Acoustical experimental analys is on worship buildings
aimed to their use as auditorium
Anna Magrini, Paola Ricciardi
Dipartimento di Ingegneria Idraulica e Ambientale, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy ,
[email protected], [email protected]
The acoustic characterisation of buildings for music performances involves not only theatres, but also
worship buildings, that with adequate acoustic quality, could held musical performances although
temporarily. In order to complete previous analyses, focus ed on Churches with rect angular plans and two
aisles, also cent ral plan Churches were investigated. Considerations on experimental values of the mai n
acoustic paramet ers obtained in a considerabl e number of Churches are here presented. Measurement
results were compared with acoustic data available in literature regarding theat res and auditoriums. The
examined Churches are cl assifi ed in agreement with the optimal values of the acoustical parameters for
the listening of music. Moreover the spatial distribution of the acoustical parameters, as a function of the
source – receiver distance, is evaluated. It is then correl ated to the presence of architectural elements,
such as lateral chapels, dome, vaults and columns.
1
paramet ers. In literature, a great number of Church
acoustical data is available, but the geomet rical
characteristics are often not indicated; therefore a wider
examination of the correl ation among various
experimental parameter and geometric characteristics is
not possible.
Introduction
The realisation of this work aims at the valorisation of
the wide historical and artistic Italian heritage through
the acoustic characterisation of buildings for music
perform ances. Most part of the experimental analyses
was focused on worship buildings that could be used as
auditoriums.
In addition, this research is aimed to find out
significant points where measurements should be
carried out, on the base of the internal geometry and
the peculiarity of the environment, in order to reduce
the high number of measurement points and, therefore,
the large amount of data to process.
The authors carried out experimental investigations on
Churches having di fferent plan configurations:
rectangul ar plan with two aisles [1, 2, 3] and circular
plan [4]. Most of the considered worship buildings
present articul ated environments, such as lateral
chapels, coupled rooms, diffusive elements or obstacles
to the sound propagation, orientation of surfaces,
convex surfaces than can creat e sound concentration.
The internal geometric complexities certainly influence
the acoustic field [5] even though do not lead to simple
correlations among acoustical paramet ers and spatial
geometric characteristics.
2
State of art of the research
In the res earch on the acoustic charact erisation of
worship buildings, a great amount of buildings was
already subject of experimental investigations.
In particular, formerly in the ’50s Raes and Sacerdote
[6] carried out acoustical measurem ents on Basilicas of
S. Giovanni in Laterano and S. Paolo Fuori Le Mura in
Rome. The same Roman Basilicas were subject of
study by R .S. Shankland and H.K. Shankland [7], who
in the ‘70s analysed also S. Peter’s Church in Rome.
In the same years Fearn [8] examined reverberation
time in Spanish, English and French Churches.
Successively Giulianini and Cocchi [9] experimentally
studied 7 Italian Churches (St. Andrea in Mantova, St.
Petronio in Bologna, St. Maria Maggiore, St. Agostino
in the region of Marche, St. Elena, N.S. Moretta and St.
Paolo in Alba, Piemonte).
With no doubts acoustical parameters such as Clarity
and Definition Indexes are quite sensitive to early
reflection components of sound and thus highly
dependent on the building shape. Nevertheless this
consideration could be ext ended to the Reverberation
Time: recent studies on Churches with a central plan
and dome [4] put in evidence the fact that, in some
cases, reverberation time below the dom e assumes
lower values than in the other measurement points.
Therefore comes the need of a deeper analysis on the
way every single geometri cal - architectural elem ent,
such as the presence and dimension of columns, arches,
vaults and surfaces with elements in relief as altar or
pulpit etc. could influence the sound paths and,
consequently, the spatial distribution of the acoustical
A few years later, another experimental analysis was
developed by Recuero, Gil and González [10] in the
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monastery of Santo Domingo of Silos in Burgos, in
Spain. In 1994 Lannie and Soukchov [11] published
experimental results taken in 5 Russian temples with
tent roof. In 1998 Hamed and Hassan pres ented
reverberation time values of the State Mosque of
Kuwait [12].
