acoustical characteristics of mosques in Saudi Arabia

Measurement of acoustical characteristics of mosquesin Saudi Arabia

Adel A. Abdoua)

Department of Architectural Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261,Saudi Arabia

~Received 19 November 2001; revised 24 May 2002; accepted 4 November 2002!

The study of mosque acoustics, with regard to acoustical characteristics, sound quality for speechintelligibility, and other applicable acoustic criteria, has been largely neglected. In this study abackground as to why mosques are designed as they are and how mosque design is influenced byworship considerations is given. In the study the acoustical characteristics of typically constructedcontemporary mosques in Saudi Arabia have been investigated, employing a well-known impulseresponse. Extensive field measurements were taken in 21 representative mosques of different sizesand architectural features in order to characterize their acoustical quality and to identify the impactof air conditioning, ceiling fans, and sound reinforcement systems on their acoustics. Objectiveroom-acoustic indicators such as reverberation time~RT! and clarity (C50) were measured.Background noise~BN! was assessed with and without the operation of air conditioning and fans.The speech transmission index~STI! was also evaluated with and without the operation of existingsound reinforcement systems. The existence of acoustical deficiencies was confirmed and quantified.The study, in addition to describing mosque acoustics, compares design goals to results obtained inpractice and suggests acoustical target values for mosque design. The results show that acousticalquality in the investigated mosques deviates from optimum conditions when unoccupied, but ismuch better in the occupied condition. ©2003 Acoustical Society of America.@DOI: 10.1121/1.1531982#

PACS numbers: 43.55.Br, 43.55.Gx, 43.55.Jz, 43.55.Mc@MK #

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I. INTRODUCTION

Mosques are places of worship used for prayer, puspeaking, preaching, lecturing, andQur’an recitations. Allactivities performed in mosques are related to speech ability and intelligibility. Therefore, the design of their acoutical features requires careful consideration if good listenconditions are to be achieved. Although mosquesuniquely important buildings in every Muslim community,general, their acoustical quality evaluation, problems~if any!and possible remedies have not received adequate attein the literature. Hammad1 in an early study evaluated speeintelligibility via rapid speech transmission index~RASTI!measurements in mosques in Amman, Jordan. He concluthat, in general, the acoustical characteristics of mosquesbeen largely neglected. In 1991, the acoustical problemshuge mosque built in Amman were investigated.2 The au-thors recommended that acoustical properties of mosqshould be considered at the early stages of design. In 199study3 established the relative influence of active enviromental control systems on the acoustical performancetypical mosque in the Gulf region. Recently, Abdou4 pre-sented and discussed the potential of utilizing room-acoussimulation in the early stages of mosque design, where dsions are made to establish the mosque geometry, sumaterials, and speech reinforcement system~SRS! distribu-tion.

a!Assistant Professor of Architectural Engineering. Electronic [email protected]

J. Acoust. Soc. Am. 113 (3), March 2003 0001-4966/2003/113(3)/1

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Acoustic evaluations of other religious buildings5–9 havebeen extensively reported. For example, the varying ofacoustics of a large cathedral for satisfactory speech intgibility, by the use of carefully designed, installed, maitained, and operated sound amplification system has bdemonstrated and discussed.5 In addition to assessing acoutical quality by using pressure-based room acoustics indtors, visualizing the directional characteristics of sound fieat the listener position is also possible. Three-dimensiotransient sound intensity impulse responses have beenlized to assess the effectiveness of a sound system in areverberant church.7 Subjective and objective acoustical fiemeasurements have been conducted in a survey9 of 36 Ro-man Catholic churches in Portugal. The idea was to evaluand predict the acoustical quality of these churches. Corrtion analyses and statistical modeling identified relationshbetween some room-acoustic indicators and speech intebility in this particular style of church. Recently clarity andefinition acoustic indices in Gothic churches were measuand compared with expected results derived from a seempirical analytical model.10 In the literature, objective andsubjective evaluation of halls used for other functions suas concert halls, opera houses and classrooms havewidely reported. However, developments employing impuresponse techniques11,12 for evaluating the acoustical qualitin different types of enclosures have not yet been appliedmosques, at least not in widely known publications. In adtion not many readers are aware of mosque design, its wship considerations, acoustical properties, and requireme

The objectives of the current work were the following:

1505505/13/$19.00 © 2003 Acoustical Society of America

FIG. 1. The basic design elements of a simple mosque~a! plan, and~b! isometric.

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~1! To give a background about the mosque’s basic deselements as influenced by worship considerationsmosque classifications;

~2! to characterize the acoustical quality of typical conteporary mosques built in Saudi Arabia and, subsequento objectively confirm~or otherwise! the existence ofacoustical problems with respect to speech intelligibiland compare design goals with results obtained in ptice;

~3! to identify the impact of active environmental contrsystems such as air-conditioning systems~A/C! and me-chanical ventilation incorporated into mosque designsthe acoustical quality; and

~4! to investigate the overall effectiveness of the SRS mcommonly operated in mosques for enhancing speintelligibility.

II. COMMON CHARACTERISTICS OFCONTEMPORARY MOSQUES

A. Basic design elements of a mosque

Historically, the first mosque built inAl-Madinah Al-Monawarahcity, Saudi Arabiaformed the model for subsequent mosques throughout the Islamic world13 in its combi-nation of basic elements. It was a simple rectangular, waenclosure with a roofed prayer hall. The long side of trectangle is oriented toward the direction of the holy mosqin Makkahcity. This wall is usually described as theqiblawall. The wall contains a recess in its center in the form owall niche called themihrab. This wall also includes theminbar which is commonly an elevated floor, to the rightthe mihrab, from which theImam preaches or delivers thFriday sermon, thekhutba. These basic elements are the esentials of mosque design in Saudi Arabia, as they are ewhere in the Islamic world. Figure 1 illustrates the plan aisometric of a simple, typical mosque design. The basicsign elements are emphasized. Since the construction ofirst mosque, the functions of every mosque have remai

1506 J. Acoust. Soc. Am., Vol. 113, No. 3, March 2003

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unchanged. However, the mosque architectural form, spconstruction system, and building materials have evolvand developed to a significant and variable extent in differparts of the Islamic world, influenced by many factors metioned elsewhere.13,14

B. Worship modes in a mosque

The mosque design is mainly influenced by worshconsiderations. Worship in a mosque consists of two mamodes. The first mode, namely theprayer mode, involvesperforming prayers either individually or in a group, as regiously prescribed. Group prayer must be performed wworshippers standing, bowing, prostrating, or sitting behthe Imam, on the same floor level, aligned in rows paralleltheqibla wall with distances around 1.2 m apart. The secomode is thepreaching mode, where worshippers are directlseated on the floor in random rows listening to theImampreaching or delivering thekhutba while standing on theelevatedminbar floor. The minbar floor height varies fromone mosque to the other but usually is in the range of onthree meters above the mosque floor. Figure 2 showsworshippers’ different postures and their orientation in retion to theImamwhile performing the two different religiousactivities in the mosque. The congregational capacity ofmosque is usually determined by the floor area dividedthe area required for a worshipper to perform the prayer,approximately 0.8031.250.96 m2.

