SSI (Selectable Smart Impedance): Most car audio system designs call for 2- or 4-ohm impedance. Reference Series subwoofers feature an exclusive dual impedance switch that lets you choose either load impedance option depending on your particular system and amplifier choice. Not available from any other manufacturer, SSI lets you reconfigure your system by simply flipping a switch. Double Stack Magnet Design for Big Power Handling: Reference subwoofers are equipped with double-stacked magnet, allowing the voice coil coupled with the high roll surround to travel over a longer excursion. Vented Basket Design for System Cooling: Reference subwoofer vented basket keeps voice coil cool even at high output levels to ensure long term reliability. High-Roll Rubber Surrounds: Reference subwoofers incorporate a high-roll surround that provides superior cone edge suspension while maximizing excursion. It not only increases the cone area, it also provides remarkable linear stability and reliability. Purposeful Design: Infinity-logo-inspired radial texture with a prominently displayed copper-printed Infinity Mobius on the dust cap. The trim ring's high gloss detail is much like a like planet ring, and the supernova-inspired outer fluting finishes the trim ring's edge. The unique surround design allows the trim ring to press fit into it and conceal all installation fasteners giving the subwoofers a sleek, elevated appearance when installed.