Study of the acoustical properties of a condenser microphone under an obliquely incident plane wave using a fully coupled three dimensional numerical model

The sensitivity of measurement microphones depends on the sound field in which the microphones have been calibrated. Typically microphones are calibrated under uniform pressure, free-field or diffuse-field conditions. In all cases, the accuracy of the calibration depends on assumptions about the behavior of the microphone, for instance, the impedance of the microphone which can be derived from the velocity of the membrane. While recently it has been possible to carry out non-contact measurements of the membrane of measurement microphones, such measurements require expensive instrumentation not easily available for any calibration laboratory. Furthermore, in order to have a set of data that could be applied to any microphone, it would be necessary to measure a large number of samples. A very cost-effective alternative is using a mathematical model of a particular type of microphone for predicting its acoustical properties. Such a fully coupled three dimensional numerical model of a Laboratory Standard microphone of the denomination LS1 Brüel & Kjær type 4160 is presented in this paper. The model includes interior domain with visco-thermal losses, membrane and exterior domain, and it is based on the Boundary Element Method. The simulated membrane movement is compared with noncontact measurements of the displacement of the membrane for verification.