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

Acoustics of Portuguese Romanesque churches
António P. O. CARVALHO1; Francisco M. C. L. M. PEREIRA2;
1,2

Laboratory of Acoustics, Faculty of Engineering-FEUP, University of Porto, Portugal

ABSTRACTThis paper summarizes the results of recent measurements in ten very typical Romanesque churches in the
North of Portugal to acoustically characterize this type of building. In situ measurements were done regarding
Reverberation Time (RT) and Rapid Speech Transmission Index (RASTI) in empty churches. The results arepresented and compared with seven architectural characteristics of the churches (area, volume, ceiling height,
length, width, etc.). Statistical correlations and prediction equations are presented among those sevenarchitectural parameters and the two acoustic parameters measured (RT and RASTI). Values up to 0.91 were
found for the related R2 coefficients.
Keywords: Reverberation Time, RASTI, churches

1. INTRODUCTION
The word church can have multiple meanings. It can be regarded as an institution, a group of people
that take the word of God as a reference and guidance, or it may be considered a s a building, where
the physical and aesthetical aspects are used to form an adequate location of prayer.
Nowadays, the design of a church considers its Acoustic as one of the strongest, if not the main,priority since this concept must acknowledge all its activities and routines (meditation, speech andmusic). As a building, a church requires moments of silence as well as moments in which thecongregation will need to understand effectively what the orator communicates.
Romanesque architecture was born in the 10th century. After a kind of political stabilization,
Western Europe emerges as a consequence of a new society, with demographic expansion, increased
mobility, economic growth and significant social and cultural changes. The term Romanesque was
first written in 1817 by historian C. Gerville, influenced by the culture of the Roman Empire (1).
The building system that defines the Romanesque architecture begins to be defined shortly after
the middle of the 11th century. It is in the regions of Burgundy, Languedoc, Auvergne and theSouthwest of France plus the kingdoms of Navarre and Castile, which resides the true original artistic
creation of this period. (2)The Portuguese Romanesque style has rural characteristics and is linked to the construction ofsmaller churches. Depending on the region, these churches would vary in terms of technical quality
as well as formal and decorative wealth. The raw materials that were used to construct such churches
were the ones more available to each region. In the North of Portugal, it was the general use of granite,in the Center limestone and to the South, brick and taipa (a kind of earth structure) (3).

2. METHOD
2.1 Sample
For the execution of this project, certain church features and conditions were chosen among asignificant sample, in order to evaluate the acoustic aspects of Romanesque churches. Ten specificchurches (show in Table 1 with their respective geometric parameters, and Figures 1 to 6), belonging
to the Rota do Românico do Vale do Sousa, a cultural and touristic route whose main purpose is topromote, preserve and enhance the architectural heritage (6), in the North of Portugal, were chosen to1

carvalho@fe.up.pt 2 miec1208717@fe.up.pt

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represent this type of building. In order to select the sample, the churches should gather some specificcharacteristics:• Be clearly identified as Romanesque, with an important historic background;• Contain the architectonic and decorative aspects that deeply describe this style;• Are in full working order, in other words, are not abandoned or in ruins;• Use granite as the main construction material (walls and facades);• Be stripped of most interior ornaments and furniture, from earlier periods, as much as possible.
Table 1 – Analyzed churches, GPS locations, and their geometric parameters
ChurchGPSAIRÃES41.315055,-8.198615

CETE
41.180636,-8.366329

ESCAMARÃO
41.065948,-8.257106

FERREIRA
41.264871,-8.343731

GONDAR
41.263531,-8.031465

ISIDORO41.207773,-8.143906

P. SOUSA41.166071,-8.344658

TELÕES41.310148,-8.108097

TRAVANCA
41.277676,-8.192871

V. VERDE
41.304861,-8.182076

V

S

H

W

L

Vn

Ln

VolumeSurface

Maximum

Width

LengthVolumeLength(m3)

area (m2)Height (m)

(m)

(m)

nave (m3)nave (m)

