18-inch active subwoofer. The SRX918S is a single 18-inch active subwoofer designed to complement SRX900 Series full-range sound reinforcement systems. The subwoofer houses an 18-inch JBL 2279-1 woofer with Differential Drive®, JBL's dual voice coil, dual gap technology, to deliver better heat dissipation, lower power compression, and a wider dynamic range than conventional subwoofers. conventional single coil designs. The DSP and amplification offer a plug and play experience while providing consistency and optimum performance anywhere in the world. The SRX918S incorporates a large low-frequency port design that improves airflow and reduces audible turbulence, even at high output levels..PZA MORE SPECS