Early energy decays in two churches in Hong Kong

Acoustical measurements based on impulse responses have been made in a Protestant and a Catholic church in Hong Kong. Analysis has concentrated on reverberation time, early decay time and C₈₀, the early-to-late ratio, as well as integrated decays. The measured results have been compared with predictions according to two different theoretical room acoustic models: a model for a single diffuse space and one for a set of coupled-rooms. The comparison has shown that treating the churches as a series of coupled spaces is more valid. However the clarity, C₈₀, at different receiver positions was found to be either under- or over-estimated by the classical coupled-room model. Following this observation, a delayed coupled-room model was developed in the hope of achieving more accurate predictions. In this model, the initial condition under the impulse excitation was modified by introducing a time delay for sound propagated from the source to achieve diffuse sound fields in each subspace. The predicted results of the coupled-room model agree well with the measured results.