I've got the original Prometheus MKI with the Beyma slot tweeters. I love them... the open, clean, uncongested sound makes it difficult for me to enjoy listening to any speaker that involves a ported box. Between 100Hz & 10kHz there's no crossover but you have woofers below that to give you real bass and tweeters so the highs aren't rolled off so you get a lot of the advantages of a single-driver speaker without the compromises.
I haven't measured the frequency response and it wouldn't make too much sense to do so now because they're in a tiny room (9'x11' or so) and I'm sure the bass would look awful. I've been meaning to get around to it though, and I probably will once I borrow a calibration disc from a friend of mine. I've also just ordered the jupiter caps and this spring I'll upgrade to the "airforce" tweeters, which are painfully expensive, and at that point my speakers will be the same as the MKII airforce version. After that, the only thing I'd like to change is the bass and I'll probably try to work on some kind of OB bass augmentation once I have a bigger room to put them in.
Gary
