Journal of Xi'an University of Architecture & Technology Issn No : 1006-7930

The Impact of -Shape on the Acoustic Performance -A Case

Study of a in Saudi Arabia

Hany Hossam Eldien* and M. Abdul Mujeebu

Department of Building Engineering, College of Architecture and Planning,

Imam Abdulrahman Bin Faisal University, 31451Dammam, Kingdom of Saudi Arabia.

*Corresponding Author

Email: [email protected]

Abstract

Acoustic performance of worship places has been a focus of extensive research. are

traditionally featured by , but there is lack of adequate scientific studies on the effect of

dome-shape on their acoustic performance. In order to address this issue, the present study has

performed a case study on a typical mosque located at Imam Abdulrahman Bin Faisal university

campus in Saudi Arabia. Simulations were performed with four different dome-shapes namely

Saucer, Drum, Onion and Pointed [1], which represent typical forms and architectural features, by

using ODEON Room Acoustics Program. The results were validated by in-situ measurements

(with DIRAC room acoustic system) and statistical analysis (by Microsoft Excel tools). In each

case, the acoustic characteristics were evaluated, by considering Imam (prayer leader) position as

the sound source. The results establish that selecting the appropriate dome-shape is crucial, as they

can have a direct positive or negative impact on the sound quality inside mosques. According to

the dome-shape, both Saucer and Pointed domes have the optimum acoustic performance, as they

meet the theoretical standards to maintain the acoustical comfort. As the results would vary

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according to the size and architectural features of the building, a case-specific analysis is important

at the early design stage.

Keywords: Dome-shape; Mosque; Acoustic Performance; Acoustic Characteristics; ODEON

Program; DIRAC Room Acoustic System.

1. Introduction

Mosques (known as ‘Masjid’ in Arabic) are important public spaces used by millions of Muslims

around the world for a variety of worship activities. Because of their international ubiquity and

various modes of use, their acoustical properties should be well understood and regularly

optimized. Acoustic performance of worship places in general, and of mosques in particular, has

been a topic of extensive research. A brief review of the pertinent litertaure is presented here to

provide a background of the current study.

El-Khateeb and Ismail [2] performed field measurements and simulation to study speech

transmission index (STI) in the main hall of the and mosque of Sultan Hassan Cairo,

Egypt. Sü and Yilmazer [3] studied the acoustical characteristics of Kocatepe Mosque, in Ankara,

Turkey; they found that the acoustical quality of the mosque was not optimal when it was empty,

but was close to optimal when fully occupied. Ghaffari and Mofidi [4] conducted comparative

analysis of mosques and churches in terms of their acoustic characteristics. Khabiri et al. [5]

presented a method for evaluating acoustic performance in a mosque’s main prayer hall by using

computer simulation. Similar studies were also reported by Inoue et al. [6], Eldien and Al Qahtani

[7], Carvalho and Freitas [8], Al Shimemeri et al. [9], Eldien and Al Qahtani [7], Putra et al.[10],

Gul and Caliskan [11], Din et al. [12], Abdullah and Zulkefli [13], Kassim et al.[14], Elkhateeb

et al.[15], Othman et al. [16], Karaman and Güzel [17], and Suárez et al. [18].

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Abdou [19] performed in-situ measurements in 21 typical cotemporary mosques of different sizes

and architectural features in order to characterize their acoustical quality and to identify the impact

of air conditioning (AC), ceiling fans, and sound reinforcement systems on their acoustics. It was

found that the reverberation time (RT) of these mosques was close to or within optimal only when

they were fully or partly (two-third) occupied; this was attributed to the relation of RT with the

absorption coefficient of the occupants. In another study [19], he focused on the effect of mosque

geometry (form) on the acoustic performance. Though significant effect was not observed,

performance of the mosque with rectangular shape was comparatively better in terms of STI, while

the octagonal shape showed the least performance. Oldham and Elkhateeb [20] studied the

acoustical characteristics of four historical patterns of mosques in Cairo: semi-closed Rewaq, semi-

closed , closed Iwan, and closed simple. Iwan is a rectangular hall with three sides walled and

one side entirely open, while Rewaq is an arcade or portico with at least one side open [21]. The

architectural parameters considered were: room area, volume, shape, form, finishing materials,

-type, and room aspect ratio. It was shown that the semi-closed Iwan pattern had the best

performance while the semi-closed Rewaq pattern showed the worst. In a study on the effect of

prayer hall geometry and finishing materials on the acoustic performance of mosques, Ismail [22]

reported that prayer halls with large hemispherical domes had low surface area –to- volume ratio,

which caused reduction of total sound absorption of the space. Also, the commonly used finishing

materials in the studied mosques were found to be warranting adequate acoustic treatment. Kavraz

[23] assessed the impact of materials on wall surfaces and density of worshippers on the acoustic

performance of mosque’s prayer hall. It was observed that these factors could influence the

performance especially at low frequencies. In a similar study, Hafizah et al. [24] focused on the

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effect of using kenaf fibers and micro perforated panel as sound absorbers, which could effectively

reduce the reverberation time.

Ahmad et al. [25] focused on the acoustic performance of (place where the leader of prayer

stands) in Mosques, by conducting case studies on typical mosques in . Din et al. [26]

studied the effect of Mihrab geometry on the acoustic performance of mosque, by considering

pyramidal and dome roof-styles. It was found that Mihrab geometry had only little influence on

the performance of speech intelligibility. Harun [27] developed speech intelligibility (SI)

prediction models for rooms with reflective domes, which were validated by case-studies

conducted in 32 mosques with domes in Malaysia. Utami [28] studied the acoustical performance

of a typical mosque in with two types (curved and pointed) of hemispherical domes. He

concluded that these domes did not produce significant impact on the speech quality inside the

prayer hall, as the geometrical proportion of the dome was small compared to the larger rectangular

hall. Kassim et al. [29] investigated the effect of angle and height of the dome on the acoustical

parameters, and observed that a pyramidal dome with a steeper angle contributed to poor sound

clarity.

