The SI-X series has three (3) subs can help: SI-12BX & SI-15BX are folded horns that give you the lowest frequencies and the punch you need. The SI-18BX is a straight forward, no nonsense 18-inch bass reflex subwoofer with exceptional low frequency response. The SI-X Series includes a range of full range systems from the SI-10X to the SI-15X plus three complimentary high power subwoofers for extended low frequency performance and increased SPL. The SI-15BX is a 15" horn loaded subwoofer that gives you the lowest frequencies and the punch you need. The SI-15BX is available in black and white version.