Reference woofers delivers the enhanced efficiency and higher output. INFINITY uses progressive spiders to provide the best possible control at the excursion limits versus much more commonly used linear spiders. The benefit is a far more controlled woofer stroke with far tighter bass characteristics. With high-roll surrounds, proprietary cone design and long-excursion, Reference woofers deliver deep, powerful bass, with greater accuracy than conventional woofer. And the exclusive SSI™ (Smart Selectable Impedance) switch lets you choose 2- or 4-ohm impedance for maximum configuration flexibility. It’s everything you want in a woofer.