The review of previous studies reveals that the literature on acoustical peformance of mosques

largely dealt with field measurements and computer simulations to identify issues and provide

guidelines for proper acoustic design. Few works focused on the effects of various factors such as

architectural design, size, shape, materials, mihrab-form and roof-geometry. However, a detailed

study on the impact of dome-shape on the acoustic performance of mosque is still lacking. Domes

are often built by consdering the aesthetics and heritages, while the acoustic performnace criteria

are not properly incorporated in the design. Accordingly, the present study examines the impact of

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dome-shape by consdiering a typical mosque inside a university campus in the Kingdom of Saudi

Arabia.

2. Design Features and Functions of Mosque

Mosques have basic common design features as spaces for worship. They typically have a simple

rectangular form, walled enclosure with a roofed prayer-hall. The long side of the rectangle is

always oriented towards the holy mosque in Makkah which is known as ‘’. The place of

prayer leader (Imam) is known as ‘Miharb’ which is usually built as a projection at the center of

the front wall facing Qibla. The pulpit for preaching is known as ‘’ which built on the right

side of Mihrab. The preacher who delivers sermons on Fridays is known as ‘Khatib’. Figure 1

illustrates Mihrab, Mimbar, Imam position, Khatib position, prayer rows, and congregation

(worshippers) performing daily individual or group prayers. The wall wainscots are sometimes

covered with marble tiles or wooden boards or panels tongued and grooved to compose a vertical

pattern. The floor area is mostly carpeted, and the ceilings are finished with painted concrete.

Depending on the climatic conditions, mosques are air-conditioned or provided with fans[19].

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a)

b)

Figure 1: Illustration of basic worship terminology in a mosque: (a) Mihrab, Mimbar,

Imam position, Khatib position and prayer rows, (b) Congregation performing individual

or group prayers [19] .

3. Dome-shapes and its Acoustic Performance

A dome is a hemispherical architectural structure, which symbolizes the Islamic architectural style

for most mosques. Though the importance of domes in worship buildings has been recognized

since ancient times, their acoustic performance has not been given the deserving research attention.

The dome-geometry is one of the most inconvenient forms in acoustics. Due to the concave form

of the domes, the incident sound energy does not go out without reflecting several times in the

dome. Consequently, the reflected sound energy from the dome reaches back to the room with a

time delay, leading to echoes or noise and reduction on STI. The behavior of sound energy in a

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dome in both plan and cross sections is shown in Figure 2. As can be seen, the reflected sound

energy that is increasingly delayed, especially in large domes, is a cause of echoes [22]. The use

of cavity resonators can prevent the reflection of sound energy and reradiate it throughout the

room. Besides getting a diffused field, the sound coming from the dome shortly after the direct

sound creates a divine effect in the atmosphere of worship. In addition to the detrimental effects

of late reflections and echoes, more complicated behavior can be expected due to the coupling of

the dome volume to the rest of the room. Thus, proper understanding of the acoustic behavior of

different types of domes is vital in choosing the appropriate dome-shape for a particular mosque-

design.

Figure 2: Sound propagation in a dome [22].

4. Methodology

4.1 The Mosque and Dome-shapes Description

The mosque under study was a typical mid-size mosque situated inside a university campus in

Saudi Arabia. Figure 3 illustrates the architectural features of the mosque. It has a prayer hall area

of 23 m × 23 m and ceiling height of 4.8 m. The interior surface materials consist of carpet and

marble tiles for the main floor, painted plaster wall, glass with metal frames for windows, and

painted plaster for ceiling. All walls are covered with marble of 1m height. Mihrab wall is covered

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with wood. Figure 4 shows the four typical dome-shapes namely (a) Saucer dome, (b) Drum dome,

(c) Onion dome, and (d) Pointed dome, considered for the present study.

Figure 3: Architectural details of the mosque under study.

Saucer Dome Drum Dome Surface Surface Area Area (m2) (m2) 3.30.05m

11..100m R4.0R7 4.05Rm4.07 25.77 1.11.10 m 60.71 5.5.500 m 5.5.500 m 44..800m R5R.10 5.10m Volume 4.48.80 m Volume (m3) (m3)

9.81 74.40

Onion Dome Pointed Dome Surface Surface Area Area (m2) (m2)

55..1177m 122.17 53.41 R3 .238.28m Volume Volume (m3) (m3) 0.90.911m

5.55.050m

4.48.800m 152.85 49.67

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4.41.155 m

RR6.1 96.20Rm6.19

5.5.500m

4.48.800 m

Figure 4: Types and dimensions of the studied dome-shapes.

4.2 Modeling and Simulation

A 3D Model of the mosque was built using AUTOCAD, and simulations were carried out by

ODEON (version 11) which is a GA (geometrical acoustics)-based software extensively used for

room acoustics simulations. ODEON uses a hybrid calculation method, which combines image

source method and ray-radiosity method for early reflections, and radiosity method for late

reflections [30]. Different materials were assigned for different sections of the mosque with

different sound absorption coefficients, as summarized in Table 1. ODEON considers the

scattering coefficient as the roughness of the material at mid-frequencies (707 Hz). As

recommended in the software’s user manual, the scattering coefficient for general smooth surfaces

and smooth painted concrete must be within 0.02–0.05 and 0.005–0.02 respectively. In our case,

all materials have smooth surfaces, so a common scattering coefficient of 0.02 was assumed. The

number of rays was estimated as recommended by the software, according to the size and number

of surfaces in the mosque geometry. The minimum number of rays was 220K rays (with saucer

dome), while the maximum was 390K rays (with onion dome) which was chosen for all models.

In all models, the maximum reflection order was set to 20K with transition order equal to 8.

