Archaeoacoustics, from antiquity to nowadays: contemporary use of the classical ancient architecture for performing arts

Present conditions of Roman and Greek ancient theatres of the Mediterranean basin are critic from the point of view of the architectural conservation. The remarkable acoustics that characterized them in antiquity was not anymore attested by the latest main researches in this field (i.e. ERATO project in 2006). This represents an obstacle for the proper usage of these spaces as contemporary performance spaces. In fact, despite their status, a high number of theatrical and musical festivals still take place in these environments every year. This research deals with the re-usage of the ancient classical theatres nowadays. Two main topics are investigated: a) the evaluation of measuring and simulating techniques in their application to the open-air conditions; b) the enhancement of the ancient theatres’ acoustics through passive-acoustic solutions. Two case studies were chosen: the ancient theatre of Tyndaris, TYN, and the ancient theatre of Syracusae, SYR. In the first part of the thesis, acoustical measurements performed in TYN and in SYR on the basis of the ISO 3382-1 are reported. Acoustical parameters Reverberation Time, RT (s) – labelled as T20 – Clarity for speech and for music, C50 and C80 (dB), and Sound Strength, G (dB), are calculated as indicated in the standard. Their analysis reveals similar results to those obtained during ERATO project, in terms of RTmid and Gmid parameters. Evaluation of the Impulse response-to-Noise Ratio, INR (dB), attests measurement quality for all the frequencies, except for 125 Hz. The critical analysis of the applied measuring protocol 3382-1, which actually refers to indoor environments, shows the necessity of a specific standard for outdoor spaces. Direct-to-Reverberant energy Ratio, DRR (dB), is proposed in this thesis as alternative parameter to characterize the open-air theatres. Measured and simulated DRR values are statistically evaluated to assess their reliability, together with the values of standard parameters T20, C50, C80 and G. Following recommendations by JCGM-100, a high number of repetitions is necessary to guarantee consistent results, and to reduce errors that could occur in open-air spaces. Measurement uncertainties due to repeatability are calculated for each parameter in the case of TYN, and compared to the relative Just Noticeable Difference, JND. Results evidence that only G and DRR are able to detect systematic differences among the different positions in the theatre. T20, C50, C80 result to be more affected by random effects, due to unstable outdoor conditions. Two acoustic software, Odeon and CATT-Acoustic, are investigated in their simulation of the open-air conditions. The reliability of simulated results is related to algorithm sensitivity to the variation of the input variables, which are controlled by the operator. Simulation uncertainty due to variability of the input values of absorption and scattering are defined for each parameter in the case of SYR. Results show that lower values than their JNDs are obtained for all the parameters, except for T20, C50, C80 when CATT-Acoustic is used. The lower uncertainty means that the software algorithm is less sensitive to absorption and scattering variation. Concerning the calibration procedure of the models, the comparison of measured/simulated results shows that, among all the parameters, only G and DRR results are in agreement. In the second part of the thesis, curved orchestra shells for the enhancement of the acoustics of TYN and SYR are defined by means of computational design. Genetic algorithms allow researches based on an optimization criterion, which in this case is the maximization of the number of reached listeners with a perceived level over the measured Background-Noise-Level, BNL + 10 dB(A). Simulated results of the orchestra shells show significant improvements of the theatres acoustics for G and DRR. This parametric approach allows the realization of feasibility studies, and it is transferable also to other similar ancient theatres.