Not all mono amps power only one speaker. Quite a few are made to power two speakers as well and a mono amp is an amp that filters out the highs and is made soley for woofers. If your amp puts out 750 rms is this @ 2 ohms or 4?? If the amp pushed 750 watts @ 2 ohms and you only run 1 -4 ohm woofer then you will only get half of the output the amp is capable of or 375 watts. Are you confused now?