and SI uses the term SQL right on the Mag D2 product page
SI Mag Subwoofers
The best just got better.
Throughout Stereo Integrity's career, there have been four different variations of our Mag series subwoofers. What you are about to read about is our most technologically advanced, best sounding, loudest subwoofer to date.
The motor of a subwoofer is one of the most critical aspects of subwoofer performance. The SI Mag D2 subwoofers have a custom-tooled motor that allows for over 26mm of one-way linear travel, plenty of motor force, and a large enough voice coil to smother a Coke can. Motor force is +/- 18 Tm for both sizes of our Mag subwoofers. The combination of our light moving mass and ample motor strength give us a winning combination for a true "SQL" subwoofer - one that can do both sound quality and SPL.
Mag subwoofers use a proprietary blend of materials in the cone, which yields a very high strength-to-weight ratio. Surround material is treated foam for longevity and elasticity and is wide/tall enough to accommodate the Mag's 3 inch peak-to-peak throw. Dual 8 inch progressive roll spiders provide most of the mechanical restoring force.
Sure we could have gone with less expensive (or even MORE expensive) materials, but that would have jeopardized the integrity of Mag subwoofers. You see, building a well rounded subwoofer is like building a well rounded race car; you can have the best handling chassis in the world, but if you've got a wimpy motor you're not going to win races. Subwoofers are all about balance too. The cone, spiders, surround, basket, motor, etc, was chosen and/or developed to bring you the loudest best sounding subwoofer money can buy.