JBL SRX818S Passive 18" SubwooferSRX818S is a single 18" subwoofer for concert, touring, or installed use. Featuring a standard M20 pole cup for use with top boxes, indexing feet for stacking in both the standard and cardioid position, and a 136dB max SPL, the SRX818S is an ideal solution for musicians, bands, and DJs, concert use, public speaking, or installations such as performance venues, corporate spaces, educational facilities or houses of worship. Tunings and presets are