Acoustics 08 Paris
The Royal Church of San Lorenzo in Turin: Guarino
Guarini and the Baroque architectural acoustics
M. Caniatoa , F. Bettarellob and M. Masoeroc
a
b
University of Trieste, Piazzale Europa, 34100 Trieste, Italy
Engineering Dept. - Univ. of Ferrara, Via Saragat, 1, 44100 Ferrara, Italy
c
Politecnico di Torino, Corso Duca degli Abruzzi 24, 10123 Torino, Italy
[email protected]
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Acoustics 08 Paris
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.
1
second position (s2) in order to investigate how the sound
field may change due to this particular architecture.
Introduction
The measurements were then analyzed with Adobe
Audition® and Dirac® software, in order to determine the
acoustical descriptors according to ISO-3382 and IEC60268-16 [1].
In 1666, Duke Emmanuel Philibert II of Savoy appointed to
Guarino Guarini the design of San Lorenzo church in Turin.
Mathematician, theologian and, above all, architect, he
conceived an octagonal central plan church. The building
has a very peculiar inner composition: neither straight lines,
nor regular volumes or parallel walls are present (Fig. 1a).
It is composed by two coupled volume (main room and
Crucifix Chapel that consists of a roughly rectangular
shape). The main room is divided in two volumes: the
bigger consist of a central plan room and the second one
consist of en ellipsoid plan room. All the lateral chapels, the
dripstones (Fig. 1b), and whatever may be found inside the
church, show a curved profile.
The average reverberation time measured in the church
main volume is shown in figure 2. The average value of T30
falls in the 2-4 seconds range. This range is indicated in the
literature as good for churches [2]. We can therefore
conclude that the reverberation time of this church, in spite
of its large dimension, provides an acceptable acoustic
quality [3].
RT average with deviation standard (S1 position)
6
5
[s]
4
3
2
1
RT average
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0
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Fig. 2 Average of reverberation time for s1 source position
a)
This particular phenomenon is probably due to the peculiar
inner conformation, which determines a good sound
diffusion, thus allowing a fair listening condition. Guarini
did not foresee this effect: in fact he knew the scatter
phenomenon but he didn’t consider the sound as a
frequency-dependent phenomenon [4].
b)
Fig. 1 a) Plan of the San Lorenzo church with measurement
positions; b) particular of the dripstones curved profile
So we investigated how the sound field may vary in the
different positions in order to point out how the Gaurini
design influences the listening.
Acoustic measurements were carried out in the positions
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
positions located only in a half of the central plan. The
points displayed with an “°” stand for measurements
performed with the heavy dividing door open between the
two coupled volume.
4.0
3.8
3.6
3.4
[s]
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3.0
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2
Measurements and results
pos. N°3
2.6
pos. N°6
pos. N°7
2.4
2.2
Impulse response measurements were carried out using the
sine sweep technique, generating two sine sweeps for each
of the three positions of the sound source (s1, s2, s3); taking
advantage to its symmetry, the source was placed in the left
part of the building only. Several measurements were
performed for source in the first position (s1) and for the
2.0
0
5
10
15
20
25
distance from the source S1 [m]
RT at receiver positions
RT average
Fig. 3 comparison between average reverberation time and
reverberation time in each receiver positions for s1
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Acoustics 08 Paris
Figure 5 shows that the reflections aren’t strong enough in
the receiver positions near the s1 source. This is due to
strong diffusion caused by the inner architecture. From the
center of the dome (about 10 meters distance from s1) the
sound field becomes more homogenous reaching the aims
of Guarini.
As shown in figure 3 the reverberation time doesn’t change
sensibly moving through the church. The sound field in the
main room is then homogenous; the three positions that
differ from the average are particular ones:
•
Position 3 is under the dome and furthermore is in
the center of the central plan. As explained in
literature this is due to the central plan
conformation of the church [5]
•
Position 6 and 7 are far from the source and this
cause the lowing of reverberation time.
EDT average with deviation standard (S1 position)
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[s]
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EDT average
a)
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Fig. 4 average T30 sound field distribution
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The average values and standard deviation of T30 at low,
middle and high frequency assure us a well-blended
ambient sound field (fig. 5)
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10
10.1
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12.1 13.5 13.8 15.1 15.9 19.6
distance from the source S1 [m]
RT at receiver positions
EDT at receiver positions
b)
Fig. 6 a) Average EDT parameter and its standard deviation
b) comparison between T30 and EDT parameters with
distance
RT average at low, middle and high frequency
4
3.5
Coupled volumes.
3
As one can notice in figure 1 a) the building is divided in
two main volumes: the main room and the Crucifix Chapel.
These volumes are divided by a heavy door which
sometimes may be opened ye the priest in order to receive
more people, especially in the summer.
[s]
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2
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1
So when the heavy door is open, the Crucifix Chapel acts as
a coupled volume influencing the sound field as shown in
figure 7.
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LF
RT average
MF
HF
[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)
D50
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D
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25
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media 0.51
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[Hz]
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
versus frequency; b) C80 versus distance from s1 source; c)
Average of D50 versus frequency
This figure shows how the coupled volume act as an
“absorber” for the low frequencies but as a slight
“amplifier” for the high frequencies. However it supplies a
good effort to the sound field lowing down these
frequencies.
3
Comparison with other measurements methods
The sound field shown is the average of the three position
measured with the door displayed in figure 1 a).
Many studies have been carried out on churches. In
particular a new measurements standard is proposed from
Cirillo and Martellotta [3]. They rightly observe that it is no
more possible to use theater measurements standards in
order to characterize churches. Thus, they suggest a new
methods which consider fix positions of the source and a
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
church in Turin, this method couldn’t be applied, as it
doesn’t takes into account the small dimension of this
building.
Other acoustical parameters.
The other acoustical parameters such as clarity (C80) or
definition (D50) behave like the reverberation time. They
show an homogenous sound field throughout the church,
with typical variations of single parameter (fig. 8 a) b) c) )
C80
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(dB)
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Conclusions
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-2.0
In this paper the acoustical parameters of the Royal Church
of San Lorenzo in Turin was investigated. The inner
architecture was used to explain how this particular
building has such a peculiar acoustics. The standard
architectural acoustics parameters were measured in order
to understand how the sound field varies in several
positions. This study tested the aims of the architect,
Guarino Guarini, of designing a building with fair listening
and good acoustics. It shows how planning an inner
architectural composition, acting as a huge diffuser, help a
large room to become a good place for listening.
-4.0
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media
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-4.7
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7.7
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[Hz]
a)
C80 - distance
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C 8 0 (d B )
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Acknowledgments
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0.0
The authors would like to thank Gabriele Piccablotto for his
assistance in the acoustical measurements, Paolo Tarizzo
for supplying his studies and prof. Vilma Fasoli for her
historical skills.
-1.0
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7
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distance from s1 [m]
firts pew
second pew
third pewi
niche
coupled volume
b)
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Acoustics 08 Paris
References
[1] ISO 3382 Acoustics - Measurement of the Reverberation 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 Bernardo Vittone”,
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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