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Technical Note

Guidelines for acoustical measurements in churches

Francesco Martellotta a,*, Ettore Cirillo a, Antonio Carbonari b, Paola Ricciardi c

aDAU, Politecnico di Bari, Via Orabona 4, 70125 Bari, ItalybDCA, Universit IUAV di Venezia, Dorsoduro 2206, 30123 Venezia, ItalycDIIA, Universit di Pavia, Via Ferrata 1, 27100 Pavia, Italy

a r t i c l e i n f o

Article history:Received 20 December 2007Received in revised form 1 April 2008Accepted 16 April 2008Available online 3 June 2008

Keywords:Church acousticsMeasurement techniquesWorship buildings

a b s t r a c t

The acoustics of churches is a cultural heritage to be preserved as carefully as the artistic and architec-tural aspects of this particular category of buildings. The acoustic characteristics of an environment couldbe measured according to different techniques varying from the numerical quantication, by means ofacoustical parameters, to the recording of the binaural or ambisonic impulse responses of several com-binations of sourcereceiver locations. The complexity of this kind of buildings can lead differentresearchers to choose dissimilar sourcereceiver arrangements, that yield incomparable results. To pre-vent different approaches to the problem and to assist in obtaining comparable data, the results of exper-imental measurements deriving from previous acoustical surveys are statistically analysed in order tobetter understand the spatial variation of acoustical parameters leading to the denition of a set of guide-lines to standardize the choice of sources and receivers locations. In addition, suitable hardware combi-nations depending on the purpose of the measurement are nally suggested.

2008 Elsevier Ltd. All rights reserved.

1. Introduction

The acoustics of worship places and churches in particular havegained increasing importance in recent years. Several researchgroups have been studying church acoustics, each one focussingon different geographical areas [17]. However, a more detailedanalysis of the studies shows that the measurement techniquesare often signicantly different in terms of measurement equip-ment and calculated parameters. A further source of differencesis the large variability of church shapes, which may induce differ-ent researchers to locate sources and receivers in different wayswith the consequence of having hardly comparable measurementefforts. The latter problem is one of the most important sourcesof uncertainties when comparing both the acoustics of differentchurches and the measurements of different teams in the sameplace.

The following proposal was developed by a team of three Italianuniversities within the framework of the national interest programof scientic research The acoustics of worship places, funded bythe Italian Ministry of Universities and Research, with the aim ofproviding a technical and operative support to measurement ses-sions inside churches of different traditions and of different coun-tries. This measurement program will be used to collect a detaileddescription of the acoustic characteristics of one of the mostimportant group of cultural heritages to be used in order to

improve the knowledge of the sound propagation inside this typol-ogy of buildings, to preserve the original characteristics in case ofrestoration, and to determine optimal approaches to improve theacoustic conditions inside existing buildings.

One of the most interesting, and worrying, aspects that arisewhen dealing with churches is represented by their dimensions(which vary from small to huge) and by their spatial complexitywhich sometimes derives from the original design but, more fre-quently, is the result of the additions and modications made overcenturies. In addition, sound sources in a church may be located indifferent positions, depending on the evolution and on the currentstructure of the liturgy.

This proposal, always keeping in mind the general requests ofthe ISO 3382 standard [8] and the similar work carried out for the-atres [9], takes into account three basic aspects of the measure-ment procedure: the choice of the source positions, the choice ofthe receiver positions, and the equipment to be used.

2. Source positions

The location of the sound sources in a church (Fig. 1) may bequite varied because even though the sanctuary (or chancel) isthe centre of the liturgical action, there are (regardless of whichChristian tradition is considered) at least two acoustic poles inthis area: the altar and the ambos (or lectern). The pulpit, gen-erally located outside the sanctuary and close to the assembly,plays a fundamental role in most Reformed churches and inCatholic churches may provide an interesting insight into the

0003-682X/$ - see front matter 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.apacoust.2008.04.004

* Corresponding author. Tel.: +39 0805963631; fax: +39 0805963701.E-mail address: [email protected] (F. Martellotta).

Applied Acoustics 70 (2009) 378388

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sound reinforcement methods used before the electro-acousticsera. In addition, choir and organ have a well dened positionin the church and when their role during the celebration is sig-nicant they should also be taken into account. The assembly ofthe faithful, being an active part during congregational singing,should be considered as a further sound source. Finally, it cannotbe excluded that other kinds of musical performance may behosted in a church (generally with several musicians in frontof the altar). For all these reasons it clearly appears that a com-plete and detailed analysis of the sound propagation inside achurch is hardly possible. However, in order to make measure-ment efforts carried out by different teams comparable, the pro-posal is to assume at least two source locations. The rst oneshould be considered as a reference source location placed ata xed position. The second one should be chosen among theothers as a function of the specic purpose of the measurementcampaign. In order to encourage the use of further sound sourcelocations, which is particularly recommended in churches wherespeech, organ, and choir are important, no upper limit to thenumber of locations is specied, the only limit being the timeavailability of the church in the desired conditions.

