Dahlquist DQ10's, 2 Dahlquist Subwoofers & the active crossover unit. Used 2 Crown 300A for subwoofers, Threshold 4000a, & Threshold Preamp, can't remember the flavor. Fulton cables. All purchased from Hoffman's House of Stereo, Cleveland, Ohio, mid 70s.
If I learned anything from the subwoofers, it was a very subtle effect, and seemed to require constant tickering with the crossover, most likely due to source material.
Lesson learned, subwoofers are generally a pain in the ass, and not screwed around with them since. But did dabble a bit with Aerial subwoofers.
This ain't no party, this ain't no disco