RE272 is a very good IEM, but I found it lacking musicality, definition and resolution, especially in the treble. The lower treble is too recessed to my liking - definitely more recessed than neutral response IMO. It was also hard for me to a get a proper fit with RE272 due to their very shallow insertion. The treble often sounded peaky to me due to the improper fit. Also, the soundstage was somewhat strange with great width, but not much depth. to be fair, the ER4 doesn't have much depth either, but it makes up for this with its tremendous definition and micro detail. I found RE272 to be lacking in definition and low level resolution compared to the ER4. In particular, RE272 just didn't provide me with vivid outlines of individual instruments in the soundstage that ER4 provides to my ears. Simply, I found RE272 to be clear and fairly detailed and natural, but somewhat dull and blurry sounding. In regards to dynamics, yes RE272 does better, but not by much IMO - ER4 has adequate dynamics to my ears. RE272's only real advantage over the ER4 IMO is its bass depth and impact.
BTW, I found RE400 to be superior to any of Hifiman's previous IEMs, including RE272. RE400 has more micro detail, significantly more soundstage depth, a more realistic bass with better sense of impact, an even better sense of dynamics, a more natural frequency response and an overall fuller, richer, more realistic and involving sound to these ears. I also preferred RE262 to RE272, because the former sounds at least 95% identical to the latter and yet was priced far lower. I also thought RE262 was a little richer and more natural sounding than RE272 and its higher impedance made it more agreeable with a wider variety of sources.
Also, here are some graphs to back up my experience:
I suppose the ER4 measurements actually disprove that ER4 is better than RE272 overall. RE272 (as well as the other two Hifimans) have noticeably less distortion and better bass extension than ER4, but ER4 seems to have the more balanced frequency response and significantly faster transients (compare the 300Hz square wave responses), especially versus RE262 and 272. Now, you can also see from the measurements that RE400 seems to be a technically superior IEM overall compared to RE262 and 272 - it has even lower distortion, a somewhat cleaner impulse response, a significantly nicer looking 300Hz square wave response (but still on the slow side, compared to ER4's 300Hz square wave response) and a seemingly more balanced frequency response too (no treble peaks, slightly more treble volume relative to bass and mids, although still a bit darker than neutral). It does appear to me that RE400 is also superior overall to the ER4, based on the graphs, but I think the graphs don't tell the whole story, especially because we are comparing different types of drivers here. The graphs can't capture ER4 armature driver's superior transients, definition and resolution IMO (ok, the 300Hz square wave response does to some extent and other measurements, like waterfall plots might too). I do feel that ER4, especially the S is superior to RE400 overall, but RE400 does have its advantages like a more believable soundstage and bass, and a fuller, richer sound, while maintaining very respectable transients resolution and definition, unlike the older Hifiman IEMs. That's why I keep both. I would not keep RE272 or 262 along with ER4 though, because I think the older Hifimans do not offer enough advantages over the Etys in sound.
Edited by Pianist - 5/1/14 at 9:32pm