I've just bought the SE535LTDs and after a day of rocking out have noticed that when connected to my iPhone the lowest volume setting is louder than is comfortable when I want to listen quietly. This is quite annoying and so now I've initiated a return with Amazon. I think this is because they are "super low impedance" but what's odd is I don't have this problem with the SE215s, and according to the specs those are lower impedance.. from shure.co.uk: SE215 - 17Ω SE315 - 27Ω SE425 - 22Ω SE535 - 36Ω Obviously I'm missing something here.. I'm now thinking that I might try the 425s as they have the closest impedance rating to the 215s which I know are good with my iPhone. Those numbers are confusing me though..