BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 Pages 109–132 109

Sounds From the PastThe Acoustics of SULTAN HASSAN MOSQUE

and MADRASAAhmed Ali El-khateeb* and Mostafa Refat Ismail**

Department of Architecture, Faculty of Engineering – Ain Shams University, Cairo / Egypt, ahmed.khateeb@iacg.com.eg, mrefat@hotmail.com

(Received 2 August 2006 and accepted 28 March 2007)

ABSTRACTThe Sultan Hassan Mosque and Madrasa is considered to be stylistically the most compact andunified of all of Cairo’s Islamic monuments. Beside its main function as a place for prayer, itsdesign also allows separate schools for teaching the four Sunni rites; both functions imply theimportance of phonological cognition and intelligibility of speech.

The acoustical environment within the main Iwan of the Madrasa and Mosque of SultanHassan has been investigated and examined through field measurements and room simulationutilizing ODEON to assess the degree of speech intelligibility. The significance of acousticalperformance within this space is highlighted in relation to form and texture. Criteria for goodacoustics are compared with the spatial requirements and design guidelines. Although fieldmeasurements show high reverberation time and echoes at some of the points examined, it doesnot badly affect the ability of worshipers to follow and understand clearly what is said either inthe Mihrab, a half cylinder directed to the Holy Ka’aba in Macca, or Minber (Pulpit). On thecontrary it adds the depth and width required for this kind of spiritual performance.

Keywords: Mosque acoustics; historical.

1. INTRODUCTIONThe acoustics of historical buildings have attracted wide interest and western historicalbuildings in particular have been extensively studied, starting with Greek amphitheatresand then via theatres of the Roman era, the middle ages, the renaissance and right up tothe nineteen century and the pioneering work of W. C. Sabine, the founder of modernacoustic science. However, no extensive work has been done to obtain a clear image ofthe acoustics of the Islamic era despite its longevity and importance. In Egypt [1–2], theearly medieval period starts with the Tulunid dynasty (868–905), followed by theFatimid period (969–1171). The high middle ages starts with the Iyyubid dynasty(1171–1250), followed by the Bahari Mamluks period (1250–1382) and then the BurgiMamluks period (1382–1517). Finally the Ottoman period (1517–1798) followed bythe family of Muhammed Ali Pasha. Thus there are centuries of Islamic history, running

parallel with the corresponding centuries of western history. However, this has receivedlittle interest from researchers in the field of building acoustics. This paper representsan attempt to address this lack of knowledge.

The subject of this paper, the Madrasa and Mosque of Sultan Hassan is a uniquepiece of Islamic architecture and possibly the most important Islamic monument inCairo. It can be regarded as a comprehensive religious university according to thecontemporary learning concepts. To guarantee continued financial support, SultanHassan endowed thousands of acres in Egypt and Syria to serve this building in additionto many other religious building in Egypt and Syria [3].

Upon his visit to the Madrasa and Mosque, Frank Lloyd Wright (1867–1959) said [4]:“How it is permissible to people having such superior arts to abandon it and replace

it with the faults of western architecture which westerners themselves try to get rid of ”Despite its importance from the historical and legacy standpoint, and the

considerable amount of research related to its architectural and historical greatness, theSultan Hassan Madrasa and mosque has not received interest in that it deserves in otherfields of research. This building has never been a subject of acoustic research in spiteof the importance of the acoustical role in the building’s function.

To successfully locate more than 800 worshipers in one room to hear and learn alesson from the delivery of the Friday prayers implies that the designers knew how tosolve the acoustical problems that could arise in such a space. This gives rise to thehypothesis stated by Cremer that “they must have had special knowledge of acoustics,but we have no information about such knowledge” [5]. This work thus represents anattempt to investigate if the architects who built such huge scale buildings did considerthe acoustical issues in their designs.

The main objective of this work was to check if the worshipers could hear andunderstand clearly the words of the Imam (Leader – especially in prayer) during boththe five daily prayers or in the weekly prayers and Friday sermon, by reconstructing theacoustical environment within the main Iwan as it was originally. The acousticalenvironment within the room was assessed through the four acoustical indicators: SPL,RT, STI and %ALCons.

2. LITERATURE REVIEWAlthough there is now a considerable body of work relating to the acoustics of Christianchurches (see for example [6–9] relatively little work has been carried out on investigatingthe acoustics of historical mosques. The most important to date is the CAHRISMA project(Conservation of the Acoustical Heritage by Revival and Identification of Sinan MosquesAcoustics). The main objectives of this project are the identification, revival andconservation of architectural and acoustical heritage of Sinan’s Mosques and ByzantineChurches in Istanbul. The project aims to develop the concept of the ‘HybridArchitectural Heritage’, which is a new system of identification that examines acousticalas well as visual characteristics in a real time virtual environment [10].

As part of the CAHRISMA project, Karabiber and Erdogan [11] compared theacoustical properties of an ancient and a recent mosque. Results showed that the 16th

century mosque, Sokullu, has slightly better acoustics than the 20th century mosque, Sisli.