The reference source location (S1), required for the comparisonsamong different teams (and among different churches), should beplaced, if possible, in front of the altar currently used for celebra-tions on the side of the listening area, at a distance of 1.5 m andon the symmetry axis provided that signicant focussing effectsdue to reecting surfaces may be excluded. In Eastern churches(both Christian and Orthodox), where an iconostasis often sepa-rates the sanctuary from the nave, the sound source should belocated in the nave side at 1.5 m from the iconostasis (in this casesource S2 may be used as the actual altar position). In case focus-sing effects cannot be excluded the source should be shifted by 1 mfrom the axis. In any case, the source height should be 1.5 m abovethe oor.

The high altar source location (S2), may be employed inchurches where the original high altar has been preserved(although not used), and its position is raised or signicantly dis-tant from the altar currently in use. The sound source should beplaced on the symmetry axis (provided that signicant focussingeffects due to reecting surfaces may be excluded) and at a dis-tance of 1.5 m from the vertical surface of the altar. In this casethe source height should be 1.5 m above the base of the high altar.In churches where the altar used for celebration is movable andhas a provisional character source location S2 may replace S1 as

the reference source location provided that the altar does notobstruct the propagation towards the assembly.

The ambos (or lectern) source location (S3), generally located inthe chancel area, should be used when the effects of unampliedspeech are of particular interest. Alternatively, the pulpit sourcelocation (S4), located nearby the audience, should be used whenaccess is possible. In both cases, the source height should be1.5 m above the oor or, if the balustrade is too high, the heightshould be increased to overcome the top of the balustrade by atleast 0.50 m. On the pulpit the source should be placed as closeas possible to the balustrade to simulate speakers natural position.Given the peculiar character of the source position it would bepreferable to use a sound source having a directivity comparableto that of the human voice [1012], aiming at the centre of the con-gregation. Since no standard sound source is available for emulat-ing human voice (ITU-T recommendation P-51 [13] providing poorconstraints on source directivity), the directivity pattern of the em-ployed directional source should be included in the documenta-tion. However, until reliable human voice simulators will beavailable, the use of an omni-directional sound source should beconsidered as a viable alternative.

The choir source location (S5), should be used whenever a per-manent choir sing in the church and should be located at the centreof the area occupied by the singers or, in case of ancient woodenchoirs (provided that they are still in use), at the centre of the cor-responding area. In Orthodox churches and in all those churcheswhere the choir is generally split into two groups, two soundsource positions should be used, located at the centre of therespective areas occupied by the singers. In any case, the sourceshould be at least 1.0 m far from reecting walls and at 1.5 mabove the oor.

The organ source location (S6), should be located as much aspossible close to the centre of the organ pipes (at a distance of atleast 1 m). In case the span of the organ pipes is larger than 6 mit is recommended to use two positions (S6a and S6b) shifted bya distance equal to half the width of the organ. In case the heightcorresponding to the centre of the pipes cannot be reached it is rec-ommended to place the source at 2 m above the oor.

The congregation source location (S7), should be used wheneverthe assembly of the faithful plays an active role during the liturgyor when the acoustic coupling between this area and the sanctuaryis thought to be poor. The source should be placed at the centre ofthe largest area occupied by the congregation at an height of 1.5 mabove the oor.

S1 S2

S3

S5

S6a

S4

S7

S6b

S8

S9

1.5m 1.5m

>1

m

1m

>2m >2m

1 m

Fig. 1. Typical location of sound sources. S1, altar; S2, main altar; S3, ambos; S4, pulpit; S5, choir; S6, organ; S7, congregation; S8, dome; S9, chapel.

F. Martellotta et al. / Applied Acoustics 70 (2009) 378388 379


The dome source location (S8), should be used in presence oflarge domes when the reference source location (S1) is located out-side the area covered by the dome. The source should be preferablylocated on the symmetry axis at 2 m from the centre of the domeand 2 m within the geometrical projection of the dome on the hor-izontal plane, and at 1.5 m above the oor.

Further source positions (S9, etc.), should be used in addition tothe others already mentioned, when the church is characterized byparts (such as transepts and side chapels) which may reasonablybehave as coupled volumes [14] or which may be used indepen-dently (i.e. to celebrate daily masses, for choir performance orrehearsals). In all these cases the sound source should be placedat the centre of the area or, in case of independent use, close tothe position of real sound sources (minister, singers, etc.), providedthat the distance from reecting surfaces is at least 1 m and theheight above the oor is 1.5 m.

Finally, inall thosechurcheswhere thesoundsystemhasapartic-ular historical value, orwhen theanalysis of the speech intelligibilityis particularly important, thewhole set of the loudspeakers of the PAsystemmight beused as a sound source, provided that the test signalis fed directly to the system. In this case the settings should not bemodiedwith respect to their normal values, and the characteris-tics of the systemand of the loudspeakers, includingmodel, positionand wiring details, should be carefully documented in themeasure-ment log. Feeding the signal directly to the system allows the exclu-sion of the microphones (and their controls) which may be moreeasily moved and modied by the users. In any case this sourceshould only be used in addition to the two conventional soundsource positions.

3. Receiver positions

The volumetric complexity and the plan layout of manychurches make the choice of the receivers locations even more dif-cult (and subjective) than the choice of the source locations. Sev-eral parameters should be taken into account in order to ease the

work, but the nal choice is generally the result of a compromisebetween two contrasting needs. On one side, the need to have anaccurate picture of the variation of the acoustic parameters insidethe church which leads to maximize the number of source andreceiver positions. On the other side, the limited time granted bythe church management for the measurements which, to assureminimum background noise, and minimize the risk of interruption,should be conducted late at night.

