Polk Audio FXI A4 Surround Speakers (Pair, Black) 5.25" Polymer Composite Dynamic Balance Woofer Dual 1" Silk Polymer Composite Dome Tweeters With Neodymium Magnet Imp: 8ohm Pair of timbre-matched surround speakers to fit any Polk Audio home theater or multi-channel music system Equipped with a 5.25-inch dynamic balance driver with polymer/mineral composite cone Features a neodynium magnet, low viscosity ferro-fluid cooling, and a heat sink on the back of the magnet Equipped with two 1-inch silk/polymer composite dome tweeters All MDF construction and extensive asymmetric cabinet bracing ensure resonance-free enclosures