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

In many acoustic simulations, particularly when using lumped parameter models or electrical analog circuits, the acoustic impedance of a component needs to be determined accurately. A widely used acoustic impedance measurement method is the ”two microphone transfer function method”, which is standardized in ISO-10534-2. When the acoustic impedance is needed over a wide frequency band, for example from 10Hz to 10kHz, this method faces some limitations. In this paper, a new calibration method will be proposed such that acoustic impedances can be measured with high accuracy over a wide frequency range. The estimation of the speed of sound has been eliminated. Using the measured transfer functions between the two sensors at two different reference sections, the sensor positions will be accurately calibrated. The calibration of the sensor mismatch has become superfluous, so interchanging positions of the sensors is not necessary. A recursive procedure has been proposed to maximize the microphone position accuracy. The resulting calibration procedure has been reduced to the accurate determination of the sensor positions.