Dayton Audio HTS545HE-4 Kraken 21" High Excursion Subwoofer with 5" Voice Coil 4 OhmIt takes a monster to deliver serious bass responseYou need to move a lot of air for high SPL and deep bass response, and Dayton Audio's HTS545HE-4 21" Kraken home theater subwoofer driver can beat most high...