A general rule to be followed is that the receivers should beplaced preferably in the main listening area (MLA), even thoughfor churches such area is much less dened than in performingspaces. In fact, in many churches (especially the very large ones)the area occupied by pews or seats may vary as a function of theperiod of the year with the largest area observed during the ma-jor holy days. In addition, it should also be considered thatstanding people are not unusual in churches. Consequently, forthe purpose of the acoustical measurements the MLA shouldbe dened as the combination of the largest area covered bypews and the area which is more likely to be occupied by stand-ing faithful (Fig. 2).

ISO 3382 standard [8] suggests that receivers should be placedat 1.2 m above the oor, at a distance of 1/4 wavelength from anyreecting surfaces (corresponding to about 1 m), and at half wave-length from each other. However, the denition of the optimumplacement of the receivers (capable of ensuring an accuratedescription of the variations of the acoustical parameters), cannotrely only on practical considerations but should take into accountthe actual distribution of the sound in the room. In order to scien-tically dene such rules the results of the acoustic measurementscarried out in several churches were statistically analysed.

3.1. Preliminary analysis of the spatial distribution of acousticparameters

A sample of 37 churches was analysed in order to investigatethe spatial variation of the acoustic parameters. All the measure-

01020405 010305

060708

09 L/6

10

LDav

Ltot

W

Fig. 2. Arrangement of the minimum number of receivers in a typical church. Six receivers are placed on one side the main listening area together with three mirroredcontrol receivers. One receiver is located in the chancel area to analyse sound perceived by ministers and one in the side aisle to analyse acoustic conditions in acousticallyunfavorable portions of the space. Area enclosed in dashed line represents the main listening area.

Table 1Octave bands used to calculate multi-octave bands average of acoustic parameters and corresponding JNDs used

T30 T20 EDT G10 D50 C80 Ts LF IACC

Octave bands 5001k 5001k 5001k 5001k 5002k 5002k 5001k 5002k 5002kJND 5% 5% 5% 1 dB 5% (abs) 1 dB 20 ms 0.05 0.075

380 F. Martellotta et al. / Applied Acoustics 70 (2009) 378388


ments were carried out in strict agreement with ISO 3382 standard[8] by using an omni-directional sound source made of twelveloudspeakers mounted on a dodecahedron combined with a sub-woofer to obtain a frequency response from 50 Hz to 16 kHz. Thesignal used was an envelope equalized sine sweep [15]. The micro-phones were a random incidence GRAS 40AR and a SoundeldMKV.

The standard deviation of the multi-octave-band averages ofthe acoustic parameters measured in each church were consideredand the corresponding standard deviations were then calculated interms of just noticeable difference (JND). The latter values for eachacoustic parameter (Table 1), were taken from ISO 3382 draft [16]circulated in 2004, with the exception of Ts. In fact, for this param-eter JND is normally assumed equal to 10 ms, but a preliminaryinvestigation carried out by the authors suggests that when thereverberation time is longer than 4 s JND should be much longer,at least 30 ms. For this reason, in the present analysis JND for Tswas assumed to be 20 ms. The results of the analysis of standarddeviations are reported in Tables 2 and 3.

It can be observed that reverberation times (T30 and T20) showthe lowest variations, with a standard deviation which is well be-low the JND limit in all the cases, indicating that both these param-eters are quite stable independent of the source and receiver used.

EDT shows higher variations with an average standard devia-tion of about 1 JND, but with one-third of the values above this va-lue and a maximum of 2.7 JNDs. In this case, as shown in Ref. [17],a dependence on sourcereceiver distance appears in most cases,with a trend to increase as a function of the distance (with an aver-age slope of 0.03 s/m). The mean slope tends to decrease as thedimensions of the church grow, and if the slope is expressed interms of distance beyond which a JND may be perceived (lateron called JND distance) the mean value corresponds to 8.7 m.The analysis of the correlations between JND distance and somearchitectural parameters (volume, total length, nave length, oorsurface, mean width, average altar-listener distance), was per-formed with the hope of nding some sort of relationship withchurch specic parameters. As reported in Fig. 2 the nave length(L) was conventionally assumed as the distance from the altar tothe entrance, the average altar-listener distance (Dav) was denedas the distance from the altar to the centre of the main listeningarea. In all the cases the regression equations were forced to theorigin. The best correlation was found with the mean altar-listener

distance. The regression equation (Fig. 3a) is statistically signicant(R2 = 0.53, p < 0.001) and shows that the JND distance is 0.45 timesthe mean sourcereceiver distance, suggesting that the spacing be-tween receivers may grow together with the church dimensions.

G shows variations of the same magnitude of EDT, with an aver-age standard deviation of 1.2 JNDs and a maximum of 2.6 JNDs. Thevariations are expected because several researches showed that Gdecreases as the sourcereceiver distance grows [6,7]. The slopevaries between 0.27 dB/m and 0.04 dB/m, with a mean valueof 0.127 dB/m (corresponding to a JND distance of 7.9 m). Again,correlations between JND distance for each church and corre-sponding architectural parameters were investigated. The best re-sults were obtained by taking into account the mean altar-listenerdistance (Fig. 3b). The regression equation is highly signicant(p < 0.0001) and shows that JND distance is about 2/5 of the meanaltar-listener distance.