C. Mosque classifications

While, in general,traditional mosques can be classifieaccording to their architectural form and configuration,con-temporarymosques may be broadly classified accordingtheir size and location in relation to the community.14,15

Large mosques are located in large cities as public lamarks. They are usually built by the government expressthe state’s commitment to Islam. They are generally grain size and of large congregational capacity. Commun

Adel A. Abdou: Mosque acoustics

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FIG. 2. The worshippers’ different postures and their orientation in relato theImam in the two religious modes,~a! sections showing congregationlistening to theFriday speech~i.e., the preaching mode! and performingDaily individual or group prayer~i.e., the prayer-performing mode!, and~b!a top-view plan showing the source–receiver path~i.e., Imamworshippers!in group prayer performing.

J. Acoust. Soc. Am., Vol. 113, No. 3, March 2003

mosques~i.e., Jammamosques, whereFriday prayer, pre-ceded byFriday speech, can be performed! are distributedthroughout urban and rural communities and may houseditional functions~e.g., a library, meeting rooms, clinic, etc.!,in addition to the prime function of a space for performinprayers. They are usually utilized for bothdaily prayers aswell as theFriday prayer and occasionally are supplementwith a separate annex on the same floor level or in a menine floor for female worshippers. Small local mosqueslocated in small neighborhoods, and are of modest dimsions and congregational capacity. The planning and deguidelines for the above three types of mosque are availin Ref. 15.

D. Mosque prototypes in Saudi Arabia: Commonfeatures

In Saudi Arabia, many prototypes of mosque desexist.16 Mosques are built in various sizes ranging from smand medium to large types. They are usually typical in laout, shape, construction system, and building material,with different types of air conditioning and electroacoussound systems. From a field survey of 90 mosques, itobserved from site visits, design drawings, and ‘‘as buisketches that mosques are fairly similar with respect to thconstruction systems. They are commonly constructed ofinforced concrete skeletal structures with flat roofs. Theroof is commonly supported on columns that are arrangeda regular grid~i.e., structural unit!. A dome is sometimesconstructed spanning the central part of the roof to eliminintermediate columns. The shape represented by the asratio ~i.e., the mosque length over width!, and the floor areaof each mosque type is mainly controlled by the size aproportion of the structural unit dimensions as well astotal number of units~e.g., 533 units!. Interior materials ofthese typical contemporary mosques vary. Walls are mofinished with reflecting materials such as painted plasThey usually contain a wainscot, around 1.0 m high, mademarble tiles. The floor area is always covered with heacarpet. Hard, painted concrete ceilings with simple to elarate decorations are commonly used. Due to the harshmatic conditions in most of Saudi Arabia’s regions, aconditioners are virtually a necessity. Therefore, almosttypes of mosques are equipped with either a central, or aunit air-conditioning system or window-type unit, in concewith ceiling fans for air circulation. Electroacoustic SRhave also been implemented in mosques of all sizes tohance the listening conditions in the mosque space, partlarly after the introduction of the air-conditioning systemand the anticipated subsequent increase of ambient noisthe mosque.

III. ASSESSMENT OF ACOUSTICAL QUALITY INMOSQUES

Nowadays, numerous subjective attributes of the listing experience in enclosures can be described by the mavailable contemporary room-acoustic indicators. A comphensive listing of these contemporary indicators, definitiocorresponding subjective attributes, and suggested toler

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1507Adel A. Abdou: Mosque acoustics

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range values can be found in Ref. 17. In mosques, the macoustical concern is verbal communication. All activitiesthe mosque are dependent on speech audibility and intebility. Speech intelligibility ~SI! is the percentage of speecmaterial that is correctly identified by the average listenThe intelligibility of speech in rooms is related to both thspeech signal-to-noise ratio and to the acoustic characttics of the enclosure. That is, it can be influenced byspeech sound level, ambient background noise~BN!, and thereverberation time~RT! of the enclosure. Reverberation afects SI by affecting the early-to-late arriving sound energSI is directly related to the early-to-late energy fractionamely sound definition. In summary, in order to measurepredict speech intelligibility, various objective-based mesures can be used. Definition (D50) which is related to soundclarity (C50), useful-to-detrimental sound ratios~e.g.,SNR95,18 U50, and U80

19,20!, Speech transmission inde~STI!,21 rapid speech transmission index~RASTI!,22,23 andthe articulation loss of consonants (%ALcons)

24 are all indi-cators of speech intelligibility with varying degrees of accracy. Many studies have investigated and compared measof SI in rooms,25–27 particularly in classrooms.28–30 In thisstudy RT, BN, C50, and STI were measured to characterthe acoustical conditions in mosques and assess SI.

IV. METHODOLOGY FOR OBJECTIVE FIELDMEASUREMENTS

The first step in this investigation was to select sammosques representative of the majority of existing mosprototypes in Saudi Arabia. Ninety mosques were field sveyed to assess their actual design and operation statusaudit form for collecting relevant and essential data suchthe ‘‘as-built’’ physical information of mosques during sivisits was developed. The audit form addressed majorpects such as the following: general information aboutmosque, including a given reference number and locatphysical data, including the number of structural units adimensions; and use whether fordaily or Friday prayers, orfor both, and the existence of a separate hall or areawomen to perform prayers. Due to the importance of idefying possible interior sources of noise as well as quantifyambient noise in the mosque, the type and unit distributionthe A/C system were also considered. The mosque’s exisSRS in terms of number of used loudspeakers, type, heand spatial arrangement was documented. A criterionthen established to select representative sample mosqThe dominance of mosque shape, size~type repetition!, andother factors contributed to the final selection in additionmosque accessibility and proximity for the ease of equment movement. Out of the total of 90 mosques, 21~i.e., aapproximately 23%! were selected for acoustical field mesurements. Subsequently, pilot experimental measuremin one of the selected mosques were implemented in ordedevelop detailed procedures for the measurements. Aftefinement of the measurement setup, systematic acousmeasurements in all the selected sample mosques werecarried out and results analyzed.


