Application of the ensemble averaging method to in situ measurements of acoustic properties of building exterior walls

In recent years, acoustic numerical simulations have been used to study noise propagation outdoors and the intelligibility of outdoor public address systems. These simulations require consideration of the acoustic properties of ground surfaces and building exterior walls. While acoustic properties of ground surfaces are becoming well known, those of building exterior walls are scarce. Therefore, this study measures in situ the acoustic properties of building exterior walls using the ensemble averaging method. The measurement targets are walls made of exposed concrete (ECW), glass (GW), concrete blocks (CBW), wood (WW), and tiles (TW). Since these materials are expected to have low sound absorption coefficients, optimal conditions are examined by varying the number of microphones (2 or 4) and the number of ensemble averaging iterations (150 or 547 with overlaps). Furthermore, 25 points are measured per target, and the specific acoustic impedance values are averaged for 7–25 points where their real parts are positive at most frequency bins. The conditions are set to two microphones and 547 iterations. The resulting sound absorption coefficients were nearly 0 across the entire frequency range for ECW and GW, increased with higher frequencies for CBW and WW, and peaked at 3 kHz for TW.