Energy ratios show the highest variations, with average valuesof the standard deviation varying from 1.6 JNDs for D50 to 2.9 JNDsfor Ts. C80 stays in between with a standard deviation of 2.6 JNDs.As shown in Ref. 6 energy ratios are strongly dependent on sourcereceiver distance with D50 and C80 decreasing and Ts increasing asthe distance grows. For C80 the slope varies from 0.12 dB/m to0.53 dB/m with a mean value of 0.27 dB/m and a JND distanceof 3.7 m. For Ts the slope varies from 2.2 ms/m to 11 ms/m witha mean value of 5.5 ms/m and a JND distance of 3.6 m. The analysisof the correlations with architectural parameters shows that forC80 the JND distance is best related to the nave length. The regres-sion is highly signicant (R2 = 0.661, p < 0.0001) and shows thatJND distance is about 1/10 of this measure (Fig. 3c). Ts also showsthe best correlation with the nave length and even though the sta-tistical signicance is lower (R2 = 0.515, p < 0.001) the regressionequation shows that JND distance is 1/11 of that measure (Fig. 3d).

LF and IACC show a similar behaviour, with an average standarddeviation of 1.4 JNDs and a maximum of 2.5 JNDs. Unlike the ener-getic parameters, whose variations are mostly dependent onsourcereceiver distance, the variations of LF and IACC are moresensitive to relative sourcereceiver position and to wall proximitywhich may cause strong lateral reections [18]. In fact, the abovecalculations are based on the whole set of receivers of each church,including side aisles, transepts and alike. If only the receivers in themain listening area are taken into account, the average standarddeviation lowers, and a further reduction may be obtained by con-sidering only receivers far from reecting walls. In this case thestandard deviation becomes 0.9 JNDs for LF and 1.0 JNDs for IACC,with maximums of 1.3 and 1.6 JNDs, respectively, suggesting amore uniform distribution with differences hard to be detectedsubjectively (about 2/3 of the churches show a standard deviationbelow the JND). A subset of churches was selected to analyse thevariations of receivers located close to walls, showing higher meanvalues (due to the stronger lateral reections) and standard devia-tions generally below the JND limit (Table 4), indicating again sub-stantial uniformity.

In terms of variation as a function of sourcereceiver distancetwo opposite trends were observed for LF. In elongated churchesLF mildly decreases as the distance grows, with a JND distancevarying between 6.5 m and 34.5 m with an average of 16.9 m.The JND distances show poor correlation with architectural param-eters but are systematically larger than the corresponding valuescalculated for monaural parameters. In squared and central-planchurches LF increases as the distance grows, with a JND distancevarying between 3.8 m and 19 m and an average value of 7.8 m.Even in this case no signicant correlation with architectural mea-sures was observed but JND distances were always bigger than thecorresponding values calculated for monaural parameters.

These observations were conrmed by simulations carried outwith the software CATT-Acoustic. Three simple shoebox rooms of

Table 3Frequency distribution of standard deviations calculated in surveyed churches

JND T30 T20 EDT G10 D50 Ts C80 LF IACC

4 0 0 0 0 0 8 1 0 0

Table 2Mean, minimum, and maximum values of standard deviations of the acousticparameters measured in the 37 churches surveyed and expressed in terms of JND

T30 T20 EDT G10 D50 Ts C80 LF IACC

Min 0.1 0.1 0.3 0.3 0.5 1.1 0.7 0.9 0.7Max 0.6 0.9 2.7 2.6 3.3 6.5 4.3 2.5 2.4Avg 0.2 0.3 1.1 1.2 1.6 2.9 2.6 1.4 1.4



xed height (20 m) and different plan (30 30 m, 20 40 m, and20 60 m) were analysed. Simulations were carried out at 1 kHzonly, all surfaces were assumed to have an absorption coefcientof 0.10 and a scattering coefcient of 0.30. The results show thatthe spatial distribution of LF is strongly dependent on room geom-etry. A signicant dependence on sourcereceiver distance can beobserved when the room is elongated (Figs. 4b and c and 5a), witha mild decrease of LF as the distance grows (and consequently theangle of the lateral reection becomes smaller). Conversely, in thesquare room (Fig. 4a) the values increase monotonically. A trans-versal variation, with decreasing LF values moving towards thecentre of the room, can be observed in all the cases, in particularat positions within 1020 m from the source, where the standarddeviation appears larger than JND (Fig. 5b). It is interesting toobserve that, as a consequence of the later arriving lateral reec-tions, in the wider room the longitudinal variation is slower thanin the narrower rooms.

In order to take into account the effect of columns and pillars,which frequently divide churches into naves, the simulations wererepeated using the same dimensional ratios but adding a series ofsimple rectangular pillars (Fig. 4df). For such surfaces the scatter-ing coefcient was assumed to be 0.7 to account for diffraction ef-fects. In this case the general trend to increase up to a distance of1020 m from the source and then decrease is still visible both inthe nave and in the aisles (Fig. 5c). However, LF values in the aislesare markedly higher (by about 0.1) as a consequence of the shad-owing effect of the columns (masking frontal sound) and of thestrong lateral reections. This also determines signicant transver-sal variations in the aisles as a function of source visibility, as illus-trated by the high standard deviation (Fig. 5d). Conversely,transversal variations in the nave are generally negligible, withstandard deviation well below JND, even at points close to thesource. Transversal variations in the main nave are signicant onlywhen its width is greater than 15 m.

