ACOUSTIC IMPEDANCE MEASUREMENT, PART II: A NEW CALIBRATION METHOD

A calibration method for input impedance sensors which permits an accurate determination of the calibration parameters is presented. The method is based on the measurement of two closed tubes of different lengths whose propagation constant is not required to be accurately known. This method is shown to be applicable to most of the impedance sensors in the literature and is extended to transfer impedance calibration which is needed for multi-post characterization. The method is applied to an impedance sensor using a half-inch microphone cartridge as a source of volume velocity. The attenuation constant of a straight tube is measured and shown to be less than 3% larger than results derived from theory of viscothermal dissipation. As an example of two-port characterization, the calibrated sensor, complete with a microphone for transfer impedance measurement, is used for the measurement of side hole parameters.