I got these as replacement for the Musical Fidelity EB-50 which I reluctantly returned thanks to hi fi headphones stellar customer care due to fit issues. I have had the T-15's for a few days now and I think that I have listened enough to form an opinion. The form factor of these could not be more different from the barrelled MF's. the T-15's are tiny. It is unbelievable that such powerful sound comes out of such small housings. It took me a while to find tips that worked. None of the supplied tips worked but happily I had all the tips that came with the IE8's and they fit the '15's fine. I found that the Sennheiser double flange worked well for me. A relief as a 100% seal is crucial to getting the best out of these, as it was with the MF's. the IE 8's I can just throw into my ears and they are fine. In fact a less than perfect seal helps them. Anyway! Once I got a good seal the T-15's showed their capabilities. The sound is amazing. Frustratingly just short of phenomenal. I am afraid I do not believe the frequency response graph on the back of the box. To me they do not go as low as first appears. The mid bass is boosted slightly. IMHO. To give body to the sound. It is well judged and does not interfere with other frequencies (unlike the mid bass of the IE 8's). There is something that bothers me about the top end too. Particularly when the music gets hectic cymbal sounds can be a bit small and "tissy". This may well be a tip issue. I intend to get the custom tips for these and that should be interesting. The midrange on these is lovely. Vocals are almost as good as the EB-50's and that is high praise as I thought the vocals on those were superb. The fact that I am prepared to shell out another £90 to bring out the best in these shows that despite my caveats I think that they are great 'phones. They don't quite have the natural sound of the EB-50's. if the form factor of those suits your ears you are very lucky. They sounded to me like IEM's that I would be happy to pay £300 for. The ACS I am very happy for the £150 I paid. It remains to be seen if the extra £90 will be justified. Stand by for another long winded waffle once I get through the palaver of ear moulds!