The Xds is a manifolded, vented-box subwoofer system utilizing two 457-mm (18-in.) woofers in the double-wide X-Array™ enclosure shell. The enclosure has been optimized for maximum subwoofer-frequency output. The two woofers face each other in a manifold chamber at the center of the enclosure. This manifolding technique (U.S. Patent Number 4,733,749) increases the acoustic loading, resulting in increased low-frequency efficiency (at slightly above box tuning) and reduced distortion compared to conventional direct-radiating designs.