he meant a low pass crossover amp with speaker-level inputs. basically, find a 5-channel amp with one channel dedicated to the subwoofer...let the other four channels (your other four speaker wires) go into the amp...)...the subwoofer will get its signal from those. Ideally, get an Alpine SBS-254C. it's a 10" sub with a 225W 5-ch amp. this is what I have in my car and it's great!