Application of vibration-based methods for estimating radiated sound power of ethylene tetrafluoroethylene facades: Validation using a scaled model

The accurate determination of the sound insulation of building facades in the field can be affected by the limitations of standardized methods based solely on sound pressure measurements (e.g., ISO 16283-3:2016), particularly for lightweight, curved, and flexible systems, such as ethylene tetrafluoroethylene cushions. ISO 16283-3 defines a practical and time-efficient procedure for objectively assessing the sound insulation properties of envelopes and facade elements, assuming that the envelope separates two acoustic environments of different nature (assuming a free acoustic field on the exterior side and a diffuse sound field on the interior side). This study discusses three vibration-based sound power estimation models: the acoustic radiation matrix method, Rayleigh's integral method, and the discrete calculation method. The surface vibration velocities of a curved ethylene tetrafluoroethylene cushion and a polyurethane cushion were measured by scanning laser Doppler vibrometry. The models were validated against full field finite element simulations and standardized sound intensity measurements (ISO 9614-2:1996), enabling a direct comparison between numerical and experimental approaches. The results show strong agreement between the methods, with acoustic radiation matrix providing particularly consistent near-field pressure and sound-power estimates when compared with FEM. Additionally, parametric studies reveal that increasing internal pressure shifts radiated energy toward higher frequencies, while greater curvature enhances radiation efficiency. Although the present work focuses on the transmitted (radiated) component, the ability to estimate radiated sound power from measured surface vibrations provides an essential basis for future extensions toward full transmission-loss metrics, such as the sound reduction index, which depend on the ratio of incident and radiated acoustic power. The framework therefore offers a non-invasive tool to complement existing pressure- and intensity-based approaches for the acoustic characterization of lightweight and adaptive facade systems.