The SRX928S is a dual 18-inch active subwoofer designed to complement SRX900 full-range sound reinforcement systems. The subwoofer houses two JBL 2279-1 18-inch woofers, featuring Differential Drive - JBL's dual voice coil, dual gap technology - to deliver better heat dissipation, lower power compression, and wider dynamic range than conventional single-coil designs.