Yamaha YST-SW012 Powered 8" Sub Woofer. Tested and works great. Also in really good physical condition with not much wear (I took pictures from all angles to try to show its true condition, the only major blemish issue is at around the 2:00 position on the speaker cover). It measures approximately 11.5"x11.5"x11.5" (if you include the amount the speaker cover sticks out that measurement would be closer to 12.5").  120V, 45W, 60Hz. Let me know if you have any questions and I will do my best to answer them.