110 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

For both mosques, the values of the measured parameters are in general outside the limitsof the generally recognised optimum values, but the results for the Sokullu Mosque showless spectral differences and are closer to the optimum values. However, the valuesgenerally recognised as optimum are not values that have been especially determined formosques and some of the early results of the CAHRISMA project indicate that theacoustics of the Sokullu Mosque are subjectively acceptable for a mosque of its size.

Karabiber [12] has investigated the acoustical problems of some historical Turkish-Ottoman mosques which usually employ vaults and domes for the ceiling rather thanflat ones. The results show that the acoustics are generally good although these concavesurfaces are potentially problematic because of the great probability of focusing soundwaves, especially in ancient mosques. The good acoustics may be due to the differentlydimensioned jugs buried in domes to absorb sound. In a sense, they are ancient versionsof Helmholtz resonators.

Kayyly [13] has studied the importance of cavity resonators in ancient societies.Cavity resonators are the oldest acoustic systems known in architectural acoustics andwere used extensively in ancient theatres. In the medieval age their use became morecommon in mosques and church buildings. In such rooms unwanted reflections andstanding waves can cause problems, especially at low frequencies. Results showed thatwith proper installation the use of cavity resonators can overcome such problems. Theyscatter the incident energy causing it to be re-radiated in all direction. Cavity resonatorshave been widely used in Anatolia with the technology having been developed overmany years. In particular they have been used successfully in domes of buildings forworship to overcome the undesirable properties of them.

3. DESCRIPTION OF THE MADRASA AND MOSQUE OF SULTAN HASSANThe Madrasa and Mosque of Sultan Hassan (Figure 1) was built in the fourteen century(1356–1362 AD) in the Bahari Mamluks Period (1250–1382 AD) [1,14]. The buildingconsists of a group of separate and integral elements in one complex compound with atotal built-up area of about 8100 m2. The main elements in the compound are [14,15]:

• A central open courtyard surrounded by four Iwans which are halls without inter-mediate columns, usually open on one side to a courtyard and raised one step fromthe courtyard level. This is a pattern well known for Islamic Madrasas (schools).Each Iwan is specified for one of the four Sunni Mazhab (rites). The courtyard is anapproximately square area of dimensions 35.8 × 31.60 m (about 1135 m2) and theratio of its area to the total built-up area of the compound is about 1:7. In the centreof the open courtyard there is an ablutary covered by a wooden dome supported oneight octagonal columns.

• The main or south-east Iwan, also known as The Qibla (the direction to the HolyKa’aba) Iwan. This was the largest Iwan, not only in the building but also in Egyptin that time. It has a rectangular shape of area 561 m2 covered by an enormouspointed vault that has a maximum height of more than 25 m. This Iwan used forJama’at (group) prayer and accommodates about 800 worshipers. It is specifiedfor the learning of Shafey’ite Mazhab [after Imam Mohamed Esh’shafee (767:819AD; 150:204 HD)). In the center of the front wall of this Iwan is the Mihrab a half

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 111

112 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

Malikite Iwan

Hanafite Iwan

Shafey'ite Madrasa

MalikiteMadrasa

Portalentrance

El-Refaie Mosque

One of the two minarets

HanafiteMadrasa

The main Iwan(Shafey'ite

Iwan)

The Mausoleum

Small Iwan

HanbliteMadrasa

Hanblite Iwan

Students cells

Kuttab & a group

of services

Open courtyard withablution fountain

El-Qibla

Direction NORTH

Y XZ

Figure 1. 3D representation of the six main items that compose the Madrasa andMosque.

cylinder directed to the Holy Ka’aba in Macca. A few metres to the right of theMihrab is the marble Minber (pulpit), on which the speaker executes the sermonof the Friday prayer. At the front of the Iwan from the side of the courtyard and on theaxis is the Caller’s marble podium that stands on eight white marble columns and threepiers and is reached by stairs from the inside. From that podium the Mue’zzin (thecaller to prayers) and the Mobal’legh (Repeater) perform (see Figure 2).

• Three small Iwans which also consist of a rectangular areas of about 200 m2. EachIwan is covered by a pointed vault that has the same height as the main Iwan. Thesouth-west Iwan is specified for the learning of Hanblite Mazhab after ImamAhmed Ibn Hanbil (780:855 AD; 164:241 HD), the north-west Iwan is specifiedfor the learning of Hanafite Mazhab (after Imam Abe Hanefa Al-No’aman 699:767AD; 80:150 HD), and the north-east Iwan is specified for the learning of MalikiteMazhab (after Imam Malek 659:795 AD; 39:179 HD).

