The key difference is the ( these days) unusual 3 way- tweeter plus "super" tweeter line up on the SP1, irrespective of which variant, Sp1/1, SP1/2 etc. When I had my first pair and my ears were more pristine, I was well aware of their "feathered" treble quality. By that I mean, the HF was all there in its natural form- not faked by the overemphasis built into present designs, usually with cheap tweeters.So if you've got the hearing apparatus, the SP1 is a finer speaker than the not inconsiderable SP2. Take your pick.