Nice Polk center channel speaker for sale. Excellent condition with great sound. $65. Unobtrusive design couples with great technology and great pricing to bring you Polk's compact CSi20 — a perfect center channel solution for budget-conscious buyers. With one 3/4" silk/polymer dome tweeter and one 5-1/4" Dynamic Balance driver, the CSi20 offers up the distinct highs and mids needed for crisp, clear dialogue. An affordable and very nice center channel choice for the RTi28. It is available.