The intensity of the acoustic fieldwhich is radiated by an acoustic baffle can be obtained, in the far field, from the acoustic pressure radiated by a flat circular piston (radius "a") in an infinite plane rigid baffle. This circular piston is a vibratory plate with a vibratory velocity denotedW ₀, which is independent of the point (the piston is the only active element of the infinite plane baffle).

The field of pressure is classically obtained from the Rayleigh integral, and the farfield acoustic intensity is given by:

The animation below represents the variation of the directivity diagram (acoustic intensity) as a function of the product k₀a