Portuguese Catholic churches as reference acoustical models for heritage Catholic churches in Goa, India

Abstract

The architectural genres of the churches built in Goa (a Portuguese colony in India) during the 16th - 19th century period, are partial derivatives of the Portuguese style considering the affinity of the latters architecture and worship ambience with that of the Goan churches. Therefore reference ranges used for the normalization of the measured objective acoustical parameters in the Goan Catholic churches of values for Reverberation Time (RT) and Loudness (G) (both regarding the medium octave frequency bands of 500 Hz and 1000 Hz); Objective speech intelligibility parame-ters such as RASTI and D50; Objective music intelligibility parameters such C80, Center Time (TS) and Early Decay Time (EDT), were obtained through a regression on the total volume of the church of the reported measured values of the same in Portuguese churches. Reverberation Time was found to linearly relate with the total volume of the church (R2 = 0.42) with significant probability (p < 0.01). Mid-frequency Loudness (G) showed exponential decay of the first order with the total vol-ume of the church (R2 = 0.76). A range was constructed using the standard deviation of the mean RT which would be the range of the optimal values of RT. A range of optimal values of Loudness was also constructed using the predicted value and the chi square value. If the measured value of Reverberation Time or Loudness belonged to their respective reference range of values then, their maximum normalized value was equal to 1. In case of RASTI, D50 and C80 the lower limit of the optimal reference range was fixed. The values of RASTI without the Sound Reinforcement System in the Portuguese churches were found to range from 0.22 to 0.56. The upper limit of this range was fixed as the lower limit of the optimal reference range for the normalization of the measured RASTI values. Thus if the measured value of RASTI belonged to this optimal reference range of 0.56 to 1 than the normalized value of RASTI was equal to 1. Definition for speech (D50) showed exponential decay of the first order with the total volume of the church (R2 = 0.56). Therefore, if the measured value of D50 belonged to its optimal reference range of values (0 - 1) then the normalized value was equal to 1. Center Time for music (TS) showed a linear regression with the total volume of the church (R2 = 0.40) (p < 0.01). Early Decay Time (EDT) showed exponential decay of the first order with the total volume of the church (R2 = 0.41). If the measured values of TS and EDT were found to be equal to or less than this lower reference limit, then their respective normalized values were considered to be equal to 1. The values of the optimal reference limits were dependent on volume and therefore gave unique results for the different acoustical parameters in each sample church.