Between 1977 and 1992 I owned several models of Acoustat's, starting with the Acoustat X, moving to the 3, then the 4 (both w/ modified Servo-Charge amps), then 2+2's modified to work with Servo-Charge amps. The 2+2's were definitely the best fit in moderate sized (less than 3500 cu ft) rooms. I briefly tried 3+3, but those would need a much larger room.