Elsevier

Applied Acoustics

Volume 170, 15 December 2020, 107530
Applied Acoustics

The acoustic of Roman theatres in Southern Italy and some reflections for their modern uses

https://doi.org/10.1016/j.apacoust.2020.107530Get rights and content

Abstract

Ancient Roman theatres represent a unique cultural heritage which is still used nowadays to host a variety of cultural activities and performances. Acoustic measurements show that the acoustics of these theatres does not always support the listening of music, which is common in modern performances. Although the acoustics of these theatres for modern use performances may be challenging, this cultural heritage offers a unique experience to the audience who can assist to a performance on the same seats once used by Romans. Nowadays, these unroofed theatres, whose walls behind and at the sides of the stage have rarely been restored, are often criticized for the weak sound strength. Moreover, these theatres are often exposed to urban modern background noise. The significant sound absorption due to the presence of the audience on the seating area (named cavea) and to the tapestries used in modern scenes makes challenging to support the acoustic reverberation in these theatres. In this paper, these aspects are described focusing on five ancient Roman theatres located in Southern Italy. The study reports acoustic measurements followed by virtual simulation results. As it was impossible to perform acoustic measurements with full audience occupancy, the presence of the audience was simulated using room acoustic software. The paper compares the acoustic characteristics of these five theatres considering their architectural characteristics, and discusses the role that the material used for their restoration had on their acoustics. Finally, some considerations about some reversible interventions to improve the acoustics of these ancient theatres for modern uses are reported.

Introduction

Open semicircular theatres have been built since antiquity to offer a better acoustic and visual experience of theatrical performance for large crowds [1]. The first theatres built in Greece adopted a semicircular shape with a concentric stepped structure, a configuration which improved the vision and allowed a homogeneous distribution of the sound. These theatres used to rest on the slope of a hill. Later, Romans remodeled many Greek theatres with the creation of more significant scenes connected to the structure of the cavea, where the audience was radially seated [2]. However, Roman theatres were also more complicated buildings; they were often built inside the cities, were composed of a series of arches, created concentrically with interconnected corridors on which the cavea was resting. Some theatres at the end of the Roman Empire were transformed into amphitheatres for the performance of gladiator shows too; however, with the fall of the Roman empire, most of these ancient theatres were abandoned, and often destroyed in the following centuries by earthquakes o by the aging [3].

While Greek theatres had a small and not too high scena (i.e., the stage for the actors) and modest-sized sidewalls, Roman theatres had a semicircular area for the orchestra, a significant wall behind the scena (Fig. 1) and were often larger. In Roman theatres, the cavea was covered with marble or bricks, and the stage and the scena were adorned with plasters, niches, and columns, which constituted beautiful scattering and reflecting elements for the sound distribution in the cavea. The stage wall was connected with the auditorium so that it closed the volume, allowing more sound reflections and an amplification of the actors' voices. The sound reflecting on the back wall of the scena represented a first first-order reflection, which was received evenly over the audience in the cavea and which increased the spatial perception of the sound (Fig. 1). The scena was also covered with a wooden roof that served as protection for the actors but also created another first-order reflecting surface. Moreover, the presence of awnings (called “velaria”) over the cavea, besides protecting the public from the sun, improved the acoustic conditions, again creating a semi-enclosed sound field. These awnings were employed in the most important theatres of the Roman Empire [3], although they did not survive to nowadays.

Many studies about the main architectural elements of ancient theatres and their related acoustic values have supported the belief that Romans knew the rudiments of sound science [4], [5]. The Roman architect Vitruvius, in the 1st century BCE, described in his book “De Architectura”, several rules to improve the acoustics during the construction of a theatre [6]. According to Vitruvius, to resolve the low strength of the actors’ voice in the theatres, several modifications to the theatres were made to support the sound resonance [7]; moreover, it is well known that vases and amphorae along the theatre steps were located to balance the reverberation between low and high frequencies [8]. Vitruvius reports several technical measures to avoid acoustic defects in theatres such as creating the section of the auditorium so that all the corners of the steps could be connected by a tight wire, and that the plan of the theatre should have a spherical profile. These elements were commonly found across the Roman Empire and during international projects conducted over the last two decades to investigate ancient Roman theatres [3], [5].

