Normally better to have a dedicated sub. But if you must......unless you have a built-in crossover feature in your mixer (i.e. Mackie CFX series), you will most likely need an outboard unit. Running the full range mix to your designated "subwoofer" defeats the whole purpose; sub frequencies are generally set around 75hz - 125hz cutoff, and a good x-over unit will do just that. BUT, you have to make sure your bass speaker can handle that frequency or you might kiss that speaker(s) goodbye when you crank the sub volume up. Best to have at least a 15" speaker in that bass cab for sub, but if you have a smaller size speaker, you could set the x-over point a little higher and turn down the volume accordingly. Best of luck.