Acoustics 08 Paris

The Royal Church of San Lorenzo in : Guarino Guarini and the architectural acoustics M. Caniatoa, F. Bettarellob and M. Masoeroc

aUniversity of Trieste, Piazzale Europa, 34100 Trieste, bEngineering Dept. - Univ. of Ferrara, Via Saragat, 1, 44100 Ferrara, Italy cPolitecnico di Torino, Corso Duca degli Abruzzi 24, 10123 Torino, Italy [email protected]

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In 1666 the architect Guarino Guarini received from Carlo Emanuele II, Duke of Savoy, the appointment to build in Turin a new church dedicated to S. Lorenzo. The architect conceived a design in Baroque style with a very particular ribbed dome and this peculiarity is a very hard to find feature throughout Europe. Acoustics measurements were performed in S. Lorenzo in order to investigate how this unique architecture affects the response parameters used in architectural acoustics. Results are discussed in this paper, comparing to the methodology suggested by Cirillo and Martellotta in order to characterize the acoustics of churches.

second position (s2) in order to investigate how the sound field may change due to this particular architecture. 1 Introduction The measurements were then analyzed with Adobe Audition® and Dirac® software, in order to determine the In 1666, Duke Emmanuel Philibert II of Savoy appointed to acoustical descriptors according to ISO-3382 and IEC- Guarino Guarini the design of San Lorenzo church in Turin. 60268-16 [1]. Mathematician, theologian and, above all, architect, he The average reverberation time measured in the church conceived an octagonal central plan church. The building main volume is shown in figure 2. The average value of T30 has a very peculiar inner composition: neither straight lines, falls in the 2-4 seconds range. This range is indicated in the nor regular volumes or parallel walls are present (Fig. 1a). literature as good for churches [2]. We can therefore It is composed by two coupled volume (main room and conclude that the reverberation time of this church, in spite Crucifix Chapel that consists of a roughly rectangular of its large dimension, provides an acceptable acoustic shape). The main room is divided in two volumes: the quality [3]. bigger consist of a central plan room and the second one

consist of en ellipsoid plan room. All the lateral chapels, the RT average with deviation standard (S1 position)

dripstones (Fig. 1b), and whatever may be found inside the 6 church, show a curved profile. 5

4

[s] 3

2

1

0 25 40 50 63 80 100 125 160 200 250 315 400 500 630 800 31.5 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 RT average [Hz]

Fig. 2 Average of reverberation time for s1 source position

This particular phenomenon is probably due to the peculiar inner conformation, which determines a good sound diffusion, thus allowing a fair listening condition. Guarini a) b) did not foresee this effect: in fact he knew the scatter Fig. 1 a) Plan of the San Lorenzo church with measurement phenomenon but he didn’t consider the sound as a positions; b) particular of the dripstones curved profile frequency-dependent phenomenon [4]. So we investigated how the sound field may vary in the different positions in order to point out how the Gaurini Acoustic measurements were carried out in the positions design influences the listening. shown in Fig. 1a. The source was located in three different positions: behind the altar, behind the lectern position and

in the middle of the central plane. We choose 17 receiver 4.0

positions located only in a half of the central plan. The 3.8 points displayed with an “°” stand for measurements 3.6 performed with the heavy dividing door open between the 3.4 two coupled volume. 3.2 3.0 [s]

2.8 pos. N°7 pos. N°3 pos. N°6 2 Measurements and results 2.6 2.4

2.2 Impulse response measurements were carried out using the 2.0 0 5 10 15 20 25 sine sweep technique, generating two sine sweeps for each distance from the source S1 [m]

of the three positions of the sound source (s1, s2, s3); taking RT at receiver positions RT average advantage to its symmetry, the source was placed in the left part of the building only. Several measurements were Fig. 3 comparison between average reverberation time and performed for source in the first position (s1) and for the reverberation time in each receiver positions for s1

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Acoustics 08 Paris

As shown in figure 3 the reverberation time doesn’t change Figure 5 shows that the reflections aren’t strong enough in sensibly moving through the church. The sound field in the the receiver positions near the s1 source. This is due to main room is then homogenous; the three positions that strong diffusion caused by the inner architecture. From the differ from the average are particular ones: center of the dome (about 10 meters distance from s1) the sound field becomes more homogenous reaching the aims • Position 3 is under the dome and furthermore is in the center of the central plan. As explained in of Guarini. literature this is due to the central plan conformation of the church [5] EDT average with deviation standard (S1 position)

• Position 6 and 7 are far from the source and this 6 cause the lowing of reverberation time. 5

4

3 [s]

2

1

0 25 40 50 63 80 100 125 160 200 250 315 400 500 630 800 31.5 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 [Hz] 10000 EDT average a)

4.0

3.8

3.6

3.4

3.2

3.0 [s]

2.8

2.6

2.4

2.2 Fig. 4 average T30 sound field distribution 2.0 5.5 6.3 7.3 7.4 7.75 9.1 9.6 10 10.1 11 12.1 13.5 13.8 15.1 15.9 19.6 distance from the source S1 [m] The average values and standard deviation of T30 at low, middle and high frequency assure us a well-blended RT at receiver positions EDT at receiver positions ambient sound field (fig. 5) b) Fig. 6 a) Average EDT parameter and its standard deviation

