19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007

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1 19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007 ACOUSTICS AS A TOOL TO SUPPORT THE ARCHAEOLOGICAL RECONSTRUCTION OF ANCIENT THEATRES : THE CASE STUDY OF OSTIA ANTICA PACS: Cs Gugliermetti, Franco 1 ; Bisegna, Fabio 1, Monaco, Andrea 2 1 Dept Fisica Tecnica, University of Rome La Sapienza ; Via Eudossiana 18, 00184, Rome, Italy; franco.gugliermetti@uniroma1.it; fabio.bisegna@uniroma1.it 2 Dept Ingegneria Industriale, Università degli Studi di Perugia, Perugia, Italy ABSTRACT Archaeologists face up with the problem of the historical reconstruction of ancient theatres that show different state of conservation and, during the centuries, have suffered for changes in their structures. The acoustics can play a very important role in supporting the choice of the best or almost the more acceptable reconstruction among different possible alternatives. Computeraided simulation can provide a well-estabilished tool for this task. The roman theatre of Ostia Antica is and was the subject of many studies devoted to the reconstruction of its architecture during the centuries, for the original construction of Agrippa (beginning of II century B.C.), with the capacity of 3000 people, to the enlargment till to 4000 seats made by Commodo (at the end of the II century), to the restoration by Celso (IV century) and its adaptation to "tetinimi" (water play) and, at the the end, the drastic reconstruction of The paper presents different hypotheses of virtual reconstruction of the Ostia Antica theatre, developed with the help of archaelogists on the base of historical data and records, and analyses their acoustic behaviour by numerical simulation, in order to support the improvement in the knowledge of the theatre in all its stages. INTRODUCTION The requalification and improvement of the conditions of ancient theatres are two extremely actual topics [1], especially in a period in which the reuse of these structures for cultural events is bringing to an increase of the archaeological tourism. Several studies have been developed to put in evidence the historical monumentality of these structures, and to point out the proper architectural solutions to bring to a new life their optimal acoustic properties. Their particular shape is enough to assure the acoustical quality of these environments: materials, geometry, ripartition of the spaces, clarify and testify the basic importance of this aspect, as well as the importance of the visual aspect, considered by all the ancient greek and roman designers [2]. In the past, a lot of projects concerning the acoustics of historical environments have been developed, and particularly for the open theatres (CAHRISMA, ERATO, MINOTEC and THEATRON projects). The ERATO (Evaluation and Revival of the Acoustical heritage of Ancient Theatres and Odea) project was mainly oriented to the reconstruction of the acoustical sensation perceived inside the greek and roman theatres, using auralisation and computer aided simulation techniques. The results obtained show that in some cases there are significative differences between simulated and measured values of acoustical quality indexes [3,4]. Vassilantonopoulus carried out a comparative study on the acoustics of several theatres, a thorough analysis on the spatial distribution of the acoustic field and its reconstruction by auralisation [5,6]. In this paper different hypotheses of virtual reconstruction of the Ostia Antica theatre, developed with the help of archaelogists on the base of historical data e records, are presented, with the aim to analyse their acoustic behaviour by numerical simulation, in order to support the improvement in the knowledge of the theatre in all its stages. The final result is the tracement of the acoustic history of the theatre, from the ancient Romans till today.

