The B4-SUB features d&b audiotechnik's patented cardioid design, using one amplifier channel and building on CSA (cardioid subwoofer array) techniques the company began using in 2004. The cabinet houses two long-excursion neodymium drivers: a front-facing 15" driver in bass-reflex design and a 12" driver in a two-chamber bandpass design to the rear. The design reduces level behind the cabinet by more than 15dB over its operating bandwidth, providing high accuracy in its low frequency reproduction from 40Hz to 150/100Hz. Each channel of a d&b D6 or D12 amplifier drives up to two loudspeakers with the B4-SUB configuration selected. The sub is specifically designed for ground-stack use; an M20 threaded flange in the top panel accepts a loudspeaker stand, and two runners extend from front to rear of the bottom panel and fit to correspondingly shaped recesses in the top to greatly aid stacking. The sub produces 128dB SPL and 131dB SPL when driven with the D6 and D12, respectively.