The QSC KSub is a dual-12-inch bandpass design subwoofer, constructed of premium birch with high-quality, low-noise casters. The subwoofer features a threaded pole receptacle for a positive, wobble free connection to a threaded speaker pole (included). The QSC KSub is a dual-12-inch bandpass design subwoofer, constructed of premium birch with high-quality, low-noise casters.