Diffusion in gap− and strip−coupled acoustic surface wave convolvers reduces the coupling of the surface wave to the semiconductor. It is shown theoretically, however, that the optimized convolver coupling coefficient, which is proportional to the ratio of the convolver coupling coefficient and the acoustoelectric attenuation, actually increases in the presence of diffusion. An equivalence between the gap− and strip−coupled devices is established so that the same conclusions are applicable to both.