Low-profile design: Because today s compact cars offer less space, the Infinity Reference Subwoofers are designed to fit into small enclosures. They re slim, sleek, stylish, and don t sacrifice on sound. Harman-proprietary SSI (Selectable Smart Impedance): Unlike most dual-voice coil woofers, which provide either 1 or 4 ohms or 2 or 8 ohms, the Infinity Reference Subwoofers give the listener 2-ohm and 4-ohm, providing the two most often used impedances. Frequency response 27Hz -175Hz: Your audio is filled with delicious sounds. Unfortunately, you re not always hearing them all. With lows that dig down into the depths of 27Hz, you ll hear the low-end frequencies you ve been missing.