• Four Madrasas (schools) for the four Sunni Mazhab placed at the corners of thebuilding with entrances through the courtyard and assigned to teach, in addition tothe specified Mazhab – the Tafsir (interpretation of the Holy Kor’an) the Hadith(Prophet’s norms and traditions) and the seven recital methods of reading the HolyKor’an. Each Madrasa consists of a small open Iwan for teaching one Mazhab andstudents’ accommodation with a capacity proportionate to the number of the stu-dents in each Madrasa. Each courtyard contains an octagon fountain in its center tomoderate the summer air temperature and which also can be used for ablution. Thelargest Madrasa is the Hanafite one which occupies the southern corner of the

building, whilst, the Shafey’ite Madrasa is located in eastern corner, the MalikiteMadrasa in the northern corner and finally the Hanblite Madrasa, which is thesmallest one, occupies the western corner of the building.

• Kuttab (a school specialized in the recitation of the Holy Kor’an as well as teachingreading and writing for the children), a group of services, utilities and a medicalunit all occupy the north-west corner of the building from consideration of theventilation needed and the direction of the prevailing winds that can be utilized inthis location. The services and utilities include stable, depots for the storage oflamps oil, chains, carpets and straw mats pertaining to the building, in addition tothe kitchen and its annexes used for the preparation of students’ meals. There is alsoan ablutary, a water well and a water wheel, operated by animals kept in the stable,to provide the building with water.

• A mausoleum located on the axis with the building in front of the Qibla Iwan,overlooking the main square. It is a square area of about 462 m2 with anotherMihrab similar to that in the Qibla Iwan. The tomb was built for the burial of SultanHassan although according to historical references it was not he was not interred init but his son Shehabi who died in 1386 AD [15]. It is covered by a huge dome ofradius 10.62 m and about 14 m in height.

4. THE MAIN IWAN AS THE TOPIC OF STUDYThe main Iwan is a rectangular room of dimensions 26.46 × 21.20 m2 and volume12826 m3 covered with a huge pointed vault with the back wall totally opened to the

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 113

Minber

Vault

Mausoleum

Two steps

Students' cells

SmallIwan

The Qiblawall

Imam position

MihrabThe Side

wall,originally

lime stoneMarble

clad

OpencourtyardShafey'ite

Madrasa

Small opencountryard

Ablutionfountain

Mainentrance to

HanafiteMasrasa

Callerpodium

Figure 2. Detailed view for the main Iwan in the Sultan Hassan Mosque andMadrasa.

114 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

courtyard (see Figure 2). The floor is covered with carpets. Originally, the walls andvault were built with limestone [14]. Recently, and due to the restoration works that havebeen carried out under the supervision of the Supreme Council of Antiquities, the wallsand the vault have been covered with cement mortar plaster except for the lower part ofthe walls that are still clad with marble as they were originally. From the acoustical pointof view, the two materials; limestone and cement mortar plaster have similar acousticcharacteristics, so it can be assumed that the acoustical environment within the room isstill as it was in the past. Table 1 summarizes room architectural and statistical data.

According to the “Endowment Deed” [3,14] dated 760 AH–1359 AD and preserved inthe Egyptian Home of Documentations; a Shekh (Professor specified in religioussciences) was designated for each Mazhab and had 100 students and three teachingassistants. It can be deduced from the deed that the total number of students in the fourMadrasas at any time did not exceed 460. This means that the maximum number ofstudents in each Iwan was about 100 to 115 which is commensurate with its area. Inaddition; it can be deduced from the same deed that those students were distributed amongthe professor and his assistants, approximately 25 to each. This is a small number thatcould be expected to hear the speaker clearly in the very low background noise of the un-mechanized civilization of that time. At the prayer times, all students had to gather in themain Iwan (its area is almost equal to the total area of the three other Iwans) which couldeasily hold them in addition to those members of the public who also attend the prayers.

Table 1: Architectural and statistical data

1. Architectural Data1.1. Dimensions:

Lengths mL W HMIN. HMAX. HAV. Area m2 Volume m3 Per. m DMax. m26.46 21.2 12.155 25.70 18.92 560.95 12825.51 95.32 28

1.2. Finishing Materials:Walls

Ceiling The Qibla The Side The Back FloorCement Mortar Lower 8.5 m Lower 1.4 m Open to Carpet

Marble Marble theCladding Cladding Courtyard

Upper Cement Upper Cement Mortar Mortar

2. Statistical DataEnvironmental

Conditions Max. Area/ Volume / RTOPT@ (Average)

Shf Capacity Person m2 Person 500Hz RH Temp.m−1 Ff % Persons Net Gross m3 Sec % C°0.17 3.215 800 0.65 0.70 16.03 0.932 36 32.4

The authors believe that the reason for making the main Iwan larger than the othersis to allow all of the students and other worshipers to congregate in one area. This leads tothe conclusion that the three small Iwans were never used for group prayer. Thisconclusion is supported by two facts, the first is the impossibility of hearing the Imamin any of those Iwans due to the design concept that ensures a long distance betweenthe Imam and the worshipers in the other Iwans. The second, is the unlikely existenceof four Imams (one in each Iwan) since this contradicts directly Islamic values thatalways call for unity and coherence and detest separation and scattering.

Based on this analysis, it would be meaningless to study the acoustical environmentwithin the three small Iwans that would not have suffered from any acoustical defectsaccording to their function, consequently this investigation was limited to the main Iwan.

