Rain noise is an important consideration nowadays in the design of schools, sports halls and many other buildings. A standard measurement method was introduced in 2006 (ISO 140:18 - based largely on research carried out at Salford during the early 1990s) which allows roof constructions to be characterised and rated in terms of their rain noise performance. The current rain noise research aims to extend earlier work so as to develop faster and more adaptable measurement methods as well as prediction models. It will also extend the ‘Rain Noise Simulator’, developed during various student projects; the simulator produces realistic simulated sounds of any type of rainfall falling on a roof tested in ‘dry’ conditions, i.e. without any real or artificial rainfall.
Conventional porous absorbers have poor low frequency performance unless very thick layers are used. This project focuses on the development of new porous absorbers which can overcome this limitation. Low frequency absorption can be improved by introducing two very different scales of the pores, however so far only very simplistic geometries have been studied. We would like to investigate whether the introduction of multiple scales (i.e. pores with more than two characteristic sizes) can dramatically improve performance. While materials with multiple pore scales are well known (e.g. vermiculite), their acoustical applications are currently limited. A general theoretical approach to modelling multi-scale porous structures needs to be developed. It will then be possible to identify and optimise those material parameters which are most important for the acoustical performance.