Ground Zero GZIB 250XBR bass reflex subwoofer 10" (250 mm).

Ground Zero GZIB 250XBR bass reflex subwoofer 10" (250 mm).

Predecessor of this box was one of the most succesfull on the market. No wonder because it had superior soundquality in its price class. 
This new model has new subwoofer that has been optimized with Klippel-device. Driver has smooth impedance response, good sensitivity and good power handling. 
These features give good sound quality and a lot of bass with very moderate amplifier power. New better driver deserves also a better enclosure. 
Previous enclosure was so good that it was hard to make it better. Solution was to invent new port type. 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. And it gives a very smooth bass response through 20-60 Hz bandwidth. 
So it is more than adequate to the required amplifier power for this subwoofer. If you are looking for a box that gives you good sound quality and a lot of bass with a moderate size amplifiers, it is here.