5. METHOD AND TYPES OF PRAYER IN ISLAMBefore describing the methodology of the analysis, it is important to briefly describe thecustoms and types of prayer in Islam since this is the main factor determining theapproach used during the analysis.

Prayer is one of the five pillars of Islam. The Moslem has to execute five prayersevery day. To do so, the Moslem has to orient himself to the Holy Ka’ba in Mecca andperform five main positions (Figure 3). These positions constitute one Raka’a (A unitin the Muslim prayer). The number of Raka’as in every prayer depends on the time. Ineach position, the Moslem has to recite some versus from the Holy Kor’an or sayspecific words. To change from one position to another he also has to say specific wordsaccording to that position. The precepts of Islam determine that it is better for Moslems(especially the men) to execute their prayer as a group in the mosque not as individuals.Consequently, for the Moslem, the mosque is the heart of his religious activities as hevisits it five times per day to execute his group prayer.

Prayer in a group is executed in the same way as for individuals except that theworshipers have to line up behind the Imam and follow him exactly (Figure 4). Tochange from one position to another, the Imam says in a loud voice the specific wordsaccording to each position to inform the worshipers behind him. The worshipers haveto repeat the words in private so as not to confuse each other. In the old days, in orderto ensure that the words of the Imam reach all worshipers specially in large mosques,one of the worshipers known as the Mobal’legh executed his prayers on an elevatedplane (such as the caller podium in Sultan Hassan’s Mosque, Figure 2) located at anintermediate point among the worshipers. This worshiper only is permitted to repeat, ina loud voice, the Imam’s words when changing the position. If the room acoustics arebad this procedure may help in notifying the worshipers about changing the position,but not in helping the worshipers to hear the recitation of the Imam.

In the group prayer, the recitation in position 1 may be carried out in a loud or privatevoice according to the time of the prayer. The words that have to be said upon changingthe position must be done in private regardless of the time of the prayer except for theImam as previously mentioned. The words that have to be said in each position must besaid in private for everyone (the Imam as well as the worshipers) regardless of the timeof the prayer (see Figure 3).

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 115

116 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

Every Friday, the Moslems execute special prayers known as the Friday prayers. Theyare executed in the same way as the other prayers except that the Imam has to perform ashort Khutba (sermon) that takes about 20 minutes before he executes the usual prayers.In this case, the worshippers are seated and distributed randomly on the floor while theImam usually mounts the Minber (see Figure 4) which has at least three steps.

Based on the previous analysis, there are three distinct acoustical requirements formosques [12]:

• To hear the voice and orders of the Imam• To understand the sermon of the Friday preacher,• To listen or to join in the recital of the Holy Kor’an.

6. ANALYSIS METHODOLOGYAccording to the method and types of prayer in Islam described above, there are threescenarios that must be considered in the analysis phase:

• The first: during the action in the daily prayers; one human sound source; the Imam,facing in the opposite direction to the worshipers and standing in the Mihrab.

ONE UNIT/ONE RAKA'A

In a private voice In a loud voice

Saying SpecialWords

RecitingKoranicVerses

Saying SpecialWords

Saying SpecialWords

Sitting Down

Another RAKA'Awith the samefive positions

StandingProstrationStandingKneelingStandingAC

TIO

NS

AY

ING

SO

UN

DS

RecitingKoranicVerses

ACCORDING TOTHE TIME OFTHE PRAYER

ACCORDING TOTHE TIME OFTHE PRAYER

IMAMONLY

UP

ON

CH

AN

GIN

GTH

E A

CTI

ON

IMAMONLY

IMAMONLY

IMAMONLY

IMAMONLY

GO

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E

GR

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GR

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T TO

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HO

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RA

ISE

SayingSpecialWords

300

1 2 3 4 5 1

1040

1065

30058

0 910

1700

1100 625 300

Figure 3. The five positions main of the Moslem’s Prayer.

• The second: during the changes of position in the daily prayers; two humansound sources; the original (the Imam) in the same situation as in the first case,and a second source (the Mobal’legh) – which can be considered as an image ofthe first one –located on the caller podium (see Figure 2) and above the wor-shipers by 2.4 m. This source has a time delay of 500 msec relative to the orig-inal one.

• The third: relating to the Friday sermon, one human sound source in front of theworshipers and above them by 4.40 m according to height of the Minber in theSultan Hassan mosque. In this case no repeater is involved.

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 117

The Imam

Worshipers aligned inraws

(a)

1200

1200

1200

1200

Listeners

Solid

Void

SpeakerVoid

(b)

Y

z x

Figure 4. The configurations for (a) Jama’at prayer, (b) The Minber for the Fridaysermon.

118 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

The form of the investigation involved the construction and analysis of a 3-D modelusing the acoustic simulation program ODEON [16] in parallel with field measurements.Figure 5 shows external and internal views of the ODEON model.

