Increasing the accuracy of ISO 354 measurements by statistical analysis of modal decays

In this thesis work, the aim was to find a method for the acoustic characterization of materials. Specifically, materials are acoustically measured by calculating the sound absorption coefficient within reverberation chambers, following ISO-354 standards. However, these standards present issues related to the sound field diffusion at low frequencies. These limitations result in a negative contribution to the absorption coefficient, overestimating it. Therefore, the focus of this thesis was to test a method that improves the precision in studying the modal behavior of reverberation chambers and how this affects the acoustic absorption coefficient. To achieve this objective, numerous impulse responses were conducted inside the chamber at the Applied Acoustics laboratory of the University of Bologna, in various configurations. Subsequently, the acquired data underwent algorithmic processing used as a modal identifier method, followed by a statistical study of the results obtained in terms of modal decay times and modal frequencies. This allowed evaluating which configurations are the best in relation to modal decay times and the octave band frequencies studied from 80 Hz to 160 Hz. Therefore, this method represents a step towards designing a scaled reverberation chamber (alpha cabin) to test even smaller samples of innovative materials, simplifying measurement procedures and reducing production costs.