The city of Ravello and its hundreds clerical buildings. Acoustic discoveries of the St Mary Gradillo’s church. Silvana Sukaj 1 Department of Engineering and Architecture European University of Tirana (UET), 1000, Tirana, Albania Nicola Chiacchio 2 University of Campania Luigi Vanvitelli Borgo San Lorenzo 81031, Aversa (Ce), Italy Rosaria Parente 3 Benecon University Consortium Via Costantinopoli, 104, Napoli, Italy

ABSTRACT Hundreds of churches and monasteries have been erected in a small town nearby Naples during the Medieval Age. A recent proposal by the local authority regards the utilization of some clerical build- ings to be part of the places selected to host musical venues during the festival that is annually re- curring in Ravello. The St Mary Gradillo’s church has been built during the 11th century, to be composed by three naves marked by columns, following the architectural features of a basilica. The different height and typology of roof, to be a double slope in the central nave and vaulted in the lateral ones, is characterised by a dome located at the junction of the wings crossed at the level of the altar. This paper deals with the assessment of the existing acoustic conditions of the church. The evaluation is based on the analysis of the main acoustic parameters in accordance with ISO 3382-1..

1. INTRODUCTION

Ravello is a small town located on the Amalfitan coast, around 350 meters above sea level, and has hosted for over twenty years a music festival, which in recent years with the denomination " ravel- lofestival " has received international valence (value). Within the " ravellofestival " are organized a series of musical events such as concerts of lyrical music, symphony, prose show, classical dance (dance), film projection, conventions and discourses in a period of the year between June and Sep- tember. The spectacles are held in different places of Ravello: auditorium, villas Ruffolo, cathedral, monumental churches (St Mary Gradillo), the cathedral square, although the most suggestive place

1 silvana.sukaj@uet.edu.al 2 nicola.chiacchio1@studenti.unicampania.it 3 rosaria.parente@benecon.it

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is the garden of villas Rufolo. The St Mary Gradillo’s church is presented as a basilica with three naves, separated by three columns for each basilica, holding acute arches on high vertical supports, transept raised three semicircular apses. The central nave is covered by a caprice roof; extrados cross vaulted laterals. The dome, on a slender drum, rises above the central span of the transept, attached by two extrados crossed vaults. From the outside, the façade divided into three parts presents three gates with bezels. The bell tower located on the right is with two orders of cylindrical columns dec- orated with polychrome geometric incrustations. The church was built in the XI century and trans- formed into Baroque style in ‘700, the church has been completely restored to its original style with the restorations followed in the years 1958 - 1963. In this church clearly appears local architecture because, above the classical scheme are engaged organically and harmoniously Byzantine and Arabic elements. In the Middle Ages the St Mary Gradillo’s church was the parochial seat of the people; here the general captain of the whole duchy of Amalfi solemnly took possession, and the people of Ravello met to discuss public matters. Figure 1 shows the (A) the external view and (B) the internal view. Figure 2 shows the (A) the internal view and (B) the internal view of the central vault.

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A B Figure 1: (A) external view. (B) internal view.

B

A

Figure 2: (A) internal view. (B) vault internal view.

Figure 3 shows the plant of the church with the main dimensions; Figure 4 shows the section with main dimensions; while Figure 5 shows the three-dimensional view of the church.

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Figure 3: Plant of the church with the main dimension.

Figure 4: Section of the church with the main dimensions.

Figure 5: Three-dimensional view of the church.

2. CHURCH ACOUSTICS

Church acoustics have been the subject of various studies in recent years [1-3]. But a problem is presented by their different dimensions and their spatial complexity. Meanwhile, the sound sources in a church can be located in different positions. Churches are acoustically complex places [4-6]. This complexity derives from the geometries and materials used for construction (plaster, marble, putty) that contribute to the formation of an excessive reversal time. A short reverberation corresponds to a dull room, where the surfaces absorb the decaying sound energy, as in the open air. When sound is emitted indoors it is reflected from different surfaces in such a way that the direct sound reaching the "receiver" is followed by reflections on the walls, these reflections can be as intense as the direct sound and depend on the relative positions of source and receiver. Readings and conversations require a short reverberation (<1 s) to give a good understanding of speech while Gregorian songs require over 3.0 s rehearsal to quench the sense of community participation. In fact the ideal values of rever- beration times derive from studies of concert halls, conference venues and theaters [7-10]. In general, the optimal values of the reverberation time are given for the average frequencies (500-1000 Hz). During the celebration of a liturgy, different typologies of voice messages coexist, each of which requires different acoustic conditions [11-13]. Organ music requires a long reverberation ( > 3 s) but instrumental music sometimes requires a rehearsal 1.5 s. the presence of the public is responsible for the greater absorption of sound, consequently the acoustic conditions vary between an empty church and a completely filled church [14-15].

3. ACOUSTIC MEASUREMENTS

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The acoustic measurements were carried out with a spherical omnidirectional sound source located on the altar, and 12 microphone measurement points placed in different positions in the area occupied by the listeners, in accordance with ISO 3382 [16]. The impulse responses were detected with a measurement microphone GRAS 40 AR. The sound source was powered with a MLS signal whilst the elaboration of the impulse responses were made with the software Dirac 4.0. During the acoustic measurements, the background noise was lower than 35 dBA, the church was empty and the furniture were hard chairs [17-21]. Figure 6 shows the plant of the church with the indication of the position of the sound source and the receiver microphone points.