Data has been collected from the field using a Maximum Length Sequence SystemAnalyzer (MLSSA) [17]. MLSSA has been used for the measurements in combinationwith a microphone (at height 1.6 m to represent a worshiper in a standing position) anda loudspeaker driven by a power amplifier as the source. MLSSA was utilized for themeasurements of the Reverberation Time, RT, and Speech Transmission Index, STI.

External view

Internal view with SS as in Case-2

TheImam

TheRepeater

Figure 5. The ODEON Model.

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 119

Measurements of the Sound Pressure Level, SPL, in the room were performed using anExtech® [18] Integrating Sound Level Meter model 407780 that meets the requirementsof ANSI S1.4 and IEC 651&804 standards, Type-II precision. During field measurements,the requirements and specifications of ISO-3381 [19] for RT measurements in enclosureswere observed.

Field measurements in the selected Iwan – which has remained almost in its originalcondition since its construction more than 600 years ago – were employed to compareODEON outputs with surface properties systematically varied until similar results wereobtained. Figure 6 shows a comparison of the RT obtained with ODEON and from fieldmeasurements.

In the field work measurements were made twice at fifteen points. The firstmeasurements were made to acquire the Room Impulse Response from which the RT couldbe calculated. For this case, the sound source was located near the corner of the room toallow for the maximum excitation of room modes. The second for the measurements of STIwhich were also performed twice, the first with the sound source located in the Mihrab tocheck the case of the Imam performing a daily prayer. The second with the sound sourcelocated on the Minber to check the case of speaker in the Friday sermon.

A subjective test was also performed utilizing a live sound source (the repeater of themosque) who was asked to stand in the Mihrab and execute a prayer during the

0.000

1.000

2.000

3.000

4.000

5.000

100 1000Octave Band Center Frequencies Hz

10000

RT

(se

c)

RT-20 Field-Unoccupied RT-20 Estimated-Occupied RT-20-ODEON

Figure 6. Measured acoustic indicators versus ODEON output. RT unoccupiedobtained by field measurements, RT calculated for the occupied case andRT obtained from ODEON.

120 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

measurements of SPL) at the fifteen points previously examined in the objectivemeasurements.

Finally, the acoustical quality in the main Iwan was characterized by the selectedacoustic indicators through contour maps generated using ODEON for the mostimportant frequencies for the intelligibility of speech (1:4kHz).

7. THE ACOUSTIC INDICATORSTo obtain conclusions regarding the acoustic performance in the selected Iwan, fourobjective acoustic indicators have been analyzed. According to their importance; theseindicators are:

7.1. Reverberation time RTThe reverberation time is defined from Sabine’s equation [20]:

(1)

The optimum value of reverberation time, RTOPT, at the mid frequency (500Hz) as afunction of room volume can be determined according to the formula [20]:

(2)

Based on RTOPT@500HZ value, the full spectrum of RTOPT@OBCF can be predicted fromthe formula [21]:

(3)

Where n is a ratio that (for F <500Hz) can be estimated to a good accuracy from [22]:

(4)

And, when F/500, n=1

7.2. The sound pressure level, SPLThe sound pressure level is defined by the following equation [20]:

(5)

7.3. The speech transmission indexThe Speech Transmission Index is defined by the following equation [23,24]:

SPL 20logPP

dB0

=

n5.6716

F0.2856=

RT n RTOPT@OBCF OPT@500Hz= ×

RT 0.3logV10

sec.OPT@500Hz =

RT0.16V

A 4mVsec=

+

(6)

And;

(7)

The relation between STI and syllable intelligibility is as follows [24]:

Poor Satisfactory Good Very good Excellent0:30% 30:45% 45:60% 60:75% 75:100%

7.4. Percentage articulation loss of consonants, %ALconsThe Percentage Articulation Loss of Consonants relates to the loss of consonants inspeech measured with single phonetically balanced words placed in short sentences.

The Percentage Articulation Loss of Consonants is defined from the followingequation [25]:

(8)

…… ….Eq.9

Where D is the source-listener distance in metres, T is the reverberation time in secondsat 1400Hz, V is the room volume in m3 and a is a correction factor.

Acceptable ranges are divided into three levels:

Very Good Good Hard0–10 % 10–15 % More Than 15%.

All field work was performed in an unoccupied room since measurements in a fullyoccupied one can be problematic [26]. To estimate the values of RT occupied, Sabine’sequation (see Equation-1) was utilized as it is the most appropriate for live rooms. Themethodology for doing so is described in detail in reference [19].

8. RESULTSFigure 7 shows a grid of measurement points and examples of the room impulseresponses obtained. As can be seen from Figure 8, the values of the measuredreverberation times, RTM, range between 3.25 sec at 1kHz to 1.69 sec at 4kHz for theunoccupied case. Even in case of the full occupation, the RT is still higher than theRTOPT for a speech room excluding 8kHz. The excessive RT was not unexpected due to

AL 200(D T

V) a %Cons

2 2

=

+

TI =SNR S

Rkk −

STI (W TI ) 100%k kk 1

7

==

∑ . .

