A description of the sound field produced by a plane array is provided, as function of distance, frequency, and geometric parameters of the array. Three different regions are defined in space, exhibiting different behaviours of the sound intensity with respect to the distance and the spatial coverage: the Fresnel region, the Fraunhofer region and the chaotic region. First we consider the case of a single flat piston, only Fresnel and Fraunhofer regions being present. Then we extend the investigation to a plane array, introducing the chaotic region and the form factor in the Fraunhofer region. An analysis of the partition of the distance/frequency plane according to geometrical parameters is provided, and criteria for arrayability are proposed.
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