Measurement Uncertainty in Random-Incidence Sound Absorption Testing: Part 1-Formulation

Random-incidence sound absorption test results are not typically presented with appropriate estimates of uncertainty attached. Here, a formulation for the uncertainty of random-incidence sound absorption testing per ASTM C423 is presented. The formulation is consistent with NIST guidelines for expressing the uncertainty of measurement results by the GUM method. Given the spatial variation in decay rates among successive fixed microphone positions, a confidence interval on the absorption coefficient can be computed in a direct fashion. Test examples are shown from various size reverberation rooms. Uncertainty estimates from a full size reverberation room are correlated to existing estimates of test reproducibility from the inter-laboratory comparison series of 1980. A follow-up paper deals with the experimental verification of the proposed uncertainty estimates in the absorption coefficient.