Bose Virtually Invisible 191 Speakers (ONE PAIR) A proprietary ported enclosure delivers smooth, consistent low-frequency response. This innovative built-in speaker design compensates for unpredictable environments behind walls that can diminish performance, and also prevents sound from radiating directly into adjoining rooms. Use as in-wall surround sound speakers with your home theater components or your stereo system. These flush mount speakers are unobtrusive and easy to install. Both rectangular and round grilles are included. You can even paint the grilles to match your decor. Proprietary ported enclosure produces cleaner and deeper low-frequency performance mainly directed into the intended listening area, not into adjoining rooms. Proprietary enclosure technology ensures consistent performance regardless of space behind wall or above ceiling. Non returnable. Never Used.