The QiCSA-SUB is a specifically designed version of the Qi-SUB for use as the rear facing element in Cardioid Subwoofer Arrays (CSA) only. It is acoustically compatible with the standard road version, differing only in cabinet construction and mounting hardware. The QiCSA subwoofer cabinet is an actively driven bass-reflex design housing a long excursion 18" driver, its frequency response extending from 40 Hz to 130 Hz.

The QiCSA-SUB cabinet is constructed from marine plywood and has an impact resistant paint finish. The loudspeaker cabinet has replaceable acoustically transparent foams fitted to both the front and rear sides of the cabinet, which are then protected by rigid metal grills. Four M10 threaded inserts on each side panel of the cabinet enclosure are provided for attaching installation hardware. Four rubber pads placed into their recessed positions prevent movement of the cabinets when two or more Qi and QiCSA-SUBs are stacked. The grill facing backwards is fitted with a single NL4 connector at the bottom left hand side. The loudspeaker cabinet is also available in Special Colour (SC) and Weather Resistant (WR) options.