The LINEAR SUB 1800 A is an 18″ bass reflex subwoofer with plenty of low end. Unbridled power, high sound pressure of up to 132 dB and thumping bass all the way down to 38 Hz make this active sub the ideal add-on for the LINEAR 3 mid/high units when you really need a little more depth and loudness. It can also be used with LINEAR 5 mid/high units or as a bass extension to the ELEMENTS BIG BASE system.