Polk Audio CSI A4 Center Channel Speaker (Single, Black) Complete your Polk home theater system with the CSi A4 center channel speaker. Its advanced driver technology and solid construction work together to clear, distinct movie dialogue and exciting special effects. Polk carefully made the woofers and tweeter using laser testing to help identify and eliminate resonance points. The acoustically inert MDF cabinet fights internal vibrations that can compromise performance. It all adds up to smooth, accurate sound with DVDs and multichannel music sources. And a real wood veneer finish gives this speaker a warm, refined look, making it an attractive addition to just about any room.