Atlantic Technology 3.1 HSB Speaker Base with H-PAS-Enabled Subwoofer (Black) Left, Center, Right and down firing H-PAS subwoofer in one sleek enclosure that fits under your TV Built-in H-PAS enabled subwoofer reaches down to 35 Hz Needs to be paired with any AV receiver for power and flexibility Simply add AV receiver and surround speakers for a complete home theater system (6) 4" woofers, (1) 6.5" woofer, and (3) 3/4" soft dome tweeters