Proposal of a simplified methodology for reverberation time prediction in standard medium size rooms with non-uniformly distributed sound absorption

Abstract

Sabine, Eyring and Millington formulas are commonly used for reverberation time prediction, mainly, as a calculation tool in building acoustics design. These classical theories are valid only for rooms with diffuse sound fields, in which the energy density is constant throughout the enclosure, an acoustic condition that is achieved only when using surfaces with low sound absorption. Despite these limitations, Sabine’s formula is still the most widely used in the prediction of the reverberation time, when spaces such as classrooms or offices are addressed. However, for these rooms, after the construction works are completed, it is quite often verified that the implemented sound-absorbent surface area is manifestly insufficient to fulfill the reverberation time requirement. In this technical note a simplified approach for reverberation time prediction, based on the use of Sabine’s formula, is proposed, that can be useful in acoustic design of classrooms or offices, due to its simplicity. A previous correction to the sound absorption coefficient of the lining materials declared by the manufacturer is here proposed, making use of an empirical correction that was achieved from in situ experimental results and through geometrical room acoustic modelling. The empirical correction can be employed for room conditions where diffuse sound field is not met, composed of small or medium volumes (volume below 300 m3), with regular geometry, approaching parallelepipedal shapes, where the average height is below 4.0 m.