The STI BS 15A drivers, delivering up to 1200W of peak system power via Sti's ultra-efficient Class-D, Fast-Recovery; amplification. These compact, all-wood construction subwoofers are ported, direct radiating designs for maximum punch and unparalleled low frequency extension. Featuring custom, high output, low frequency transducers Experience the power and clarity of a completely optimized and perfectly tuned system. Class-leading power, precision crossovers, phase and driver time alignment and patented acoustic correction processing work in harmony to create high-definition sound that was previously only found in high-end stadium touring systems. Simply put, BS Series loudspeakers deliver unmatched power and unparalleled sound quality in designs that are not only rugged and user-friendly... they are an extremely cost-effective solution for professional applications.