Kicker 47KBRW12 Car Audio Tuned Passive 12" Radiator for Sub Box Enclosure 

Ports require larger enclosures to be effective and can sometimes produce unwanted noise. When paired with a compatible 12" subwoofer, Kicker's 47KBRW12 12" passive radiator lets you get the punch of a ported box in a small sealed enclosure that can fit in more places in your vehicle. Kicker recommends using a subwoofer with a recommended box volume of 0.7 cubic feet, such as a Kicker CompRT subwoofer.

Note: This passive radiator will not produce sound by itself. It must be paired with a subwoofer in an enclosure.