DESC: Perfect for adding to smaller surround sound set-ups, this stylish powered Yamaha YST-SW030SL subwoofer provides 75 watts of output power (150 watts of dynamic power). It features an 8-inch woofer cone that's magnetically shielded for safe placement near a television or monitor. The Advanced Yamaha Active Servo Technology (Advanced YST) feature is a unique system in which the speaker and amplifier work together to cancel out impedance so the speaker unit has a perfectly linear motion. Advanced YST helps to ensure the highest levels of sound pressure and overall performance.Yamaha's QD-Bass (Quatre Dispersion Bass) technology uses down-firing drivers with square, pyramid-shaped reflective plates to radiate the sound efficiently in four horizontal directions. The reflective plates negate any effects caused by the floor surface and reduce resonance between sound waves reflected from the floor and the unit.