Frontiers of Architectural Research (2013) 2, 30–41

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RESEARCH ARTICLE

A parametric investigation of the acousticalperformance of contemporary mosques

Mostafa Refat Ismailn

Department of Architecture Engineering, Ain Shams University, 1 Elsarayat Street, Abasya district Cairo, Cairo 11566, Egypt

Received 1 September 2012; received in revised form 1 November 2012; accepted 8 November 2012

KEYWORDSAcoustics;Mosques;Sound propagation;Acoustic computersimulation

igher Education P0.1016/j.foar.2012

93; fax: +2 22274ostafa_ismail@en

r responsibility of

AbstractAcoustics is an important factor in mosque prayer halls that had not been given extensiveconcern during the architectural design stages. Eventually, the importance of speech intellig-ibility became more important, given the integration of other activities into the prayer halls,such as the holy Quran recitation, speeches, and lectures. Early attempts have been made tocontrol the propagation of sound and to maintain good acoustic quality within the prayerspaces. Architects during the conceptual design stage had barely paid attention to the designissues that affect the acoustic environment inside the prayer zones, which is either due to lackof time during the project development or, in most cases, a lack of simple design guidelines toovercome any drastic acoustical defects arising from the incorrect design, shape, or materialselection. The basic guidelines for designers to select the appropriate shape, geometry, size,and finishing materials are an essential design tool. This work examines the three commondesign topologies of mosques, which differ in size, shape, and finishing materials. In this study,a geometric and material parametric analysis was conducted based on the shape, surface area,volume, and finishing materials of each of the three designs. For the geometric acoustics, acomputer model employing the ray tracing theory was employed to investigate the threeconfigurations. Different acoustic treatments were tested relative to the geometric dispositionof each design. Finally, basic recommendations and design guidelines were presented.

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1. Introduction

Since Sinan (Mutbul Kayili, 2005) drew significant attention tothe acoustics of mosque design, mosques have been consideredmulti-use architectural indoor spaces where various activitiesare performed. Several activities take place inside the mosquein separate or connected order. The primary activity is theperforming prayers led by the Imam (Khateeb and Ismail, 2007).Another activity is a preaching speech, which may be delivered

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31A parametric investigation of the acoustical performance of contemporary mosques

in an individual lecture or in conjunction with the weekly Fridayprayers. An additional activity is the recitation of some of theverses of the holy Quran. Thus, the quality of the acousticenvironment is important in the conduct of these multidisci-plinary activities in the mosque.

Based on the prayer hall functions inside the mosque,acoustics should be the greatest determinant of the architec-tural design strategy (Hammad, 1990). The acoustical environ-ment in the mosque is expressed in terms of its reverberationtime (RT) value. Most contemporary mosque designers do notpay attention to such requirements during the conceptualdesign stage. Based on the prayer function, wherein theworshippers are ordered in subsequent rows, most of themosques are generally rectangular with high length-to-widthratios and relatively elevated ceilings. A previous work (Abdou,2003) examining different mosque shapes showed that therectangular mosques exhibited better spatial distribution foracoustical quality indicators than other shapes. In addition, allmosque designs include a Mihrab (prayer niche) and Minbar(preacher platform). Most of the mosques also have a hemi-spherical dome constructed on the roof level as part of thebasic design topology. Such geometrical characteristics wereexamined using computer modeling to study the variousimpacts of mosque size and form on the acoustic spatialdistribution.

2. Contemporary mosque design

Nowadays, most contemporary mosques have sound-reflecting materials on most of its internal surfaces, exceptat the floor level and on horizontal surfaces that are usuallylaid out with carpet. Doors are constructed from wood, andlarge windows are probably filled with single glazing. Thepositioning of the central chiller units or stand-alone splitunits inside designated spaces or on roof tops amplifies the

Fig. 1 Relative scales o

Table 1 Geometrical parameters of the mosques.

Dewela Mosque main prayer hall

Area 11204.913 m2

Effective volume 186369.000 m3

Max. length 138.80 mMax. width 82.00 mMax. height 48.00 mMin. height 16.70 mTotal effective surface area 27047.330 m2

background noise levels inside the prayer areas, and affectsthe acoustic spatial tranquility of the space.

