This boom is made for all shapes and sizes. Infinity's latest Reference subwoofers offer incredible installation flexibility. Their low-profile design allows them to fit perfectly into even the most shallow of enclosures — great for today's compact cars. Polypropylene woofer cones deliver exceptional bass response at frequencies as low as 27Hz. But what makes these subs really stand out is their Harman-proprietary SSITM (Selectable Smart Impedance), which allows the subwoofer to present the amplifier with either a 2 or 4 ohm load at the flip of a switch.