DESC: Yamahas Advanced Active Servo Technology is a complementary amplifier/speaker system utilizing negative impedance feedback in the amp and a Helmholtz resonator in the speaker to provide strong and accurate bass. High amplifier power assures enough power to deliver shattering movie theater-like bass effects, and the down firing 8-inch cone driver translates the power into clear bass sound. The YST-SW215 has a frequency range of 30 to 200 Hz.