PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

The church building secularization through its sound in acontemporary case study
Maria CAIROLI1; Livio MAZZARELLA2;
1

Politecnico di Milano, Italy

2

Politecnico di Milano, Italy

ABSTRACTThis work describes a novel approach in designing new churches, explaining the case study Sant'Ambrogio
Church in Trezzano, Milan (IT) in detail. The article presents a room acoustics analysis of the church throughimplementation of computer simulation techniques, emphasizing the continuity and breaking elements withhistorical churches.
In the past the sacred sense in a church was greatly reinforced by the surrounding atmosphere of very
reverberant spaces with possible echoes that infatuated the perception of God and his presence. On thecontrary, nowadays concentration and intimacy are preferred, the reverberation is reduced, the speech
intelligibility of the homily to understand the message of God is increased, while music or songs steel
accompany the choral word of the church goers.
The proposed acoustic design includes a new approach with an acoustic response suitable for both speech andmusic, considering also the recent room acoustics studies in other typologies of building such as congress
centers and multipurpose auditoria.
Keywords: room acoustics; intelligibility; computer simulation

1. INTRODUCTION
At the time of prophets and epic, the Hearing was a more vital sense than the Sight. The God’s Word
and all the other fundamental communications were not read but heard, and also in the clandestine
Christian church of the 1st and 2nd centuries was the listening of rites to have a decisive influence on
the liturgy’s development. Only during the Romanesque and the Renaissance period the Hearing loses
its main role although it continued to play an important role (1). One of the most obvious consequenceis the change in the divinity conception. With the Renaissance, God becomes definitively represented
by an image, before it was conceived as a sound, or as a vibration (2).
An analysis of the dimensions of the churches according to the architectural style shows a singulartransformation of the sound field, up today.
In the Romanesque period, a close relationship between architecture, music and liturgy, focuses on
the multisensory experience of architecture, complementing the visual space with the sound field (3).
The literature includes researches with different approaches to this relationship, either through theanalysis of the relationship between architecture and acoustics in religious buildings in their current
condition (4-5) or from the perspective of the acoustic evolution connecting liturgy, music andarchitecture (6-8), or studying the interconnections in the origins of Christianity.
From the Hebrew tradition, the early Christian church inherited the taste for the intonation offragments of sacred texts to give an emphatic value to the rite and the attainment of transcendent statesand only in the XX century, with the introduction of the national languages in the catholic churches,
the Second Vatican Council sanctions the importance of the active participation of the church goers in
the liturgy, the understanding of the priest's word, and the formative value of the lectures. Thus a new
acoustic requirement is created that is in contrast with the acoustic answer of a historical church.
A historical church, in fact, is characterized by a long reverberation time, able to encourage choral
singing and to create that emotional involvement that, for a long time, was the only possible form of
1
2

maria.cairoli@polimi.it
livio.mazzarella@polimi.it

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participation for most of the people who did not know Latin.
The necessity to make the entire liturgical celebration comprehensible has then led to a global
rethinking of the acoustics of the churches while maintaining the need not to penalize the more"emotional" aspects of participation. This study aims to underline the main acoustic requirements fora new church building, explaining the new project of Sant’Ambrogio Church in detail, finding guidelines that can be followed in every new church acoustic design.