In 1973, Shankland measured speech intelligibility in several ancient theatres [8]. In the theatre of Epidaurus, he found that the listener in the most distant position along the central axis clearly perceived 72% of the words of the speaker placed in the center of the orchestra. Shankland also reported that in a Roman theatre, a moderate wind noise could reduce the intelligibility from 80% to 40%. The scores are arrived at by reading aloud from word lists at the center of the orchestra and noting the number of words correctly heard at different points in the cavea. For these measurements, the background noise and wind are extremely important factors for speech intelligibility in outdoor theatres.

Over the last fifty years, many studies have focused on the importance of first-order reflections from the orchestra. In 1967, Canac discussed how a better understanding of the voice was obtained by having hard surfaces on the orchestra to guarantee stronger first reflections [9]. He defined the listening angle of the inclination of the line connecting the speaker and the listener, as an indicator of the acoustic quality of a theatre; this angle decreases with the increase of the height of the stage and to preserve the integrity of the reflection so that Canada clarified that low stages are preferable to the orchestra. Canac also noted that when the orchestra was made of bricks, greater diffusion of the sound field occurred [9].

The original design of the ancient theatres is often significantly different from their current characteristics. Most of the restorations of the ancient theatres of the last decades, have tried to minimize the interventions. For example, it is common that only the bottom part of the cavea (e.g. the ima cavea) has been rebuilt. At the same time, the perimeter walls and the stage are rarely present, and consequently, the sound often lacks surfaces against which to reflect. These architectural characteristics make the listening conditions for the music particularly detrimental, often creating issues for modern performances [10]. To avoid complaints about the poor understanding or the insufficient levels of the sound, electroacoustic sound amplification systems are typically used [11], [12]. As evident, the modified architectural characteristics, together with new modern fruition approaches, have led to changes in the acoustics of these spaces, as they will be discussed in this paper. In particular, this paper aims to investigate the acoustic characteristics of five Roman theatres in Southern Italy that are currently used for performances during the summer seasons. The investigation will focus on the challenge of the acoustics of these theatres for modern use, and how their acoustics changes when they are fully occupied for modern performance.

The next section presents the five selected theatres; then, Section 3 reports the acoustic measurements performed in each theatre in empty conditions; Section 4 describes the virtual modelling of these theatres and discusses how their acoustics changes in different conditions; final remarks are reported in Section 5.

Section snippets

Selected theatres

This section described the theatres considered in the present study, which are shown in Fig. 2, and whose main characteristics are reported in Table 1. The sizes of the theatres are highly different, from the large theatre of Taormina (70 m of radius) to the small one of Cassino (27 m of radius) (see Table 2).

The selected theatres have all been heavily restored in the last two centuries, but they were “rebuilt” differently, some with terracotta brick blocks (such as the theatre of Benevento),

Methodology

The acoustic characteristics of the theatres were measured in-situ using an omnidirectional dodecahedron sound source in the central area on the stage in a common position for actors [23]. MLS signals of order 16, approximatively 5-second-long, were generated by a 01 dB Symphonie system [24]. The impulse responses were detected by omnidirectional microphones placed on the steps of the cavea with a fixed pitch along with three radial directions, one central and two laterals, to obtain average

Virtual acoustic model calibration

As discussed in previous sections, the current theatres are often particularly different from the original structures built during the ancient Roman Empire. It has been already discussed that these theatres were only partially restored and typical the restoration used modern materials such as cement or terracotta bricks, which have often changed their acoustic characteristics. Moreover, the reconstruction of the theatres only limited to portion of the cavea, while the scenic building behind the

Concluding remarks

The paper reports acoustic measurements made in some ancient theatres in Southern Italy that have been partially rebuilt and are nowadays used for summer performance. The results show that the absence of reflective surfaces such as the walls of the scenic building or part of the reconstructed cavea makes the acoustics challenge. The results show some insufficient acoustic characteristics, and as expected, values of the reverberation time that typically do not exceed 1 s. Given the also low

CRediT authorship contribution statement

Umberto Berardi: Conceptualization, Result discussion, Writing. Gino Iannace: Measurement, Modelling, Writing - editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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