The Yamaha KS-SW100 is a compact subwoofer designed for keyboard instruments. It incorporates a number of Yamaha's advanced, high performance bass technologies, including Twisted Flare Port and Advanced YST II (Yamaha Active Servo Technology II). This results in sensational bass response that adds significantly to the enjoyment of music performance. The Yamaha KS-SW100 adds powerful bass to your Yamaha PSR-S series keyboard instrument. The KS-SW100 is compatible with PSR-S970 PSR-S770 and PSR-S670 instruments, as well as older PSR-S series models. There is no comparison in the sound between a keyboard without the KS-SW100 vs a keyboard with the subwoofer attached. This low cost addition to your keyboard gives the depth of sound you've missed for so long and negates the requirement for additional amplification at home.