A Practical Application of Ensemble Averaged Surface Normal Impedance Measured In-Situ

Abstract

This paper presents the application of an in situ measurement technique of sound absorption characteristics, namely the “Ensemble Averaged Method”. Previously, a measurement technique of material surface normal impedance by using a twomicrophone (p-p) technique and ambient noise was proposed by some of the authors. This includes the concept of “ensemble averaged” surface normal impedance to extend the usage of the obtained values to various applications, such as architectural acoustics and computational simulations. With the development of a particle velocity (p-u) sensor, the practicality of techniques for the direct measurement of impedance becomes feasible. A concept of the ensemble averaged surface normal impedance is addressed, including a basic technique to measure it by using p-p and p-u sensors. Then, the agreements between p-p and p-u sensors are discussed and the discrepancies of absorption coefficients are shown to be small. The paper reveals the reliability, applicability and feasibility of the method throughout the investigation as an in situ measurement technique.