||Sony ES II, Milbert BaM-235 amps, Zapco sub amps, B&W 801 Signature Series speakers with 15" woofers in front floorboards using fenders as enclosures, StraightWire Maestro interconnect and speaker wire.
Earl's first car had two 13" woofers mounted up front, under the dash, using the fender cavities as enclosures. His second car had two 15" woofers mount up front, under the floorboard, using the floor and other cavities as enclosures. This was done at least ten years before the 2005 patent mentioned below. Other subwoofer-up-front leaders included Harry Kimura's Acura and the SpeakerWorks Buick Grand National. It's no new idea.
Did Earl's car show Mercedes how to do bass? "...the frame utilizes an unconventional body structure that enables the 'front bass' music system design, and indeed the 2012 'SL' models will be the first to feature mercedes's 'front bass' audio system, which provides clearer bass and dynamic range...instead of featuring bass speakers installed in the doors, the system places them in the footwell in front of the driver and front passenger...cavities behind the speakers act as resonating chambers, while the location at the vehicle's front, framed by the floor and underside of the dashboard, funnels and concentrates the sound." designboom
Sep 2012: "...Mercedes-Benz has created a novel technique for greatly improving the sound of car audio. The technology, called FrontBass, moves the woofers from the door panels to the footwells and uses the car's structural beams as enclosures behind the woofers...The primary reason for this unusual placement was the opportunity to load the woofers in the 'longitudinal beams,' two hollow rectangular structural members that run parallel to the ground from the footwell toward the engine compartment. Loading the woofers in relatively large sturdy metal chambers of just over half a cubic foot each instead of the doors confers significant sonic virtues, as you might imagine." The Absolute Sound