Abstract: The theory of sound field in a room is re-examined. It is found that the normal-mode expression of Morse is not the exact, at least not complete solution of the wave equation in the room, its derivation is incorrect. The exact theory calls for both the free space solution (direct sound field) and the standing wave solution (reverberant sound field) in the room, the latter is formed by all the reflected waves to result the allowed modes of vibration (normal modes) in the room.