - Libertango (16/44 ALAC)
UHT - Pic de pollution - Mr K (16/44 FLAC)
Bill Evans - The Paris Concert - My Romance (16/44 FLAC)
Charles Mingus - Oh Yeah - Wham Bam Thank You Ma'am (24/192 FLAC)
Alisson Krauss - O Brother, Where Art Thou? - Down to the River to Pray (24/192 FLAC)
Night Spirit Masters - Gnawa Music of Marrakesh - Baba l'rouami (16/44 FLAC)
Boubacar Traoré - Mariama - Mariama Kaba (16/44 FLAC)
Les Witches - Mr Playford's English Dancing Master - Nobody's Jig (16/44 FLAC)
Charles Mingus - Tijuana Moods - Ysabel's Table Dance (Alternate Take) (16/44 FLAC)
Toumani Diabaté - The Mandé Variations - Elyne Road (16/44 ALAC)
John Coltrane - A Love Supreme - Resolution (24/96 FLAC)
Stephan Bodzin - Liebe Ist... - Mondfahrt (16/44 FLAC)
Flying Lotus - Until the Quiet Comes - Putty Boy Strut (16/44 ALAC)
Keith Jarrett - The Köln Concert - Part II (24/96 FLAC)
Miles Davis - Kind of Blue - So What (16/44 ALAC)
Isaac Hayes - Hot Buttered Soul - Walk On By (24/96 FLAC)
Fleet Foxes - Helplessness Blues - Montezuma (24/96 ALAC)
Stan Getz & João Gilberto - Getz/Gilberto - The Girl from Ipanema (24/192 FLAC)
The Chemical Brothers - Further - Escape Velocity (16/44 FLAC)
Nina Simone - Pastel Blues - Sinnerman (16/44 FLAC)
The Dust Brothers - Fight Club OST - Hessel, Raymond K. (16/44 ALAC)
Ella Fitzgerald - Ella and Louis - Isn't This a Lovely Day? (24/192 FLAC)
Jimi Hendrix - Band of Gypsys - Power of Love (16/44 FLAC)
The Rolling Stones - Beggars Banquet - Sympathy for the Devil (24/88 FLAC)
Cypress Hill - Black Sunday - Hits From the Bong (16/44 ALAC)
Richard Galliano & Michel Portal - Blow Up - Leo, estante num instante (16/44 ALAC)
Miles Davis - Kind of Blue - Freddie Freeloader (16/44 ALAC)
Noir Désir - Des Visages des figures - L'Europe (16/44 FLAC)
Flying Lotus - Cosmogramma - Zodiac Sh|t (16/44 ALAC)
John Zorn - Bar Kokhba - Abidan (16/44 FLAC)
Bill Evans - Waltz for Debby - My Foolish Heart (24/192 FLAC)
- Erin Boheme - What Love Is
- Half Moon Run - Dark Eyes
- In Flames - The Jester Race
- Infected Mushroom - Vicious Delicious
- Julia Fischer - Bach Concertos
- Katy Perry - Prism
- Massive Attack - Mezzanine
- Megadeth - Countdown To Extinction [MFSL]
- OSI - Fire Make Thunder
- Phantogram - Eyelid Movies
- Sarah Jarosz - Build Me Up From Bones
- The Civil Wars - The Civil Wars
- The Crystal Method - Tweekend
- The Devin Townsend Project - Deconstruction
- The Prodigy - The Fat of the Land
- Trivium - Shogun
Comparison to: AKG K712
The AD2KX and K712 were quite different from each other and I'd sum up the key differences between them this way: the AD2KX was “sort-of upfront but not too close-up with a full-bodied mid-range” while the K712 was “separated, airy, & spread-out with less bass quantity and more-forward female vocals”. Neither headphone was particularly bassy, and in fact I considered both of them bass-light, substantially less bassy than the HiFiMan HE-400 and Shure SRH1540 that I previously owned. The AD2KX was sort of complementary to the K712, as its mid-range was more filled-out and it had more mid-bass quantity, which made it sound more active & sweeping on music with bass & overdriven guitars. Plus its smaller soundstaging gave it much more of a “throw you in with the band” feel than the K712, which had the opposite effect with a “sitting in front of the band” feel. If there's anything that the two headphones had in common, they both had a distinct non-emphasis on the upper treble, so neither sounded “bright”.
