Subwoofer bases designed by Dan D'Agostino, using two servo-controlled 12" woofers with Krell amplification.
Servo Sealed Kit and Flatpack (Single) | GR-Research
Martin Logan Grotto Servo Controlled Subwoofer - Very Good Cond. | eBay
SW-12-08FR Servo Sub Woofer | GR-Research
Rythmik Audio • Servo technology survey of different systems
Martin Logan Grotto Servo Controlled Subwoofer - Very Good Cond. | eBay
Genesis Advanced Technology Genesis Genesis ServoSu 4/8 The Ultimate In Loudspeakers! Home Theater Speakers, Subwwofers, Servo Control Genesis Advanced Technology Genesis Genesis ServoSu 4/8 The Ultimate In Loudspeakers! Home Theater Speakers, Subwwofers,
Analog Servo Sub | diyAudio
Martin Logan Grotto Servo Controlled Subwoofer - Very Good Cond. | eBay
Rythmik Audio F12G Direct Servo Subwoofer In-Depth Review
Servo-Control in Mainstream Audio: From Motional Feedback to the Bend-Sensor | audioXpress
Velodyne Servo Controlled Subwoofer System F-1000 for Sale in Orlando, FL - OfferUp