Petrarca Theatre: A case study to identify the acoustic parameters trends and their sensitivity in a horseshoe shape opera house

This article is intended to describe possible acoustic parameters’ trends and their sensitivity in a horseshoe theatre, considering the characteristics of the Petrarca Theatre in Arezzo (IT), one of the co-called ”teatri all'italiana”. In this theatre's typology, the public is distributed in the stall and in surrounding little boxes (the “palchetti”), located on more levels of balconies. Several authors have come up to a fairly unanimous definition of the descriptors characteristics in a Opera House and have assigned their optimum values. In this case study the physical parameters, that contribute to the sound quality, are evaluated in relation to geometry and materials of which the theatre is made and they are compared with the values of another rectangular hall with a similar room volume, the so called Sassi di Verbania (IT) Theatre, to understand the possible merits of the horseshoe shaped hall for Opera. A percentage deviation Δ% is defined and the results are linked to the specific horseshoe shape which characterizes the space geometry. The precious boxes, in particular, are identified through a grid in which rows represent the balconies’ levels and columns the different sectors. To evaluate the acoustic parameters’ sensitivity the JND (just noticeable difference) is considered. The parameters’ trend for the different levels and sectors and for the receivers in the stall is described. Because more than one receiver is placed in a single box, the local sound distribution is related to the global one of the hall. It comes out the success of the Italian theatre shape is undoubtedly linked to its sound quality, thought for the genre it was represented first, namely the Melodrama and the Opera, but also to the fact that the introduction of the balconies with boxes symbolically represented the social structure of Italy of the time: in the stall of public theatres poor people gathered together; the boxes at different levels were rented annually to the aristocrats. A earlier shorter version of this paper was presented at AIA meeting 2017 [1].