Analysis of Some Empirical Equations for Modeling Sound Absorption of Porous Absorbers

The empirical Delany–Bazley model and several of its subsequent modifications were evaluated to determine their ability to predict the sound absorption coefficient spectra of porous materials. The study considered three porous materials (foam, mineral wool and samples made from recycled cigarette butt) with different thicknesses. Model performance was assessed by comparing theoretical predictions with impedance tube measurements using the root mean square error (RMSE). Although some models yielded lower prediction errors for specific materials and thicknesses, the results showed that sample thickness—and the associated changes in the shape of the sound absorption spectrum—have a greater influence on model performance than the material itself. No single empirical model consistently provided the best agreement over the entire thickness range. These findings suggest that the applicability of Delany–Bazley-type empirical models appears to be more closely related to the shape of the sound absorption spectrum than to the material for which they were originally developed. These findings provide practical guidance for selecting suitable models for both conventional and recycled porous sound absorbers.