2 HISTORICAL EVOLUTION OF THE ROMAN THEATRE OF ANCIENT OSTIA Historical and architectural information available on the ancient theatre of Ostia are not complete, and the lack of knowledge especially concerns the kind of materials used in the last stages of construction, and the definition of some structural elements that, although marginal from an architectural point of view, they could be of some importance for the acoustical point of view. Thanks to the work of many researchers [7,8,9,10], anyway, the historical development of the theatre during the years could be considered known, and it basically follows the stages of the Roman Empire and of the town of ancient Ostia. The theatre is part of a very big roman city planning, city that was built around the VI sec. b.c. Firstly, it was a military settlement, whose aim was to control the coast. Then, thanks to the harbour on the bridge, that represented a link between Rome and the rest of the world, Ostia received a strong economic growth, followed by a cultural and artistic development, and still today Ostia can be recognized as one of the most important evidence of the roman civilization, thanks to excellent state of conservation of the site. Figure 1.- A view of the theatre, as it is today. The construction of the theatre belongs to the I sec. b.c. An inscription ascribes it to Agrippa, son in law and powerful minister of the Imperor Augusto, dead in the 12 b.c. In its historical evolution, the theatre passed through four different steps of construction. In the first three steps, no substantial alterations of the façade, for what concerns the stage, and of the cavea were introduced. The most important modifications were a progressive increase of floor, owing to the development of the sewer system, and the outer side of the building, with the recovery of the porticus post scenam, that is the back side of the scene, overlooking Piazzale delle Corporazioni. In these stages, the cavea was composed of two levels quite totally realised with tuff, and two entrances placed at the two sides of the scene (paradoi) were destined to control the entrance of the public. The dimensions of the stage were comparable to the last structure. In the fourth and last stage, II sec. d. C., the most relevant modifications were introduced. The construction work started with Commodo, and was finished by Settimo Severo and Caracalla. A third line of steps was added, the stage was enlarged to reach the height of the portico created on the top of the cavea (porticus in summa cavea), and a third doorway to the theatre was created in the central part of the cavea, to assure an easier entrance and exit of the public. The steps of the cavea were completely covered of marble plates, and the scene was furtherly adorned with niches, porticos and frescos. In this historical period we could set the construction of cisterns by the two side flow corridors. It is suppposed that the cisterns were needed to set special kinds of performances, which make use of the flooding of the orchestra for about a meter and a half [9]. The performances represented scenes of marine wars, on a smaller scale respect the impressive naumachiae represented in some roman places, or love scenes of nynphs [10]. The actual configuration of the theatre is due to the heavy recovery done in As it was foreseen, it can hold an audience of 3000 persons, and it is 80 m in length and 40 m in width. 2

3 METHOD By the use of software to evaluate the acoustic field, it is possible to reconstruct the acoustical behaviour of completely lost spaces, as well as damaged or ruined environments, or still never existed places [11]. The auralisation mechanism, combining an impulse response with an anecoic signal, allows a faithful reproduction of the acoustical sensation produced in the environment. A model, very similar to real structure, in the shape and in the materials used, and then a proper definition of the calculation hypotheses and of the parameters used in the simulation is required to obtain results of some value. In this study, the Brüel & Kjær software Odeon 6.05 Combined has been used. In the case of Ostia, archaeologists agree on the historical changes in the structure of the theatre, while some disagreements appear in the definition of the materials and in some structural elements. The knowledge of the influence of these elements is consequently required for a global evaluation of the acoustics of the theatre. This is why several models of the theatre have been created and analysed by software simulations. For the two structural tipologies examined, the first one corresponding to the initial configuration of the theatre, and the second one corresponding to the final configuration realised by Commodo, Settimo Severo and Caracalla and previously described, several cases, based on different boundary conditions have been studied (Fig. 2-4): the presence of a tilted covering at the top of the stage, considered in some reconstructions of the theatre, compared to the standard situation without the covering; the presence of water in the orchestra and in the first steps, for a total height of the water up to 1.4 m, to simulate the acoustic field of the performances representing marine contexts; the presence of marble or sand to characterise the floor of the orchestra. All these conditions have been analysed referring to the base case, that is the theatre in the actual configuration, studied by the authors [12,13] by both numerical and experimental approaches, following the ISO 3382 standard [14]. Figure 2.- A Reconstruction of the theatre, II sec. d.c. a) b) Figure 3.- A reconstruction of the theatre (II sec. d.c.), without a tilted covering (a) and with an orchestra full of water (b). 3

