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Open-air acoustics is today a developing research field. The latest trends reveal the growing interest for this topic, especially in brand new disciplines, such as Archaeoacoustics and Soundscape, where a great variety of (unroofed) historical venues, like ancient theatres and public squares, are investigated by means of acoustical measurements and simulation tools to potentially be (re)adapted as performance spaces. The measurements in such spaces have a number of shortcomings, from several points of view. The lack of protocols for open-air spaces obliges to use indoor standard parameters from ISO 3382-1; i.e. Reverberation Time (T20), Clarity for speech and for music (C50 and C80), and Sound Strength (G). Furthermore, measuring signals (e.g. MLS, sweep) can be strongly influenced by outdoor environmental conditions, such as high background noise level, and temperature or wind speed changes. In this article, the acoustical measurements performed with two different measuring chains are investigated on the example of an open-air theatre, i.e. the ancient theatre of Tyndaris. Two omnidirectional impulsive sound sources – dodecahedral source and firecrackers – are both used in unoccupied conditions, following the indications stated in ISO 3382-1. The resulting acoustical parameters T20, C50, C80 and G, derived by the Impulse Responses (IRs) collected in 9 different receiving positions, are compared. The comparison of the two chains shows differences at the limit of their Just Noticeable Differences (JNDs) for all the parameters, in particular for G. This is significant for the assessment of the reliability of open-air measurements, especially when indoor standards based on the diffuse field assumptions are applied. In fact, their application to the open-air case study could be not completely suitable, and limited in giving indications on the evaluation of cliff-type decay curves, on the measurement uncertainty (using Integrated Impulse Response method), and on the repeatability of the IRs. Thus, an extension of the standards including also acoustical measurements in open-air conditions should be taken into consideration.
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