The Mihrab was initially designed to point towards thedirection of Mecca and to give the Imam space to lead allworshippers who stand in rows behind him during prayers(Khateeb and Ismail, 2007). The circular shape and quarterspherical top of the Mihrab was geometrically developed toimprove the reflected sound component towards the wor-shipper’s direction. However, in some contemporary archi-tectural designs, the Mihrab was altered in size and shapewithout any attention to its acoustical implications.

The mosque plan, the conventional rectangular shape,and the large prayer halls are similar and have a commondesign topology that is still tied to the past. The rectangularprayer halls have better acoustical quality and performancethan other shapes (Abdou, 2003). The advance in publicaddress system technology and the use of loudspeakersoffers the architect flexibility to shape up the prayer spaceaccording to his conceptual criteria. However, the rectan-gular shape is still applied in the modern design of mosquesbecause of its historical significance. In old designs, the highceiling, domes, and large windows allowed natural ventila-tion, acted as a passive environmental control, and pro-vided day lighting. Furthermore, arches and domes wereused as main structural elements to cover larger spans. Withthe advance in artificial air-conditioning and ventilation,natural ventilation is less of a determining factor in modernmosque designs. Moreover, daylight became less importantafter the development of artificial lighting technologies.

3. Mosque geometric parameters

The purpose of this work is to identify some of the commonfactors and differences in the acoustics of mosques ofdifferent sizes. The acoustic data and information about

f the three mosques.

Dewela Mosque daily prayer Damascus City Centre Mosque

2372.343 m2 1458 m2

20689.637 m3 9556.322 m3

113.91 m 69.2 m21.44 m 21.2 m8.40 m 23.6 m7.00 m 5.957002.034 m2 4106.869 m2

M.R. Ismail32

the mosques were obtained from architectural design data,as well as the material schedules, offered by the mosquedesigners, considering real case scenarios. The goals of thisresearch are:

�

To characterize mosques according to main acousticaland architectural features. � To compare the acoustical behavior of mosques of

different sizes and shapes.

The acoustic and architectural parameters implementedin this work were based on the selection of three different-sized prayer halls. Two of the prayer halls selected arelocated in the Dewela Mosque in Kuwait. The third prayerhall selected is the Damascus City Centre Mosque, MudunCities of Arabia Project. The mosque geometrical data arepresented in Table 1.

The set of prayer halls examined presented the main designtopologies related to the historical roots of mosque design. Asshown in Fig. 1, the Dewela Mosque main prayer hallrepresents a big enclosed prayer space and crowned at thecentre by a big hemispherical dome, which is a typical designof many old historical Ottoman period mosques such as theSuleymaniya and Selimiye Mosques in Istanbul (Mutbul Kayili,

Fig. 2 Volume plot

Fig. 3 Prayer halls geometric

2005). The daily prayer hall in the Dewela Mosque representsan extended rectangular space that is relatively smaller thanthe main prayer hall with a flat roof and ornaments. TheDamascus City Centre Mosque represents an internal pitchedroof prayer hall (Rowaq), which is lifted on an array of internalvertical columns and covered centrally by a lifted dome. TheDamascus City Centre Mosque contains an open prayer zone(Sahn). However, this part was excluded in the simulation, andonly the enclosed iwan was simulated.

The selection criteria were set to maintain various crossrelationship geometrical parameters with increasing mos-que size, as shown in Fig. 1. The relationship of the mosqueplot area and volume is shown in Fig. 2. Evidently, the linearrelationship demonstrated by the graph proves that theselected mosques maintain a linear volume and plot arearelationship. The volume increases with increasing plotarea. The linear relationship should ensure a linear increasein RT with the increase in volume, and any deviation is dueto the effect of the geometrical disposition of each mosqueand its design aspects if the finishing materials are of similarabsorption characteristics.