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A. Grouping of the sample mosques

Considering the mosque volume as an important pareter influencing acoustical characteristics, the sammosques were grouped in five categories. Table I presdata summarizing the main physical characteristics ofchosen 21 mosques. It includes information such as numof structural units, mosque’s length, width, height, area, vume, and congregational capacity, all sorted in ascendingder with respect to the mosque volume. Group~A! includesvery small local mosques with volume,1000 m3; Group~B!includes small mosques with volume>1000 m3 and,1500m3; Group~C! includes medium mosques>1500 m3 ,2000m3; Group ~D! contains large mosques with volume>2000m3 and ,3000 m3; and Group ~E! contains very largemosques with volume>3000 m3. The architectural plans othe selected mosques grouped into five categories as idfied above and indicated in Table I are shown later in part~a!of Fig. 11. The selected mosques varied from very smlocal mosques with an average volume of around 630 m3 anda capacity of as few as 140 worshippers to large mosqwith volumes over 3000 m3 and a capacity of over 800 worshippers. Mosque shape is represented by the aspect~AR!, i.e., length,L of qibla wall over mosque width,W,capacity, and volume per worshipper is also indicated. Tmosque shapes varied from a square~AR51! to an elongatedrectangular shape~AR52.7! with an average AR of 1.7. Allhad rectangular cross-sectional shapes of various aspectios. Group ~F! includes a single huge~i.e., landmark!mosque with a volume greater than 10000 m3 and an occu-pancy of over 2800 worshippers, used forFriday prayeronly. The minimum, average, and maximum value rangestandard deviation~STD!, excluding the mosque referenceDM43 in Group ~F!, of the physical characteristics of thsample mosques, are shown in Table I.

B. Measurement system and procedures

In order to characterize and evaluate the acoustical cacteristics of the selected mosques the maximum lengthquence system analyzer~MLSSA!31 was utilized. It is a PC-based acoustic measuring system and analyzer formeasurement and evaluation of room acoustics. MLSSAploys a maximum-length sequence~MLS! for the excitationsignal as a preferred alternative to the conventional whnoise stimulus. The MLS signal technique measures thepulse response—the most fundamental descriptor of anyear system—from which a wide range of important acousindicators can be determined through computer-aided pprocessing. MLSSA was used for the measurement, in cbination with an ‘‘omnidirectional’’ sound source of dodechedral configuration. The sound source was located incenter of theqibla niche 1.0 m away from theqibla wall. Theheight of the excitation sound source was maintained at 1m from the floor to represent a person talking in a standposition. This source was used to determine RT30, EDT, andC50. Since SI is affected by the directivity of the sounsource, a small test loudspeaker was used as the ssource radiating with sound directivity approximating thata human speaker for STI and %ALcons measurements to im


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TABLE I. Summary of main physical characteristics of the selected sample mosques sorted in ascending order with respect to mosque’s volumaverage, and standard deviations are also indicated.
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Dimensions~geometry! AspectratioL/W

Area ~A!m2

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1 TH16 D 333 11.55 11.55 3.90 1.0 133 139 520 Group~A! 3.7 4.22 TH32 D 332 13.57 9.65 4.49 1.4 131 136 588 ~,51000 m3! 4.33 DM242 D 332 15.00 10.00 4.50 1.5 150 156 675 mean V5630c 4.34 TH27 D 333 13.49 12.04 4.60 1.1 162 169 747 4.4

5 TH48 D 533 24.65 14.66 3.33 1.7 361 376 1203 Group~B! 3.2 4.36 DM16 FD 1/2,3,1/233 19.50 14.70 4.25 1.3 287 299 1218 ~.1000,51500 m3! 4.17 DM260 D 333 18.00 15.00 4.61 1.2 270 281 1245 mean V51290 4.48 KH45 D 532 24.85 9.80 5.63 2.5 244 254 1371 5.49 KH17 FD 534 19.73 15.75 4.52 1.3 311 324 1405 4.3

10 KH03 FD 734 24.25 13.70 4.70 1.8 332 346 1561 Group~C! 4.5 4.211 TH42 D 333 24.20 18.35 4.00 1.3 444 463 1776 ~.1500,52000 m3! 3.812 KH12 D 933 35.14 13.22 4.20 2.7 465 484 1951 mean V51820 4.013 DH14 FD 1/2,5,1/233 29.56 15.33 4.40 1.9 453 472 1994 4.2

14 DM125 D 533 25.00 15.00 5.40 1.7 375 391 2025 Group~D! 5.2 4.715 KH59 FD 533 24.80 14.85 5.65 1.7 368 384 2081 ~.2000,53000 m3! 5.416 TH06 FD 733 37.45 15.88 3.70 2.4 595 619 2200 mean V52200 3.617 DM06 FD 733 32.10 15.80 4.94 2.0 507 528 2505 4.7

18 DH03 FD 934 43.43 19.43 6.05 2.2 844 879 5105 Group~E! 5.8 5.019 TH13 FD 736 42.25 29.68 4.80 1.4 1254 1306 6286~.3000,510 000 m3! 4.820 TH01 FD 937 44.85 34.70 4.52 1.3 1556 1621 7034 mean V56140 4.3

21 DM43 F 939 52.00 52.00 8.65 1.0 2704 2817 23 390 Group~F! 8.3 8.3~.10 000 m3!

Minimumd 11.6 9.7 3.3 1.0 131 136 520 3.2 4.2Averaged 26.2 16.0 4.6 1.7 462 481 2175 4.4 4.5Maximumd 44.9 34.7 6.1 2.7 1556 1621 7034 5.8 5.0STDd 10.0 6.0 0.7 0.5 359 374 1780 0.6 0.3

aD5Daily prayers only, FD5Friday andDaily prayers.bCapacity is calculated by considering a required area of~0.8031.2050.96 m2! for each worshipper.cAverage volume for each group to the nearest 10 m3.dExcluding DM43, Group~F!.

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prove results. The small loudspeaker was located at the tcal Imampraying position.

