this is wired as a stereo sub with a high pass for a satellite. The Lower terminal cup lower binding posts are for the lower 15 inch sub. The binding posts above that on the same terminal cup is for a satellite speaker, The terminal cup on the top is for the upper 12 inch sub; with te upper binding posts for another satellite. I have sold both mono ands stereo versions of this sub. So what you want to use for a left channel or a right channel the choice is yours. You don't have to use the high pass out if you don't want to. The crossover is @100hz low pass @6db and the high pass is at @100hz 12db. THe level control on each cup is a level control of for output of the satellite.
so to repeat the lower binding posts on each terminal cup is the input from the amp to the subwoofer. the upper binding posts are for high pass filter to a satellite speaker(if so desired) This was designed by B.C for use of one amp channel versus biamping.