In the same period, another It alian Church, the Gesù
Church of Ancona, was analys ed by Iannotti e Mattei
[13], while Galindo and others [14, 15] carried out
measurem ents in 8 Churches of the Gothic - Mudej ar
period, in Spain. Carvalho [16] analysed 41 Portuguese
Churches and, in collaboration with Desarnaulds,
Swiss Churches [17].
In the fi rst measurem ent campaign, ten Churches [1, 2]
of the city of Genoa were select ed, with rectangular
plans and two aisles with and without lateral chapels
and/or cupol as, with volume vari able from 2183 to
43540 m3 . The typical Church plan and section
considered in this measurem ent session are shown in
Figure 1.
The second experiment al analysis was developed in 14
Genovese Churches [4] with central plan, with volume
variable from 1409 to 43756 m3 . Plan and section of
one of them are reported in Figure 2.
In the late years, worship buildings were widely
studied both in the north and in the south of Italy:
Martellotta [18] analysed Romanic Churches in Puglia,
Magrini and Ricciardi carried out experimental
campaigns in the city of Genoa on 10 Churches [1, 2],
with rect angular plans and two aisles, on 14 Churches
[4], with central plans. Moreover Magrini A. and
Magrini U. [3, 19] investigated 6 Medieval Abbeys of
the Cistercian order, 3 in the North of Italy and 3 in the
South of France.
3
Experimental analysis
Subject of the investigation were numerous Churches,
with various geometrical configurations, various
historical periods and, consequently, various typologies
of furnishing.
Figure 2 - Plan and Section of St. Zita Church
Most recent measurem ents were developed in
Medieval Cistercian Abbeys with volume variable
from 3390 to 14970 m3 [17]. Plan and section of one of
them are shown in Figure 3 and 4.
The method, common to all the measurements, was
based on the backward integration of Schroeder [20].
Churches were unoccupied during measurem ent. The
source was positioned near the altar and the
microphone positions were chos en as function of the
various configurations of the plan, variable from a
minimum number of 6 to a maximum number of 28 for
each Church.
Figure 1 - Plan and Section of St. Donato Church
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Magrini, Ricciardi
cupolas and it was built in Baroque style (start ed in
1592 by Marcello Pallavicino and completed in 1637).
Figure 5 - Reverberation Time RT at 500 Hz as
function of the volume V of the Churches and the
optimum trend of RT for various types of music
Figure 3 - Plan of Morimondo Abbey and Cloister
Moreover, other 3 rectangular plan Churches could be
employed for the listening of cl assical or organ music:
the cathedral of Genoa, St. Lorenzo, St. Vallisa of Bari
and St. Nicola of Bari.
Some other Churches, mainly with rectangular plans
and two aisles could be us ed for organ music, such as
the small St. Cosma and Damiano, the Romanic St.
Donato and St. Maria di Castello. It can be noticed that
almost all the central plan worship buildings are not
appropriat e to be used as auditorium, unless some
acoustic corrections are realised.
Figure 4 - Section of Morimondo Abbey
4
Discussion
In Figure 5 experimental values of the Reverberation
Time at 500 Hz are plotted as function of the Church
volumes. Data referred to the Church investigated by
the authors [1, 2, 3, 4] and by other s cientists [14, 15,
18] are reported.
In order to classi fy their potential musical fruition, RT
values are compared with the optimal param eters for
the listening of music and speci fi cally for organ music,
classical music and modern (pop) music.
The Church that better agrees with the listening of
modern music is St. Agostino [2], which was, in effect,
quite recently acoustically restored.
Only one central pl an Church s eems to be suitable
either for modern (pop) or classical music: Gesù
Church. It is also the most articulated, since it has 7
Figure 6- Mean Reverberation Time as function of the
V/S ratio for various worship buildings
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In Figure 6 experimental values of the Reverberation
Time (125 - 4 kHz average values) are plotted as
function of V/S ratio [m] (volume of the
Church/pavement surface) of the Churches subject of
investigation [1, 2, 3, 4] and of other ones analysed by
Italian and Spanish scientists [14, 15, 18].
For a deeper comparison, additional data referred to
theatres are present ed on the graphic [21]. Considering
only the values referred to worship buildings, a
regression line was traced, defined by the equation y =
0.25 x, with R 2 = 0.53. It identifies two zones with
distinguished geometrical characteristics, one above
and one below the regression line.
