This paper investigates the use of geometric simulation algorithms to model the acoustics of a church as it would have sounded in the late 16th century. Based on measured acoustic parameters, an average absorption parameter is developed for the heterogeneous walls of the Church of the Ospedaletto, obtaining a good match between the simulated model and modern acoustic measurements. Using these data, the model is altered to simulate the church’s acoustics before the large organ gallery was installed in the late seventeenth century. This method allows a high degree of confidence in the model’s ability to reconstruct accurately the soundscape as it would have been experienced during the Renaissance.