BS21 is a passive, band-pass subwoofer featuring a single 21-inch low-frequency driver. The cabinet is built from multilayer birch plywood to minimize vibrations and is finished with a scratch-resistant waterproof polyurea coating for durability. It covers 30100 Hz and handles 1500 W RMS (6000 W peak) into 8 8, delivering up to 139 dB SPL at 1 m. Designed for omnidirectional low-frequency distribution, it is intended for use with SERIE A digital power amplifiers.