2. SHORT HISTORICAL EXCURSUS
2.1 Acoustics in the churches of the past
With the Pope Gregory the Great (590e604) (1), among the elements that connect acoustics witharchitecture in a church, the choir and the organ became the most important ones. It was the organ, in
fact, to be erected as the liturgical instrument par excellence, thanks to its special characteristics. The
organ, with the imposing presence of the pipes and its versatility for ornamentation, was able to adopt
a preeminent place in the church, since it was considered as an element of prestige and constituted partof the ornamentation and architecture.
About the choir, already in many medieval monastic churches, it was located in the main nave. In
the latter monumental spaces, the choir ends up being the pretext for the furnishing of the interior,acquiring a sculptural character and obviating the functional and acoustic requirements. Gothic
architecture encloses the choir with highly decorated walls and with chairs that used to be double inheight: high choir, for the canons and low choir, for the clerics.
In this period Church buildings were characterized by a progressive growth of their volume, tosymbolize the political power of the civil or religious communities that had erected them.
In the Renaissance architecture, and later Baroque, however, the choir was eliminated from thecentral nave, since it was considered as an obstacle by the architects of the time in the perception of theunique space and for the perspective. It should also be noted that in the years preceding the Lutheran
Reformation, only the clergy participated actively in the liturgical celebration, while the church goers,already unable to understand Latin, were further penalized.
The Counter-Reformation sanctioned by the Council of Trent constituted an important turning
point after which the Church of Rome opted for a form of conviction based on the splendor of the"amaze" the church goers. In practical terms, after the Counter-Reformation the churches became
smaller and richly decorated, with an improvement in the acoustic conditions (1).
In the reality it is steel difficult to find references to the acoustic diagnosis of these spaces inarchitectural and musical historiography, despite the large number of documentary sources that deal
with the relationship between ecclesial architecture and music (9). In order to understand the acoustic
characteristics of the Christian church in the 21st century, some main information will be given in thenext paragraph.
2.2 Acoustics in contemporary churches
In contemporary churches, greater attention should be given to architectural aspects that influence
the room acoustic answer, in particular the volume dimension, the plan shape and the used materials(10).
The reverberation time should not be too long, in order to guarantee a good speech comprehension
related to the values of the acoustic parameters Definition (D50 ) and Intelligibility (STI), but also not
too short to take into account the musical conditions expected in the frequent celebration of solemn
masses, controlling also the acoustic parameter related to the Clarity (C 80) of music.
In some cases contemporary churches have to host also the organ accompanied by choral singing(Gregorian). As a result, several activities with different acoustic requirements, can coexist also during
the same ceremony. Therefore, the requirements needed to achieve suitable acoustic conditions mayvary and a new approach with a response suitable for both speech and music is needed, independently
from the church goers presence that can vary from time to time.
On the reality, however, there is often a substantial absence of acoustically absorbing materials
inside, like heavy carpets, upholstered benches, curtains and decorations with acoustic diffusive anddiffractive properties, with consequent criticalities due to the increase in reverberation time. This is
the reason why in most of the cases a significant variation of the acoustic conditions is demanded to themere presence of the church goers (with sound-absorption properties). Churches that have very poor
acoustic characteristics in conditions of modest occupation can reach acceptable levels when they are

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completely full of people. The dependence of the acoustic response on the presence of people, however,represents a problem from the acoustic point of view since it introduces a variable and unpredictablecharacter.

3. THE SANT’AMBROGIO VESCOVO CHURCH
The project of the new Church of Sant'Ambrogio in Trezzano started on 2011 as a part of a moregeneral plan of redevelopment and modernization of the urban context of Trezzano sul Naviglio.
A long churchyard, a place to welcome the church goers and where to stay with pleasure after the
liturgy, acts as a counterpoint to the pure liturgical area.
In spite of the formal complexity of many modern religious buildings, the Church ofSant'Ambrogio, rectangular in plan with only a central nave, recovers some traditional styles, as thesimplest Romanesque Churches, reinterpreting them.
The verticality of the building (21 m high), with a volume of 8100 m3 (width equal to 20 m andlength equal to 33 m), seems to guide the eye upwards, as it happens in medieval Gothic churches,
constituting a continuous reference to the Divine. The cross of Christ in the middle nave is an elementthat also inspires the architectural choices, both in the building plan and in the lateral views so theexternal side facing Milan allows to see clearly the profile of the cross on the roof top, while inside of
the church the cross is inverted and delimits the spaces, creating a clear perception of the volumes inwhich the light radiates strongly.
The interior of the structure shows a remarkable awareness in the realization of liturgical places.
The baptismal font, made of shiny marble, is illuminated by a skylight that once again attracts the view
upwards. White marble is the formal language of the altar, the point where the focal lines of the entire
room converge, slightly raised above the level of the church goers. The ambo, raised in the most classicof architectural traditions, is integrated into the white of the room thanks to the marble that covers it.
The light is the clearest leitmotif: it is as natural as possible, thanks to the articulated system ofskylights, windows and light points that can radiate all the space. A careful game of alterations in lightintensity allows to create more intimacy in the confessional area or to emphasize the altar, the ambo
and the baptistery (Figure 1- 4).