Based on the shape and floor area of each sammosque, an adequate number of listener positions waslected for measurement in order to achieve a proper coveof the mosque floor area. The guidelines set by the ISO 3~1997!32 were adhered to. Impulse responses were then msured sequentially in each of the chosen listener locatioMeasurements were acquired using a calibrated 1/2 in. cdenser microphone mounted on an adjustable microphholder fixed to a tripod, maintained 1.65 m above the florepresenting the location of a listener’s ear in a standposition. The measurement was also repeated in the slistener positions but with the microphone height lowereda height of 0.85 m above the floor representing the locaof the ear of a listener in a floor-seated position. Measuments were carried out with the mosque unoccupied,with both the ceiling fans and the A/C system set to‘‘OFF’’ condition. The average of measurements taken ontwo different heights at all listener locations in the mosqwould represent worshippers at the two worship modespreaching and prayer performing and therefore would chacterize the spatial value of the acoustical indicator.


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It was necessary to measure the mosque BN and suquently determine the noise criterion~NC! rating. Theoctave-band sound pressure level~SPL! of ambient BN wasmeasured at each selected measurement location usinsame calibrated 1/2 in. condenser microphone maintaine1.65 m above the floor. The same was conducted at the msurement point located in the center of the mosque floor awith all ceiling fans operating. A wind screen was usedreduce the effect of airflow due to the operation of the ceilfans. The measurement of BN was repeated with onlyA/C system set to ‘‘ON’’ and then with the A/C system anfans operating concurrently The idea was to quantify thefect of these active environmental control systems onmagnitude and spectral content of BN.

With the use of the small test loudspeaker, STI aRASTI were also measured from the acquisition of londuration impulse responses~.1 s!. The A-weighted SPL ofthe generated MLS signal at a location 1.0 m directly in froof the test loudspeaker was adjusted to achieveA-weighted sound of 67–68 dB~A!. A 65535-point impulseresponse was then acquired, and analyzed for STI calctions. To determine the overall STI value, the origin


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SRS commonly used in a mosque consists of threemore microphones for picking up theImam’svoice, pream-plifiers, a power amplifier, and several loudspeakersreradiate the amplified speech sounds. Additional comnents like mixers and equalizers are added to the basiccomponents in very few mosques. Many factors affectperformance of SRS such as the acoustical power, qualitthe system components, loudspeakers directivity andquency response, and reverberation time of the roomwhich the system is operated. The purpose was to determthe overall effectiveness of installed speech reinforcemsystems as set and operated in the chosen sample mosMeasurements were conducted at each of the chosen lispositions without operating the mosque’s SRS. The SRSthen put ‘‘ON’’ and the MLS signal was sent via the ampfier ~when accessible! or via the microphone of the mosqueSRS. The volume controls and component settings ofsystem were kept as usually set without any alteration.impulse responses were captured at a height of 0.85 mresenting worshippers seated on the floor listening toImam.

C. Sample field measurements and analysis:Unoccupied mosque

Pilot field measurements were conducted in one mosreferenced TH06, Group~D! ~see Table I! to test the mea-

FIG. 3. Plan view of theTH06 mosque showing a geometric configuratioof the prayer hall, A/C unit distribution, and the mosque’s SRS wmounted loudspeaker distribution. The measurement positions and ssource location are also shown.


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surement setup for appropriateness, to identify potentialficulties, and to assess on-site data analysis. Figure 3 dethe mosque’s geometry, physical characteristics, and msurement positions performed in the mosque. The mosqshape being symmetric, ten measurement points were exined on one side of the floor area. These are denoted R0R10. Each measurement location was considered to reprethe floor area of one structural unit as defined on the pview of the mosque. Measurement positions were selecterepresent listeners in the front, center, and back areas ofloor. It was ensured, while selecting the measurement lotions, that the distance between any two selected listenlocations was more than two meters, and the distance fthe microphone position to the nearest reflecting surfacemore than one meter,~i.e., approximately equal to half thwavelength of the lowest octave-band frequency of inter125 Hz!. Measurement positions were also considered wregard to existing A/C units and the location of the louspeakers of the mosque’s SRS.

Figure 4~a! depicts the spatial minimum, average, amaximum values of RT30 i.e., the value range of themosque’s RT30 spectrum in octave-band frequencies fro125 Hz to 8 kHz resulting from the processing of theimpulse responses captured at heights of 0.85 and 1.6above the floor. As can be seen, the spatial-averaged Rmid-frequencies~500–1000 Hz!, RT30 m is 1.90 s with a neg-ligible STD. From a knowledge of the mosque volume~2200m3!, the optimum RT30 m value for speech is approximatel0.90 s. Therefore the mosque can be said to have a highwhen unoccupied. In the literature, there is no specific dof the absorption coefficients of worshippers or audienstanding or seated directly on a carpeted floor in rows 1.2

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FIG. 4. The spatial average~l! of ~a! RT30 and ~b! C50 measured in theTH06 mosque. The shaded area represents the measured value rang~i.e.,spatial minimum and maximum!.


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apart. Assuming the absorption area of worshippers wstanding in parallel rows 1.2 m apart is around 0.4 mesabines per person at mid-frequencies~500–1000!,35 then themosque’s RT would be approximately 1.32, 1.01, and 0.8with one-third of the mosque occupied, two-thirds and fuoccupied, respectively. The measured RT would thereforeoptimal with the mosque occupied up to two-thirds ofcongregational capacity. The spatial-averaged value ofmid-frequency C50 as shown in Fig. 4~b! was22.4 dB, vary-ing from 25.1 to 1.4 dB with a STD of approximately 2.dB. A C50 value higher than 1.0 dB or more is required fsatisfactory speech intelligibility. This value corresponds tsound definition, D50, of about 0.56.

Both the RT and the ambient BN affecting speech intligibility were measured, in standard octave-band frequcies, at all selected measurement locations in different oating conditions. Both the overall A-weighted and LineSPL were determined along with the NC rating. The spaminimum, average, and maximum values of all measuments were then calculated. These spectra ranges aretrated in Fig. 5. Operating either the fans or the A/C onlyboth proved that the BN increased from NC35 to NC60. Tspatial-averaged spectrum of the BN in a mosque canconsidered quite high compared to the recommended vrange of NC25–NC30 for rooms intended for speech suclecture halls and classrooms. It can be expected thatsound quality will further deteriorate when the ceiling fansthe A/C units or both are operated. The causes of the hNC rating of ambient noise can be attributed to intrudiexterior noise due to the low transmission loss of the extewall system, particularly windows and glazing types comonly installed in mosques, in addition to interior noissuch as buzzing and humming resulting from defective liging units and accessories.