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After fixing the calculation parameters, the selected receiver surfaces were divided into grids

assigning 0.96 m2 for each worshiper [19]. The standard acoustical characteristics measured were

Reverberation Time (T30), Early Decay Time (EDT), Clarity (C80), Sound Pressure Level (SPL),

Speech Transmission Index (STI), and Center Time (Ts). These characteristics were measured by

assuming the mosque as empty, which is justifiable as the focus of the current study was to study

the influence of dome-shape only.

Table 1: Sound absorption coefficient in octave bands [31], [32].

Surface Material 125Hz 250 Hz 500 Hz 1kHz 2 kHz 4 kHz

Walls Marble tiles cladding 0.01 0.01 0.01 0.01 0.02 0.02

Walls Painted plaster on brick 0.013 0.015 0.02 0.03 0.04 0.05

Mihrab Wall 8mm wood veneer 0.28 0.22 0.17 0.09 0.1 0.11

Ceiling Plasterboard (12mm, 1/2″) 0.15 0.11 0.04 0.04 0.07 0.08 in suspended ceiling grid)

Dome surface Smooth painted concrete 0.01 0.05 0.06 0.07 0.09 0.08

Floor Carpet on concrete 0.02 0.06 0.14 0.37 0.60 0.65

Corridors Marble 0.01 0.01 0.01 0.01 0.02 0.02

Windows Ordinary glass 0.35 0.25 0.18 0.12 0.07 0.04

The worshippers (hereafter termed as receivers) perform the prayer by listening the loud recitation

of Imam. As presented in Figure 5, there are 82 receiver points that represent the receivers who

are aligned in 9 parallel rows. The receiver points 1-7 make prayer Row 1, and 8-4, 15-24, 25-34,

35-44, 45-54, 55-64, 65-74, and 75-82 make Row 2, Row 3, Row 4, Row 5, Row 6, Row 7, Row

8, and Row 9 respectively. For the measurements, 22 receiver points were selected randomly (2 to

3 points from each row) to cover the whole mosque area.

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Figure 5: Sound source, simulated receiver points, and prayer rows (red circles represent the 22

measurement points).

The background noise levels in the mosque was measured using analyzer type B&K 2250, in two

2 minutes interval, which were used for the simulation (Figure 6). The HVAC (heating, ventilation,

and air-conditioning) system is the major source of background noise. The ear height of the

receivers was taken to be 1.65 m from the floor.

40 35 30 25 20 15 10 5

Banckground Banckground Noise Level (dB) 0 63z 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz 8000 Hz Octave band

Figure 6: Measured background noise levels in octave bands.

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4.3 In-Situ Measurements

For the purpose of validating the simulation results, in-situ measurements were performed on the

study mosque. The experimental setup (Figure 7) consisted of DIRAC room acoustics system,

analyzer type 2250, a B&K power amplifier type 2734, a reference Omni Power Sound Source

Types 4292, and ½ inch B&K microphone type 4134. The B&K Echo Speech Source Type 4720

was used for the speech intelligibility measurements. Measurements were carried out in octave

bands for the frequency range from 125Hz to 8 kHz. The loudspeaker source was positioned at

Imam position (at the center of Mihrab) at 1.65m height. Subsequently, the sound level meter was

moved to each measurement position (receiver points). The DIRAC PC-based program instantly

calculates the speech intelligibility and other room acoustics parameters from the sound level

meter’s microphone signal.

Figure 7: In-situ measurement system.

The acoustical parameters to be assessed (T30, EDT, SPL (A), STI, C80, and Ts), the octave bands

used to calculate multi-octave bands average of acoustic parameters, the recommended ranges, and

the corresponding just noticeable differences (JNDs) are presented in Table 2.

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Table 2. Acoustical parameters and allowable limits [33], [34], and [35].

Parameter Recommended range (for given volume) Just noticeable difference (JND)

T30 (for 500–1000 Hz) From 0.9s to 1.9s 5% (lowest value)

EDT (for 500–1000 Hz) From 0.8s and 2.1s 5% (lowest value)

SPL(A) Minimum variations in SPL < 10 dB 2 dB A

STI Greater than 0.45 0.05

C80 (for 500–2000 Hz) Between +4 and −4 dB for speech 1 dB

Between -1 and +3 for choral (our case)

Ts (for 1000 Hz) From 70 ms and 150 ms for speech 10 ms

From 80ms to 130ms for choral

5. Results and Discussion

5.1 Validation

In-situ measurements were conducted inside the study mosque with Saucer dome (base case) for

the 22 selected receiver points. The comparison between the simulated and measured values of

T30, EDT, SPL(A), STI, C80, and Ts are presented in Figure 8. The average, minimum, and

maximum values, and the corresponding correlation coefficients (R2) of the acoustic parameters

(measured and simulated) are given in Table 3. The JNDs were calculated for all parameters

according to the values presented in Table 2. The simulation results could be calibrated when the

difference between simulation and measurement is less than the JND of each acoustical parameter

[30]; thus, the calibration was realized by comparing the simulated values with the measured ones

in real conditions. Table 4 summarizes the differences between simulated and measured values of

all parameters, and comparison with their JNDs, which shows a good match between the simulated

and measured values.

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Table 3: Minimum, maximum, average, and the correlation coefficients, of simulated and measured values

Parameters T30 (s) EDT (s) SPL (dBA) STI C80 (dB) Ts (ms)

S M S M S M S M S M S M

Min 1.88 1.90 1.42 1.30 48 48 0.39 0.40 -7.4 -7 62 65

Max. 2.00 2.00 2.25 2.30 55 53 0.68 0.70 4.2 4 232 228

Average 1.96 1.97 2.03 2.02 50.0 50.5 0.47 0.48 -3.2 -3.3 153 155

Correlation coefficients

(R2) 0.83 0.75 0.81 0.91 0.99 0.99

a) T30

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b) EDT

c) SPL (A)

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d) STI

e) C80

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f) Ts

Figure 8: Comparison of simulated and measured values for selected receiver points.