Figure 1 and 2. The church longitudinal section and plan(source position are colored blue, receivers are colored red)7017

Figure 3 and 4. Church external rendering and internal rendering from the rear wall

4. COMPUTER SIMULATION MODELING
4.1 Acoustic simulations
SketchUp 3D modelling software was used to create a virtual acoustic model of the Church ofTrezzano, based on plans and sections which describe the geometry of its interior space.
The model was exported to CATT Acoustic (11) (version 8) to carry out the acoustic assessment, acalculation engine known to be effective in the prediction of the acoustic parameters (12). The lengthof the room impulse response was set manually, because it was not possible to use measured data tocalibrate the model being the church not yet built at that time.
A complete calculation of all the acoustic indicators was carried out to verify the consistency of theobtained results. The absorption coefficients of all materials foreseen by the design were accurately
defined. Most of them have been measured in reverberant chamber following the UNI EN ISO 354.
The main ones are reported in detail in table 1. The acoustic evaluation method and the predictedacoustic parameters are those presented in ISO 3382-1. Based on this approach, most acoustic
parameters were considered in seven receivers positions (figure 2) and their average values calculated
to describe the acoustic quality of the space (13). The analysis focuses primarily on the musical qualityof the church and the speech intelligibility, thus the parameters considered in the objective analysis are
as follows: Definition (D 50 ), Sound Transmission Index (STI), Clarity (C 80), and the Centre Time (T s ),associated with the balance between early and late energy reaching the receiver.
 the reverberation time (T30) and Early Decay Time (EDT).
Table 1. main absorption coefficients.
Surfaces
Internal surfaces of the
crucifix
Perimeter
ceilingaround the skylights
Higher part of thelateral walls
Lower part of the lateralwalls and Wall behind
the altar
Audience
Floor
Entrance wall
windows

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Materials
polyester fiberboard coated withsound-absorption plaster,density 60 kg/m3, sp. 50 mm
Polyester fiberboard,
density 60 kg/m3, sp. 70 mm
light absorbing plastermoderately upholstered chairs,
marblepolyester fiberboard coated withsound-absorption plaster,density 60 kg/m3, sp. 50 mm
glass

125

Absorption Coefficient
250
5001000 2000

4000

0.12

0.25

0.68

0.94

0.94

0.94

0.12

0.25

0.68

0.94

0.94

0.94

0.10

0.15

0.25

0.35

0.35

0.42

0.51
0.02

0.64
0.02

0.75
0.03

0.80
0.03

0.82
0.04

0.83
0.04

0.12

0.25

0.68

0.94

0.94

0.94

0.12

0.10

0.07

0.06

0.06

0.05

4.2 Computer simulation results
The presented output maps (figure 5-10) at central frequencies 500 Hz, and 1 kHz, derive from thepreprocessing analysis concerning the main acoustic parameters (just the much more significant
parameters related to source SRC1 are plotted in this paper), considering two different source
positions SRC1 and SRC2. SRC1 is situated near the central axis of the church, near the altar, theSRC2 is put near the lateral walls in the choir position (figure 2).
For both source positions the acoustic parameter results are very similar and there are no significant
changes between them, according to the JND (Just Noticiable Difference) evaluation (14).
The predicted parameter Definition D 50 is over 50%, as requested for a good intelligibility,
considering that D50 > 45% guarantees more than 90% of the syllables comprehensible (15) (asrequested in congress centers), according to the standard ISO 33382-1, and the STI predicted values
are between 60% and 80% in every order of seats, a values’ range classified as a good result according
to the IEC 60268-16 scale quality.

