Indoor ceiling mount (including the horn speaker) Example: An office with a ceiling height of 2.5m (8ft) makes one speaker cover an area with a 7.5m diameter (3 x 2.5m), which makes the cover area 44m2 (3.14 x (7.5/2)2). If the total floor area of the room is 700 m2, then you need sixteen (700/44) speakers.