For the Clarity Index there is not a clear subdivision
among the values lying below and above the regression
line. The more dispers ed dat a from the regression line
are the ones rel ated to Churches with rectangul ar plans
and two aisles and precisely, N.S. Consolazione, St.
Annunziata and St. M. di Castello, having volumes
respectively of 18842, 26603 and 21100 m3.
In addition an analysis on the spatial distribution of the
acoustical paramet ers was carried out. The RT average
values (125 Hz – 4 kHz), as function of the S-R
(source-receiver) distance were examined. The S-R
distance was referred to the central nave, for
longitudinal plans [1, 2, 3], and to the direction linking
source (altar) and centre of the plan, up to the end of
the Church, for central plan Churches [4].
The RT values of Cistercian Abbeys [3] and of Spanish
Churches [14, 15] are distributed above the line, as
well as the values detected in almost all the Churches
with rect angular plan and two aisles [1, 2]. RT values
referred to an analysis conducted in Southern Italy [18]
are all located below the regression line. Values of RT
correlated to central plan Churches are more dispersed
[4].
In details, Figure 8 shows that for values lower than 3.5
s, the RT remains quite constant towards the back. For
values higher than 3.5 s the variation of RT is more
evident. More precisely, the highest vari ation of 1.46 s
is reached in St. Maria Assunta in Carignano, which is
the central plan Church with the biggest volume
(43756 m3 ).
Moreover the unique Churches with rectangular plan
and two aisles [1, 2] that are below the regression line
are without cupola (St. Agostino, St. Donato e St.
Siro). Among the ones with central plan, more
dispersed values from the regression line are the ones
related to Churches having higher volume of cupolas
(St. Zita, and Gesù Church), respectively 7657 m3 e
7310 m3 [4].
Figure 7 shows experimental values of Clarity Index
C80 as function of the volume of the Church –
pavement surface ratio (V/S), of the Churches subject
of investigation [1, 2, 3, 4], and of other ones [14, 15,
18]. The regression line has the equation y = - 0.2 x 2.33 y and R2 = 0.5.
Figure 8 – Mean Reverberation Time as function of the
source – receiver distance
Figure 7- Clarity Index as function of V/S of various
worship buildings
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In some of the analysed Churches there is a di fference
of behaviour as a function of the major and minor
distance to the altar: in Chiaravalle for a distance minor
than 27-30 meters the RT varies of 0.6 s. Over this
limit, this effect seems to be less evident. In
Morimondo the same trend is shown in the first 15 m
[22].
than 35 m, C80 values tend to be more constant, apart
from Morimondo Abbey [22]. This behaviour confirms
previous analyses regarding C80 distribution,
speci fically for longitudinal plan Churches [1, 2].
The plot of the Definition Index versus the sourcereceiver distance is shown in Figure 10. The same
decreasing tendency of C80 is here only for sourcereceiver distance shorter than 20 m. Beyond this limit,
D50 values are more constant.
5
Conclusions
Experimental measurements taken in 10 Churches with
two aisles, 14 with central plans and 3 M edieval
Abbeys, were examined, aiming to classi fy them in
accordance with the optimal values of the acoustical
paramet ers for the listening of music.
The results put into evidence that worship buildings
with more articulated volumes, for example Gesù
Church, with 7 cupolas, are more adequat e for music
perform ances. Almost all the central plan Churches are
not appropriate to be used as auditorium, unless some
acoustic corrections are realised.
The most evident characteristic of the spatial
distribution of the acoustical param eters, as a function
of the source – receiver distance, was associated with
the presence and the volume of cupolas.
It was observed that reverberation time as function of
the V/S ratio follows a regression line common to
Churches available from literature.
Figure 9 – Clarity Index as function of the
source – receiver distance
The RT distribution for Churches with rectangul ar plan
and two aisles without cupol as was signi ficantly
different from the ones with central plans, and, among
these last ones, bigger volume Churches pres ented
more scattered RT values.
The Clarity Index distribution showed decreasing
values when the source – receiver distance was
increasing up to 35 m. The same effect was evident
also for the Definition Index, but only for sourcereceiver distance lower than 20 m.
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