The linear increase in volume with increasing surfacearea is represented in Fig. 3. The relative data arerepresented in terms of its relationship to the plot area ofthe mosque prayer hall. The steady relationship betweenthe effective surface areas relative to the surface area of

area relationship.

al parameters relationship.

33A parametric investigation of the acoustical performance of contemporary mosques

the plan is shown by the solid circle lines. However, theresultant volume from the integration of these surface areasresulted in a relative increase in the effective volume toplan the surface area ratio for some geometries. This resultis most probably due to the presence of the dominanthemispherical domes in the main prayer and daily prayerhalls of the Dewela Mosque.

The ratio of the effective surface area to the effectivevolume for the three prayer halls is plotted in Fig. 4. Theeffect of the large hemispherical domes in reducing thesurface area is represented by the solid square plots. Theupper curves in Fig. 4 clearly show the low surface area/volume (SA/V) ratio of the sphere compared with the othergeometrical shapes.

Fig. 4 SA/

The SA/V ratio for a unit volume of a sphere is 4.836. Bycontrast, the SA/V ratio of a cube is 6 (Schmidt-Nielsen,1984; Vogel, 1988). Thus, using geometrical shapes that aresimilar to the curved surface of a sphere, such as icosahe-drons and dodecahedrons, reduces the SA/V ratio.

4. Characteristics of the architecturalfinishing materials of mosques

The acoustical behavior, impact of acoustical material, andperception of sound inside the mosque prayer halls arerarely considered during the conceptual design stage.Although acoustics is an important factor due to the

V ratio.

M.R. Ismail34

importance of speech intelligibility in such spaces, theselection of materials is always subject to other designfactors of architectural and visual impacts.

In most contemporary mosques, the walls and ceilings areprobably constructed of hard reflective materials becauseof the ease of maintenance and hygienic issues. A commonmaterial used in walls because of its luxurious and richvisual characteristics is marble. The hand-crafted orna-ments in marble have been replaced in present-day mosqueswith GRC because of its mass production potential and easeof construction. In most cases, the materials selected forwalls and ceilings are made of hard reflective materials. Thefloor is commonly laid with carpet. The high acousticabsorption characteristics of the carpet regulate the effectof creating a highly reverberant space, if installed abovethe underlay. A list of common finishing materials used incontemporary mosques and the three halls examined in thiswork is shown in Table 2.

The analysis of the relative relationship of the geome-trical parameters and selected material characteristics isshown in Fig. 5 for each octave band frequency. The equaltrends shown by curves a and b also reflect the linearincrease in volume with increasing surface area. The curvesreflect an increase of 2.5 times of an order in the main anddaily prayer halls of the Dewela Mosque and 2 times in theDamascus City Centre Mosque (Fig. 3).

Table 2 Summary of common used materials in contemporary

Place Height Size

Summarized list of common finishing materials1. WallsMarble Panels, on plastered masonry

Brickwork+1.5 mF.F.L.

As per draw

Single Glazed window panels ATD As per drawPaint on 1.5–2.0 cm cement plaster ATD As per drawWalls [plastered Brick work] ATD As per drawGranite Panels, on plastered masonry

BrickworkATD As per draw

1.1 Parapet, windows sills and cross beamsSingle Glazed window screen ATD As per drawPaint on 1.5–2.0 cm cement plaster ATD As per draw

2. CeilingGypsum Boards ATD Ceiling embPaint ATD Ceiling embGRC ATD Ceiling emb2.1 Ironmongery, and HandrailsMetal - As per draw

3. FloorsCarpet – As per archi

designCarpet Underlay – As per drawWooden floor – As per archi

design

4. Windows –

5. Doors Doors

ATD—according to design.

The results show the common absorption characteristicsin the three prayer halls examined.

The SA/V ratio effect is also shown in Fig. 5c, with thepresence of curved surfaces, such as the hemispherical domes,in the main and daily prayer halls of the Dewela Mosque andthe rectangular shaped abstract form of the Damascus CityCentre Mosque. Plotting the absorption characteristics relativeto volume, resulted in lower values for the Damascus CityCentre Mosque prayer hall because of its low SA/V ratio.

