Polk Audio RM6005-BK 5-Piece Home Theater Surround System (Black) Compact Satellite and Center speakers feature the same integrated rear Power Port bass vent technology used in full size Polk Audio speakers. This enhances low end response and Sub/Sat blending Dynamic Balance driver technology w/ mineral filled polymer cones Anti-diffraction system for spacious imaging & excellent off-axis performance Integrated keyhole slots & threaded screw inserts 5-way binding posts