Figure 6 shows the STI values along with the %ALcons

and SI ratings measured at all selected measurementtions with and without the operation of the mosque’s SRMeasurement positions are shown in ascending order

FIG. 5. Spatial average of BN spectra~d! measured in theTH06mosque atdifferent operating conditions A/C ‘‘ON’’~n! Fans ‘‘ON’’ ~—! and A/C andFans ‘‘ON’’ ~L!. The shaded area represents the measured value range~i.e.,spatial minimum and maximum!.


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respect to distance from the sound source. The SI averating was be poor without the operation of the mosque SFigure 6~a! shows a comparison of STI measured values vsus the distance from the sound source with and withoutSRS being operated. The STI values improved when the Swas used, shifting the SI rating to a higher range in almosmeasurement locations. STImodified values showed the samtrend, however, this modified parameter was found notcontribute to a significant difference or a different evaluatiof SI rating for the case under study. Since STImodified is notalso in general use as STI, only STI results will be reporin this study. The %ALcons also shows the same trend oimprovement at all locations except measurement locaR09. Usually the SRS is installed to achieve an adequsound level in areas of the mosque remote from theImamlocation. The %ALconsvalues versus distance from the sousource with and without using the SRS are illustrated in F6~b!. It further confirms the efficiency of the SRS of reducinthe %ALcons, particularly in the more remote locations.can be concluded from the above measurement resultsthe mosque’s acoustical characteristics and quality aresatisfactory for speech intelligibility when used without thoperation of the SRS. The SRS was found to be quite ecient in improving speech intelligibility frompoor to fair andreducing the %ALcons, particularly in the more remote locations. However, when operating either the fans or the Asystem, the ambient noise in the mosque significantlycreases to unacceptable levels and SI can be expectedegrade.

FIG. 6. ~a! A comparison of STI measured at all positions with~l! andwithout ~L! the operation of the SRS, and~b! a comparison of %ALcons

values versus distance from the sound source with~m! and without~n! theoperation of the mosque’s SRS. SI ratings are shown on the righty axis. I5(%ALcons,10%) very good, II5(%ALcons.10%,15%) good, and III5(%ALcons.15%) insufficient.


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1512 J. Acoust. S

TABLE II. Spatial-average spectra of RT30 and C50 for each mosque group. The Mid-frequency averageshown in the last two columns. Note that Group~F! is excluded from calculating the value range~minimum,average, and maximum!.

Groups

Octave-band frequencies~Hz! Average

125 250 500 1000 2000 4000 8000 500–1000 500–20

Group ~A! 2.79 2.54 2.28 1.64 1.18 1.10 0.77 2.0 1.7Group ~B! 2.26 1.71 1.37 1.25 1.19 1.10 0.86 1.3 1.3Group ~C! 2.26 1.36 0.97 1.32 1.42 1.31 1.06 1.1 1.2Group ~D! 2.66 2.13 1.83 1.49 1.36 1.20 0.89 1.7 1.6Group ~E! 2.89 2.70 2.44 1.95 1.69 1.50 1.08 2.1 2.0Group ~F! 2.91 2.74 2.85 2.47 1.91 1.56 1.01 2.6 2.4Minimum 2.3 1.4 1.0 1.2 1.2 1.1 0.8 1.1 1.2Average 2.6 2.1 1.8 1.5 1.4 1.2 0.9 1.6 1.6Maximum 2.9 2.7 2.4 1.9 1.7 1.5 1.1 2.1 2.0STD 0.3 0.5 0.5 0.2 0.2 0.2 0.1 0.4 0.3

Group ~A! 26.0 25.1 24.1 21.2 0.4 2.0 5.4 22.7 21.7Group ~B! 23.3 21.9 20.2 0.6 0.9 2.3 4.8 0.2 0.4Group ~C! 22.9 20.3 1.0 0.5 0.7 1.7 3.6 0.8 0.7Group ~D! 24.7 24.1 23.0 20.2 1.0 2.2 5.5 21.6 20.7Group ~E! 26.6 26.6 25.3 22.5 20.9 0.4 4.2 23.8 22.9Group ~F! 28.1 28.8 29.2 23.8 21.3 0.0 4.4 26.5 24.7Minimum 26.6 26.6 25.3 22.5 20.9 0.4 3.6 23.8 22.9Mean 24.7 23.6 À2.3 À0.6 0.4 1.7 4.7 À1.4 20.8Maximum 22.9 20.3 1.0 0.6 1.0 2.3 5.5 0.8 0.7STD 1.5 2.3 2.4 1.2 0.7 0.7 0.7 1.7 1.3

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V. RESULTS COMPARED TO DESIGN GOALS FORALL SAMPLE MOSQUES

The type of measurement and analysis described abfor one single mosque was systemically performed for allsample mosques. The purpose was to document the acocal characteristics of mosques and compare design goalsobtained results in practice. This eventually would indicthe overall acoustical quality of the different prototypesthe selected mosques and how significant they deviate foptimal.

A. Acoustical characteristics of mosques

To summarize the measurement results of all sammosques in a comparative study, the average spectra of30

were processed in Table II. The average spectrum of emosque [email protected]., Groups~A!–~F!# is presented in Fig.7~a!. The mid-frequency region of 500 and 1000 H(RT30 m), usually provides a relative indication of the listeing conditions in most rooms. The RT30 m values ranged from1.1 to 2.1 s with a mean value of 1.6 s and a STD of 0.4The mid-frequency mean C50 m is 21.4 dB, varying from23.8 d to 0.8 dB with a STD of 1.7 dB. Figure 7~b! illus-trates the C50 average spectra range as measured in allsample mosques.

The measured RT30 of 20 mosques out of the total of 2was found to be greater than the 1.0 s that is consideoptimal upper limit for speech intelligibility. The averagRT30 spectra depicted in Fig. 7~a! can be considered representative of all the sample mosques. It shows a long reberation time at low frequencies~125–250 Hz! which ismore than 45% of RT30 m with high variations of 0.5 s at 250Hz. This long sound decay at low frequencies can be demental for speech intelligibility. For good speech intelligib

oc. Am., Vol. 113, No. 3, March 2003

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i-FIG. 7. Spatial average spectra of~a! RT30 , and ~b! C50 in each mosquegroup compared to the value range, i.e., spatial minimum, maxim~shaded area!, and average~——! of all groups except Group F.


