Uncertainty in the measurement of acoustic characteristics of sound absorption

The experimental determination of the acoustic properties of sound absorption materials is dependent on numerous factors. The accuracy level in the determination of each property is influenced by, for example, the measurement apparatus and the type of material. The objective of this study is to highlight the main sources of uncertainty in the measurement of properties such as sound absorption coefficient, acoustic impedance, flow resistivity and porosity. The uncertainties of the apparatuses used to measure each property are quantified. Also, the uncertainty of the material heterogeneity is assessed and its individual contribution highlighted. Important aspects of the Standards ASTM C 522 and ISO 10534-2, which contain, respectively, recommendations and procedures for flow resistivity and sound absorption measurements, are discussed. The methodology to calculate the uncertainty of each property is discussed in detail, emphasizing the relevance of each uncertainty source.