Diffuse field sound absorption measurement uncertainty: A comparative study of chamber sizes and air absorption correction

Building upon prior work analyzing uncertainty in diffuse field sound absorption measurements in small reverberation chambers, this study extends the analysis to compare uncertainties between small and large chambers over the expanded frequency range of 100 Hz to 10,000 Hz. While small chambers, defined by SAE J2883, offer practical advantages in material testing due to space and cost efficiency, their uncertainty profiles differ significantly from those of large chambers, which comply with ASTM C423 or ISO 354 standards. Results indicate that small chambers exhibit greater accuracy at higher frequencies, as their reduced size reduces the effects of air absorption. Conversely, large chambers demonstrate superior performance at low frequencies due to their higher modal density, which enhances sound field uniformity and measurement reliability. Factors such as air absorption, chamber volume, sample area, and environmental conditions are analyzed using partial derivative uncertainty propagation. The impact of correcting for air absorption for each set of measurements, eliminating the allowable temperature and relative humidity tolerance is analyzed as well. Practical recommendations are provided to optimize measurement accuracy for both chamber sizes. These findings aim to assist manufacturers and researchers in analysing and achieving more reliable diffuse field sound absorption measurements across diverse testing environments.