FIG. 8. ~a! Recommended RT~optimal! for speech versus room volume~adapted from different sources!, and ~b! mid-frequencies~500–1000! RT valuesmeasured in all sample mosquess unoccupied,l with 1/3 andd 1/1 of the mosque’s occupancy in comparison with suggested optimal values~shaded area!.~A! In large rooms~Stephen & Bate equation! ~Ref. 36, p. 34!. ~B! ~At 500 Hz! ~Ref. 36, Fig. 3.9, p. 36!. ~C! In conference rooms~Ref. 37, Fig. 2.29, p. 68!.~D! ~At an average of 500–1000 Hz! @Ref. 38, Fig. 26.25~after E. B. Magrab!, p. 1352#. ~E! Maximum RT in large rooms@Ref. 38, Fig. 26.26~after Brueland Kjaer!, p. 1353#.

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ity, RT values at low octave-band frequencies should remflat down to 100 Hz.35 An increase, at low frequencies oaround 10%–20% of RT30 m values would still be acceptablto yield a natural sound impression.

Various values and ranges have been proposed by mauthors36–39 for optimal RT values for speech. These weobtained and are presented in Fig. 8~a!. The RT30 m of theoccupied mosques was then determined from measRT30 m in the unoccupied conditions. The RT30 m values werecalculated for 1/3, 2/3, and full mosque occupancy. Fig8~b! depicts the measured RT30 m ~unoccupied! compared toRT30 m in the three occupancy conditions compared with


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several suggested optimal value ranges and trends. As caseen, only a few mosques, particularly those in Group~C!,were found with an RT30 m close to the optimal RT rangewhen unoccupied. The RT30 m values of half of the samplemosques were greater than optimal, even with each mosassumed to be 1/3 full, which is usually the case durperforming Daily prayers. The RT30 m of all the samplemosques came close to the boundaries or within the optiRT range only with the mosques fully occupied, with thexception of mosque DM43 built with a huge volume aslandmark mosque intended for use by worshippers to pform Friday prayer only.


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FIG. 9. A comparison of the BN and NC rating measured in all sample mosques at different operating conditions of fans and A/C systems agaratings. I5‘‘very quiet’’ to ‘‘quiet,’’ II 5‘‘moderate noisy’’ to ‘‘noisy,’’ III5‘‘very noisy,’’ and VI5‘‘extremely noisy.’’ ~See Table III.!
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B. Impact of air-conditioning and mechanicalventilation systems

To characterize the BN in mosques at different operatconditions, the spatial-average spectra of BN measured wfans and the A/C system were ‘‘OFF’’ are shown in Fig.The spectra total A-weighted and linear values are ashown along with the NC ratings. It also includes the mimum, average, and maximum of mean spectra measureall the sample mosques. Figure 10 depicts the BN averand value range compared to the average spectra measuthe three conditions of operating the active environmencontrol systems. The NC rating of measured BN ranged frNC-35 to NC-45. However, for very good speech listeniconditions in spaces such as meeting rooms, conferehalls, and courtrooms, NC is preferred to range from NCto NC-30. Similarly, the maximum NC-30 criterion shounot be exceeded because higher levels can be noticeableannoy many occupants~worshippers! or interfere withspeech communication. The measurement of BN in mosqindicates amoderately noisyto noisyenvironment, but whenthe fans and A/C systems were operated the BN ratingcreased, resulting in avery noisyto extremely noisyenviron-ment. This can be expected to negatively affect speech inligibility. Figure 10 compares measured BN at all selecmosques at different operation conditions with the NC-NC-30 range as a design goal.

C. Speech intelligibility and overall effectiveness ofSRS

Following the measurements procedure motioned elier, it was possible to characterize and rate speech intelbility in the sample mosques. Figure 11~b! comprehensivelycompares speech intelligibility expressed by the STI. Avage measured values are indicated by a vertical tick on ehorizontal bar, which presents the value range of minimamaxima or all measurements conducted in each mosque.number of measurement points is indicated along with therating with and without the SRS being operated. As canseen, the average SI ratings, for almost all mosques noterating the SRS, determined from STI values, lie in the raof poor to fair SI rating. The effect of using the SRS d


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improve SI in many, but not all, mosques. The effectivenof many of the installed SRS can be clearly seen in the nrowing of the wide range of STI~without using the SRS! toa smaller value range~i.e., shortening the horizontal bar tnarrower limits!. This indicates that the SRS was effectivereducing the wide variation of SI to a more uniform valuover the mosque floor area and improving SI. It mustindicated that the SRS were operated without the operaof fans and A/C systems, i.e., with BN rating ranging froNC35 to NC-45. Operating the fans and A/C systemcreased ambient BN to NC-60 and above. The effectivenof the SRS in this case was not assessed and is question

VI. CONCLUSIONS

Typical mosques of different sizes and shapes are ually designed considering the functional requirements w

TABLE III. Average BN measured in all sample mosques in compariswith NC curves at different operating conditions of fans and A/C system

Mosquereference

Overall SPL NC

dB~A! dB~L!Average

BNFANS‘‘ON’’

A/C‘‘ON’’

A/C1FANS‘‘ON’’

TH16 45.4 63.3 45 55 60 65TH32 48.7 62.7 45 50 55 60DM242 42.9 56.8 40 45 60 60TH27 39.1 54.7 35 45 60 60TH48 39.4 57.0 35 35 60 60DM16 45.2 65.9 40 60 55 60DM260 40.5 60.4 35 45 55 55KH45 39.4 51.1 35 45 50 50KH17 37.7 59.5 35 60 55 60KH03 36.8 54.6 35 45 55 55TH42 42.9 61.1 40 50 70 70KH12 36.6 57.1 35 45 65 65DH14 34.9 53.8 35 45 60 60DM125 36.6 58.4 35 55 60 60KH59 38.3 56.0 35 35 60 60TH06 40.3 60.4 35 50 60 60DM06 36.6 58.4 35 50 60 60DH03 37.5 54.7 35 55 65 65TH13 40.1 56.8 40 45 65 70TH01 44.2 63.0 40 60 55 60DM43 39.3 57.1 35 NA 60 NA


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regard to size and aesthetics, but with little attention paidtheir acoustical quality. Acoustics in mosques are generconsidered after mosques are built and involve mainlyprocess of providing sound system equipment. Audibilnot speech intelligibility is considered important and tacoustical considerations are not thought of either in thesign phase or in the selection or installation of SRSmosques. In this study, field measurements employingpulse response techniques were conducted to identifyacoustical characteristics and performance of selemosques in Saudi Arabia. Representative sample moswere objectively selected and investigated. A database ofpulse responses captured in the sample mosques~unoccu-pied! utilizing impulse response measurements was eslished. The impulse responses were then analyzeddocument and indicate the overall acoustical performancthe different mosque prototypes. Room-acoustic indicaincluding RT30, C50, BN, and STI were examined. Obtaineresults were compared to design goals. The following cclusions can be drawn.