Table 4: Differences between the simulated and measured values of the acoustic parameters, and their JNDs (differences higher than one JND are highlighted in bold)

Receivers Diff-T30 (s) Diff-EDT (s) Diff-SPL(A) Diff-STI Diff-C80 (dB) Diff-Ts (ms)

1 0.02 0.05 0 0.05 0.3 3

3 0.04 0.1 1.8 0.02 0 7

5 0.04 0.12 1.7 0.02 0.2 3

8 0 0.2 1.4 0.02 0.1 2

9 0 0.11 0.9 0 0 7

11 0.02 0.11 0.4 0.02 0.2 13

15 0.02 0.07 0 0.04 0.3 7

17 0.02 0.05 0 0 0 3

20 0 0.07 1.3 0.02 0.1 9

28 0 0.07 0.2 0.04 0.2 9

32 0.05 0.03 0.4 0.03 0.1 4

39 0 0.05 0.3 0.06 0.2 5

42 0.05 0.05 0.6 0.01 0.4 1

46 0 0.05 1.3 0.03 0.4 4

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51 0.05 0.02 0.5 0.03 0.1 2

57 0.02 0.07 0.3 0.01 0.1 4

60 0.02 0.02 0.2 0 0 6

63 0 0.1 0.3 0.01 0.2 7

69 0 0.05 0.1 0 0 5

71 0.05 0 0 0 0.3 8

76 0 0.1 0 0 0 9

79 0.04 0.1 0.3 0.01 0 4

JND 0.1s 0.07s 2 dB A 0.05 1 dB 10 ms

5.2 Reverberation Time (T30)

Figure 9 presents the T30 values with different dome-shapes as a function of source-receiver

distance. Previous studies have established that the optimum T30 for mosques ranges from 0.9s to

1.9s (Abdou, 2003a; Eldien and Al Qahtani, 2012; Imam et al., 2009). T30 was calculated as the

average of T30 at 500Hz and 1000Hz. It can be observed that all receiver points for Saucer and

Pointed domes have T30 near to the optimal value, while for the Onion and Drum shapes it is

greater than optimal (between 2.25s and 2.45s); this is due to the higher volume and surface area

of Onion and Drum domes compared to the other domes. Homogenous T30 values are observed

in all points for both Onion and Drum forms, but with Saucer, T30 increases at points near the

dome and decreases at points located at the sides of prayer rows.

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Figure 9: T30 values at all receiver points with different dome-shapes.

Reflection from the dome-surfaces was visualized by ‘Reflector coverage’ which is one of the

ODEON tools. The 5th order reflector coverage of all dome surfaces is presented in Figure 10. We

can observe that sound reflection of the Onion dome surfaces covers the area around the dome and

near to the Mihrab. Therefore, T30 values increase in the first rows. The impact of the Drum dome

on the back area of the mosque is not strong, so T30 values on the back area of the mosque are

lower than the values on the front area. The effect of Saucer dome appears clearly on the back area

of the mosque, where T30 values increase. The Pointed dome surfaces reflect the sound energy

randomly to cover the whole area of the mosque with a slight increase at the left side of the mosque

hall. For this reason, the majority of receiver points have the same T30 value.

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0 5 10 15 20 25Onion 30 35 40 metres Drum 0 Reflector5 coverage:10 5. order reflections15 included20 25 30 35 40 metres Reflector coverage: 5. order reflections included

25 metres

20 metres 20

15 15

10 10

5 5

P1 P1 0 0

Saucer Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted versionPointed - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! 0 5 10 15 20 25 30 0 35 5 40 metres10 15 20 25 30 35 40 metres Reflector coverage: 5. order reflections included Reflector coverage: 5. order reflections included

20 metres 20 metres

15 15

10 10

5 5

P1 P1 0 0

Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted versionFigure - research 10: andOdeon©1985-2011 teaching 5th only! order Licensed reflector to: Dammam University, coverage IMT, Saudi Arabiaof all Restricted domes. version - research and teaching only!

The warmth or the bass ratio (BR) is the relation between T30 in the frequency range 125Hz -

250Hz to the frequency range 500Hz -1000Hz, which is expressed as:

푅푇 125퐻푧 + 푅푇 250퐻푧 퐵푅 = 푅푇 500퐻푧 + 푅푇 1000퐻푧

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For music, BR should be between 1.0 and 1.3, while it should be between 0.9 and 1.0 for speech

(Ballou, 2008). As known, speech is the main activity in mosques. The spiritual context of the

male Imam’s voice proves different than the normal speech. Hence, we can consider it to have BR

closer to the optimal BR value for music. As shown in Figure 11, mosques with saucer and pointed

domes achieve good BR values while mosques with drum and onion domes have low BR values.

1.25

1.2

1.15

1.1

1.05

1 Average (s) Ratio Average Bass 0.95

0.9 Saucer Pointed Drum Onion

Figure 11: Average BR for various domes.

The difference of T30 average values in octave bands between the base case (Saucer dome) and

the other cases are calculated. As evident from Figure 12, with the Drum and Onion domes, T30

increases at medium and high frequencies, and decreases at low frequencies. This explains the

decrease in BR values in these two cases. Adding materials in the space which absorb energy at

high frequencies can increase the warmth. On the other hand, Pointed dome has the same effect as

the Saucer dome where the difference of T30 average values is negligible.

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Saucer - Pointed Saucer - Drum Saucer - Onion 0.5

0.4

0.3

0.2

0.1

0

T30 Average T30Average (s) 63 125 250 500 1000 2000 4000 8000 -0.1

-0.2

-0.3 One Octave Bands (Hz)

Figure 12: Difference of T30 average between the base case and other cases.