Comparison to: Audio-Technica AD2000 (original)
This linked post says most of how I feel the AD2KX stacks up against the original AD2K: http://www.head-fi.org/t/631998/audio-technica-updates-their-open-headphones-ad-series-ad2000x-ad1000x-ad900x-ad700x-and-ad500x/1290#post_9663275
To further expand on that post, especially with additional listening since then, I'd say the AD2KX's more “balanced” sound is one of its obvious strengths, as that made it more musically versatile. Although it didn’t become my first choice for classical or jazz either (which the original never was), at least it made both of those genres slightly more natural-sounding, but not completely. Like the original AD2K, it didn't sound entirely tonally natural & realistic and had just a trace of Audio-Technica's trademark wonky mid-range colorations. It also lacked the overall clarity & soundstaging that I think is necessary for particularly classical music.
From the perspective of the original AD2K which had a bowed-out C-curve in the mid-range & mid-bass, the AD2KX also had that to a degree but was more flattened out, as it clearly had less mid-bass and mid-range quantity. So it wasn't quite as heavy- & forward-sounding as the original AD2K, though with just a slight subtraction, nothing huge. And overall it still sounded similar enough to the original that I could easily call it a minor sonic variation on the original, just with less x-factor for fast percussion & aggressive metal music.
Comparison to: HiFiMan HE-400
The AD2KX was even more different versus the HE-400 than versus the K712, almost a polar opposite in terms of both imaging & tonal balance, and even more sonically complementary to the HE-400 than the K712. To re-use the K712's summary above, the HE-400 was “separated, airy, distant, spread-out, diffuse, & thin with emphasized bass & treble”, which contrasted with the AD2KX's “sort-of upfront but not too close-up with a full-bodied mid-range”. Essentially I thought of the HE-400 as bright & bassy but wouldn't use those words to describe the AD2KX at all and would just call it “mid-range-oriented” instead.
The best specific example I can think of to describe the opposing sound signatures between the AD2KX and HE-400 is: percussion consistently sounded like it was in the background on the HE-400, and on tracks that used drums of some sort, the drums were never very noticeable. The AD2KX, on the other hand, brought percussion to the foreground and made it an active part of the music—very distinct & upfront, borderline in-your-face, and the only reason it was borderline is because it was actually a slight reduction on the original AD2K in that aspect (which went past borderline for full-on “in-your-face”). So for those who really want to hear drums & other percussive elements in their music, I highly recommend avoiding the HE-400 and getting something more like the AD2KX.
Comparison to: Sennheiser HD598
There weren't really any similarities to the HD598 either, as the AD2KX was just different. As in the case with the K712 and HE-400, the AD2KX simply had more mid-range & mid-bass than the HD598, enough that it was a sonic complement to the HD598 as well. Another key difference was that the AD2KX had very front & center-type imaging while the HD598's imaging was diverged & distant. If there's a recurring theme here, it's that the AD2KX was generally just an upfront, full-bodied headphone in general, which made it unique-sounding in my headphone collection. The HD598 had a definite advantage in certain areas though, as it was substantially clearer-sounding (the AD2KX was hazy-sounding) & flatter in the upper mid-range (no overt emphasis on vocals), and had more treble quantity too (it could be said that the AD2KX lacked treble quantity to an extent). Musically this meant that I found the HD598 played certain genres better than the AD2KX, specifically anything using acoustic guitars (folk, bluegrass) and treble-dominant music (ambient electronica).
