Theory of sound field in a room

In the classical theory of the forced vibration in a room it gives a series of normal modes as the solution. The reason for this result is because only normal modes are assumed for the source. In fact, the source inside a room serves two functions: It radiates directly as in free space before limited by the boundaries of the room, and after being reflected by the boundary surfaces, the first reflected waves loss the spherical wave characters and become a number of wavelets, randomly distributed in space and time on the boundaries but all traced back to the original source, and it is these wavelets that produce the normal modes. With this in view, the wave equation may be formulated, and exact sound pressure obtained, with both direct radiation and reverberant terms explicitly expressed. The steady-state sound field and the reverberation property of the room are obtainal. Both are influenced by the introduction of the direct radiation term, these are all discussed.