The T30 distribution maps of Saucer and Pointed domes for 500 Hz and 1000 Hz are presented in

Figure13. In the base case (Saucer dome), at 500 Hz, the minimum and maximum T30 values are

2.02s and 2.08s respectively, and the corresponding values at 1000 Hz are 1.82s and 1.98s. The

T30 distribution map of Pointed dome shows a great similarity with the Saucer dome. The

maximum T30 value is 2.10s at 500 Hz and 1.98s at 1000 Hz, while the minimum value is 2.04s

at 500 Hz and 1.92s at 1000 Hz. The positive effect of the Saucer shape can be seen at the half left

side of the mosque hall, whereas the positive effect of the Pointed shape appears clearly around

the dome. For the Pointed dome, the maximum T30 values are situated at the left side of the

mosque hall. This is due to the multiple repeating sound reflections between the dome surface and

the Mimbar (located at the left side of Mihrab).

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0 3 5 8 10 13 15 18 20 23 25 28 300 333 355 388 4010 43 13 45 15 4818 50 20 53 23 55 25 58 28 60 30met res 33 35 38 40 43 45 48 50 53 55 58 60 metres

0 3 5 8 10 13 15 18 20 23 25 28 30 33 35 038 5003 40 5Hz43 8 45 10 48 13 50 15 53 18 55 20 58 23 6025metres 28 30 33 35 38 100040 43 Hz45 48 50 53 55 58 60 metres

28 met res 28 metres

T(30) (s) at 1000 Hz >= 1.98 28 metres 28 metres T(3 0 ) (s) at 5 0 0 H z > = 2 .0 8 25 25 T(30) (s) at 500 Hz >= 2.08 T(30) (s) at 1000 Hz >= 1.98 25 25 2 .0 7 1.97 23 23 2.07 1.97 23 23

20 20 20 20

18 18 18 18

1.95 2 .0 5 15 2.05 1.95 15 15 15

13 13 13 13

Saucer 10 10 10 10 2.03 1.93 1.93 2 .0 3 8 8 8 8 0 3 5 8 10 13 15 18 20 23 25 28 30 0 33 3 35 5 38 8 40 10 43 13 45 15 48 18 50 20 53 23 55 25 58 28 60 metres30 33 35 38 40 43 45 48 50 53 55 58 60 metres

5 5 5 P1 5 P1 <= 2.02 <= 1.92 0 3 5 8 10 13 P115 18 20 23 25 28 30 33 35 38 40 43 45 48 50 53 55<= 1.92 58 60 metres 0 3 5 8 10 13 15P1 18 20 23 25 28 30 33 35 38 40 43 45 48 50 53 55 < = 2 .058 2 60 metres 3 3 3 3 0 28 metres 0 28 metres 0 0 28 metres T(30) (s) at 500 Hz >= 2.10 T(30) (s) at 1000 Hz >= 1.98 28 metres Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! 25 Odeon©1985-2011 Licensed25 to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! T(30) (s) at 1000 Hz >= 1.98 Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! T(30) (s) at 500 Hz >= 2.10 25 O d eo n © 1 9 8 5 -2 0 1 1 L icen sed t o : D ammam U n iv ersit y , I M T, Sau d i Arab ia R est rict ed v ersio n - research an d25 t each in g o n ly ! 2.09 1.97 23 23 1.97 23 2.09 23

20 20 20 20

18 18

18 18 2.07 1.95 1.95 15 15 2.07 15 15

13 13 13 13

Pointed 10 10 10 10 2.05 1.93 2.05 1.93 8 8 8 8

5 5 P1 5 5 P1 <= 2.04 <= 1.92 P1 P1 <= 2.04 3 3 <= 1.92 3 3 0 0

0 0 Figure 13: T30 distributionOdeon©1985-2011 Licensed to: Dammam maps University, IMT,for Saudi Arabia Saucer Restricted version -and research and teachingPointed only! domes at 500 Hz and 1000 Hz. Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only!

Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only!

Figure 14 presents the reflection density for both Saucer and Pointed domes at receiver point 16

located at the left side of the mosque hall. We can observe similarity of the early reflection for two

types of domes, while the late reflection produced by the Pointed dome is greater than that

produced by the Saucer dome.

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Figure 14: Reflection density produced by Saucer dome (a) and Pointed dome (b) at receiver

point 16.

The T30 distribution maps for Onion and Drum domes at 500 Hz and 1000 Hz are presented in

Figure 15. In the case of Onion dome, minimum and maximum T30 values at 500 Hz are 2.27s

and 2.30s respectively, while these are 2.38s and 2.41s, at 1000 Hz. The T30 distribution pattern

of Drum dome is almost similar to that of Onion dome, minimum and maximum T30 values 2.20s

and 2.26s respectively at 500 Hz, while these are 2.30s and 2.37s, at 1000 Hz. The negative effect

of Onion shape appears clearly at the back, left , and right areas of the mosque hall, while the Drum

shape caused increase of T30 in the right have area of the mosque hall. The positive effect of both

types can be observed in the front area of the mosque hall and near to Mihrab.

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0 3 5 8 10 13 15 18 20 23 25 28 30 33 0 35 3 38 5 40 8 4310 4513 4815 5018 5320 5523 5825 6028 3063 metres33 35 38 40 43 45 48 50 53 55 58 60 63 metres 0 3 5 8 10 13 15 18 20 23 25 28 30 33 0 35 3 38 5005 40 8 43Hz10 45 13 48 15 50 18 53 20 55 23 58 25 60 28 63 metres30 33 35 38 100040 43 Hz45 48 50 53 55 58 60 63 metres

28 metres 28 metres

28 metres 28 metres T(30) (s) at 500 Hz >= 2.30 T(30) (s) at 1000 Hz >= 2.41

25 25 T(30) (s) at 500 Hz >= 2.30 T(30) (s) at 1000 Hz >= 2.41

25 25 2.30 2.40 23 23 2.30 2.40 23 23

20 20 20 20

18 18 18 18

2.29 2.29 2.39 2.39

15 15 15 15

13 13 13 13

Onion

10 10 10 10 2.28 2.38 2.28 2.38 8 8 0 8 3 5 8 10 13 15 18 20 23 25 28 300 333 8 355 388 4010 4313 4515 4818 5020 5323 5525 5828 6030 6333metres 35 38 40 43 45 48 50 53 55 58 60 63 metres

