Pros: fast and extended bass, mid-range, large sound-stage, not fatiguing
Cons: Short Y split on cable, big size, french manuals, recessed treble
I'm a bit late to the party, the last review on here was posted a year ago, but here we go.
Comfort/Design: I could never get the Foam tips to form a good seal with my ear canals. I ended up using Shure olives. The IEMS are a bit big and I am not liking the straight uncurved edges rubbing against my ear. They are a bit uncomfortable but nothing too bad. The biggest problem is the cable is very short after the Y split. The plastic does feel a bit fragile and slightly cheap. The braided cable on the other hand is very high quality. It is very similar to cables used on other high end Westone IEMS. Little or no microphonics can be heard while walking & the cable feels strong and sturdy. Noise cancellation is not as good as the Etymotic Er4p, however these provide excellent isolation and require less insertion depth than the ER4P. I can not hear cars passing me when walking & people talking (Unless they yell).
Bass: Tight, fast, and controlled. This is one of my most favorite aspects of this IEM, it is quite dynamic. It can go from being precise and controlled when listening to orchestra and then go low and have rumble for Hip-Hop and Rap. Their are better options if you're looking for bass quantity (FX700/IE80) but I think the SM3 wins with its perfect balance of quantity and control. Compared to the HD 598 these have more sub-bass and slightly better mid bass. Compared to the Etymotic Research ER4P they have a-lot more sub-bass and a bit more mid-bass.
Mids: Very forward, some what in-your-face like. The midrange is even more forward compared to the HD 598. Vocals are beautiful on these. Tiny details such as the lightest breathing can be heard. I feel that the mids were a bit too forward and maybe somewhat exaggerated.
Highs: The treble is definitely a bit laid back. Not so much so that I would say the SM3 is dark, but not so much that I would say it is bright. They do have high treble extension but it fails to show it. The midrange and bass seem to be the star of the show. I always felt these needed a bit of a boost with an equalizer, it has a bit of sparkle but high hats and other items lacked authority. Since the treble is laid back I heard little sibilance at all.
Soundstage: Slighty above average for an IEM. They can handle orchestra and classical just fine but you can tell how much smaller these sound when compared to open full size headphones. While listening to Hip-Hop, Rock, and Electronic the SM3 has a bit of a surround like effect. In rock and metal it sounds as if I was on stage with the band, instead of towards the middle row of the audience which is what the AKG Q701/HD598 do.
Synergy: These are not very picky about source but can exhibit some hissing when presented with some amps. The SM3 can be driven from a portable source and not sacrifice sound quality. I hooked these up to my desktop amp and noticed little differences, but nothing worth mentioning. Out of my iPod or phone these get very loud and sound excellent.
Overall very impressed with this IEM. Build quality can use some work but the sound these produce are fantastic. I think these are a good deal if you can get them for $250-300, I just can't fathom how these used to be over $400.