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 121

122 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

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the nature of room boundaries. Except for the back wall and carpeted floor (or theworshipers in the case of full occupation), all other room surfaces are poor acousticabsorbers. It should be noted that the tradition of Islamic Madrasa to incorprate a totallyopen back wall to the courtyard may be very beneficial. If this wall were closed; theIwan could be acoustically unendurable.

The %ALCONS calculations shown in figure 9 indicate that the points 7 and 9–15(8 points out of 15) according to the %ALCONS rating are located in the hard zone. Distinctechoes can be seen in the room impulse responses corresponding to points 10–15 shownin Figure 7. These echoes were expected as they can actually be heard in the Iwan.

The most noticeable feature of these room impulse responses is the pattern ofreflections that appears dense at the points 2, 3, 5, 6, 8, 9, 11, 12, 14 and 15 and sparseat points 1, 4, 7, 10 and 13. This relates to the vault that covers the room and the wayit reflects the sound waves and the resulting pattern of reflections. The phenomenon canbe explained from the stand point of geometrical acoustics. Points 1, 4, 7, 10 and 13 donot receive any 1st order reflections but only higher order ones. In Figure 10 the whiteareas represent locations where no reflections are present. In figure 10a the white areathus indicates no first order reflections, in Figure 10b it indicates no 2nd orderreflections and in Figure 10c no 1st or second order reflections. This explains therelatively density of the room impulse responses acquired at the other points whichreceive both 1st and higher order reflections.

It should be noted that the high RT also means a high sound pressure levelthroughout the room and this plus the low background noise level helps the worshipersto follow their Imam without difficulty. Measurements and simulation data both

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 123

0.000

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124 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

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Figure 10. 1st and 2nd-Order reflections inside the room: white area indicate lack ofrelections.

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 125

indicate that the values of SPL range between 53–76 dB at the subjectively importantfrequencies for speech (Figure 11).

The most critical case investigated is the first, when the Imam is performing alone(i.e. without the repeater). The results show that the Minber creates acoustic shadows inthe area just beside it (see Figure 11). The same effect is also true for the area behind thecaller podium. These shadows (dips) are due to the mass and position of the Minber andcaller podium in the Sultan Hassan mosque relative to the position and orientation of theImam. Since the Minber is not a totally solid mass but contains some voids, it is to beexpected that SPL dips due to the Minber will not occur in the areas around these voids.

(a) At 2kHz

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126 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

05

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Figure 12. STI contour map for Case-1 showing the effects of the Minber and caller podium.

Figure 12 shows that the STI values for case 1 indicate good speech intelligibility.About 68% of the mosque area lies between STI 45 to 60% which means a goodintelligibility according to the STI rating [23]. Except for a very small area (about 4%)that lies in the satisfactory zone, the remaining area lies in the very good zone (21.5%)and the excellent zone (about 6.5%). The adverse effect of the Minber is again apparentin the dip that can be seen in the contour map.

The peaks that appear in the contour map of STI reflect the effect of the podium on theEDT and RT. Analysis results indicate a very short EDT (≤0.5 sec) for the area under thepodium which explains the high value of STI. This may be due to the isolated volume thatexists under the podium which does not receive the long delayed reflections from the vault.The irregularity of the maps for positions close to the walls, especially the right wall, canagain be related to the pattern of the reflections which appear very dense at that wall.

From the SPL point of view, the situation is better for the other two cases: Imam withRepeater and the sermon. As expected, the introduction of the repeater in the secondcase helps in minimizing the shadow area behind the podium in addition to making theSPL higher than in the first case (Figure 13a). The positioning of the caller podium inthe rear third part of the Iwan is significant as it is relatively far from the original soundsource and consequently the loudspeaker-like nature of the repeater is very useful. Incase 3, with the elevated speech source, almost all shadow areas disappear (Figure 13b).

It can be seen in Figure 14a that for case-2, most STI values are in the satisfactoryzone which covers 72.5% of the area. The remaining area lies between the very goodzone (21.5%) and the excellent zone (about 6%). Case-3 is the best in terms of STI, 76%of the area lies in the satisfactory zone, the remainder lies in the very good zone (18.5%)(Figure 14 b). The effect of caller podium as noted for case 1 also applies for both cases2 and 3.

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 127

(a) Case 2

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Figure 13. SPL contour maps.

Finally, it worth mentioning the many lanterns hung by steel chains from the vault andact as Helmholtz resonators. These lanterns help in lowering the RT at the low frequencies.The lanterns were originally present in the building and utilized for lighting at night [15].

9. DISCUSSIONThe findings demonstrate that the 800 worshipers were able to hear and understandclearly the Imam in all cases. This suggests that the architects of those days may havehad some knowledge of acoustic principles.

Although both the field measurements and the ODEON outputs indicate anexcessively long RT even for the case of full occupation, this long RT is very importantfor the majesty of the space as it adds the depth and width required for this kind ofspiritual performance. The SPL findings (both measured and calculated) show levels that

128 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

enable the worshipers to hear and understand the Imam’s words without difficulty. Thisconclusion is in agreement with that of other researchers in this field. It has been reportedthat data, taken in the unoccupied rooms, show that the values of reverberation are veryhigh, providing the room with a unique feeling of majesty and that Mosques are goodaccording to some acoustical criteria, such as total sound pressure levels and roommodes but inadequate according to the others, such as reverberation time [12,27,28].