Comparison to: Shure SRH1540
The SRH1540 was the only headphone that disrupted the “sonic complement” theme, as the AD2KX ended up being more similar to it than different. They both shared a similarly full-bodied mid-range and had similar tonal balances as well, down to the properly-weighted mid-bass. Even the imaging wasn't that different between them, as they were both “front & center” and had small-scale soundstaging. The only major difference between them was the fundamental difference with closed versus open headphones—the AD2KX was properly open-sounding while the SRH1540 felt like a soundproofed room and didn't carry reverb, sound-wave reflections, & decay very well. And of course there was the bass, which the SRH1540 had a large emphasis on due to being closed. The AD2KX simply didn't have the SRH1540's low-bass kick and felt distinctly weak & rolled-off in comparison. It made me wish that the AD2KX had more bass quantity in general to better play synthesized bass in electronica.
The original AD2K and Dynalo was one of the best headphone & amp synergies that I've ever heard, and I expected that the AD2KX would share that synergy but when I actually paired it up with the Dynalo in the form of the HeadAmp GS-X MK2 (which technically has the newer Dynalo+ modules) and HeadAmp Gilmore Lite, it seemed to be a sonic mismatch. Because of the AD2KX's different sound from the original AD2K, the Dynalo ended up doing nothing sonically for it. The Burson Soloist did nothing of note either. The only amps that seemed to help with anything were the Micromega MyZic and Garage1217 Project Ember, for the same reason: they both organized the soundstaging better and improved on the mid-range qualities by adding more texture & tonal richness. The Project Ember was definitely the strongest amp pairing, at least with 12AU7 and 6DJ8 tubes. For those who'd prefer a more inexpensive amp than the Project Ember, I might suggest starting with Garage1217's Project Starlight, which is almost as tube-rollable as the Project Ember. Not that I've heard the Project Starlight though, just mentioning it as a possibility.
And to try to clear up a common misconception about low-impedance headphones, the AD2KX shouldn't be considered “easy to drive”. It's more accurate to consider it as “easy to make loud”, as it's very sensitive (103 dB/mW). The headphone cable is conveniently terminated to a 3.5mm mini-plug (with a screw-on 1/4” adapter provided in the box), so it can be easily used out of anything with a headphone jack, but those who want to optimize the AD2KX experience as much as possible should look into adding a proper high-current headphone amp (plus a quality source component, if applicable). Look for power output specs that list higher power into low-impedance loads.
The AD2KX's looser clamp compared to the original was also an issue, as I was never able to get a secure fit because of it and the headphones always felt like they were about to fall off. For that reason I'd advise that those with small heads should probably avoid the AD2KX. The fit would probably be much better for those who have larger heads.
Like the original AD2K, the new AD2KX was similarly unique and offered a sound unlike any other set of headphones that I've heard, so unique in fact that the only comparable headphone I've heard is the original. It was unique because most >$300 headphones I've come across simply don't have a significant focus on the mid-range (most expensive headphones tend to go for brighter or clearer sonic signatures with expanded soundstages), and of the headphones that I've heard that do focus on the mid-range, most aren't very upfront-sounding too, and none have its mean percussive streak. Hence, in the same way that the original AD2K was and still is one of the most sonically unique headphones to ever exist, the AD2KX takes on a similar position. There's no other headphone that's remotely like it. It may not have the sheer enjoyment x-factor of the original for certain types of music, but on its own it still makes for a very enjoyable listen on the same genres while also being more versatile with other genres as well.
I do think that the average exported price (it can vary based on the current exchange rate) is a little bit steep for the AD2KX, although it is now in the range of the original's when that first came out. I'd recommend trying to buy it used instead of new, or at least as close to $500 as possible or lower, especially for those who might have never heard the original and thus won't have much of an idea of what to expect from it sonically.
AD2KX loaner program (2013): http://www.head-fi.org/t/688438/loaner-program-audio-technica-ad2000x AD2K 5-year re-review: http://www.head-fi.org/t/574882/5-year-re-review-audio-technica-ath-ad2000