Measuring the free field acoustic impedance and absorption coefficient of sound absorbing materials with a combined particle velocity-pressure sensor

Acoustic surface impedance of sound absorbing materials can be measured by several techniques such as the impedance tube for normal impedance or the Tamura method for normal and oblique surface impedance. In situ, the acoustic impedance is mostly measured by use of impulse methods or by applying two-microphone techniques. All these techniques are based on the determination of the sound pressure at specific locations. In this paper, the authors use a method which is based on the combined measurement of the instantaneous sound pressure and sound particle velocity. A brief description of the measurement technique and a detailed analysis of the influence of the calibration, the source type, the source height, the sound incidence angle, and the sample size are included.