Whilst I am fairly entrenched in on-ear and over-ear headphones, I am not so passionate about IEMs. I don't have a dozen other monitors lying around, just for the test, and I won't be able to make adequate comparisons with similarly priced IEMs. With that disclaimer out of the way, I have to say, the S1 seems like a pretty decent offer.
After the aforementioned burn-in, the sound took its final form. The highs are slightly rolled off, whilst the lows are really punchy. Not emphasised, but instead carrying a very pleasant and satisfying kick behind them. The interesting bit is that S1 doesn't need an amp to have a decent output, it sounds great even on your average smartphone.
The lows are the most noticeable. Not because the earphones emphasise 'em too much, but because they carry a really potent punch. However, they're not all that tight, and at times they don't recover quickly enough. Yes, the bass carries some impressive presence, and it never becomes hollow or less articulate, aided by the fact that there's a great deal of instrumental separation.
One thing worth noting is that the upper-mid sequence is somewhat harsh. If you're into metal, you'll have to deal with at least a bit of sibilance before the IEMs are burned in, and become smoother. That being said, the mids overall, whilst they're not shadowed, they do lend a mellow quality to most vocals. In a way it doesn't have the right presence you'd expect from them. It isn't something noticeable on simple, straightforward tracks, where there's not much going on, but listen to a crowded song like Nico Vega's Beast or DSO's Guerilla Laments, you will notice it.
The highs are also slightly harsh at the beggining, but they do become quite pleasant after a while. After let's say, 15 hours, they feel slightly rolled off, with a great deal of clarity still present. They carry plenty of sparkle and detail not to become dark, but there's still room for a bit more definition and detail.
The S1 carries a wide soundstage, but not a very deep one. However, the stereo imaging is great, and the panning correctly portrayed. Whilst I would like to see a bit more depth and height, i have to say, I'm not necessarily dissapointed.