1249

209

9.55

13.60

20.40

1111

13.49

1515

155

11.80

5.40

28.70

1201

20.20

724

103

7.73

6.20

18.90

596

12.30

2957

230

14.40

8.77

29.40

2400

19.40

786

119

7.05

6.60

20.35

626

13.54

574

87

7.56

5.73

17.32

444

10.25

6028

546

16.80

15.90

43.00

4564

25.10

1390

159

9.46

7.60

23.40

1186

17.00

2801

330

12.80

14.60

28.00

2547

20.30

399

61

7.08

5.37

13.35

293

7.80

Figure 1 - Airães church

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Figure 2 - Ferreira church

Figure 3 - Cete churchFigure 4 - Escamarão church

Figure 5 - Gondar church

Figure 6 - Paço de Sousa church

2.2 Investigation
Two types of in situ measurements were done during April 2019: Reverberation Time (RT) and
Rapid Speech Transmission Index (RASTI). RT values were measured in 1/3 octave bands in each of
three set points within each church (Figure 7). RASTI values were studied in each of nine different set
points within each church (Figure 8), that were divided into three specific zones (front, middle andback) as a function of church length, in order to understand the depth of decay and mean RASTI for
each of these zones. The equipment used was a sound level meter B&K 2260 B&K, a sound source
B&K 4224 and RASTI B&K 4419 and 4225.
The ideal RT average value in Catholic churches should be approximately 1.0 s (for speech), while
for music this value should increase to around 2.0 s or a little more (for example, for organ music).
RASTI values should be as high as possible in order to achieve suitable speech perception, although
values above 0.50 would be acceptable in these cases (4).

Figure 7 (left) – The three typical RT measurement positions in each church, SS (sound source)
Figure 8 (right) – The nine RASTI measurement positions in each church, SS (sound source), (points 1, 2
and 3 are in zone named front; 4, 5 and 6 in zone middle; 7, 8 and 9 in zone back)3. RESULTS
3.1 Reverberation Time
Figure 9 displays the mean RT results obtained from the three measurement points in each church(in total six measurements were used in each point) and Table 2 shows the mean RT results. Throughthe analysis of the mean RT values (Figure 9), a decrease from low to high frequencies is observed.
This phenomenon occurs in every church, but it is particularly revealed in ones with larger volumetricdimensions, such as the Ferreira, Paço de Sousa, Cete, and Travanca churches, as they present a higher
sound absorption. The slight decrease in RT values observed in some low frequencies, namely between
the 100 and 250 Hz 1/3 octave bands, could be caused by the sound absorption of the existing materials(such as wooden ceilings, paving and ornaments).

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Figure 9 - RT values for each 1/3 octave bands in all ten churches of the sample.
Table 2 - Mean RT values for each octave band (arithmetic mean of the three bands of the corresponding
1/3 octave band) and mean RT values between 400 and 1250 Hz (average of six 1/3 octave bands)
ChurchFrequency (Hz)125 250 500

1k

2k

4k

RTavg(400-1.25k Hz)AIRÃES1.46 2.06 2.54 2.49 2.29 1.75

2.51

CETE

3.03 2.70 3.21 2.97 2.78 2.13

3.09

ESCAMARÃO 1.30 2.04 2.51 2.48 2.20 1.71

2.49

FERREIRA

4.74 4.00 3.49 2.97 2.61 1.88

3.23

GONDAR

1.61 1.34 1.76 2.37 2.16 1.63

2.07

ISIDORO

1.56 1.77 2.23 2.09 1.93 1.53

2.16

P. SOUSA2.29 2.33 2.95 3.13 3.00 2.23

3.04

TELÕES1.89 2.39 2.65 2.56 2.26 1.83

2.60

TRAVANCA

3.07 2.39 2.74 2.90 2.50 1.92

2.82

V. VERDE

1.40 1.53 1.51 1.76 1.65 1.36

1.64

3.2 RASTI
Table 3 and figure 10 show the mean RASTI results obtained in each of the ten churches. RASTI
results were compared according to the usual classification conversion table relating to speech
intelligibility, as stated in CEI 268-16 that categorizes RASTI results on a subjective scale. For values
0 to 0.3 the predicted speech intelligibility is poor; 0.30 to 0.45 is mediocre; 0.45 to 0.60 is fair; 0.65
to 0.75 is good and for 0.7 to 1.0 is excellent (8).
Once the RT values are analyzed it can be verified that the churches with larger dimensions present
a mediocre mean RASTI, particularly Paço de Sousa and Ferreira, with a RASTIavg of about 0.38. The
remaining churches are also on a mediocre intelligibility scale, with the exception of V. Verde andIsidoro that classify as fair since they present values of about 0.47, which is probably explained bytheir smaller volume that enhances speech intelligibility (6).
It is expected for the RASTI value to be higher in the front zone of the church, however the averagevalue for this zone never exceeds 0.60, which classifies these churches as fair, even at their presumed
higher speech intelligibility zone.

