A method of evaluating surface diffusivity of rooms - I: computer modelingand field measurement

The present study aims to express the possibility of a new criterion to mea sure the diffusivity of surfaces in rooms through computer modeling and fie ld measurements. The new criterion (Deltax) means the phase difference of t he values of the room acoustical parameters between two microphones of whic h, the first microphone (M1) is pointed toward the forward part of a room w hile the other microphone (M2) is facing the rear wall of the room. To make this microphone layout possible a specially designed device, microphone ho lder panel, was employed to measure Deltax. Computer simulations, as the pi lot survey, were undertaken to analyze the change of Deltax values accordin g to the different surface diffusivity using two imaged three-dimensional ( 3D) halls. As the next step, field experiments were carried out to measure sound level (SPL), early decay time (EDT) and clarity index (C-80) in the t wo existing halls which have different surface diffusivity conditions. The results show that difference of three acoustic parameters (SPL, EDT, C-50) captured at two microphones, decreases according to the increase of the int erior surface diffusivity. Especially, it was found that in the hall of hig h diffusivity; Delta SPL, DeltaC(80), Delta EDT decrease in the range of hi gh frequencies (above 500 Hz) but, the same Deltax values increase in the r ange of low frequencies (below 250 Hz). This means that the high frequency sound may easily reflect, diffuse in the hall of high diffusivity but, low frequency sound may diffract on the surface. It was demonstrated that the d ifference (Deltax values) of acoustic parameters are low in the halls of hi gh surface diffusivity. Thus, Deltax values could be used as a criterion to evaluate the surface diffusivity of rooms. (C) 2001 Elsevier Science Ltd. All rights reserved.