MPP sound absorbers investigation to optimise a lecture hall speech intelligibility

The recent pandemic has drawn attention to the built environment’s hygiene, sustainability, and durability. Furthermore, studies on micro-perforated panels (MPPs) have recently highlighted their potential for sound absorption in such a context. On the other hand, metal additive manufacturing has become a very popular and convenient method to test acoustic metamaterials (AMMs) performance; however, their deployability in several civil indoor environments and functions still lacks assessment. So, the present work assesses the suitability of metal 3D printed MPP systems to fulfil speech requirements in lecture rooms. Firstly, an analytical optimization process defined two MPP steel specimens in terms of sound absorption performance. Secondly, these models were physically manufactured through 3D additive metal printing, and their acoustic performance was measured experimentally on a double-layer configuration. Finally, experimental results were used as input data for characterizing finite-difference time-domain (FDTD) simulations, highlighting the potential enhancement of oral communication through double-layer MPPs on the ceiling of a historical university lecture hall. An FDTD code with a full-spectrum wave-based method was chosen to better handle time-dependent signals, like verbal communication. The outcomes of the process show the influence of the acoustic treatment in terms of reverberation time (T30).