Yamaha YST-SW215PN 8", 150 watt powered subwoofer, piano black YSTSW215PN 8" Down Firing Driver with QD-Bass technology QD-Bass (Quatre Dispersion Bass) utilizes down firing driver surrounded by square, pyramid shaped plates which negate sound wave resonance and reflection between the floor and the unit while diffusing the sound effectively in 4 directions. Built-in 150W YST Amplifier Advanced Active Servo Technology created by Yamaha ensures strong and accurate bass by utilizing negative feedback in the amp coupled with a Heimholtz resonator in the speaker Continuous Variable High Cut Filter User adjustable variable high-cut filter will set the highest frequency the subwoofer will reproduce. With settings from 50-150Hz, the filter can match the output to the other speakers in the system as well as the room's acoustics Signal Sensing On/Off For efficiency, the YST-SW215PN automatically turns on when it senses an audio signal. After several minutes of idling, the unit automatically shuts down. Bass Selector BASS (Bass Action Selector Switch) is Yamaha's technology that allows the user to custom tailor the sub's output for music or video with one touch convenience Phase Switch Phase switch can be utilized to phase the YST-SW215PN with other speakers in your system Volume Control Overall volume of system can be matched from the subwoofer's rotary volume control