# Measurements of Acoustical Parameters in the Ancient Open-Air Theatre of Tymdaris (Sicily, Italy) +
## 3 In Situ Measurements  
Acoustical measurements were performed in the theatre in unoccupied conditions, with omnidirectional sound sources and receivers, as per the protocol of the ISO 3382-1:2009 [26]. Further guidance on practical aspects related to the applicability of the ISO standard in the context of ancient open-air theatres was retrieved from other works in literature [1; 25]. Figure 1: Present conditions of the ancient theatre of Tymdaris: view from the scenaae (**a**) and from the cavea (**b**). Nine receivers were positioned on three radial axes of the cavea (Figure 2), 1.2 m off the ground (ear height). An omnidirectional microphone (Schoeps CMC 5-U) was used to record the impulse responses (IRs). For most of the measurement positions, 2-3 repetitions were performed to subsequently evaluate the repeatability of the results. Two source positions were considered: S1 was shifted horizontally by 1 m from the centre of the orchestra, and S2 was located behind S1, closer to the ancient scaenae frons position. The distance between S1 to S2 was 6.6 m.  
Table 1 shows the distances between the sources and the receivers. Two types of sources were used to measure the IRs as it was considered acoustically and metrologically relevant [36]: firecrackers (\"Raudo Manna New Malb\" and \"Perfetto C00015 Raudo New\") and a dodecahedral source (Bruel & Kjaer Omnipower sound source 4296). In the former case, the IRs were measured directly by recording the impulse produced by the firecracker blast, while in the latter case, the IRs were obtained after deconvolution of the recorded exponential sine sweep signal, which was 2.73 s long [26]. The firecracker measurements were only carried out with the source in position S1, apart from one measurement replication that was conducted at receiver R6 with the source in position S2. The IRs from the dodecahedral source were obtained for both source positions S1 and S2. Firecrackers maximize the signal-to-noise ratio (SNR) which is a considerable advantage in outdoor measurements, but they are also more affected by random effects (e.g., atmospheric conditions) [25; 36]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Receiver** & **S1-R (m)** & **S1-\(\beta\) (\({}^{\circ}\))** & **S2-R (m)** & **S2-\(\beta\) (\({}^{\circ}\))** \\ \hline R1 & 32.4 & 25 & 35.7 & 35 \\ R2 & 24.0 & 25 & 27.4 & 37 \\ R3 & 17.0 & 25 & 20.7 & 42 \\ R4 & 32.1 & 52 & 37.5 & 58 \\ R5 & 23.7 & 51 & 29.1 & 59 \\ R6 & 16.7 & 50 & 22.2 & 61 \\ R7 & 31.6 & 83 & 38.1 & 85 \\ R8 & 23.2 & 82 & 29.7 & 84 \\ R9 & 16.2 & 82 & 22.7 & 84 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Source to receiver distances and angle \(\beta\) from the scenery line and the direction that joins the source and the receivers, related to the measurement campaign in September 2015 at the theatre of Tyndaris. Figure 2: Measurement set-up: S1 and S2 indicate the source positions. R1–R9 indicate the receiver positions. O is the centre of the orchestra (at a distance of 1 m from S1, to the left, on the same horizontal axis) and \(\beta\) is the angle from the scenery line and the direction that joins the source and the receiver. The Background Noise Level (BNL) was measured as an A-weighted equivalent sound level over a period of 10 min (L\({}_{\text{Aeq, 10 min}}\)), in between measurement sessions and did not overcome 34 dB(A). The air temperature and relative humidity were monitored during the whole measurement campaign, using a thermometer/hygrometer, Testo 608-H1 (Croydon South, VIC, Australia). The wind speed was measured by means of an anemometer, Testo 450-V1 (Croydon South, VIC, Australia). Table 2 shows a summary of the environmental conditions during the measurement campaign. The dodecahedral source, powered by an amplifier (Lab.gruppen LAB-300), was connected to a laptop through a soundcard (Tascam US-144). The sound source was positioned at a height of 1.5 m off the ground, and a custom-made tripod was used to hold the firecrackers in a fixed position.