However, after 20 hours, or so listening, the IE8s had settled down (loud speakers and other audio devices often need to burn/break-in before they sound their best) to a point where the bass was still huge and powerful but much tighter and responsive. Listening back to back with a variety of alternative earphones and the difference in bass level is still very pronounced but in isolation the IE8s sound perfectly natural.
That said, there's definitely a secret to getting the best out of them - they need to be cranked up reasonably loud to enable the clarity at the top end to break free of that colossal bass. In this respect they are almost the direct opposite to the Shure SE530s, which have all the clarity in the world even at very low volumes but need to be cranked up to get a decent bass kick out of them.
However, loud you drive these, though, there's no denying they lack that last bit of top end sparkle that the various multi-driver headphones we've mentioned have. In some respects this isn't a bad thing as I actually find my very sensitive ears can get tired of the Shure SE530's trebly sound (I was astonished to learn that Riyad and Hugo listen to their SE530s and SE420s at well over half volume on their iPhones whereas I can't tolerate higher than a quarter with my SE530s) whereas I can listen to these Sennheisers all day and not feel a thing.
Another aspect of the Sennheiser's unique timbre is they sound more like over-ear headphones than most in-ear types. Couple this with the single coil-driver's seemingly endless frequency response and you have a sound that makes you feel more like you're actually in the room with the musicians than any other earphone I've used before. Not that you hear more detail - you certainly don't - but you get more of a sense of distance and placement from the music and the bass goes some way to emulating the feeling that you get at concerts where the bass travels not through your ears but up through your body, and that's something that I've simply not experienced with other in-ear headphones.
In essence, then, these have to be one of the most enjoyable everyday headphones I've used for casual listening and most fans of rock and pop music will lap them up. However, if you're more into your jazz, acoustic, and classical music and want to here every nuance then you're still better off with our long-time earphone of choice, the Shure SE530s.
Sennheiser has taken a slightly different approach to creating its high-end in-ear earphones, the IE8s, and has come up with something that sounds quite astonishing. Their huge bass response will certainly please rock and pop music fans and even those that prefer the finer things in life will find these represent a good listen. However a few issues with the package as a whole make it hard to recommend these outright.