5. The computer model simulation

Given the nature and complexity of the interior geometry ofthe three prayer halls examined, implementing a feasiblecomputer model theory is important to obtain good qualitydata. The examined halls are large architectural spaces. Thus,aside from the near field effect, the far field contribution isimportant to model in the three-dimensional space. Simplifiedand two-dimensional approaches (Clayden et al., 1975;Holmes and Lyon, 1974) are not suitable.

Thus, in this work, the ray tracing model was implementedduring the computer predictions. The ray tracing technique(Heutschi, 1995) is based on following the reflections on thesurface areas of each ray emitted from the source location(Fig. 6) as it undergoes reflections and diffraction at buildingsurfaces until the order of the reflection of the rays exceeds

mosques.

Mounting Remarks

ings Mechanical If above +4.5F.F.L

Columns, Mihrab, sidewalls

ings Wall embedded –ings Wall partition –ings Masonry Wall partition –ings mechanical Columns, Mihrab, side

walls

ings Wall embedded –ings Wall partition –

edded As per drawings –edded As per drawings –edded As per drawings –

ings As per drawings –

tectural As per architecturaldesign

Most of the floor

ings As per drawings Under carpettectural As per architectural

design–

– Single glazed window

–

a

s

Fig. 5 Architecture finishing materials characteristics. (a) Total absorption/surface area, (b) total absorption/effective surfacearea, (c) total absorption/effective volume.

35A parametric investigation of the acoustical performance of contemporary mosques

specified amount. The intensity at a point due to directsound is calculated using the inverse square law. Thenumbers of rays generated in each run must be large enoughto acquire quality data. The generation is repeated severaltimes and usually more than 100,000 rays are used. The raytracing approach (Heutschi, 1995) has proven to be veryaccurate and reliable, as long as a sufficient number of raysare used. The number of rays is easily verified for each spaceand volume individually by increasing the number of rays inpackets of 500 until a convergence criterion is reached.

Fig. 6 Ray tracing analysis.

6. RT evaluation

Once the source position was determined, the softwaregenerated the number of rays required, which interacted withthe modeled surface reflections, to obtain an estimated RT.The rays continued to lose energy with increasing reflectionorder until it attenuated to a certain quantity (e.g., 40–60 dB).At this point, the rays were considered completely absorbedand contributed no more energy to the resultant sound field.The collective behavior was resumed in the estimation of theRT for each frequency. The resultant decay curves for thethree examined prayer halls are shown in Fig. 7, whichpresents the geometrical features of the three prayer hallsand the absorption coefficients of materials.

The RT values extracted from the decay curves are shownin Fig. 8.

The predicted RT values exceeded the optimum values.Previous studies (Marsilio et al., 2001; Karabiber, 2000) showthat the values of RT are high, providing the room with apreferred feeling of majesty and confers a holy atmosphereamong the worshippers. The prayer halls are generallypoorly suited for delivering speeches because of the excessreverberation, although the situation seems somehow com-pensated by the additional absorption contributed by thefloor area. These provide better speech communication that

Fig. 7 Decay curves before acoustic treatment. (a) Dewela Mosque main prayer, (b) Dewela Mosque daily prayer hall, (c) DamascusCity Centre Mosque.

M.R. Ismail36

can be established in the short range. This treatment andthe addition of some acoustic treatments to the internalbuilding fabric regulate the RT.

The results of the reverberation time shown in Fig. 8 areclearly inversely proportional to the total absorption shownin Fig. 9. The high absorption rates obtained at highfrequency ranges in the main prayer hall of the DewelaMosque are due to the large surface area of the gypsumornaments of the dome and the dome cylindrical supportingneck. This phenomenon was also observed in the DamascusCity Centre Mosque, and supports the previous finding, giventhat these two types of prayer halls have hemisphericaldomes constructed in the ceiling. Thus, providing additionalabsorption for this large surface area of hemisphericalgeometry at mid- and low-frequency ranges is important.On the other hand, at the Dewela Mosque, the prayer hallneeds additional absorption at mid-frequency ranges. TheRT values predicted were compared with the preferredvalues suggested in previous literature (Sinan EserlerindeAkustik 1989; Everest, 1994), as shown in Fig. 10. Thesestudies reported plots of RT values versus room volume fordifferent purposes. The values of the three prayer hallswere not suitable for the purpose of prayer, and the RTvalues were too high to ensure good speech intelligibility.

