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Measurement and Computer Simulation of the Acoustics of a Large Courtyard of “Reggia di Caserta” Gino IANNACEa and Elvira IANNIELLOb a
The Built Environment Control Laboratory (Ri.A.S), Second University of Naples, via San Lorenzo, Aversa (CE), ITALY,
[email protected] b
Department of Mechanical Engineering (DIMEC), University of Salerno, via Ponte Don Melillo, 1, 84084 Fisciano (SA), ITALY ABSTRACT
Music festivals are offered to public in one of the four large courtyards of the Royal Palace of the “Reggia di Caserta” (Italy). The event named “Leuciana Festival” is organized during summertime and most often pop music concert are performed in this large square surrounded by tall buildings. Sound reinforcement and electronic sound effects are used regularly by singers and musicians. This paper reports the results of a set of acoustic measurements carried out in the unoccupied courtyard fitted for a pop music concert and computer simulations implemented to study if the location is suitable for the performance of classical and symphonic music without the use of electroacoustic systems for sound amplification. A number of room-acoustics parameters were obtained from measurements; they were useful to calibrate a simple virtual model of the courtyard. The computerized simulation allowed the calculation of more parameters in a larger number of occupied seats. Results showed that the objective acoustics of the courtyard are not much far from acceptable conditions for symphonic concerts performance. In particular, the rate of decrement of the sound pressure level vs. the distance from the stage seems to be good enough.
1. INTRODUCTION Outdoor locations are used often for public shows during summertime. There are various reasons that can explain this choice. For example, a location that can host a large number of spectators, temporary installations that are cheap enough with respect to permanent venues, attractive factors like architectural surroundings, appealing natural sights, comfortable environmental conditions and site valorisation are possible motivation that inspire the managers of a show for the selection of a site outdoors. Urban squares, large terraces, foot-ball fields, open fields and similar sites are not conceived for good acoustics. However, attention is paid now to existing acoustic conditions in some places where public performances are organized [1,2,3]. Acoustic measurements and computer simulations are carried out to obtain both objective and predictive data to study possible enhancements of the acoustics for the intended purpose. This paper reports a study about the acoustics of one of the four large courtyards in the huge Royal Palace in the “Reggia di Caserta” (Italy). The construction of this monumental site started in the 18th century under the directions of the famous architect Luigi Vanvitelli at the order of King Charles III of Bourbon. Fig. 1 displays two views of the courtyard fitted with a stage and about 4,000 plastic chairs on the occasion of a pop concert of “Leuciana Festival 2009”. The courtyard has a length of 78 m and a width of 53 m. The height of the surrounding buildings is about 35 m. Large passages interconnect the four courtyards through pillars with arches while other large openings lead to rooms at the same level and to stairs to reach higher floors.
Figure 1. Views of the courtyard in the Royal Palace of the “Reggia di Caserta) fitted for a pop concert: (a) toward the stage; (b) toward the back.
2. ON SITE MEASUREMENTS AND RESULTS Measurements were carried out in the unoccupied courtyard with only one location of a dodecahedral loudspeaker on the axis of the stage floor, at the height of 1.6 m and about 5 m from its frontal edge. A total of 15 microphone locations at the height of 1.3 m in the area of chairs (blue and black in Fig.1) arranged on the flat ground were considered. The analysis of the responses to powered MLS signals yielded single channel room-acoustics parameters. As an example Fig.2 shows the average octave-band values of EDT, T30, D50 and C80. The dashes above and below an average value represent an interval of two standard deviations.
Figure 2. Measured average values of EDT, T30, D50 and C80 ± 1 standard deviation.
3. VIRTUAL MODEL AND SIMULATION A rather simple virtual model (Fig.3a) of the courtyard was first calibrated by trial and error in the aim of minimizing the difference between the measured space-averaged values of T30 and the corresponding calculated values (Fig.3b). The parameters for the room-acoustics software stemmed from the empirical minimization process were used to calculate parameters accepted for the description of the sound quality in concert halls.
Figure 3. (a) Simple geometrical model of the courtyard in the Royal Palace in the “Reggia di Caserta”. (b) Comparison between measured and calculated space-averaged values of T30 and standard deviation.
The calculations were carried out with the consideration of one sound source on the stage and 50 receivers distributed almost uniformly in the seating area at the height of 1.3 m, sloping part included (red chairs in Fig.1b). Results reported in Fig.4 refer to the full occupation of chairs. For the sake of brevity only four maps of calculated room-acoustic parameters are reported, i.e. EDT, C80 and SPL (ref 20 Pa) averaged in the three octave bands at 500, 1000 and 2000 Hz and Early Lateral Fraction LF averaged in the octave bands from 125 to 1000 Hz. For the evaluation of SPL it was assumed that the sound source radiated the sound power
of 1/3 W in each one of the three considered octave bands. This is a very rough approximation for the sound power radiated by a full symphonic orchestra in “tutti and fortissimo”.
Figure 4. Maps of selected room-acoustics parameters obtained with the computer simulation.
4. CONCLUSIONS The results stemmed from the present study suggest that the courtyard in the Royal Palace of the “Reggia di Caserta”, as fitted for pop music concerts, could be used also for the performance of orchestral symphonic music with no high risk of bad acoustics. As expected, the considered room-acoustic parameters depend on the seating area in a certain degree. However, it can be noted that the important aspect of the sound level attenuation vs. distance from the sound source in partially open venues is a negligible problem in this large courtyard. 5. REFERENCES 1 D. Paini, J. H. Rindel, A. C. Gade and G. Turchini “The acoustics of public squares/places: a comparison between results from a computer simulation program and measurements in situ”, Proceedings of Internoise 2004, Prague, 2004. [2] D. Paini, A.C. Gade and J.H. Rindel, “Is reverberation time adequate for testing the acoustical quality of unroofed auditoriums?”, Proceedings of the Institute of Acoustics, Vol. 28. Pt.2, 2006, pp. 66-73. 3 T. Halmrast, “The acoustics of a quarry, who needs an acoustician? ”, www.akutek.info.
