Pros: Styling and comfort, tangle-free cord, detailed treble with very little sibilance, decent amount of sub-bass, great isolation (with other eartips)
Cons: Microphonic and springy cable, congested soundstage, recessed mids and mid-bass
The CK323M is a Japan-only budget IEM from Audio-Technica. There is also a version with an in-line mic and controls, the CK323i. When my CKM500 broke during a flight to a transfer stop to Japan, I bought this IEM at the airport store for around 20$ USD. I knew it wouldn't sound as good as the CKM500 but hoped it would at least have some good sound coming from Audio-Technica.
Design and Comfort
These are some of the best-looking headphones by Audio-Technica. They come in many different colours though I like the red one. The cord is semi-flat and not prone to tangles (CKM500's cord tangles quite a bit in my pocket), but at the same time it's springy and makes a lot of noise while moving around unless a clip is used. There is a cinch, but only when it's moved just below your chin will it reduce some of the microphonics.
Out of the box, the sound signature was a sharp V-shape with emphasis on the highs. They were a bit bright but otherwise sounded detailed, and not much sibilance at all. I actually prefer this type of sound to that of the CKM500 which has a rather thick-sounding treble. The deep low end is also noticeable but unfortunately the bass lacks definition and the mids are deeply recessed and lack warmth. Burning them in helped tone down the treble and boost the mids a bit but the overall sound quality still sounds dry, there is also a considerable amount of sub-bass now. However, the bass is still muddy and bloated, lacking the definition of the CKM500 - the midbass still sounds recessed as with the lower mids. The soundstage is rather small on these cans (similar to the CKM500 but a bit more congested) and instrument separation is passable. They are forgiving of harsh highs and not as good for vocals or bassy music. A bit of EQ can add a bit of the warmth to the sound though. Dare I say, these are one of the few headphones that I prefer with Beats Audio EQ on my HTC smartphone, as it does boost the mid-bass and sub-bass considerably.
FILTER MOD: Taking out the filters makes them overly bright, though this can be relieved with some foam (eg from cheapo earpads). As a result there is a bit more shimmer in the highs and more sub-bass, approaching the signature of the ATH-M50x but the mid-bass is still very muddy.
The CK323M is a half-in-ear design like other CKM headphones, which provides decent isolation but is not the best for very noisy environments. It uses the same eartips as the CKM500, so the isolation with the stock tips is about the same, though it can fit in your ear just a tad deeper due to the driver design (the CKM500 has a disk-shape preventing the earpiece from going in as much). The CKM500 has air vents on the outside of the housing, while the CK323M has air vents in the nozzle. Because this region is covered by the eartip, they don't really help with pressure or the soundstage.
Phillips SHE3590's tips significantly improve the isolation, so much the cans "suck" into your ears - the best isolation out of all my IEMs so far.
I do not recommend these for sports because they have quite a bit of cable noise, although it does come with a clip/cord manager. They are also extremely awkward to wear over the ear. (I actually lost these but I didn't find them useful, they do reduce cable noise but due to the springy cord, it's hard to actually wrap the cord around it)
You're mainly buying these for the looks and I think they are the most stylish IEM made by Audio-Technica so far. Unfortunately, the sound quality is the big deal-breaker here. They aren't the worst sounding at this price but there are better options. For 20$ I consider these somewhat disappointing but perhaps my expectations were too high coming from the CKM500. I do think the Phillips SHE3580 is a better option at this price.