7. Acoustic treatment

The results for the predicted RT values require the need foran acoustical corrective design for the three prayer halls.

The data analysis revealed high RT values, especially formid- and low frequencies. This configuration is not suitablefor the intelligibility and perception of speech in prayerenvironments. Thus, the acoustic treatment proposed aimsto reduce the RT. The ideal behavior of sound rays in theprayer halls was modeled using the Autodesk& Ecotectsoftware (Square One, 2004) in the previous stage andacoustic treatment evaluation stage. This software is abuilding design and environmental analysis tool that simu-lates and analyzes the acoustical response of a building.Moreover, this tool allows designers to work with threedimensions and furnish an impressive presentation of thefinal design and acoustical behavior of the architecturalspace under analysis. The actual geometry of the threeprayer halls was fully modeled using the Ecotect softwareframework. The first step was drawing the project geome-trically. The acoustic characteristics of the different con-struction materials were considered, which is very criticalto the purpose of modeling sound absorption. The simula-tion of the source was performed by assuming an isotropicsource placed at the center of the hall near the Minbar.Different analyses were then performed, such as RT evalua-tion, reflection analysis, and materials analysis, amongothers.

As outlined previously, the Dewela Mosque main prayerhall and the Damascus City Centre Mosque require moreabsorption applied to the hemispherical dome surface areaat low- and mid frequencies. The dome form is one of themost inconvenient forms in acoustics design because of theconcave curvatures. The propagating sound energy does not

Fig. 8 Reverberation time before acoustic treatment. (a) Dewela Mosque main prayer, (b) Dewela Mosque daily prayer hall,(c) Damascus City Centre Mosque.

Fig. 9 Total absorption.

37A parametric investigation of the acoustical performance of contemporary mosques

escape without reflecting several times inside the domeshell. Given this effect, the reflected sound energy from thedome returns to the main space with a time delay, resultingin echoes or noise in the main prayer hall and the reductionin the percentage of intelligibility. The reflected sound

energy that is increasingly delayed, especially in largedomes, is the cause of echoes.

The traditional solution implemented during the Ottomanperiod (Mutbul Kayili, 2005) is the installation of cavityresonators inside the dome structure. Helmholtz resonators,

Fig. 10 Recommended reverberation time RT for mosques.

Fig. 11 Equivalent absorption cross section areas ratio of resonators vs. quality factor Q.

M.R. Ismail38

or cavity resonators, built inside the dome absorb aconsiderable amount of sound energy and reradiate theresidual sound throughout the main hall. By diffusing theincident sound energy in all directions, the room becomes adiffuse sound field, preventing dangerous echoes due to thedelayed reflections from the dome shell. Aside from creat-ing a diffused field, the sound energy directly reflected fromthe dome, creates a divine atmosphere of worship. Thisapplication became a tradition in Ottoman architecture.The cavity resonator system absorbs a narrow frequencyband with the frequency concentrated at the site whereresonance frequency occurs. By decreasing the systemquality factor (i.e., by increasing the interior resistanceand volume), widening the absorption frequency band to acertain degree is possible (Mutbul Kayili, 2005), as shown inFig. 11.

In this situation, a slight decrease in absorption wasobserved. The cavity resonators are usually installed asshown in Fig. 12.

In designing the correct Helmholtz resonator to beinstalled in the dome, numerous design issues needed tobe resolved such as obtaining the right frequency, thenumber and size of resonators, as well as placement ofthe damping.

