M 12.1 UNLIMITED and M 15.1 UNLIMITED subwoofers are exclusively designed for SPL competitions. In order to achieve the best performance on each individual race circuit, the SPL Monster subwoofers offer the ability to choose the moving assembly which is most appropriate for the overall system design, achieving maximum SPL in every competition. MM 15.1 UNLIMITED is a 15 in. (380 mm) motor group. In order to ensure constant, even flux, it features high magnetic permeability plates. The oversized magnet provides perfect control even under very high excursion conditions. Basket and motor are coupled and damped through a special epoxy glue.