Audiophilepure

https://www.soundandvision.com/content/martinlogan-s-new-grotto-series-targets-big-bass-compact-cubes

“The Hybrid Woofer System used in the Grotto series, pairs either a 12″ or 15″ active aluminum woofer with two equally sized, custom-designed aluminum passive radiators.”

“Thanks to the computational power of this sophisticated DSP engine, Grotto subwoofers are also compatible with the award-winning Anthem Room Correction system.”