The B4-SUB is an actively driven cardioid subwoofer, powered by a single amplifier channel, and solely designed for use in a ground-stacked setup. It houses two long-excursion neodymium drivers in an integrated cardioid setup: a 15" driver in a bass-reflex design facing to the front and a 12" driver in a two-chamber bandpass design radiating to the rear. The cardioid dispersion pattern resulting from this approach avoids unwanted energy behind the system, greatly reducing the reverberant field at low frequencies and providing the greatest accuracy of low frequency reproduction.