An as diffuse as possible acoustic field is pursued when performing measurements that make use of a reverberant room. The diffusivity descriptors that are commonly used to qualify the actual sound field in such a room are calculated in the room volume, away from boundaries. This is somewhat contradictory with the fact that for sound insulation and sound absorption measurements as examples, specimens are placed at room boundaries either a wall or the floor. This work presents a characterization of the sound pressure field at the boundaries of a reverberant room in order to evaluate the diffusivity of the excitation at these specific locations. A boundary diffuse field index is proposed, numerically evaluated and then tested in two reverberant chambers in steady state conditions. It is shown that this index allows evaluating the boundary diffusivity in a given reverberant room according to its geometry and other relevant parameters, such as the sound source location or the presence of sound diffusers.
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