Powered subwoofers from Martin Audio covering the common working formats. The SXP118 drives a long-excursion 18-inch driver with a 2000W peak Class D module for 135dB peak output, while the double-18 SXP218 doubles that to 4000W and 143dB, with onboard DSP handling EQ, delay and presets, set over Ethernet or from the plug-and-play rear panel. The Blackline XP118 is a single-18 voiced for systems built on XP12 or XP15 tops, taking the system down to 42Hz, with crossover, EQ and control handled from a rear-panel encoder and colour screen.

Amplification and processing live in the cabinet, so each box needs mains as well as signal, and subs draw more current than tops, so plan power distribution early. Match subs to tops from the same family, since onboard presets are voiced for those pairings; if you own amplifier channels, the Passive Subwoofers category is the cheaper route in.