Sound absorption properties of sustainable fibrous materials in an enhanced reverberation room

In this paper, the measurement of sound absorption coefficient of novel sustainable fibrous materials is investigated. Nowadays the use of such materials is becoming wider for various applications, being ecological, biodegradable and renewable: they differ from traditional fibrous materials, as rock or glass wool, for their very low toxicity and polluting effects. These materials can be used in many ways: noise mitigation and building acoustic correction are surely among the most important. Sound absorbing layers made of natural fibres and of recycled raw materials have been tested in the reverberation room of the Acoustics Laboratory of the University of Perugia according to ISO 354 standard, in order to quantify their sound absorption properties and to make a comparison with traditional fibrous sound absorbers. An optimization of the reverberation room characteristics has been also carried out. Good sound field diffusivity inside the room is a fundamental requirement for the measurement accuracy. Among the parameters that mainly affect room diffusivity are the room shape and the sample disposition inside the room. In order to obtain accurate values of the sound absorption coefficient, specific actions were adopted. Test specimens were placed on the floor with edges nonparallel to the room walls. A partial closing of the lower room corners with absorbing and reflecting diffusers and suspended plane diffusers were also tested, obtaining a significant improvement of the results. The measured performance of the tested materials seems to be fully comparable with that of mineral wool fibres: because of their low impacts on the environment and the human health they can be seen as a valid alternative to conventional materials.