In this paper the problem of coupling of acoustic sources in a confined space is treated. By considering the coupling of sources in a rectangular enclosure the set of coupled equations governing the acoustical behavior of enclosure are solved. The resulted model can be used to analyze the behavior of a multi-input multi-output (MIMO) active noise control (ANC) system in real application where coupling of sources can not be neglected. Comparison of results to the case that coupling will be ignored among loudspeakers shows that coupling will effectively change the strength of sources and hence the required voltage signals to drive the loudspeakers. The developed model gives an improved description of the acoustic environment inside the rectangular enclosure, especially in an ANC system when sources are placed in a fraction of wavelength and the interaction among sources will change the radiation impedance of other sources.