Energy criteria in Italian historical opera houses: a survey over 11 theatres

In 2014 a detailed measurement campaign was carried out over eleven historical opera houses in Emilia-Romagna, a region in northern Italy. These theatres date back to the period in which the typology of the Italian opera house was coming to a standard; in fact they share the same typological features, being built approximately in the same period and, in most of the cases, by the same constructors. This investigation comprises theatres of different volumes, ranging from 2,000 to 15,000 m3, allowing to span the analysis by somehow varying a scale factor. In each theatre, IR measurements were performed in each seat in the stalls area and each front seat in the boxes. Two different source positions were used, resulting in over 7,000 monaural measurements. The early decay time and the strength factor are analysed in the octave bands 500-2000 Hz and commented in relation to the geometrical features of the halls. The availability of such great number of data allowed to realise interpolation maps that revealed the spatial distribution of the energy criteria, pointing out the peculiar effects due to the particular horse-shoe shape of the halls. In particular, the strength was calculated with different time thresholds and significant correlations were found with the EDT in relation to the spatial distribution of these criteria. The peculiarity of the concave shape and the early reflection pattern typical of these halls in facts call for a revision of the hypotheses upon which the most significant theories about energy distribution in concert halls lie