I've had the SM64 for a while now, might as well leave some impressions.
I've never heard a headphone change so much in the first two hours out of the box. I literally felt it become smoother, the bass rising up after a rather subdued start, the highs mellowing a bit, the mids coming forward. It was a strange experience, hearing it change so much.
The detail on the SM64 is INSANE. I've lost count of how many times a different headphone let me hear details I'd never heard before, but I'd never heard this with an IEM. It's... insane, really. Fells like I can hear everything that's on the record. Every single thing.
Separation is good, but luckily (for me), not as much as with some separation monster like the Senn HD650. To me, too much separation between the instruments is not a good thing for enthusiast listening. Cans like the HD650 are meant for monitoring, and I find that very distracting. I want my music to have some cohesion. Live music sounds nothing like the HD650. The SM64 gives space to the various parts of the recording, but doesn't isolate each one from the others.
Soundstage isn't very wide. An IEM like the Sennheiser IE8 easily trounces the SM64 here.
The overall sound signature is quite balanced, but the vocals are very forward at all volumes. I feel the SM64 is very mid-centric, even if I understand that its frequency response curve suggests anything but. Vocals are lush, natural, not at all honky or shouty.
Bass is present, quite deep, with a bit of rumble. It's not very powerful, nor very authoritative. "Neutral" is a good word to describe it. Sub-bass is a bit more present than mid-bass.
Treble is detailed and controlled. Not a hint of graininess or sibilance. It lacks the slam and the bite of more aggressive cans.
One thing that strikes me is that the SM64 can be very engaging at moderate-to-high volumes, with a lot of PRAT and a very lively, feet-tapping sound. But at lower volumes, it's a very flat headphone, with an emphasis on vocals.
The SM64 requires quite some power. I do use it with my iPod, but I need to push the DAP to about 70% of max volume to bring out the true character of the SM64.
The fit is close to excellent for me. The cable is fantastic, and while I usually don't care for memory cables, the SM64's does help me get and maintain a good fit. In-ear fit is almost perfect with the stock biflanges.
I guess that, if you're looking for an end-all and be-all IEM in this price range, the SM64 may just be it, provided you like neutrality and use an amp all the time. Me, I definitely like it, but I'm still looking for alternatives. I like a livelier sound.
