JBL PRX715XLF 15-Inch Self-Powered Extended Low Frequency Subwoofer System Highly efficient Class-D amplification drives Maximum Sound Pressure Levels are the best indication of the performance of a powered speaker and all PRX700 Series excel in this critical specification. 56 LB For Easy Portability 37 HZ/113 HZ Extended Frequency Range Normal or reverse polarity can be switched for matching to varied sub/satellite system configurations. A seriously rugged package that will withstand the brutality of constant road use.