The equations for the resonant frequency were derivedassuming open-air conditions. Under a closed room, theinteraction between the resonator and the room can alterits resonance frequency, but this effect is marginal andcould be neglected (Unnikrishnan et al., 2010). In theequation below, f is the resonance frequency, v is the speedof sound in air, A is the surface area of the hole, V is thevolume of air in the resonator body, and L is the length of

39A parametric investigation of the acoustical performance of contemporary mosques

the neck or port.

f ¼vp

ffiffiffiffiffiffiAVL

r

Unnikrishnan et al., 2010 recommend that the resonatorvolume should not be more than 1% of the room volume. Aresonator volume higher than this value does not lead tomore absorption. In the Dewela Mosque, the volume in themain prayer hall dome is 3407.913 m3, and 1% of it is34.08 m3. The single resonator volume (Fig. 12) is about0.002 m3. Thus, a 17,000 resonator should be installed.However, changing the dimensions of the resonator andincreasing the volume were not feasible because of thestructural constraints of the dome. Thus, 1800 resonatorswere equally distributed along the inside of the domehemispherical surface, as shown in Fig. 12. Ingard (1953)constructed an excel worksheet for the design of acousticresonators, which is used to calculate the designed reso-nator absorption with and without internal lining on theresonator base. The results are displayed in Fig. 13.

The resonators were designed to provide absorption at alow-frequency range. Other absorptive materials wereinstalled in the ceiling of the three prayer halls to providethe rest of the absorption needed at the mid-frequencyrange. The model was rerun for the three spaces, and thedecay curves after acoustic treatment are shown in Fig. 14.

Fig. 12 A detailed cross section and installation in a cavityresonator.

Fig. 13 Absorption cross section of designed

Based on the RT curves in Fig. 15, the installation ofHelmholtz resonators inside the dome shell, as well as theadditional absorptive materials in the ceiling of prayerhalls, adjusted the acoustic environment inside the prayerhalls to acceptable limits. Fig. 16 shows the RT values of thethree prayer halls plotted against the recommended RTvalues for mosques indicated by Mutbul Kayili (2005).

8. Conclusion

In this work, the acoustic environment of contemporarymosques was evaluated. The sound behavior in mosqueslacked adequate research in all relevant technical sciences.As with acoustics, many technical data have yet to besufficiently evaluated. The common types of mosquedesigns were discussed and analyzed. A geometrical para-metric analysis of three examples of contemporary mosquesthat represent the three different common configurations ofprayer halls was conducted. The prayer halls that have largehemispherical domes have a low-SA/V ratio relative torectangular prayer halls.

This low-SA/V ratio in prayer halls with hemisphericaldomes resulted in a reduction of the total absorption of thespace. The computer simulation for the three prayer hallswith finishing materials specified by each consultantrevealed that the materials commonly used for the threedesign topologies needed acoustic treatment. This treat-ment will introduce more absorption to the spaces andreduce any negative acoustic phenomena that might occurfrom having surfaces that focus large amounts of acousticenergy at certain areas of the prayer halls. The decaycurves at each frequency revealed that additional absorp-tion was needed at low- and mid-frequency ranges.

The installation of Helmholtz resonators in domes wherethe scattering of sound attenuates any focusing phenomena,as well as the addition of absorption by changing the ceilingmaterial characteristics-enhanced acoustic quality, indicat-ing that these techniques are effective. A decrease in RTwas observed. This decrease was not restricted to theresonant frequency, considering additional damping layerswere introduced inside the resonators.

Another effect is the increase in clarity and definition ofspeech. These effects should be investigated along with theincrease in the number of resonators used. On the other hand,

resonator continuous line with damping.

Fig. 14 Decay curves after acoustic treatment. (a) Dewela Mosque main prayer, (b) Dewela Mosque daily prayer hall, (c) DamascusCity Centre Mosque.

Fig. 15 Reverberation time after acoustic treatment. (a) Dewela Mosque main prayer, (b) Dewela Mosque daily prayer hall,(c) Damascus City Centre Mosque.

M.R. Ismail40

Fig. 16 Predicted reverberation time against recommended.

41A parametric investigation of the acoustical performance of contemporary mosques

the position of the Helmholtz resonators in the corners wherethe efficiency is greater shows a kind of knowledge on theacoustic behavior of closed spaces by Tilemachos and Dimitris(2007). This area needs therefore further investigation.

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