Optimization of sound absorber: Design of sound absorber for the study of sound incidence in long narrow spaces such as corridors

Abstract

Noise mitigation is of importance in areas where health and well-being of individuals is needed and this is especially true in spaces such as schools were noise can hinder learning and cognitive development of children. While acoustical treatment is often focused on classrooms where children and teachers spend large amount of time, corridors remain neglected despite their role in amplifying noise. Corridors with their unique dimension, non-diffuse sound field and source for housing furniture pose a challenge in sound proofing and hence an approach to optimise absorbers is needed and to understand the impact of sound incident angle. This thesis explores the design and optimization of a sound absorber system tailored for such environments, with a focus on mitigating noise levels in school corridors. The study investigates the performance of a resonant sound absorber, combining a micro-perforated panel, air gap, and porous material, aimed at absorbing sound in the mid-to-high frequency range 850 Hz-4000 Hz in diffuse and non-diffuse sound field conditions. Using theoretical modeling via the Transfer Matrix Method (TMM) and empirical validation through free-field and diffuse-field measurements, the absorber’s performance was analyzed under various sound incidence angles. The results demonstrate that the designed system effectively absorbs sound, with a resonance peak at 2000 Hz. The study also evaluates the impact of parameters such as porous material thickness, perforation size, and air gap on the absorption coefficient for varied incident angle. While the absorber achieved good efficiency, especially at the targeted resonance frequency, edge effects were observed in finite-size samples, leading to overestimation of absorption coefficients in certain cases. This research highlights the importance of optimizing sound absorbers for nondiffuse sound field environments like corridors, particularly at high frequency range, and offers a practical solution for enhancing acoustic comfort in schools