The JBL Professional SRX818S - 18" Passive Subwoofer System is designed for concert, touring, or installed applications. With a standard M20 pole cup for use with top boxes, indexed feet for stacking in both standard and cardioid positons, and a maximum SPL of 136 dB, the subwoofer is suitable for musicians, bands, DJs, PA systems, performance venues, corporate spaces, houses of worship, and more. A variety of tunings and presets is available for Crown ITech HD and XTI 2 amps as well as the dbx VENU signal processor.