JNDdist = 0.103 LR2 = 0.649

0

1

2

3

4

56

7

8

9

10

0 20 40 60 80 100

Nave length (m)

JND

dist

ance

forC

80(m

)

JNDdist = 0.092 LR2 = 0.515

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100

Nave length (m)

JND

dist

ance

for T

S(m

)

JNDdist = 0.45DavR2 = 0.531

0

5

10

15

20

25

0 10 20 30 40 50

Average Source-receiver distance (m)

JND

dist

ance

forE

DT

(m) JNDdist = 0.383Dav

R2 = 0.6062

0

2

4

6

8

1012

14

16

18

20

0 10 20 30 40 50

Average Source-receiver distance (m)

JND

dist

ance

forG

(m)

a b

c d

Fig. 3. Plot of JND distance calculated for EDT (a) and G (b) vs. mean altar-listener distance, and for C80 (c) and Ts (d) vs. nave length.

Table 4Mean values and standard deviations (in brackets) of average values from 500 Hz to 2 kHz of LF and 1-IACC measured in a selection of four churches as a function of the distancefrom walls

C1 C2 C3 C4

LF 1-IACC LF 1-IACC LF 1-IACC LF 1-IACC

Walls 0.31 (0.048) 0.68 (0.045) 0.27 (0.046) 0.56 (0.12) 0.36 (0.072) 0.79 (0.043) 0.35 (0.032) 75.8 (0.09)Centre 0.23 (0.073) 0.49 (0.058) 0.19 (0.024) 0.49 (0.037) 0.26 (0.036) 0.76 (0.072) 0.20 (0.042) 0.66 (0.012)Difference 0.078 0.192 0.076 0.119 0.099 0.029 0.155 0.095



3.2. Effect of geometrical symmetry on acoustic measurements

Six different churches, having different plan and typology, butall being substantially symmetrical were analysed. The results ofthe comparisons between the measurements carried out in 22pairs of receivers placed in symmetric locations when the soundsource was located in front of the altar on the symmetry axis arediscussed. As well as in the previous discussion the differences be-

tween pairs of corresponding receivers were expressed in terms ofJND (Table 5). It appears that for all the acoustical parameters,apart from LF, the mean differences are within the JND limit.

Reverberation and strength show the highest accuracy, whileearly decay time and energy ratios show relatively higher differ-ences due to their much higher sensitivity to small differences inthe sound eld. Similarly, lateral fraction is sensitive to small dif-ferences in time and direction of arrival of early reections and

Fig. 4. Plot of calculated LF distribution at 1 kHz. Top panel: simple rectangular rooms: (a) 30 30 m; (b) 20 40 m; (c) 20 60 m. Bottom panel: rectangular roomssubdivided into naves: (d) 30 30 m; (e) 20 40 m; (f) 20 60 m.

0

5

10

15

20

25

30

0 10 20 30 40 50 60Longitudinal distance from source (m)

Mea

nLF

(%)

30x3020x4020x60

0

5

10

15

0 10 20 30 40 50 60Longitudinal distance from source (m)

Sta

ndar

dD

evia

tion

(%)30x3020x4020x60

05

10152025

303540

4550

0 10 20 30 40 50Longitudinal distance from source (m)

Mea

nLF

(%)

Nave 30x30Nave 20x40Nave 20x60Aisles 30x30Aisles 20x40Aisles 20x60

0

5

10

15

0 10 20 30 40 50Longitudinal distance from source (m)

Sta

ndar

dD

evia

tion

(%)

Nave 30x30Nave 20x40Nave 20x60Aisles 30x30Aisles 20x40Aisles 20x60

a b

c d

Fig. 5. Plot of averages (a) and standard deviations (b) of LF values calculated in the rooms reported in Fig. 8, along transversal axis and plotted as a function of longitudinaldistance; (c) and (d) are the same as (a) and (b) but calculated in the rooms with pillars.



consequently shows an average value (and an upper condencelimit) slightly exceeding the JND limit. When only perfectly sym-metrical churches are taken into account the mean difference forLF lowers to 0.86 JNDs with an upper condence limit of 1.04,showing a considerable improvement of performance, indicatingthat good matching between symmetrical positions may only beobtained if the room is symmetrical and the receivers are accu-rately placed.

3.3. Practical considerations

Taking into account the results of the above mentioned analy-sis a few practical rules may be proposed for the receivers place-ment. In particular, it appeared that the maximum distancebetween receivers that allows an acceptable description of thespatial variability of monaural parameters may be assumed pro-portional to the church dimensions and, taking into account thestrictest conditions deriving from Ts, for which JND distance isL/11, it may be concluded that each receiver may cover a circulararea with a radius equal to the JND distance. Consequently, allow-ing some superposition among circular areas, the resulting dis-tance between receivers should be about 1/6 of the length ofthe main listening volume, approximated by the entrance-to-altardistance (Fig. 2).

In churches where the nave has an exceptional width (>15 m)the receivers should be preferably arranged according to a quin-cunx pattern in order to have some receivers within a distance of5 m from the walls and take into account the variations in LF andIACC as a function of the distance from the reecting surfaces. Innarrow churches with pillars or columns dividing the nave fromthe aisles, the receivers should be arranged along a single line atvarying distances from the columns in order to account for their ef-fect on lateral reections and inter-aural correlation.

