A solution is presented for the problem of the diffraction of a constant‐frequency spherical wave by a plane surface with constant normal specific acoustic admittance. By the use of a bidimensional Fourier transform, the transformed solution, obtained in the classical manner, is decomposed into a sum of products of functions, each of which is the Fourier image of a known function. The recognition of this enables one to readily invert the transform and, in this manner, a new representation of the exact solution is obtained. The particular case of grazing waves (source and receiver on the plane) is examined and asymptotic farfield expressions are derived. Comparison with experiments indicates that, if the plane‐wave admittance for normal incidence is used in the theory, the farfield sound‐pressure level can be predicted to within ±1.5 dB or better.