I've got about 30 hours in these, but still waiting to listen some more before giving my complete opinion. Out of the box I really disliked them, it was if the mids were sitting in a vacuum, vocals were not nice. It also made them sound WAY brighter than they are now. 10-15 hours tho they opened up and far smoother. I'd still like some more air in the mids. I should add, my listening up to then was the FIIO FD5 which is a quite a hard hitting Beryllium single DD and the HifiMan re800s (which had its own custom DD), both pretty smooth, so I knew to give myself some brain burn in with the S12.
Early positives - Bass is nice, it has that "elastic, bouncy" quality I like. Depth and hit are very good. Mids are smooth, with decent body and lovely resolution. Treble smooth after burn in, bright but not sharp or overly so. Soundstage has a nice open feel, with very good height, good depth and note weight is nice. All round it has decent scale. Percussion is extremely well done, a real highlight.
Detail is just okay, I expected better at the price point. It really depends on genre and how busy the track is. With less going on, instruments have a very organic and realistic quality... You can hear good micro details in each instrument. BUT with lots happening and on busy tracks, that individual detail gets lost. I'm not saying it's congested or muddy, but it's harder to pick instruments out and layering isn't spectacular.
I was surprised that classical or big orchestra pieces - although musical - certain instruments get lost in the mix. Again, this could be down to a lack of air in the mids at times? The same happens with some of my favourite rock tracks. It's far from bad though. Like I said, with less going on, tracks can sound beautiful.
Source - on my FIIO M6, they sound good, but can find thinner and more bright. On my FIIO K5 Pro, scale is much more epic and I enjoy them far more. Everything is just... Bigger.
Negatives - there is a HORRIBLE amount of driver flex in the left shell. I've never heard an earphone with such noticeable and off putting flex. Obviously when music is playing it's not an issue, but it's always there, regardless of position when wearing them.
The cable took a bit of getting used too, but it's fine now. I wore outside with sunglasses, and it's pretty uncomfortable, so those wearing glasses MIGHT take this into consideration.
This is just a personal opinion and not a dig at anyone. I've read some people who own this (or have reviewed it) tell potential buyers looking for information or feedback that they "need" to have heard the planar sound, instead of just answering their questions, especially when asked for comparisons. I think this is ridiculous and a little over exaggeration. To me it's just hyping a planar at a decent price, but end of the day, it's not some radically different sound. There's no reason you can't compare to say a single DD or BA. Yeah, drivers have a certain flavour, but the S12 sounds similar to many other non-planar IEMs I have, the same way my Hifiman He400se planar headphones sound similar to some Dynamic headphones at the same price. If someone asked me to compare it to a single BA they had, I'm not gonna say, "that is impossible, go demo a planar" lol.
It may be a strange one to compare it too, and I admit it's been a while since I've heard it so might be wrong, but the S12 reminds me of the BQEYZ Spring 1. Same open soundstage, same not weight, similar mids and treble.
Anyway, I do enjoy the S12 and look forward to some more listening.