JBL GT-BassPro12 12-Inch (300mm) Car Audio Powered Subwoofer System 12-Inch (305mm) woofer with die-cast aluminium basket for solid sounds under all conditions Slipstream port eliminates port noise and provides distortion-free bass at high output levels System optimisation: amplifier is precisely matched with woofer, enclosure and Slipstream port to ensure best performance and value Signal-sensing turn-on automatically turns the subwoofer on and off when the head unit sends an audio signal; can be defeated for use with aftermarket radios that include a remote turn-on lead Input level, low-pass, bass-boost and phase controls make it easy for any user to get the desired sound