5 5 0 3 5 8 10 13 15 18 20 23 25 28 30 33 0 35 3 38 P15 40 8 43 10 45 13 48 15 50 18 53 20 55 23 58 25 60 28 63 metres30 33 35 38 P1 40 43 45 48 50 53 55 58 60 63 metres 5 5 <= 2.27 <= 2.38 P1 P1 <= 2.27 <= 2.38 3 3 3 3 0 28 metres 28 metres 0

0 T(30) (s) at 500 Hz >= 2.26 T(30) (s) at 1000 Hz >= 2.37 0 28 metres 28 metres

25 Odeon©1985-2011 Licensed25 to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! T(30) (s) at 500 Hz >= 2.26 T(30) (s) at 1000 Hz >= 2.37

25 25 Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! 2.25 2.36 23 23 2.25 2.36 23 23

20 20 20 20

18 18 18

18 2.23 2.34 2.23 2.34 15 15 15 15

13 13 13 13

Drum

10 10 10 10 2.21 2.31 2.21 2.31 8 8 8 8

5 5 P1 P1 5 5 <= 2.20 <= 2.30 P1 P1 <= 2.20 <= 2.30 3 3 3 3

0 0 0 0 Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only!

Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi ArabiaFigure Restricted version 15: - research T30 and teaching distribution only! maps of Onion and Drum domes for 500 Hz and 1000 Hz.

The coefficient of variation (CV) and standard deviation/mean (SD) of RT values, are calculated

for all receiver points. As shown in Figure 16, CV indicates a relatively high variation in the case

of Saucer and Drum domes, while it can be considered low in the case of Pointed and Onion domes.

This means that Pointed and Onion domes achieve good distribution of RT values.

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0.018 0.016 0.014 0.012 0.01 0.008 0.006 0.004

Coefficient Coefficient variation of RT of 0.002 0 Saucer Drum Onion Pointed

Figure 16: Coefficient of variation of RT values.

5.3 Early Decay Time (EDT)

The initial rate of decay of reverberant sound is more important than the total reverberation

time. A rapid initial decay is interpreted by the human ear as a short reverberation time. The

Early Decay Time (EDT) is defined as 6 times the time interval from 0dB to -10dB on the decay

curve after the source has stopped emitting. If we take into consideration the definitions of EDT

and T30, we will realize that they must have the same value. EDT should not be higher than

±10% of T30 for good acoustics (Beranek, 2008); in the present case, it should be between 0.8s

and 2.1s (see recommended values in Table 2). EDT is calculated as the average at 500Hz and

1000Hz. Figure 17 presents the EDT values obtained with different dome-shapes at all receiver

points. Minimum EDT value could be obtained by Saucer and Pointed domes where the EDT

is 1.2s at the 1st row. This short EDT value keeps the early sound strong and clear. This is due

to the reflection effect of the Mihrab wall. EDT value increases with the distance from the sound

source and the maximum EDT (2.2s) is found in the 8th row. On the other hand, the Drum and

Onion shapes show increase of EDT values in all prayer rows where EDT values are longer

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(1.9s to 2.6s). It is known that short EDT is an important indicator of speech clarity. In this case,

the early reflected sound rays that reach to human ear within the first 50ms integrate with the

direct sound rays. In general, the best EDT values are obtained by the Saucer and Pointed

domes.

Figure 17: EDT average values at receiver points with different dome-shapes.

The difference of EDT average values in octave bands between the base case (saucer dome) and

the other cases are presented in Figure 18. We can note that Drum and onion domes cause increase

of EDT values in the medium and high frequencies and decrease of EDT values in the low

frequencies. Pointed dome has approximately the same EDT values as the Saucer dome where the

difference of T30 average values is negligible for all frequency ranges. For Saucer and Pointed

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domes, the receiver points located at the 1st and the 2nd rows have an optimal value, while for

Drum and Onion domes, the optimal value is obtained only at the 1st row, as shown in Figure 19.

Saucer - Pointed Saucer - Drum Saucer - Onion

0.5

0.4

0.3

0.2

0.1

EDTAverage 0 63 125 250 500 1000 2000 4000 8000 -0.1

-0.2

-0.3 Octave Bands (Hz)

Figure 18: Difference of EDT average between the base case and other cases.

The CV of EDT for all receiver points in all cases are presented in Figure 20, which indicates a

relatively high variation in the case of Saucer and Pointed domes, where both domes have

approximately the same CV value. The low CV values of Drum and Onion domes indicate good

distributions of EDT values. For Saucer and Pointed domes, the receiver points located at the 1st

and the 2nd rows have an optimal value, while for Drum and Onion domes, the optimal value is

obtained only at the 1st row.

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Saucer dome/ 14 points Pointed dome/ 11 points

Drum dome/ 5 points Onion dome/ 5 points

Figure19: Location of receiver points achieved the optimal EDT.

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0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02 Coefficient Coefficient variation of EDTof 0 Saucer Drum Onion Pointed

Figure 20: Coefficient of variation of EDT values

The optimal acoustic performance (short EDT) was obtained in the first and second rows for

Saucer and Pointed domes, and in the first row for Onion and Drum domes. To determine the cause

of variation in EDT, three points (1, 11, and 14) were selected for all the domes and compared at

500Hz and 1000Hz, as presented in Figure 21. The Drum and Onion domes caused EDT to increase

at 500Hz and 1000Hz, which can be explained by the number of reflections per second arrived at

each point. Schroeder (1962) suggested that 1000 echoes per second was sufficient for the sound

to be indistinguishable from diffuse reverberation. In the case of Saucer and Pointed domes, the

maximum EDT values were obtained at point 14 at 500 and 1000 Hz. Thus, point 14 did not

achieve the recommended EDT value.

