Why are the Infinity IRS, Reference 1b, Beta ect speakers passive on the mids and highs?

I think it's a practical matter. How many amplifiers do you want to have in your system? While it makes practical sense to separate the bass frequencies from the rest of the speaker system - especially when the manufacturer has already committed to using separate bass towers, as in the RS-1 and various IRS systems - there's less advantage to be gained by separating the mid from the high frequencies.

Separating the bass and using an active x-over also allows use of a servo system for those frequencies, which Infinity did with great success. I don't think it's feasible to use a servo on higher frequencies, however.

Why are the Infinity IRS, Reference 1b, Beta ect speakers passive on the mids and highs?

I think they found as I did. (with both ways bi-amped)
I found good passive 18db xovers on the upper bass/ mids and highs of my Martin Logan ESL Monoliths III sounds more natural than any active crossover I tried, they all had a sterility to sound.
But on the 12" bass 150hz down I use and my own 24db active.

Cheers George

My favorite speakers of all time....I remember them fondly.

I don't think adding another amp would be too much in cost or space but it might be that the sound is actually better passive. Has anyone compared both ways all other factors being equal?
Marc