Applying the ensemble averaging method with a pressure–velocity sensor to measure sound absorption characteristics of porous clay bricks

Abstract

This study focuses on the application of the ensemble averaging (EA) method that uses a pressure–velocity sensor (pu-sensor) to measure the sound absorption coefficient of porous clay bricks. It investigates factors including sample sizes, positions, and material properties of the porous clay bricks. The samples used in this study were produced from local red clay in Lampang, Thailand, whereby 2 mm charcoal was added to the mixture at a ratio of 30 wt%. Subsequently, the samples were formed by hydraulic pressing at 50 kN and were fired at 1100 °C. Testing was conducted in a reverberation room, whereby the selected frequency used was 100–3000 Hz. The validation found that the EA method with pu-sensor (EApu method) is applicable for the measurement of porous clay bricks. Samples of 30-cm square or larger are sufficient for the EApu method, and the optimum measurement position is at the center of the sample which presented small standard deviations. Sound absorption coefficients measured at positions far away from the center are in higher values. At 100–800 Hz, the sound absorption coefficient values are similar across every sample, despite the samples having different physical properties. On the other hand, the sound absorption coefficient, when observed with a frequency of over 1000 Hz, shows a clear difference. Moreover, the correlation indicates that the bulk density is an essential factor for porous clay bricks, as made evident by its high correlation value of 0.92.