Polk Audio RTI A1 Bookshelf Speakers (Pair, Black) Pair of real wood bookshelf speakers with all MDF construction and resonance-free enclosures Equipped with one 5.25-inch dynamic balance mineral/polymer composite cone driver Features Power Port technology to reduce "chuffing" or "port noise" Equipped with one 1-inch silk/polymer composite dome tweeter Features a neodynium magnet, low viscosity ferro-fluid cooling, and a heat sink on the back of the magnet