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Figure 10 – Mean RASTI values measured in each of the three zones (as in figure 8) of each sampledchurch.
Table 3 – RASTI average results in each of the three zones (defined in figure 8)

3.3

ChurchFront Middle Back RASTIavg

AIRÃES

0.48

0.40

0.39

0.42

CETE

0.49

0.40

0.34

0.41

ESCAMARÃO 0.53

0.41

0.38

0.44

FERREIRA

0.46

0.38

0.33

0.39

GONDAR

0.49

0.43

0.40

0.44

ISIDORO

0.54

0.46

0.41

0.47

P. SOUSA

0.45

0.34

0.31

0.37

TELÕES

0.55

0.41

0.38

0.45

TRAVANCA

0.49

0.40

0.36

0.41

V. VERDE

0.51

0.46

0.43

0.47

Regression Models

3.3.1 Reverberation Time
The calculated regression models according to the geometric parameters are presented in Table 4.
After attempting to raise the correlation coefficient, a sub-set sample containing only the churcheswith a volume below 2000 m3 was chosen, as this is the usual size for most the Romanesque churches
in this area.
Figure 11 shows that the church with the largest volume (Paço de Sousa), with almost a three times
larger volume than Ferreira and Cête churches, presents an inferior RT avg (400-1.25k Hz). This may
well be due to the abundance of wooden ornaments and surfaces, and probably because it has been
recently renovated as a result of a fire accident. Cête church has a high RT avg(400-1.25k Hz) oncecompared to its counterparts with similar volumetric characteristics, which could be due to its archedfeatures (coupled spaces) yet mainly because of its large height.

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Table 4 – Regression models among RTavg(400-1.25k Hz) and geometric parameters of each church.
Geometric parameters

Regression models

R²

V -Total Volume (m3)RTavg = 0.5192 ln(V) - 1.169

0.74

V - Total Volume (sub-set < 2000 m3)

RTavg = 0.1955 V0.367

0.80

S - Surface Area (m2)RTavg = 0.6915 S0.253

0.61

H - Maximum Height (m)RTavg = 1.4346 ln(H) - 0.733

0.79

0,243

W - Maximum Width (m)RTavg = 1.5071 W

0.24

L - Length (m)RTavg = 1.3497ln(L) -1.672

0.78

Vnave - Volume Nave (m3)RTavg = 0.5102 ln(Vnave) - 0.998 0.75

Lnave - Length Nave (m)RTavg = 0.5865 Lnave0.537

0.83

Figure 11 (left) - Relationship between RTavg(400-1.25k Hz) and Volume for each church
Figure 12 (right) - Relationship between RTavg(400-1.25k Hz) and Volume (subset V < 2000 m3).
3.3.2 RASTIThe RASTI regression values as a function of each geometric parameter are presented in Table 5.
Unlike the data observed in the RT, these equations show the decrease in RASTIavg values as Volume
increases. This illustrates that the acoustic quality of a church is strongly dependent on its Volume,
which means that, the larger the volume, the more surface areas are available to produce destructive
reflections, thus this will originate a lower speech intelligibility.
Table 5 – Regression between RASTIavg and the geometric parameters of each church
Geometric parameters
V - Total Volume (m3)2348

Regression models

R²

RASTIavg = 0.7988 V-0.087

0.87

V - Total Volume (sub-set < 2000 m3) RASTIavg = -0.037 ln(V) + 0.693

0.64

S - Surface Area (m2)

RASTIavg = 0.7399 S-0.108

0.81

H - Maximum Height (m)RASTIavg = 0.5333 e-0.022H

0.88

W - Maximum Width (m)RASTIavg = 0.5571 W-0.127

0.48

L - Length (m)RASTIavg = 0.8453 L-0.218

0.85

Vnave - Volume Nave (m3)

RASTIavg = 0.7678 Vnave-0.084

0.85

Lnave - Length Nave (m)RASTIavg = -0.0055 Lnave + 0.515 0.81

3.4 RASTI vs RT
Figure 13 demonstrates the relationship between RTavg(400-1.25k Hz) and the RASTIavg in thissample. The combination of these two parameters is important in order to understand and validate theveracity of the tests carried out, since they create a negative linear relationship in which hi gh RASTI
values are linked to low RT values.
Table 6 illustrates the best regressions between RASTI and isolated 1/3 octave frequency bands of
the RT. The best regressions belong to the higher frequency bands (especially 1.25 and 2 kHz) which
is probably partially due to the lower standard deviation value observed between these bands,
demonstrating their homogeneity, and the importance of the RASTI values in this frequency domain.