RT average at low, middle and high frequency b) comparison between T30 and EDT parameters with distance 4

3.5 Coupled volumes. 3 As one can notice in figure 1 a) the building is divided in 2.5 two main volumes: the main room and the Crucifix Chapel. 2 [s] These volumes are divided by a heavy door which 1.5 sometimes may be opened ye the priest in order to receive more people, especially in the summer. 1

0.5 So when the heavy door is open, the Crucifix Chapel acts as a coupled volume influencing the sound field as shown in 0 LF MF HF figure 7. RT average [Hz] Fig. 5 Average of low, middle and high frequencies of reverberation time for s1 and their standard deviation

The comparison between T30 and EDT parameters (fig. 6) shows how the sound field varies among different positions. This comparison is useful to understand how the first reflections act in the receiver position.

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Acoustics 08 Paris

influence of the coupled volume on RT (S1 position) 6 D50

5 1.00

4 0.80

3 [s] 0.60 50 D 2 0.40

1 0.20

0 0.00 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 25 40 50 63 80 100 125 160 200 250 315 400 500 630 800 31.5 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 media 0.51 0.40 0.46 0.53 0.49 0.51 0.44 0.40 0.29 0.21 0.22 0.20 0.23 0.24 0.24 0.25 0.25 0.30 0.39 0.43 0.35 0.39 0.47 0.58 0.66 0.75 0.84 [Hz] 10000 [Hz] average w/o copled volume average with coupled volume c) Fig. 7 Influence on the Crucifix Chapel for s1

Fig. 8 Other acoustical parameters for s1: a) Average of C80 This figure shows how the coupled volume act as an versus frequency; b) C80 versus distance from s1 source; c) “absorber” for the low frequencies but as a slight Average of D50 versus frequency “amplifier” for the high frequencies. However it supplies a good effort to the sound field lowing down these frequencies. 3 Comparison with other measure- The sound field shown is the average of the three position ments methods measured with the door displayed in figure 1 a). Many studies have been carried out on churches. In Other acoustical parameters. particular a new measurements standard is proposed from Cirillo and Martellotta [3]. They rightly observe that it is no The other acoustical parameters such as clarity (C80) or more possible to use theater measurements standards in definition (D50) behave like the reverberation time. They order to characterize churches. Thus, they suggest a new show an homogenous sound field throughout the church, methods which consider fix positions of the source and a with typical variations of single parameter (fig. 8 a) b) c) ) fix number of receivers. Using this standard a full comparison of classical churches may be successfully carried out. But in particular cases like the San Lorenzo C80 church in Turin, this method couldn’t be applied, as it 12.0 doesn’t takes into account the small dimension of this 10.0 building. 8.0

6.0

4.0

(dB) 2.0 4 Conclusions 0.0 -2.0 In this paper the acoustical parameters of the Royal Church -4.0 of San Lorenzo in Turin was investigated. The inner -6.0 25 31.5 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 media -1.0 -1.5 0.9 0.5 0.5 2.0 0.8 -0.2 -2.2 -3.5 -4.2 -4.7 -3.9 -3.7 -3.4 -3.0 -3.3 -2.2 -0.5 0.1 -1.0 -0.1 1.5 3.4 5.4 7.7 10.5 architecture was used to explain how this particular [Hz] building has such a peculiar acoustics. The standard a) architectural acoustics parameters were measured in order to understand how the sound field varies in several C80 - distance positions. This study tested the aims of the architect,

7.0 Guarino Guarini, of designing a building with fair listening

6.0 and good acoustics. It shows how planning an inner

5.0 architectural composition, acting as a huge diffuser, help a

4.0 large room to become a good place for listening.

(dB) 3.0 80 C 2.0

1.0 Acknowledgments

0.0

-1.0 The authors would like to thank Gabriele Piccablotto for his 5 7 9 11 13 15 17 19 21 23 25 27 distance from s1 [m] assistance in the acoustical measurements, Paolo Tarizzo firts pew second pew third pewi niche coupled volume for supplying his studies and prof. Vilma Fasoli for her historical skills. b)

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Acoustics 08 Paris References

[1] ISO 3382 Acoustics - Measurement of the Reverbe- ration Time of Rooms with Reference to other Acoustical Parameters [2] H.A. Mueller, “Room-acoustical criteria and their meaning”, Proceedings of International conference on “Acoustics and Recovery of Spaces for Music”, Ferrara 1993 [3] E. Cirillo, F. Martellotta, “Worship, Acoustics, and Architecture”, Multi-Science publishing, 2006 [4] M. Caniato, V. Fasoli, M. Masoero, “ “Istruzioni diverse concernenti l'officio dell'architetto civile”: l'acustica negli scritti di ”, Proceedings of 35th Italian Acoustic Association conference, Milano (Italy) 11-13 June 2008 [5] P. Ricciardi, Effetti geometrici in due chiese a pianta centrale: misure e simulazioni, Proceedings of 34th Italian Acoustic Association conference, Firenze 13-15 giugno 2007

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