The 211ST 21" subterranean subwoofer was developed for high SPL bass output outdoor applications. It features a powerful 21" transducer for maximum excursion and SPL. Due to the high power handling of the 211ST, no 70V version is offered. The 211ST can be directly driven by an M1000 subwoofer amp which produces 70V of output, or 1000W+ at the 4ohm rating. However, at 1000W, wire loss needs to be considered and calculated as with any other 4 ohm wire run. In all applications, the 211ST should be bi-amped.