Calibration of the two microphone transfer function method to measure acoustical impedance in a wide frequency range

The acoustical impedance of a component is one of its most important characteristics. It is needed when acoustical simulations using lumped elements or electrical analog circuits are carried out. The calibration procedure for the two microphone transfer function method described in ISO 10534-2 is not sufficiently accurate in most cases. In this paper, a new calibration method for the two microphone transfer function method has been proposed such that acoustical impedances can be measured with high accuracy over a wide frequency range. In this method, the estimation of the speed of sound has been eliminated. Next, in the calibration of the sensor mismatch, the deviation in sensor position after interchanging the pressure sensors has been taken into account. Finally, a recursive procedure has been proposed to refine the microphone position calibration. This refinement can be continued until the required calibration accuracy has been obtained.