The THE21 Sub PRO ACTIVE SEALED is a jewel in the pool of subwoofers designed for the highly educated customer that is on the quest for the highest performance and understands how to differentiate sound quality. When this customer experiences the THE21 SUB PRO AS’s unparalleled output and uncolored sound, the measured test results we publish translate perfectly to realized performance. ASCENDO’s policy is to be completely transparent and publish measurements done by independently certified third-party labs to provide factual data, thereby enabling informed, educated decisions. The THE21 SUB PRO AS is so far above and beyond the competition in every aspect; refined musicality, tightness, and output levels suitable for a 21"" driver. It is also engineered to operate perfectly in sync (in phase) with our Infrasonic subwoofers; THE24/32/50/80 SUB PRO SEALED when there is a desire to reproduce movie content below 20Hz with the same authority, precision, and musicality.