If the church is symmetrical the receivers may be located onlyon one half of the church, provided that at least three controlreceivers are located symmetrically on the other half of the mainnave. The receivers should be distributed throughout the wholearea if more than 30% of the multi-octave-band averages of theacoustical parameters (as suggested by ISO 3382 draft [16]) calcu-lated in control points show differences higher than the corre-sponding JND when the source is in position S1. However, if thisanalysis cannot be carried out on-site and the discrepancy appearsafter the survey is completed, the lack of acoustical symmetryshould be clearly stated in the measurement report. For non-sym-metrical sound sources the control receivers should also be in-cluded in order to determine the differences in soundpropagation. In any case, the main line of receivers should coincidewith the centreline of the main pew area, with the rst receiver lo-cated at the centre of the third row from the altar.

In addition to the above mentioned rules, in order to analysethe acoustical behaviour of all the parts of a church, it is recom-mended to place one receiver close to the sound source (within adistance of 1 m, in order to analyse what speakers and musiciansperceive), and at least one receiver in each secondary volume.This group should include the sanctuary, transepts, choirs, largechapels and all those accessible volumes which, because of a par-

ticular combination of acoustical materials and shape, indepen-dent of their degree of acoustic coupling with the main volume,may rise place to a different acoustic behaviour. In these casesthe receiver should be placed at the centre of the oor area cor-responding to the secondary volume or in proximity of xed seat-ing positions (such as the ministers seat or behind the altar inthe chancel or at the centre of the stalls in the choir, if present).In case of stringent time limitations, priority should be given tothe receiver close to the source and to those areas which aremore likely to be occupied by a signicant number of persons(aisles, transepts, choir).

In case of large domes, especially if the focal point is close to theoor (or better to peoples heads), at least six receivers should beused in order to detect possible irregularities in the sound eld[19]. The receivers should be distributed according to a quincunxpattern, as reported in Fig. 6. In case of small domes only the rstthree positions could be used. When the symmetry of the church isnot perfect or when a more detailed analysis is required, additionalpositions mirrored along the main axis may be used.

Combining all these things together, the actual minimumnumber of receivers may be dened and a convenient layout orga-nized (Fig. 2). Even though the use of an optimum number ofreceivers, obtained by doubling the minimum number of receiversin the MLA is strongly encouraged, in most cases the best solutioncould be an adapted conguration, with a number of receivershigher than the minimum but tted to the geometry of the churchunder analysis and to the selected sound sources, ensuring the bestcompromise between accuracy, time restrictions, and ease of plac-ing the receivers. A simple rule of thumb to better t the layout ofthe receivers to the geometry of the church could be to alignthem to the architectural grid (i.e. of the spans), trying to locatethe rst receiver as close as possible to the centre of the thirdrow of pews. Possible adapted arrangements of receivers areshown in Figs. 79 for three typical church plans.

Table 5Mean differences, standard deviations, and condence limits of acoustical parameters measured in symmetrical positions in nearly symmetrical churches (all values expressed interms of JND)

T30 T20 EDT G10 D50 C50 C80 Ts LF

Mean 0.19 0.28 0.69 0.22 0.34 0.67 0.50 0.62 1.10Standard deviation 0.15 0.18 0.51 0.14 0.21 0.43 0.34 0.45 0.57Condence interval 0.06 0.08 0.22 0.06 0.09 0.19 0.14 0.19 0.24

05

03

01

02

04 06

Fig. 6. Suggested arrangement of the receivers under large domes.



4. Source and receiver combinations

The acoustic characteristics of a church are strongly dependenton the combination of sourcereceiver positions taken into ac-count. A complete description of the acoustic behaviour of a placeshould involve the use of the largest set of source and receiverlocations. However, time restrictions often prevent such degreeof detail because moving two or three microphones with theircables in many points is a very time consuming activity. It was sta-ted in the previous sections that a minimum measurement set-up should involve at least two source locations (S1 and anotherone depending on the main purpose of the measurement) andthe minimum number of receivers. However, in order to encouragetesting the church with more than two source positions it is sug-gested that, apart from source location S1 which should be alwaysused in combination with all the receivers, when more than 2source locations are used, a reduced number of receivers may beused in agreement with the scheme reported in Table 6.

The choice of the receivers to be used in the simplied set-upsshould be made by taking into account the principle of the maxi-mum coverage of the MLA including, preferably, the extreme posi-tions (the closer and the farther receiver location). In symmetricalchurches where the receivers are located only in one half of theMLA the control receivers should be used to ensure a better cover-age of the MLA when non-symmetrical sound sources are used.Examples of combinations of sources and receivers in typicalchurch plans are reported in Figs. 79.

Given the signicant inuence that occupancy may have on theacoustics of churches, measurements in occupied conditions arestrongly encouraged in addition to the unoccupied set of measure-ments. In this case, a single source position (preferably S1) may beaccepted, in combination with at least three receivers locatedrespectively on the front and on the back of the assembly, andone located in the chancel area. In order to make comparison be-tween occupiedunoccupied conditions receiver locations shouldcoincide with those used in the empty conguration. Care shouldbe taken in order to prevent unwanted noise entering the micro-phones. The occupants should be distributed throughout the MLAand their number (together with the area they actually cover)should be reported in the measurement log.

