Ground Zero 400 SPL Basskit includes a 12″ SPL-subwoofer in a ported box. Box has a large port that gives a good air flow and Klippel-optimized subwoofer handles lots of power. This combined to a good sensitivity of the driver makes this box one of the LOUDEST in its price class. High Quality Tiatanium-series mono amplifier feeds this box with sufficient amount of power. This enclosure uses EFP ( Enchanced Flow Port ) port. It has cross-section like aeroport. This gives significantly better air flow without side effects. More air throught the port = more bass! Despite the better air flow in same size enclosure, tuning frequency is the same than before. Bass remote knob is included in the package.