The use of the Sabine and Eyring reverberation equations to churches

Abstract

Reverberation time measurements were taken at several source/receiver locations in 41 Catholic churches in Portugal built in the last fourteen centuries, using the impulse response method. The use of the Sabine and Eyring reverberation time equations was tested to estimate the measured RTs in this sample of churches. The effect of coupled spaces was analyzed and a new algorithm for the application of the Sabine equation in churches was developed producing an average of 16% in the differences between the predicted and measured RTs compared to 71% using the standard Sabine equation. Coupled spaces were found to act as windows with a characteristic absorption coefficient depending on their dimensions. The recesses in churches were grouped in three types: main altar area, chapels and lateral aisles, each having a particular acoustical behavior. It was found that those recesses only acted as coupled spaces if their length/opening_width > 0.6 or if the aisle_width/opening_height > 0.4 in lateral aisles. The remaining differences found between the RTs measured and predicted with this new algorithm were hypothesized to be related to what was called a reverberant ceiling effect, which is presumed to be due to a two dimensional reverberant sound field that builds up near a very tall ceiling.