In any case, a measurement of the background noise in one-third octave bands should be made, possibly during daytime in or-der to provide a complete description of the acoustic environment

of the church during the celebration and to allow STI calculationsby means of impulse responses. Measurements should be prefera-bly made at each receiver position, but the minimum congurationshould include at least three receivers located respectively on thefront and on the back of the assembly, and one located in the chan-cel area to take into account different parts of the church in theirrelation with the envelope and its opening. Each measurementshould last for at least ve minutes.

5. Measurement equipment

Four different equipment set-ups are proposed as a function ofthe purpose of the measurement, of the instruments available andof the time given for the measurement. The basic set-up is mostlyintended for a simple and quick characterization of the place bymeans of the measurement of the reverberation time and monau-ral acoustic parameters, consequently it is also the less demandingin terms of equipment and also non-repetitive sound sources maybe used. The intermediate set-up is intended for a more detailed

030507 0109

101112

02

13

14

08 04

S1 S5S4

06

15

Fig. 7. Arrangement of an adapted number of receivers in combination with three source positions in a typical basilican-plan church. Source S1 (altar) should be used incombination with all the receivers. Source S4 (pulpit) should be used in combination with odd receivers from 01 to 09 and with receivers from 10 to 12. Source S5 (choir)should be used in combination with receivers 01, 02, 05, 08, 09, 10, 12, and 15.

0503

0102

0406

S1

S6

0708 10

09

1213

11

S8

Fig. 8. Arrangement of an adapted number of receivers in combination with threesource positions in a typical central-plan church with large dome. Source S1 (altar)should be used in combination with all the receivers. Source S8 (dome) should beused in combination with receivers from 01 to 06, 11, and 12. Source S6 (organ)should be used in combination with receivers 01, 04, 06, 08, 09, 11, and 13.



characterization of the place by means of the measurement ofmonaural acoustic parameters and lateral fractions. In this caseonly electro-acoustic sound sources are accepted but the octave-band analysis is restricted to the six bands from 125 Hz to 4 kHz.The advanced set-up is intended for the more complete character-ization of the place by means of the measurement of the impulseresponses and of all the acoustic parameters. In this case the octavebands taken into account should include 63 Hz and 8 kHz and mul-ti-channel microphones should be used (including 1st order ambi-sonic, higher-order ambisonic and microphone arrays). Therendering set-up is intended to measure high quality impulse re-sponses, allowing both the calculation of all the acoustic parame-ters and, above all, a realistic laboratory reproduction, by meansof convolution with anechoic material, of the actual listening con-ditions observed in the church. High signal-to-noise ratio and a atresponse of the system (up to 16 kHz) are the additional require-ments in this case. The playback systems may include headphoneand transaural presentation for binaural signals, ambisonic decom-position on 2D or 3D loudspeaker arrays for both 1st order orhigher-order ambisonic measurements respectively made withfour-capsules or spherical arrays of microphones [20,21]. Detailsfor each conguration are reported below and a summary isreported in Table 7.

5.1. Basic set-up

Sound source: every sound source complying with the ISO 3382requirements [8], including impulsive sources such as blank pistol-shots, balloons, etc. In exceptional cases, when the use of pistol-shots and balloons may lead to low signal-to-noise ratio at thelowest frequencies the organ (if present) might be used as an addi-tional sound source, provided that it is mentioned in the measure-ment log. In fact, a reverberation time of several seconds should bescarcely affected by the decay time of low organ stops which israther short, normally less than 250 ms, as the volume of the windcase is rather small compared with the pipes. Low open ue pipesshould be used, and in order to avoid the excitation of only someseparated frequencies of the room, clusters of at least four semi-tones should be played.

Sound signal to be used with electro-acoustic sources: pink/whitenoise, MLS, sweeps in agreement with ISO 18233 [15,22].

Microphone: omni-directional.Frequency range: from 125 Hz to 4000 Hz in octave bands, or

from 100 Hz to 5000 Hz in one-third octave bands. A sampling rateof at least 44.1 kHz at 16 bit is recommended.

Measurable parameters: reverberation times (as a function ofthe available signal-to-noise ratio), EDT, and (only for impulsivemeasurements and omni-directional sources) energetic parame-ters and stage support indices. In order to calculate strength(G) the power level of the electro-acoustic sound source mustbe measured in anechoic or reverberant room, in agreementwith ISO 3382. Speech Transmission Index (STI) may also be cal-culated provided that background noise measurements are alsodone.

The signal acquired by the microphone may be stored on a high-delity digital recorder in order to be post-processed.

5.2. Intermediate set-up

Sound source: electro-acoustic omni-directional sound sourcecomplying with ISO 3382 standard.

Sound signal to be used with electro-acoustic sources: MLS, linear,logarithmic, and equalized sweeps in agreement with ISO 18233[15,22].

Microphones: omni-directional and gure of eight (or B-format).Frequency range: same as basic conguration.

0204

010305

06

07

08

0913

12 11 10

S1

S514

S6

S1015

Fig. 9. Arrangement of an adapted number of receivers in combination with four source positions in a typical single nave church. Source S1 (altar) should be used incombination with all the receivers. Sources S5 (choir) and S6 (organ) should be used in combination with receivers 01, 02, 05, 08, 09, 10, 12, and 14. Source S10 (chapel)should be used in combination with receivers 01, 05, 13, and 15.

