These are not noise-canceling headphones, but they do a tremendous job of blocking out background sound. This fact became immediately obvious when I tried my old iPod earbuds again after I'd been using the E3cs for a while. At the gym, especially, I couldn't believe the difference. My iPod earbuds basically let in every outside noise, sometimes to the point that even while I had my own music playing I'd hear the music being piped into the gym. Sure, I could turn up the volume to drown out the ambient sound, but I don't always like to blast music into my head. I didn't realize that this background noise was such a problem, but the E3cs did such a good job at blocking things out that they spoiled me. They don't block out absolutely everything, but they do reduce outside noise to the point where I really don't notice it when my music is playing. That makes it a lot easier to appreciate what I'm hearing.
The E3cs produce some of the crispest, clearest music I've ever heard. Every time I take off the earphones, I'm amazed that such good sound comes out of such small devices. I've actually heard layers that I had never heard before, even on songs I've listened to for years on CDs. Sometimes it's an extra instrument track, other times a background vocal track that's new to me on hearing the songs through the E3cs. High range is bright and clear, never cutting out or becoming distorted at higher volume. Electric guitars sound almost live, and the voices of sopranos (the singers, not the New Jersey thugs) really stand out.
Midrange is clean and not overpowering. Rock music, which in my opinion is often muddled by too much midrange, comes through loud and clear, with no distractions to the high end of the singers and guitarists or the low end of the bass and drums. Classical and jazz music, which use instruments that naturally fall into the midrange, sound equally live and full. The E3cs accurately reproduced the range of whatever type of music I played through them.
If there's a weakness with E3c sound reproduction, it's in the low end. Bass guitars and drums don't always come through the way I'd like. The Shure marketing copy mentions that these earphones were designed to deliver "enhanced bass." However, from my own experience I'd say that the E3c is "bass neutral." That is, the earphones reproduce the bass as it was encoded in the original recording and don't artificially boost it at all. As a result, some songs sound really good, and other songs are noticeably lacking at the low end. I can't easily hear some jazz bass solos, and some drum-heavy rock songs lose their heavy pounding pulse.
Why do some songs sound good and others not so much? I'd have to guess it all goes back to the original recordings. If they were mastered well (that is, to include high highs and low lows), they sound fabulous when heard through E3cs. If the engineers didn't do such a good job mixing the album, however, I can tell. I could hear the difference in mixing quality simply by putting my iPod on shuffle and listening to the differences in songs from different albums. This is especially true on older albums that were re-released on CDs and not remastered for digital playback.
Shure could have taken the route of many other speaker manufacturers and artificially boosted the bass response in their earphones. In many songs, that would have resulted in more powerful low-end sounds. But doing so would have also added a "muddy" sound to many recordings. Yes, you'd hear the bass drum, but there would be no question whether it was live or a recording. Personally, I think Shure made the right decision here. I just wish more audio engineers working in the recording industry were better at mixing albums.
One more note about fit. When the E3cs were not inserted correctly, I lost even more low end. Therefore, let me reiterate the importance of proper fit to enjoy the capabilities of these earphones. As I mentioned earlier, I've detected more nuances in music, and despite the weak bass from some albums, I quite simply have never found a better-sounding set of earphones/earbuds. Come to think of it, these units rival most of the full-sized headphones I've tried, too.