Figure 5 and 6: 3D model SRC1 - Definition (D50) at 500 Hz and 1kHz

Figure 7 and 8: STI Values and Trend and RT Sabine (SabT), RT Earying (EyrT), T30 and T15

Figure 9: RT Trend related to the use destination of the volume (1 speech, 2 jazz and chamber music, 3symphonic music, 4 religious music)

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Even if the STI values are according to the range requested for congress centers, the predicted
Reverberation Time in the church of Trezzano is not so short at middle frequencies, in comparison withthe values proposed by literature for speech auditoria (figure 9). In the church of Trezzano the T30 isequal to 1.25 sec. at 1kH while in congress centers it is suggested do not exceed the value of 1.1 sec.
also when the space volume is very big. The increase of the reverberation time in the Church is helpful
to reach the Clarity range -3<C 80<3 to respect its optimal values for music (16).
The acoustic answer behavior in the church looks much more similar to that one of an Italian Opera
House with horseshoe shape, in which the reverberation time has not to be so high in comparison withother Opera Houses in Europe and Concert Halls to respect simultaneously both the speechcomprehension and the clarity for music. In those spaces rarely le C80 value is negative and his interval
is usually 0<C80<4 (17).
From those considerations a new quality trend for the Reverberation Time in a contemporary
church is here proposed (figure 10): it can till 20% longer than the RT suggested for congress center,even if a deeper study that goes beyond this article would be desirable to identify properly the new
acoustic range upper limit related to the church volume, considering numerous case studies.

Figure 10: Trend Area for contemporary churches RT colored in blue
In contemporary churches this trend is important to help the acoustic quality for the singing andmusic creating spaciousness and intimacy without distortions in the words comprehension.
If the organ instrument has to be included (Sant’Ambrogio church is not the case), it is suggested to
introduce a design for a variable acoustic answer, as it happens in most of contemporary multipurpose
auditoria (18) to increase the reverberation time to be similar to that one of the Churches of the past.

5. CONCLUSIONS
Some main indications for acoustic design of contemporary churches, consider the influence of therecent room acoustics studies applied to other buildings typologies such as congress centers, concert
halls, multipurpose auditoria, creating a contamination, a secularization in the church spaces and theiracoustic answer.
In particular to maintain a stable acoustic answer, independent from the number of church goers,absorbing benches are introduced. Their absorption coefficient is similar to that one of people. This
indication comes from the acoustic design of concert halls.
In addition, from the design of concert halls it is suggested to respect the NC25 curve to reduce thenoise produced by different systems (air conditioning system, ventilation, etc.) or by other equipment
and to listen to the silence.
Values of STI considered Good and D50>45% are suggested as it is required in Congress Centers,
but a little higher reverberation time is recommended to reach also a range for Clarity similar to that
one of Italian horseshoe shape Opera House 0<C80<4. A response suitable for both speech and music is
possible, optimizing the reverberation time and studying the absorbing distribution in the room.
A trend of the RT optimization is suggested, with the upper range limit 20% higher than that one forcongress centres, but more case studies should be considered to better define it according to the church
volume.
In detail, in the Sant’Ambrogio Church, the choice to use only slightly sound-absorbing materials
in the areas close to the church goers guarantees the contribution of the first reflections, creating a7020

sense of spatiality that envelops the listeners. On the contrary, highly sound-absorbing materials
placed far from the source and the listeners, reduce the late reverberation field.
In the Sant’Ambrogio Church the organ instrument is not included. However, if there had been arequest, it would have been necessary to consider the acoustics of the church asvariable, extending thereverberation time to that one of an Historical Church.
In the Sant’Ambrogio church people can clearly hear the word of the priest and participate to theassembly listening the other voices. That creates a strong sense of participation, an Ensemble, thathelps to find the atmosphere of concentration and introspection increasingly absent in everyday life,
redefining a new sense of participation, of ecumenism.

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