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2.5 2.4 2.3 2.2

EDT(s) 2.1 2 1.9 Saucer Drum Onion Pointed

Point 1 Point 11 Point 14

a) EDT at 500 Hz.

2.5 2.4 2.3 2.2

EDT(s) 2.1 2 1.9 Saucer Drum Onion Pointed

Point 1 Point 11 Point 14

b) EDT at 1000 Hz.

Figure 21: EDT at points 1, 11, and 14.

Figure 22 demonstrates the reflection density (RD) at the selected points. It is known that RD is

inversely proportional to the room volume (Schroeder, 1962). Owing to the architectural

proportions, the Onion and Drum domes have greater volumes compared to Saucer and Pointed

domes. Furthermore, the shape of Onion and Drum domes causes multi-reflections inside the

dome, thereby delaying the arrival of reflected sound from the dome surfaces to the receiver points,

as shown in Figure 23. For the previous reasons, Onion and Drum domes caused increase of EDT

and T30.

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1050 1000 950 900 850

800 Reflections Reflections per second 750 Saucer Drum Onion Pointed Point 1 940 820 800 950 Point 11 1000 800 850 970 Point 14 940 830 810 900 0 3 5 8 10 13 15 18 20 23 25 28 30 33 35 38 40 43 45 48 50 53 metres

0 Point3 15 8 10 Point13 1115 18 20 2Point3 25 1428 30 33 35 38 40 43 45 48 50 53 metres

30 metres

30 metres 28 Figure 22: Reflection Density at points 1, 11 and 14.

28 25

25 23

20 23

18 20

15 18

13 15

Receiver level Receiver level 10 13 P1 P1

8 10

5 8 (a) (b) 3 5

0 Figure 23: Reflected3 rays by (a) Onion Dome, (b) Drum Dome.

Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only! 0 5.4.Clarity (C80) Odeon©1985-2011 Licensed to: Dammam University, IMT, Saudi Arabia Restricted version - research and teaching only!

The speech clarity parameter C80 is defined as the logarithmic energy ratio between early and late

arriving sounds of the impulse response [38]. In the case of the mosques acoustics, the clarity of

Quran recitation and the ability to hear the recital of the choral music versions of the Holy Quran

is significant. According to Imam et al. [37], the preferred values of C80 for speech are between

+4 and −4 dB, while it is -1 and +3 for choral (our case). The C80 values for 500Hz, 1000Hz and

2000Hz are averaged and presented in Figure 24. The C80 values between the black center lines

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are the preferred values for speech, while those between the red dashed lines are acceptable for

choral music.

Figure 24: C80 average values at receiver points for different dome-shapes as a function of receiver-sound source distance.

The C80 average values obtained by Saucer and Pointed domes range from +6 dB to -9.5 dB, and

it ranges from +4.5 dB to -10 dB for Drum and Onion domes. Table 5 presents the C80 minimum,

maximum, average, and standard deviation values for all types. The maximum positive values can

be obtained by Saucer and Pointed domes, while Onion and Drum domes achieve the minimum

negative values. The negative values of C80 mean reverberant spaces and the positive values

denote small reverberated spaces [39]. Figure 25 shows the relationship between STDEV of C80

and dome volume. We found that Clarity decreases with dome volume. Increasing of dome volume

and surface caused increase of late reflections and therefore decrease of Clarity, where Clarity is

the ratio of early to late sound energy.

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Table 5: Maximum, minimum, and average C80 values obtained by all domes

Saucer Drum Onion Pointed

Maximum 6.7 4.6 4.9 6.6

Minimum -9.9 -10 -10.4 -9.4

Average -1.3 -2.1 -2.0 -1.3

STDEV 3.5 3.3 3.2 3.4

Figure 25: Clarity index as a function of room volume

Figure 26 depicts the CV values of C80 for different domes, where a high variation is shown in

the case of Saucer and Pointed domes, compared to the Drum and Onion domes. Generally, Drum

and Onion domes achieved better distributions of C80 than Saucer and Pointed domes.

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0 Saucer Drum Onion Pointed -0.5

-1

-1.5

-2

-2.5 Coefficient Coefficient variation of C80 of -3

Figure 26: Coefficient of variation of C80 values.

Center time (Ts) is a reference value for spatial impression and clarity. It is the ratio between the

energy components of the arriving sound reflections and the corresponding delay times and the

total energy component [40]. This parameter can be used to describe the balance between clarity

and reverberance. According to Reichardt [41], there is an analytical correlation between C80 and

Ts, as given by:

C80 = 10.83 – 0.95Ts (1)

According to Ballou (2008), the desirable Ts for speech ranges from 60 ms to 80 ms in the octave

bands (500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz). From Equation (1), the recommended Ts at

octave band of 1000 Hz for the preferred C80 (+4dB to -4dB) is between 70 ms and 150 ms, and

from 80ms to 130ms for choral music (-1db to +3dB).

Figure 27 shows the Ts values at 1kHz as a function of source-receiver distance; the majority of

points in the front half of the main hall provide the recommended Ts with all types of domes. As

presented in Table 6, the best results can be obtained by Saucer and Pointed domes, where 30 and

33 receiver points achieved the recommended Ts. In the case of choral music, 11 receiver points

for both Saucer and Pointed domes achieved the recommended Ts. This presents 13.4% of the total

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number of receiver points, which can be considered quite low. Generally, the majority of receiver

points in all types did not achieve the recommended Ts for choral music.