An important problem that has been identified is that there is no specific dataregarding the absorption coefficients of worshippers or audience standing or seateddirectly on a carpeted floor in rows 1.2 m apart [23]. This reflects some of theproblems that face the acousticians who design the acoustics of mosques. Thishighlights the need for more research in this field to develop new acoustical criteria

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Figure 14. STI contour maps.

BUILDING ACOUSTICS · Volume 14 · Number 2 · 2007 129

that can be applied when designing or evaluating the acoustics of mosques. Valuesconsidered as optimum, are not values that have been especially determined formosques [11,27]. This fact illustrates once more the necessity to establish specificacoustical criteria and parameters to be used for the acoustical evaluation ofMosques [12,27]:

10. CONCLUSIONThis work represents the first investigation of the acoustical characteristics of the mainIwan in the Sultan Hassan Mosque and Madrasa, considered stylistically to be the mostimportant Islamic monument in Cairo. The acoustical environment within the mainIwan of the Madrasa and Mosque of Sultan Hassan has been investigated and examinedthrough field measurements and room simulation utilizing ODEON to assess the degreeof intelligibility. The results of field measurements were utilized to validate ODEONoutputs. Criteria for good acoustics were compared with the spatial requirements anddesign guidelines. Although field measurements revealed high reverberation time andechoes at some of the examined points, these do not affect badly the ability ofworshipers to follow and understand clearly what is said either in the Mihrab or Minber.The authors believe that this phenomenon may relate to the temporal characteristics ofthe Arabic language and this will be the subject of further research.

ACKNOWLEDMENTSThe authors would like to express their thanks and deep appreciations to all persons andauthorities who help in doing this work, on the top: Dr. Abdollah Kamel the presidentof the Islamic and Coptic Antiquities sector in the Supreme Council of Antiquities, Mr.Essa’eid Helmee the general director of south Cairo antiquities. Thanks also go to Dr.Ali El-khateeb, Dr. Essra El-khateeb, Dr. Sabah S. Soliman, Eng Mo’ataz Abdel Fattahand the Mue’zzin of the Mosque. Finally; special thanks go to Dr. Ahmed Zakaria forhis effort in revising and editing the text.

REFERENCES[1] The People Book (1960), the Encyclopaedia of People* (Parts-1, 2 and 3). Elshab

Press, Cairo.[2] D. Behrens-Abouseif (1996) Islamic Architecture in Cairo – an Introduction. The

American University in Cairo Press.[3] M. Pash (1980) The New Tawfeeq Plans for Egypt Cairo and its Old Famous

Towns and Cities* Part 4 – the 2nd Edition from Polaq printary 1305 AH. ThePublic Egyptian Institute for Book.

[4] T. M. Mahmoud (1967), Frank Lloyd Wright, his Life, Works and Opinions*.Franklin institution, Cairo and New York.

[5] L. Cremer (1975) The Different Distribution of the Audience. Journal of AppliedAcoustics, Vol. 8 No. 3. pp. 173–191.

[6] M. Miomir Mijic and A. Sumarac-Pavlovic (2004), Analysis of Contribution ofAcoustic Resonators Found in Serbian Orthodox Churches, Building Acoustics,Vol. 11, Number 3, pp. 197–212.

130 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

[7] M. D. Fernández and M. Recuero (2005), Data Base Design for Acoustics: TheCase of Churches, Building Acoustics, Vol. 12, Number 1, pp. 31–40.

[8] A. Magrini and L. Magnani (2005), Models of the Influence of Coupled Spaces inChristian Churches. Building Acoustics, Vol. 12, Number 2, pp. 115–142.

[9] U. Magrini and A. Magrini (2005), Measurements of Acoustical Properties inCistercian Abbeys, Building Acoustics, Vol. 12, Number 4, pp. 255–264.

[10] Z. Karabiber Yüksel, C. Binan and R. Ünver (2003), A Research Project In TheIntersection Of Architectural Conservation And Virtual Reality: Cahrisma. CIPAXIXth International Symposium, 30 September – 04 October, 2003, Antalya, Turkey.

[11] Z. Karabiber and S. Erdogan, (2002), Comparison of the Acoustical Properties ofan Ancient and a Recent Mosque. Forum Acusticum, Sevilla, Spain. September2002.

[12] Z. Karabiber (1999), Acoustical Problems in Mosques. ASA/EAA/DAGA Meeting,15–19 March 1999, Berlin, Germany.

[13] M. Kayyly (2002), Evolution of Acoustics and Effect of Worship Buildings on it.The 3rd European Congress on Acoustics – Forum Acousticum Sevilla, 16–20September 2002. European Acoustics Association, Sociedad Espanola de Acustica(Spanish Acoustic Society), Organized by Architectural School and CivilEngineering School of Sevilla University, Sevilla, Spain.

