A numerical study of the random-incidence and diffuse-field sensitivity of laboratory standard microphones using BEM

The difference between the random-incidence sensitivity of a microphone and the diffusefield sensitivity is that according to the definition of the former, plane waves coming from different angles of incidence impinge successively onto the microphone under free-field conditions, whereas according to the definition of the latter, a number of plane waves coming from random directions and having random phases impinge simultaneously upon the microphone. The random-incidence sensitivity can be estimated using measurements made in an anechoic chamber, while the diffuse-field sensitivity requires a reverberation room. It is widely accepted that the two definitions are equivalent. The purpose of this paper is to examine this equivalence using numerical simulations. A laboratory standard microphone can be considered rotationally symmetrical around the axis; thus, an axi-symmetric formulation of the Boundary Element Method has been used to study different aspects of the two realizations, such as the influence of the number of plane waves impinging on the microphone, the required amount of spatial averaging, etc.