Barrera-Figueroa S., Rasmussen K., Jacobsen F.

The random-incidence sensitivity of a microphone is defined as the ratio of the output voltage to the sound pressure impinging on the microphone's sensing element when it is immersed in a sound field with incident plane waves coming from all directions. The random-incidence sensitivity of laboratory standard microphones has been determined experimentally. Although the measurement procedure seems to be straightforward, some practical and fundamental problems arise: i) Reflections from the mounting rig contaminate the measured frequency response, and whereas some of these reflections can be removed using a time-selective technique, others coincide with the direct impulse response and consequently cannot be removed in the time domain and thus affect the accuracy of the estimate; ii) the accuracy of the estimate is heavily dependent on the rotational symmetry of the microphone and on the angular resolution. The effect of the angular resolution has been compared with the analytical solution of the diffraction around a solid sphere. Numerical results supplement the experimental results. Although the procedure has so far only been applied to laboratory standard microphones, it is not restricted to such microphones and may be applied to other types of measurement microphones.