4 a) b) Figure 4.- A reconstruction of the theatre (I sec. a.c.) with orchestra in marble (a) and sand (b). To better evaluate the acoustical properties of the considered structures, three more source points have been introduced next to the stage, and six more receiver points have been placed on the third line of steps, to represent the theatre of the II sec d.c. (Fig. 5). Figure 5.- Positioning of the source and receivers on the plot of the actual theatre RESULTS The results of the simulations are very interesting. All the models are characterised by the presence of a reverberation field that is missing in the actual configuration of the theatre, lacking of the stage and of the marble that covered the steps. So, to better understand the acoustic quality of the different models implemented and to compare them with other cases [15,16], simulations were performed in the case of presence of audience. Higher values of the reverberation time were obtained inside the theatre of the II sec. The reason of this fact could be found in the presence of a great number of surfaces (basically marbles) characterised by a low assorbance coefficient, in the shape of the structure, that is open towards the outside only in the upper part, and in the presence of specific architectural elements, like the porticus in summa cavea and the tilted covering. Their positioning in the upper part of the theatre infact makes easy to keep the sound energy inside the structure. We have values of the reverberation time (T 30 ) up to 1.5 s, and this value is smaller of about half a second when the tilted covering is not present. A further reduction of the reverberation field is obtained moving the source to the orchestra (Tab. I), reduction due by the smaller acoustical support given by the stage [5]. 4

5 Table I.- Acoustical parameters when the source is in S1 and the receiver in 12. Historical Period EDT (s) T30 (s) G (db) C80 (db) D50 Ts (ms) STI I sec a.c I sec a.c., orchestra with sand II sec d.c II sec. d.c. no cover II sec. d.c. orchestra full of water Actual state (measure) Actual state (simulation) The same considerations could be done considering the energetic parameters [17]. We found high values of the reverberation field in the case with the orchestra full of water, owing to the increase of the number of reflecting surfaces. This factor contributed to the creation of the austere atomosphere required to show marine battles. The acoustic field related to the first age theatre (I sec. b.c.) is of lower entity, and consequently we found values of the reverberation time up to 1,5 s. This factor influences also the value of the sound pressure level, evaluated with the parameter strength, G, that is referred to the value of the sound pressure level we have in a free field. In this case, we obtained a value of G lower than the one we obtained for the theatre of the II sec. We find an opposite situation instead when we considered the energetic parameters, that are directly linked to quality of the acoustical perception. A narrower structure that is close to the outside does not result fit for performances that require a more accurate comprehension of the syllables, and higher values of clarity and definition. It is still interesting to note that when the orchestra in completely full of sand there is a light increase of all these parameters, owing to the higher value of the assorbance coefficient, whose effect is a reduction of the secondary reflections, especially when the source is placed on the stage (table I). In Fig. 6 it is possible to have a graphic outlook of the variation of T 30 for all the examined cases and in function of the frequency. The trends are similar to those found in previous works [15,16], the presence of audience affects values of parameters corresponding to mid and high-levels frequencies causing a lowering of trends. T30 (s) Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Freq (Hz) 5 T30 I sec b.c. T30 I sec sandy floor T30 II sec a.c. T30 II sec naumachie T30 II sec no covering Figure 6.- Simulated data of Reverberation time (T30), as a function of frequency (Hz) Results obtained for source placed on the orchestra were compared with those obtained by experimental sessions of measurements and simulations (Tab. I, last line) for the actual state of the structure [12]. Due to the absence of the stage, to the deterioration of materials and consequently to the acoustic characteristics much similar to an open space, reverberation field in the actual configuration is almost absent and so energy parameters are higher then those in the other case, so for this reasons it s more suitable for spoken performances.