RT30 m relating to the mid-frequency region of 500 an1000 Hz usually provides a relative indication of the listeing conditions in most rooms. The RT30 m of 20 mosques~unoccupied! out of a total of 21 was found to be greater th1.0 s. The types of mosque investigated in this study cancharacterized by long sound decay at low frequencies. Tlong sound decay can be detrimental, especially for speintelligibility. For good speech intelligibility, RT values alow octave-band frequencies are preferred to remaindown to 125 Hz. The RT30 m of the occupied mosques wadetermined from measured RT30 m. The RT30 m was calcu-lated for 1/3, 2/3, and full mosque occupancy. Only a f

FIG. 10. The average BN measured in all sample mosques in compawith NC curves at different operating conditions of fans and A/C systeThe shaded area represents the measured average value range.


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mosques, particularly those of Group~C!, possessed anRT30 m close to the optimal RT range when unoccupied. TRT30 m of half of the sample mosques was greater than omal values even with the mosques 1/3 full. The RT30 m of allsample mosques~except mosque DM43! approached theboundaries came within the optimal RT value range owith the mosques fully occupied. The recommended volu~m3/occupant! for rooms intended for speech is 3.0 m3 up toa maximum of 5.0 m3. Volumes per worshipper in all samplmosques ranged from 4.2 to 5.0 m3 expect the mosqueDM43, which had an 8.3 m3 per worshipper, exceeding threcommended value range.

In all mosques, the NC ratings obtained from measuBN range from NC-35 to NC-45. In the literature there isexplicit preferred NC range specified for mosques. Howevfor very good speech listing conditions in spaces suchmeeting rooms, conference halls, and courtrooms NC isferred to range from NC-25 to NC-30. The cause of high Nratings obtained from measurements can be attributed totruding exterior noise due to low transmission loss of exrior wall systems, particularly windows and glazing typcommonly installed. An additional factor includes interinoise such as buzzing and humming from defective lightunit accessories. It is recommended that the NC-30 criteshould not be exceeded because higher levels can be noable and annoy most worshippers as well as interfere wspeech communication. The measurement results of BNmosques indicated a moderately noisy to noisy mosquevironment. The measurements also showed that when cponents of active environmental control systems such asand A/C units were operated the NC rating increased, resing in a very noisy to extremely noisy environment. This cbe expected to adversely affect speech intelligibility. Cashould therefore be taken to select and install or mount Asystem units with low noise output and lighting units wihigh quality ballast and accessories that require minimmaintenance. The mosque exterior wall should be desigto minimize intruding exterior noise to satisfy the NC-2criterion.

The average SI ratings resulting from measurementthe sample mosques without operating the SRS determfrom STI values, were found to be in the range of poor to fSI. The use of SRS did improve SI in many but not incases. Many of the installed SRS in mosques contributedreduction in the variability of SI. This indicates that SRwere generally effective in reducing the wide variation ofto a more uniform one over the mosque floor area, partilarly at more remote locations away from theImam’s posi-tion and slightly improving SI. It must be indicated that thSRS were investigated with fans and A/C units set to‘‘OFF’’ condition ~as is the case in the autumn, winter, aspring conditions!, resulting in an average ambient BN witNC-40 rating. Operating either the fans or the A/C systonly, or both, proved to increase ambient BN to NC-60 aabove. The effectiveness of the SRS in this case wasassessed and is questionable. The developed database cutilized as a valuable source of objective acoustical inditors and comparative information for further investigationResearch work is needed to characterize the freque

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FIG. 11. ~a! Grouping of the selected sample mosques based on volume and congregational capacity of prayer-performing hall~a relative scale is used!. Note:The distribution of loudspeakers installed in each mosque is shown, and~b! a comparison of STI measured in all sample mosques with and without operthe mosque’s SRS. The target value range is highlighted.~Note: mosques are arranged in ascending order with respect to volume.!
1516 J. Acoust. Soc. Am., Vol. 113, No. 3, March 2003 Adel A. Abdou: Mosque acoustics

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dependent absorption coefficients of worshippers in mosqin the different worship modes. In the mosque design phthis would help architects to reasonably estimate, with sodegree of accuracy, the reverberation time with varyingcupancy compared to recommended value ranges. In ation, the use field measurements, such as those reportedin combination of utilizing computer model studies can beeffective approach for developing better information for dsigning better mosques from the acoustical viewpoint.

ACKNOWLEDGMENTS

The author would like to express his gratitude athanks toKing Abdulaziz City for Science and Technolo(KACST)for funding this research project and facilitating iimplementation. Thanks are also due toKing Fahd Univer-sity of Petroleum and Minerals (KFUPM)for its continuoussupport and encouragement. Gratitude is also extended tlocal authorities of theMinistry of Islamic Affairs, Endow-ments, Da’wah and Guidancefor their cooperation and fothe provision of information. The efforts of the UniversiEditorial Board are appreciated.

1R. N. Hammad, ‘‘RASTI measurements in mosques in Amman, JordaAppl. Acoust.30, 335–345~1990!.

2M. K. Abdelazeez, R. N. Hammad, and A. A. Mustafa, ‘‘Acoustics of KinAbdullah mosque,’’ J. Acoust. Soc. Am.90, 1441–1445~1991!.

3A. El Bashir and A. Al-Gunaimi, ‘‘Evaluation of acoustical performancof mosques: a case study on a typical mosque in the Gulf region,’’Pro-ceedings of the 4th Saudi Engineers Conference, Kingdom of Saudi Ara-bia, Jeddah, 1995, Vol. 1.