Table 6Recommended sourcereceiver combinations

Source Receivers in themain volume

Receivers in secondary volumes

S1, altar All + 3 control rec. All

S2, high altara

50% + 2 control rec.At least one in the same volumewhere the source is located

S3, ambosS4, pulpitS5, choirS6, organ

S7, congregation At least 2 receivers at10 m from the source

All

S8, dome At least 6 receiversunder the dome

None

S9. . ., extra At least 2 At least one in the same volumewhere the source is located

PA system 50% None

a If S2 is used as reference position in place of S1, then the same receivercombination suggested for S1 should be applied.



Measurable parameters: all the monaural acoustic parameters(as specied in the Basic conguration) plus lateral fractions LFand LG.

5.3. Advanced set-up

Sound source: equalized electro-acoustic omni-directionalsound source, complying with ISO 3382 standard, with an addi-tional sub-woofer to cover the lowest frequencies.

Sound signal to be used with electro-acoustic sources: equalisedMLS or equalized sweeps in agreement with ISO 18233 [15,22].

Microphones: omni-directional, gure of eight (or B-format),and dummy head simulator with binaural microphones. Experi-mental microphones, such as anemometric pu probes or micro-phone arrays may be used provided that their characteristics areclearly specied in the measurement log.

Frequency range: from 63 Hz to 8000 Hz in octave bands, orfrom 50 Hz to 10,000 Hz in one-third octave bands. A sampling rateof at least 44.1 kHz at 16 bit is recommended.

Measurable parameters: same as intermediate conguration plusinter-aural cross-correlation coefcients.

5.4. Rendering set-up

Sound source: same as advanced conguration. In order to pro-vide a suitable signal-to-noise ratio, the use of a source with apower level of more than 100 dB is recommended in very bigchurches (with volumes larger than 50,000 m3).

Sound signal to be used with electro-acoustic sources: constantamplitude equalized sweep [15,22] is recommended. However,any signal capable of providing a S/N ratio of at least 45 dB overthe whole spectrum may be accepted.

Microphones: B-format, dummy head simulator with binauralmicrophones. Higher-order ambisonic microphones and any exper-imental microphone set-up may also be accepted provided that itscharacteristics are clearly specied in the measurement log.

Frequency range: from 63 Hz to 16,000 Hz in octave bands, orfrom 50 Hz to 20,000 Hz in one-third octave bands. A sampling rateof at least 48 kHz at 24 bit is recommended.

Measurable parameters: same as advanced conguration plusallowing a realistic laboratory reproduction, by means of convolu-tion with anechoic material, of the current listening conditions ob-served in the church.

6. Conclusions

A set of guidelines was proposed to simplify and normalize thechoice of source and receiver locations and to suggest suitable

hardware combinations for acoustic measurements in churches.The aim was to improve the comparability of measurements madeby different teams and, above all, allow comparisons of the acous-tic characteristics of different Christian worship buildings. The pro-posed criteria, mostly based on the experience of the authors inmeasuring acoustic characteristics of a large number of churches,took into account practical, architectural, and liturgical aspects,pointing out, where necessary, problems relevant to a particularreligious tradition. Proposals were also supported by quantitativeobservations based on the results of previous measurements. Theguidelines were nally improved by the contribution of research-ers and specialists of both acoustic measurements and worshipbuilding acoustics. Anyway, further suggestions to improve themethod are welcomed.

Acknowledgements

The authors would like to thank Dr. Davide Bonsi, Dr. DavidLloyd Klepper, Dr. David Lubman, Prof. Jrgen Meyer, Dr. RendellTorres, Prof. Michael Vorlnder, and Prof. Teolo Zamarreo fortheir invaluable help in reviewing and improving this proposalwith their comments. The authors are also indebted to Most Rev.Nicola Bux for his precious advice on liturgical problems. Thisstudy has been carried out within the national interest programof scientic research The acoustics of worship places, funded bythe Italian Ministry of Universities and Research.

References

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Table 7Summary of the four measurement congurations

Conguration

Basic Intermediate Advanced Rendering

Sound source Every source complying with ISO 3382 Electro-acousticomni-directional

Electro acoustic, omni-directional + sub-woofer

Same as advanced, Lw > 100 dB if V > 50,000 m3

Signal Noise, impulse, deterministic Deterministic (MLS,sweep)

Deterministic (MLS, sweep)preferably equalized

Same as advanced, but constant amplitudeequalized sweep is preferred

Microphones Omni-directional Omni + gure of 8 Omni + gure of 8 (or B-format) + dummy head

B-Format + dummy head

Frequencyrange (Hz)

1254000 1254000 638000 6316,000

Sampling 44.1 kHz, 16 bit 44.1 kHz, 16 bit 44.1 kHz, 16 bit 48 kHz, 24 bitMeasurable

parametersT30, EDT and, with restrictions on thesource, C, D, Ts, G, STIa

T30, EDT, C, D, Ts, G,STIa, LF, LG

T30, EDT, C, D, Ts, G, STIa, LF, LG,IACC

Same as advanced + realistic laboratoryreproduction

a STI measurements based on impulse responses may be made provided that background noise is measured.



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[16] ISO/CD-3382-1. Acoustics measurement of the reverberation time Part 1:performance spaces. Geneva, Switzerland: ISO; 2004.

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