6 CONCLUSIONS Aim of the present paper is the evaluation of the historical evolution of the acoustics of the open air roman theatre of ancient Ostia, from its construction till now. Through a collection of information concerning the structural changes of the theatre along the centuries and the materials used in its construction, it has been possible to get ready some models to simulate in a software for the evaluation of the acoustic field (Odeon 6.05 Combined). Once defined the two basic structures of the theatre, several hypoteses concerning the building and the materials have been considered. It has been possible so far to analyse the structural evolution of the building, that on one side implied an increase of the seats destined to the public, on the other side caused a progressive depletion of the acoustical quality and of the intelligibility of the theatre, and an increase of the reverberation field and of the acoustic energy inside the structure. All these aspects were obtained basically using architectural elements that were probably added to the basic structure of the theatre appositely to create these phenomena. Once defined for sure the kind of performances on the stage in the different ages, it will be possible to quantify the role of the structure and to better comprehend how much the kind of performance influenced the design of the theatre. Aknowledgements This work was carried out within the national research program ATLAS Ancient Theatres Lighting and Acoustic Support co-founded by the Italian Ministry for University and Research (MIUR). We wish to thank for their active collaboration Prof. Pensabene, for the historical reconstruction of the theatre, and the Monuments Office and especially Ms Bedello for giving us the permission to develop our experimental studies on the theatre of ancient Ostia. References: [1] F. Gugliermetti, Le Metodologie per l Analisi e il Recupero Funzionale dell Acustica nei Teatri Antichi, Atti II Cong. Int. La Materia e i segni della storia:teatri antichi nell area del mediterraneo, Siracusa ott [2] R. S. Shankland, Acoustics of Greek Theatres, Physics today, vol.26, (1973) pp [3] A. C. Gade, M. Lisa, C. Lynge and J. H. Rindel, Roman Theatre Acoustics; Comparison of Acoustic Measurement and Simulation Results from the Aspendos Theatre, Turkey, Proc. Symp. 18th International Congress of Acoustics, Kyoto, (2004) [4] M.Lisa, J. H. Rindel and C. Lynge Chr., Predicting the Acoustics of Ancient Open-Air Theatres: the Importance of Calculation Methods and Geometrical Details, Proc. Symp. Joint Baltic-Nordic Acoustics Meeting, pp. 8-10, Mariehamn Aland, (2004) [5] S. L. Vassilantonopoulus and J. M. Mourjopoulos, A study of Ancient Greek and Roman Theater acoustics, Acta Acustica United With Acustica, vol. 89, (2003) pp [6] S. L. Vassilantonopoulus and J. M. Mourjopoulos, Virtual Acoustic Reconstruction of Ritual and Public Spaces of Ancient Greece, Acta Acustica United With Acustica, vol. 87, (2001) pp [7] I. Gismondi, La Colimbetra del Teatro di Ostia, Anthemon pp [8] P. Battistelli, G. Greco, Lo sviluppo architettonico del complesso del teatro di Ostia, alla luce delle recenti indagini nell edificio scenico, MEFRA Tome (2002) pp [9] G. Calza, Il Teatro Romano di Ostia, SEAI Milano [10] [11] A. Farina and A. Avanzini, Registrazione della Risposta Acustica delle Sale da Concerto per i Posteri, AES Italia Workshop sulle tecniche di ripresa, Adria (2003). [12] F. Gugliermetti, F. Bisegna, A. Monaco, Il recupero funzionale dei teatri antichi: l analisi acustica nel caso studio del teatro romano di Ostia. Atti del 61 Congresso Nazionale ATI (2006) [13] F.Gugliermetti, M.Bedello, F. Bisegna, Studi acustici sul teatro di Ostia Antica: primi risultati, Atti III Cong. IGIIC Lo stato dell Arte, Sett. Palermo, Italia [14] UNI EN ISO 3382, Misurazione del Tempo di Riverberazione di Ambienti con Riferimento ad altri Parametri Acustici, (1997). [15] M. Lisa, J.H. Rindel, A.C. Gade, C.L. Christensen, Acoustical computer simulations of the ancient roman theatres. Erato Project Symposium, 20 th January 2006, Instanbul, Turkey, pp [16] M. Lisa, J.H. Rindel, A.C. Gade, How did ancient Roman Theatres sound? Proc. Forum Acusticum 2005, Budapest, Hungary [17] ODEON Room Acoustics Program Version 6.5, User Manual, Industrial, Auditorium and Combined Editions 6