4A. Abdou, ‘‘Predicting and assessing the acoustical performancemosques employing computer simulation:a case study,’’ Proceedings ofthe Symposium on Mosque Architecture, 1999, Vol. 6, pp. 73–87.

5D. L. Klepper, ‘‘The distribution column sound system at Holy CroCathedral, Boston, the reconciliation of speech and music,’’ J. AcoSoc. Am.99, 417–425~1996!.

6J. Anderson and T. Jacobsen, ‘‘RASTI measurements in St. Paul’s Cdral,’’ London, Bruel & Kjaer Note No., 1985.

7R. W. Guy and A. Abdou, ‘‘Acoustic quality via sound intensity measuments in a church,’’Proceedings of Inter. Noise 94, Yokohama, Japan1994, pp. 1851–1854.

8A. P. O. Carvalho, ‘‘Relationships between objective acoustical measand architectural features in churches,’’Proceedings of the W. C. SabinSymposium, the 127th Meeting of the Acoustical Society of Americ1994, pp. 311–314.

9P. O. Carvalho, A. E. J. Morgado, and L. Henrique, ‘‘Relationship betwspeech intelligibility and objective acoustical parameters for architectfeatures in catholic churches.’’, J. Acoust. Soc. Am.101, Pt 2, 3051~A!~1997!.

10M. Galindo, T. Zamarreno, and S. Giron, ‘‘Clarity and definitionMudejar-Gothic churches,’’ J. Building Acoust.6~1!, 1–16~1999!.

11M. Barron, ‘‘Impulse testing techniques for auditoria,’’ Appl. Acoust.17,165–181~1984!.

12H. Tachibana, H. Yano, and Y. Hidaka, ‘‘Measurement of impulsesponse and its applications in room acoustics,’’ J. Acoust. Soc. Am.89,1856 ~1991!.


ese,e-di-ere,n-

the

,’’

f

t.

e-

es

nal

-

13G. R. D. King,The Historical Mosques of Saudi Arabia~Longman GroupLtd., United Kingdom, 1986!.

14I. Sergeld and J. Steele, inArchitecture of The Contemporary Mosqu,edited by Ismail Serageldin and James Steele~Academy Group Ltd.,London, 1996!.

15H. M. Ibrahim, Planning Standards for Mosques~in Arabic!, Ministry ofMunicipal & Rural Affairs, Kingdom of Saudi Arabia, 1979.

16Documents of the Ministry of Islamic Affairs, Endowments, Da’wah aGuidance~MIAEGD!, Kingdom of Saudi Arabia.

17A. Abdou and R. W. Guy ‘‘Spatial information of sound fields for roomacoustic evaluation and diagnosis,’’ J. Acoust. Soc. Am.100, 3215–3322~1996!.

18J. P. Lochner and J. F. Burger, ‘‘The influence of reflections on auditoracoustics,’’ J. Sound Vib.1, 426–454~1964!.

19J. S. Bradley, ‘‘Predictors of speech intelligibility in rooms,’’ J. AcousSoc. Am.80, 837–845~1986!.

20J. S. Bradley, ‘‘Speech intelligibility studies in classrooms,’’ J. AcouSoc. Am.80, 846–854~1986!.

21T. Houtgast and H. J. M. Steeneken, ‘‘A review of the MTF conceptroom acoustics and its use for estimating speech intelligibility in audria,’’ J. Acoust. Soc. Am.77, 1069–1077~1985!.

22H. J. M. Steeneken and T. Houtgast, ‘‘RASTI: a tool for evaluating autoria,’’ Technical Review, Bru¨el & Kjaer, No. 3, 1985, pp. 13–30.

23‘‘The objective rating of speech intelligibility in auditoria by the ‘RASTImethod,’’ IEC 268, part 16, Sound System Equipment, 1988.

24V. M. A. Peutz, ‘‘Articulation loss of consonants as a criterion for speetransmission in a room,’’ J. Audio Eng. Soc.9, 915–919~1971!.

25J. S. Bradley, ‘‘Relationships among measures of speech intelligibilityrooms,’’ J. Audio Eng. Soc.46, 396–405~1998!.

26P. W. Barnett, ‘‘A review of speech intelligibility indicators—their relationship and applications,’’ J. Acoust. Soc. Am.101, No. 5, 3050~A!~1997!.

27J. van der Werff, ‘‘Speech intelligibility in rooms,’’Proceedings of Inter-Noise 97, 15–17 June 1997, pp. 349–354.

28M. Hodgson, R. Rempel, and S. Kennedy, ‘‘Measurement and predicof typical speech and background noise levels in university classroduring lectures,’’ J. Acoust. Soc. Am.105, 226–233~1999!.

29M. Hodgson, ‘‘Experimental investigation of the acoustical characterisof university classrooms,’’ J. Acoust. Soc. Am.106, 1810–1819~2000!.

30S. R. Bistafa and J. S. Bradley, ‘‘Reverberation time and maximbackground-noise level for classrooms from a comprehensive studspeech intelligibility metrics,’’ J. Acoust. Soc. Am.107, 861–875~2000!.

31D. D. Rife, ‘‘Maximum length sequence system analyzer,’’ ReferenManual, DRA Laboratories, 1987–1996, p. 86.

32ISO 3382, ‘‘Acoustics measurement of reverberation time of rooms wreference to other acoustical parameters,’’ 1997.

33H. J. M. Steeneken and T. Houtgast, ‘‘A physical method for measurspeech-transmission quality,’’ J. Acoust. Soc. Am.61, 318–326~1980!.

34N. R. French and J. C. Steinberg, ‘‘Factors governing the intelligibilityspeech sounds,’’ J. Acoust. Soc. Am.19, 90–119~1947!.

35H. Kuttruff, Room Acoustics, 3rd ed.~Elsevier, London and New York,1991!, p. 164.

36B. J. Smith, R. J. Peters, and S. Owen,Acoustics and Noise Contro~Longman, London/New York, 1988!, pp. 34–36.

37D. Templeton, P. Sacre, P. Mapp, and D. Saunders,Acoustics in the BuiltEnvironment, 2nd ed.~Architectural Press, City, 1997!, pp. 58–68.

38B. Stein and J. S. Reynolds,Mechanical and Electrical Equipment foBuildings, 8th ed.~Wiley, New York, 1992!, p. 1325.

39M. D. Egan, Architectural Acoustics~McGraw-Hill, United Kingdom,1998!, p. 370.
