DESC: The Yamaha NS-SP1800 5.1-channel speaker package offers authentic audio quality . Yamaha NS-SP1800 includes a powerful 100-watt subwoofer for full surround home theater enjoyment. This affordable speaker system features Advanced YST (Yamaha Active Servo) Technology -- a unique system in which the speaker and amplifier work together to cancel out impedance to ensure high levels of sound pressure and overall performance.