[Also being posted in the 'SE535 - High tier' thread and SM3 appreciation thread]
I put the SM3 through music break-in for almost 48 hours (jumping in a couple times to test progress), and if it needs any more, the changes would be very minimal. The sound actually changed a lot within the first 24 hours, but then not so much afterward. I did some more testing this morning to music and test tones. The biggest area of change occurred in the lower highs, they became much more apparent and less recessed. The overwhelming bass calmed down quite a bit and became very nice... though still just a bit over-emphasized for my taste.
For me, the negative issue with the SM3 is the recessed upper-mids. There is a dip from about 1khz to about 8khz, with the recess bottoming out at about 5khz. This causes a slightly 'veiled' or dark sound to these cans. Somewhat muted and muffled in overall tone, with sparkling extended highs (well past 13khz) and mighty bass (strong through 20hz !). There also appears to be a hump at about 300hz. It's not as prominent as the recession at 5khz, but adds to the prominence of the upper bass. It's an odd mix.
In comparison to the SE535, the SM3 fails where the 535 excels and vice-versa. The SE535 is clear, clean and open. The SM3 is closed and a bit claustrophobic. The SM3 has recessed upper-mids, where the SE535 has them in spades: accentuated and articulate. The SE535 has a lack of bass in the way the DT880/600 has: It's there, but not prominent. It's extended, but not pronounced. The SM3 kicks the bass in your face. The SE535 lacks the warmth of the lowest mids, upper bass and gives it a somewhat thin feel.
Overall, the SM3 is warm, sonorous, somewhat dull (tonally) but fun. If you like your bass, this is the place to find it. They remind me of the M50 somewhat, but with slightly more recessed upper-mids.
The SE535 is clean, open, and spacious. Instruments are articulated with amazing exactness and clarity. There is no murk here, but there also is little sonority.
These are both great IEM's. Taste in music styles has nothing to do with which one of these you might purchase, but how you like to hear that music will be everything. For example, some of the music I listened to (Classical, bluegrass, rock, jazz, etc.) sounded great with the SM3. Downright gorgeous. But some of all these types sounded like crap. The exact same thing is true of the SE535, but almost diametrically opposite.
So if you like the overall sound of all your music to have a certain warmth, or if you are purchasing the SM3 because you want your Classical music to be relaxing, rich and mellow... these are your IEM's. If you like your Classical (rock, jazz, etc) to have a lively sparkle with forward mids, the SE535 is your man. For rock and other high energy music, the SM3's will give you a thumping power that the SE535's just can't. That added to the sparkle on top can add to the 'fun' factor of these. In some ways they remind me of the D5000, but with more recessed mids.
More time will yield more listening. I had thought I'd be putting the SM3 on the FS thread today, but between the break-in and 'brain burn-in' mentioned above (not really psychoacoustics because it's not the sound that is changing after break-in, but my appreciation for it), I may have developed a liking and appreciation for their sound. I want to hold on to these at least until my DBA-02's come in so I can compare them directly.
Cheers
shane