Figure 6: Plant with the position of sound source and of the measurement points.

The sound source was placed at a height of 1.6 m from the floor and the microphone 1.3 m from the floor, in the area occupied by the audience. The measured sound impulse is processed with Dirac software, which gives us monaural acoustic parameters (T30, EDT, D50, C80 and STI). The receivers

are collided at different points of the hall, in different positions evenly distributed. During the acoustic measurements the room was empty, the public was not present. The most widely used monaural pa- rameter is the reverberation time (T60), ie the time required until, after the interruption of the sound emission of a sound source, the sound pressure level in the room is reduced by at least 60 dB. This parameter varies as a function of the volume of the room and the total acoustic absorption of the surrounding surfaces. While the acoustic absorption of materials varies with frequency, the RT pa- rameter also changes with frequency and is rated at frequencies in the octave band from 125 Hz to 4.0 kHz. Often in a room it is not possible to obtain a sound drop of 60 dB, due to the excessive presence of background noise or objective difficulties: in these conditions, the sound level drop, for estimating the reverberation time, comes above a change 30 dB and the relative parameter is set T30. Other parameters for the evaluation of acoustic characteristics are: EDT, Definition (D50), Clarity (C80), STI. EDT (Early Decay Time): the time used for the sound level to drop from 0 to -10 dB; takes into account the components of direct voice and evaluates the subjective perception of sound loss. The definition, D50, evaluates the meaning of speech. In an environment where reverberation and excessive background noise are present, achieving word comprehension can be particularly dif- ficult. The definition, D50, introduces the ability to distinguish sounds that follow each other in time or that arrive simultaneously from different sound sources. The clarity, C80, is a function of rever- beration time; it is also a function of the listener's distance from the sound source and consequently depends on the subjective intensity of the direct sound. The literature of the applied acoustics sector brings tables and diagrams that determine the optimal reverberation time (also for other parameters) in function of the destination of use and the volume of the considered room. In the field of architec- tural acoustics, in order to offer good acoustic prestige, a room must respect the values of the param- eters given in Table 1. Meanwhile, a conference room should have a short reverberation time (no longer than one second) to allow a good understanding of speech. While a hall intended for musical listening, there should be a longer reverberation time, in such a way as to generate multiple reflections that improve the perception of musical listening. Therefore a room, depending on the destination of use, must have an optimal reverberation time. In order to objectively evaluate the acoustic behavior of the room, surveys with valuable instruments were followed [22].

Table 1. Optimal acoustic parameter values for the different listening conditions.

Parameters EDT, s T30, s C80, dB D50 Value for listening the music

1.8 < EDT < 2.6 1.6 < T30 < 2.2 -2 < C80 < 2 < 0.5

Value for comprehension,

meaning of speech 1.0 0.8 < T30 < 1.2 > 2 > 0.5

The STI (Speech Transmission Index) parameter is a value for the objective definition of the intelli- gibility of speech in a room. The STI index aims to objectively quantify the comprehensibility of speech in a specific position in a room: (bad < 0.32); (poor 0.32 – 0.45); (fair 0.45 – 0.60); (good 0.60 - 0.75); (excellent > 0.75). The monaural acoustic parameters were analyzed: T30, EDT, D50, C80 and STI. Figure 6 shows the average values of the acoustic parameters EDT (s) in the octave bands from 125 Hz to 4.0 kHz. Figure 7 shows the average values of the acoustic parameters T30 (s) in the octave bands from 125 Hz to 4.0 kHz. The EDT and T30 parameters have a constant value from the frequency of 125 Hz to that of 1.0 kHz and it is equal to 4 s, and then rapidly decrease to 1.5 s at the frequency of 4.0 kHz at this frequency the absorption of the air. The values of EDT and T30 are however excessive for speech understanding.

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Figure 6: Average values of the acoustic parameters EDT (s) in octave bands

Figure 7: Average values of the acoustic parameters T30 (s) in octave bands

Figure 8 shows the average values of the acoustic parameters C80 (dB) in the octave bands from 125 Hz to 4.0 kHz. The parameter C80 increases with the frequency from - 5 dB at the frequency of 125 Hz to 3.0 dB at the frequency of 4.0 kHz. In the frequency range between 250 Hz and 2.0 kHz, parameter C80 falls within the interval considered optimal for good music listening. Figure 8 shows the average values of the acoustic parameters C80 (dB) in the octave bands from 125 Hz to 4.0 kHz. The parameter D50 increases with the frequency from 0.2 at the frequency of 125 Hz to 0.5 at the frequency of 4.0 kHz. The values of D50 indicate that the church does not have good conditions for speech understanding. Excessive sound tail indicates that speech understanding is poor. In fact the church has modest dimensions and the walls and the floor are rigid and smooth surfaces and therefore acoustically reflective due to the presence of plaster, marble and wooden seats, in the church there are no sound absorption elements such as carpets or paintings. The measured mean value of the STI is equal to 0.43.

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Figure 8: Average values of the acoustic parameters C80 (dB) in the octave bands

Figure 9: Average values of the acoustic parameters D50.

4. CONCLUSIONS

This work reports the acoustic measurements in the interior of a used church, built in the Middle Ages, both for sacred functions and in recent years it is used for the shows of the "ravellofestival". Acoustic measurements confirmed that the church does not have good characteristics for speech un- derstanding, but has good conditions for listening to music 6. REFERENCES

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