Characteristics and prediction of sound level in extra-large spaces

This paper aims to examine sound fields in extra-large spaces, which are defined in this paper as spaces used by people, with a volume approximately larger than 125,000m³ and absorption coefficient less than 0.7. In such spaces inhomogeneous reverberant energy caused by uneven early reflections with increasing volume has a significant effect on sound fields. Measurements were conducted in four spaces to examine the attenuation of the total and reverberant energy with increasing source-receiver distance, which was then validated by the simulations with image-source method. Results show that the reasons for the total energy's exponential decrease are not only the direct sound, but also the reverberant energy. The prediction difference of total sound pressure level (SPL) between classical formula and the image-source method increases with the volume and decreases with the surface absorption, based on which a critical line separating extra-large spaces from large ones is proposed. Moreover, a newly modified model based on the importance of first reflection from floor is proposed, showing more advantages of sound level prediction in extra-large spaces.