[14] Principles of Architectural Design and Urban Planning During Different IslamicEras. (1992) Organization of Islamic Capitals and Cities.

[15] M. H. Nowiser (1996), Islamic Architecture in Egypt, The Iyyubid and MamluksPeriod*. The Library of Zahra’a Esh’shurq.

[16] C. Lynge (1999), Odeon Room Acoustics Program, Version 4.0, Industrial,Auditorium and Combined Editions. I/S ODEON. The Department of AcousticTechnology, Ørsteds Plads, Technical University of Denmark.

[17] D. D. Rife (2002), MLSSA. Maximum Length Sequence System Analyzer ReferenceManual Version 10WI-6, DRA Laboratories.

[18] Extech Instruments (2005) Catalog.[19] Acoustics-Measurement of the Reverberation Time of Rooms with Reference to

Other Acoustical Parameters. ISO. 3382 International Standard, 2nd Edition 1997.

[20] A. A. El-Khateeb (2003), Architectural Acoustics, Theory and Application*. TheAnglo Egyptian Library.

[21] V. O. Knudsen and C. M. Harris (1978), Acoustical Designing in Architecture TheAmerican institute of Physics.

[22] A. A. El-Khateeb (April 2005), Sounds In Lecture Rooms In Ain Shams UniversityAcoustical Environment Assessment For The Main Auditoria, Problem Analysis andSolution Discussion. Part One: Faculty of Engineering. First Ain Shams UniversityInternational Conference on Environmental Engineering. Vol. II pp. 1860–1895.

[23] H. J. Steeneken and T. Houtgast (1980), A Physical Method for MeasuringSpeech-Transmission Quality. The Journal of the Acoustical Society of America,Vol. 67, No. 1. pp. 318–326.

[24] W. Ahnert (2002), Implementation of Intelligibility Algorithms into AcousticSimulation Programs pp. 79–88. A symposium on: Past, Present and Future of theSpeech Transmission Index. TNO Human Factors, The Netherlands.

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[25] V. M. A. Peutz (1971), Articulation Loss of Consonants as a Criterion for SpeechTransmission in a Room. J. Audio Eng. Soc.Vol. 19, No. 11, pp. 915–919.

[26] M. Barron (1993), Auditorium Acoustics and Architectural Design. E&FN SPON.

[27] A. A. Abdou (2003), Measurement of acoustical characteristics of mosques inSaudi Arabia The Journal of the Acoustical Society of America, Vol. 113, No. 3,pp. 1505–1517.

[28] P. Fausti, R. Pompoli and N. Prodi (2003), Comparing the Acoustics of Mosques andByzantine Churches. CIPA XIXth International Symposium, 30 September–04October, 2003, Antalya, Turkey.

[29] A. A. El-Khateeb (2002), Acoustical Environment Assessment in EnclosuresDeveloping a New Parameter Among Speech Intelligibility, Shape and VolumeUsing Digital Simulation. PhD thesis Ain Shams University–Faculty of Engineering.

APPENDIXIn Alphabetical order, whenever the following abbreviations or terminologies appear,they mean:A : Room Absorption in metric Sabins.a : Correction factorα : Absorption Coefficient (Ratio).C80 : ClarityD : Source-listener Distance in m.DMax. : Maximum source-listener Distance in m.EDT : Early Decay Time in sec.F : Frequency in HzFf : Form factor, the perimeter to area ratio multiplied by room height

(see Reference 29).HAV. : Room AVerage Height in m.HMAX. : Room MAXimum Height in m.HMIN. : Room MINimum Height in m.IR : Impulse Response.L : Room Length in m.mic. : microphone.msec : milli seconds.NC : Noise Criterion or Noise Criteria Curves.OPT. : OPTimum.P : Sound Pressure recorded at receiver position in Pa.P0 : Reference Sound Pressure (2 × 10−5 Pa).Per : Perimeter in m.R : RangeRH : Relative Humidity %.RIR : Room Impulse Response.Room(s) : Indicates Iwan(s)RT : Reverberation Time in seconds.RTM : The Measured Reverberation Time in seconds.

132 The Acoustics of SULTAN HASSAN MOSQUE and MADRASA

RTOPT : Optimum Reverberation Time in seconds.RTOPT@500Hz : Optimum Reverberation Time in seconds at 500Hz.RTOPT@OBCF : Optimum Reverberation Time in seconds at Octave Band Center

FrequencyS : Shiftsec : seconds.Shf : Shape factor, the perimeter to area ratio multiplied by the distortion

factor (see Reference 29).SNR : Signal-to-Noise Ratio.SPL : Sound Pressure Level in dB(A).SRS : Sound Reinforcement System.SS : Sound Source.STI : Speech Transmission Index.T : Reverberation Time in seconds at 1400Hz.TI : Transmission Index.Temp. : Air Temperature during measurements C°. V : Room Volume in m3.W : Room Width in m.Wk : The octave band weighting factor.4mV : Air absorption in metric Sabins.