Pros: Detailed but shy treble. Warm, intimate mid-range. Tight, controlled bass.
Cons: Mid-range sometimes over-emphasized. Peak at upper-mid/lower-treble an issue in some recordings.
I purchased these for my wife two years ago. She's always liked the warm sound of my ATH-A9X, so for portable use I got her the ATH-EW9, which reportedly has a very warm sound signature These were her first pair of "hi-fi" headphones.
Construction Quality & Presentation
The packaging is understated, elegant, and classy. It comes with an extension cable and a black carrying pouch.
The headphones themselves are quite simply gorgeous. Audio-Technica's line of high-end clip-ons have always been very unique-looking and well-constructed, and the EW9 is no exception. The wooden housing is rich and beautifully textured, and the 35mm plug is very elegantly shaped and seems to be of very high-quality plastic. The letters "ATH-EW9 JAPAN" is printed in soft gold letters on the plug.
The included accessories, unfortunately, aren't as gorgeous as the headphones themselves, which was a little bit of a let-down. The carrying pouch is the same one that used by lower-end models (EM7, EM9d, EM700, etc.), and the netting used on the inside is a bit on the rough side - I worry a bit about it scratching the delicate wood housing.
The included extension cable is also the same one used by lower-end models - I wouldn't complain about it if the EW9 uses the same kind of 35mm connector as on the other units, but they don't. As the result, the contrast in aesthetics is rather stark when the EW9 is plugged into the extension cable.
I understand it wouldn't be economically feasible for Audio-Technica to manufacture special accessories just for one model of headphones, but the EW9 is so beautifully designed and made, it's hard not to nitpick.
All of the Audio-Technica clip-on headphones are extremely comfortable in my opinion. They use a very unique type of earclip that's self-adjusting and doesn't put pressure on the ears. The earpads are also very soft and plush, very comfortable. I often forget that I am wearing them.
I have a bit of a mixed feelings in this department concerning the EW9, as much a fan of Audio-Technica's warm presentation as I am.
The EW9 seems to put a little bit too much emphasis on the mid-range, so much so that the treble feels recessed (even though the drivers used in the EW9 are very capable and the treble does not at all lack details, they feel drowned out by the mid-range). There also seems to be a peak in the upper-mid-range/lower-treble that causes certain songs to sound sharp and unpleasant (not sibilance... this peak makes certain female locals and instrument sound too loud and drown out everything else). Fortunately, this is not an issue with most genres of music - but on recordings that are already warm, this can be an issue.
Treble: Treble is a bit shy, but with good clarity and extension. Sibilance is pretty much non-existent (big plus for me).
Mid-Range: The mid-range is generally pleasant, (very) warm, and intimate on the EW9. Female vocals are particularly intoxicating when listened to on these headphones, and classical instruments sound great as well. That said, the upper-mid/lower-treble peak I mentioned makes the overall presentation a bit uneven, and certain recordings simply don't sound that good on the EW9, which is a shame because these headphones are otherwise very excellent and capable.
Bass: I am actually surprised by how tight and extended the bass is, and the quantity is fairly ample as well (given that these headphones sit over your ears with a thick padding and no seals whatsoever). They are not bass-heavy (I don't think clip-ons can be, anyhow), but the bass is present and beautifully delivered. Drums, pianos, cellos are rendered gorgeously. If you want to shake your head to bass-heavy genres like rap or techno, please look elsewhere.
Sound Stage: A bit narrower than the EM9d (the only other AT clip-ons I own, so easy comparison) - but still decently wide. Sound positioning is good.
Instrument Separation: Separation is good, but not as good as the EM9d in my opinion. I think partially this is due to the details in the trebles being drowned out by the mids in certain recordings.
Isolation: Ah.... non-existent. Just pretend you aren't wearing any headphones. Not too great for noisy bus rides or public places, but they will be okay for quiet car trips or in quieter settings like cafes or bookstores.
The ATH-EW9 is a very beautiful, very well-constructed pair of headphones. They are not all-arounders; they will perform great for certain genres while coming up short in others. If you listen to slower, more relaxed music with lots of classical instruments or human vocals, then these are great. If you want a more balanced presentation, the ATH-EM9d is the way to go (its successor, the EM700, is inferior to the EM9d in my opinion).