Figure 13 – Relationship between mean RASTI avg and RT avg (400-1.25k Hz) values
Table 6 – Best regressions between RASTIavg and isolated RT 1/3 octave frequency bands
1/3 octave frequency band (Hz)Regression models

R2

800

RASTIavg = -0.0611 RT800 + 0.587

0.79

1000

RASTIavg = -0.0733 RT1k + 0.613

0.83

1250

RASTIavg = -0.0736 RT1.25k + 0.616 0.88

1600

RASTIavg = -0.0704 RT1.6k + 0.601

0.91

2000

RASTIavg = -0.0771 RT2k + 0.607

0.86

2500

RASTIavg = -0.0821 RT2.5k + 0.609 0.82

3150

RASTIavg = -0.0976 RT3.15k + 0.629 0.82

4000

RASTIavg = -0.1142 RT4k + 0.628

0.77

RTavg(400-1.25k Hz)

RASTIavg = -0.056 RTavg + 0.571

0.73

3.5 RASTI vs RT and geometric parameters
The combination between RASTI avg and RTavg values resulted in a high R2 value, which represents
that the mean RASTI values are strongly explained by the variations in RT avg.
A multiple linear regression was elaborated with RASTI average values as a function of RT avg andall geometric parameters (Table 7). The high values of R 2 (about 0.9) clearly show that there is astrong correlation among these parameters.

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Table 7 – Multiple regressions of RASTI average values as a function of RTavg(400-1.25k Hz) and geometricparameters
Geometric parameters

R2

Regression models

V - Total Volume (m3)

RASTIavg = -0.0324 RTavg - 1.026x10-5.V + 0.529

0.89

S - Surface Area (m2)

RASTIavg = -0.0351 RTavg - 1.158x10-4 S + 0.540

0.89

H - Maximum Height (m) RASTIavg = -0.0156 RTavg - 0.00706 H + 0.540

0.88

W - Maximum Width (m)RASTIavg = -0.0446 RTavg - 0.003085 W + 0.569

0.85

L - Length (m)RASTIavg = -0.0225 RTavg - 0.002479 L + 0.545

0.87

3

-5

Vnave - Volume nave (m ) RASTIavg = -0.0309 RTavg - 1.363x10 Vnave + 0.527 0.89
Lnave - Length nave (m)RASTIavg = -0.0186 RTavg - 0.00399 Lnave + 0.538

0.82

4. CONCLUSIONS
Regarding RT, none of the examined churches demonstrated the ideal acoustical values for speech(between 0.8 and 1.0 s), solely the ones of smaller volume attained a better performance (but we mayneed to remember that in Romanesque times, religious services were held in Latin…). This is also theresult of the Romanesque constructive system that is a quite simple style, with small amounts ofornaments, and in this area, predominantly uses the granite, which causes strong reflections. The best
RT avg results belong to the churches with volume below 2000 m 3 , obtaining values between 1.6 and2.5 s, which prove to be suitable for most musical purposes.
The values of speech intelligibility (RASTI) are in general fair and the worst results registered(about 0.38 in P. Sousa and Ferreira) can be justified by the fact that these were the churche s with thelargest volume.
The calculated regressions that were analyzed for RT and RASTI resulted in R2 values that were all
close to 0.9, which represents a positive correlation and reliable use of these models for prediction.
The geometric parameter that most influenced Romanesque church acoustics was Length of nave (Ln)for the RTavg, and Height for the RASTI avg.
Maximum Width obtained very low individual R 2 values for both acoustic parameters (RT andRASTI); however, by crosschecking this feature with a multiple regression model, it reached figures
close to the maximum.
The best regression in this paper, with an outstanding R 2 value of 0.91 was observed for the
RASTI avg values as a function of the 1600 Hz 1/3 octave frequency band values.

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