Pros: Excellent tonal balance. Great performance in all frequency regions. Superb construction, materials, and comfort level.
Cons: Poor isolation.
An elusive model that was never sold in the United States - I picked these up in Taiwan during a trip to Taiwan in 2008. Production had already ceased at the time of purchase, with the new ATH-EMx00 series replacing the old line.
Comparison to ATH-EM700
Even though the ATH-EM9d was being replaced by the ATH-EM700, the older model remained more expensive than the new one (the old EM9d was $190, while the EM700 was $150 brand new). I asked the shop owner (who is a long-time audiophile himself, and participated actively on several headphone forums) what he thought, and he said quite simply: "The new ones are junk. AT cut corners in materials all over the place."
One thing that was easily noticeable was the difference in the plastic used on the cords. The EM9d has the same kind of high-quality tangle-free plastic used on expensive headphone, while the kind used on the EM700 feels like the ones used on budget earbuds. There's also a lot more metal components on the drive housings of the EM9d. I would say the older model does indeed seem much higher quality in both the materials and construction.
ATH-EM700 (left) & ATH-EM9d (right)
I did some brief listening of both, and the conclusion was easily arrived at... The EM9d trashed the EM700. The EM9d has a lot more bass (pretty important for an unsealed on-ear model), the mid-range is more neutral (which is very forward and congested-sounding on the EM700), and the treble has a lot more clarity and detail. The EM700 just sounded like a muddy mess with no bass or treble.
Materials & Craftsmanship
The packaging of the EM9d is the same as the rest of the Audio-Technica's clip-on line - very understated but classy. They come with a carrying pouch and an extension cord.
As you can clearly see, the EM9d are very sharp-looking headphones. Construction quality is on-par with the EW9. It uses the same grade of cord and the same earclips (which were redesigned on the EM700, and were not as comfortable). Comfort level is nothing short of excellent - I've worn these to sleep many times; you simply forget they are even there.
The earclip design of the EM9d. Note the flexible rubber cushion and the height adjustment.
Audio-Technica is the only headphone manufacturer that makes high-end clip-on type headphones, so I read up on both the ATH-EW9 and the ATH-EM9d extensively before I went down to the shop. The EW9 is popularly referred to as the "Queen of Female Vocals" in the Taiwanese audiophile circles, while the EM9d reportedly has a very neutral tonality.
I now own both the EW9 and the EM9d, and can confirm that the reviews I read were accurate. The EM9d is indeed very neutral; tonal balance is nothing short of excellent. The EW9, while indeed great for vocals with its thick, sweet mid-range, is only suitable for some types of music and lends too much coloration to the music for my taste.
It's worth mentioning that the drivers on the EM9d are titanium-plated. I had worried this would make them sound sharp and metallic (I owned an old pair of full-sized Koss that had titanium plated drivers, and they were exactly that). Fortunately, this was not that case at all.
Treble: The treble has very good clarity, with just enough roll-off for comfortable long listening sessions.
Mid-Range: The mid-range is a bit warm, but still within neutral territory. Clarity is good instruments don't sound congested.
Bass: For clip-ons, the EM9d actually packs quite a punch. The bass has good control and extension, and the quantity is decent (as long as you are listening in fairly quiet environments)
Sound Stage: The sound stage is excellent on the EM9d, being a semi-open design with good treble clarity. Imaging is likewise excellent.
If for any reason you want to invest in a good pair of clip-ons, you should try hard to find yourself a pair of ATH-EM9d. These are my absolute favorite in the category.