Figure 27: Ts values at receiver points for different dome-shapes as a function of receiver-sound source distance. . Table 6: Number and percentage of receiver points achieved the recommended Ts

Saucer Drum Pointed Onion

Number of points 30 14 33 13 SPEECH Percentage (%) 36.58 17.07 40.24 15.85

Number of points. 11 8 11 9 CHORAL Percentage (%) 13.41 9.75 13.41 10.97

Figure 28 (a-d) shows the C80 values as a function of Ts at 1kHz. We can note that Ts required to

obtain the preferred C80 ranges from 85ms to 190ms for Saucer and Pointed domes, and from

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90ms to 200ms for Onion and Drum domes. With regard to choral music, the Ts values for the

preferred C80 are between 100ms and 150ms for Saucer and Pointed domes, while they range from

110ms to 160ms for Saucer and Pointed domes. Lower Ts and higher C80 correspond to a clear

sound, while higher Ts and lower C80 indicate dominance of the late and reverberant energy. In

general, majority of the receiver points at the front half of the mosque’s main hall provide

acceptable C80 and Ts values.

Figure 28a: C80 versus Ts for Saucer dome.

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Figure 28b: C80 versus Ts for Pointed dome.

Figure 28c: C80 versus Ts for Drum dome.

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Figure 28d: C80 versus Ts for Onion dome.

5.6 Sound Pressure Level

The A-weighted sound pressure level values with reference to the distance of receivers from

sound source are presented in Figure 29. It is found that A-weighted SPL decreases with the

distance from the sound source. The Onion and drum domes have approximately the same A-

weighted SPL values, while the Saucer and Pointed domes have similar A-weighted SPL values.

The receiver points close to the sound source and receiver pointes at the back area of the mosque

have approximately the same A-weighted SPL values for all dome-shapes. The impact of dome-

shapes appears clearly at the middle area of the mosque, where there is more than 2dB difference

of A-weighted SPL between Onion and Drum domes, and the other types.

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Figure 29: SPL-A values in relation with the distance of receivers from sound source.

Table 7: SPL-A, Max, Min, and Average values obtained by all domes

Saucer Drum Onion Pointed

Max 56.3 57.1 57.1 56.2

Min 47.8 48.2 48.3 47.6

Average 50.3 51.2 51.1 50.2

The values of SPL-A for the Saucer dome range from 56.3 dB (A) to 47.8 dB (A), and from

56.2 dB (A) to 47.6 dB (A) for the Pointed dome. The Drum and Onion domes share the

maximum value of 57.7 dB (A) (Table 7). Figure 30 demonstrates CV of SPL-A, which

indicates a low variation in the case of Saucer and Pointed domes, and a high variation in the

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case of Drum and Onion domes. In general, Saucer and Pointed domes achieve a good

distribution of SPL-A.

0.042 A

- 0.041

0.04

0.039

0.038

0.037 Coefficient SPLvariation of of Coefficient

0.036 Saucer Drum Onion Pointed

Figure 30: Coefficient of variation of SPL-A values.

Figure 31: Lines, A, B, and C

Based on the assumed architecture, only three vertical lines passing through the dome (lines A,

B, and C in Figure 31) were selected to study the extent of variation of SPL when the receiver

point moves away from the sound source. Figures 32, 33, and 34 present the results of A-

weighted SPL on receivers situated on the lines A, B, and C respectively. In general, there is a

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steady decrease in A-weighted SPL with increase of distance from the sound source. In the case

of Onion and Drum domes, the A-weighted SPL decreases by 2.16 dB, 3dB, and 2.1dB along

the lines A, B, and C respectively, for every doubling of distance (dd). However, the respective

values for Saucer and Pointed domes are 1.53dB/dd, 2.5 dB/dd, and 1.7 dB/dd. This indicates

that Onion and Drum domes cause a greater increase of sound attenuation than Saucer and

Pointed domes.

Figure 32: A-weighted SPL values at points situated on line A as a function of distance from the

sound source.

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Figure 33: A-weighted SPL values at points situated on line B as a function of distance from the

sound source.

Figure 34: A-weighted SPL values at points situated on line C as a function of distance from the

sound source.

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5.7 Speech Transmission Index (STI)

STI is a measure of speech transmission quality, which indicates the degree to which a

transmission channel degrades speech intelligibility. It is measured on a 0 to 1 scale; ST1 =1

indicates that when speech is transferred through a channel, it will remain perfectly intelligible

[40]. The closer the STI value approaches zero, the more the information is lost. STI for all

domes as a function of the distance from the source is presented in Figure 35. As shown in

Figure 36, the best values are found at locations at the 1st row and near to sound source. With

regard to the impact of dome-shape on STI, Saucer and Pointed domes show better performance

compared to the other domes, since both of them function exactly in the same manner and

achieve the level above 0.45 for 50 points with only 42 points for the other two types.

Figure 35: STI values in relation with the distance of receivers from sound source.

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Saucer Pointed 0.8 0.8

0.75 0.75

0.7 0.7

D D

O O

O O 0.65 G 0.65 G

0.6 0.6

I I

T 0.55 T 0.55

S S

R R

I I

A A 0.5 F 0.5 F

0.45 0.45

0.4 0.4

R R

O O

O O

0.35 P 0.35 P

0.3 0.3 4 5 2 12 9 1 7 8 18 22 23 29 31 32 24 40 33 26 42 34 43 49 51 52 44 53 60 61 54 45 63 70 71 64 72 73 79 74 77 81 82 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 Receiver Points Receiver Points

Poor Fair Good Poor Fair Good

32 points 42 points 8 points 32 points 42 points 8 points

Onion Drum 0.8 0.8

0.75 0.75

0.7 0.7

D D

O O

O O 0.65 G 0.65 G

0.6 0.6

I I

T 0.55 T 0.55

S S

R R

I I

A A 0.5 F 0.5 F

0.45 0.45

0.4 0.4

R R

O O

O O

0.35 P 0.35 P

0.3 0.3 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 Receiver Points Receiver Points

Poor Fair Good Poor Fair Good

37 points 40 points 5 points 40 points 37 points 5 points

Figure 36: STI values analysis for all domes.

6. Conclusion

This is the first study on the impact of dome-shape on the acoustic performance of mosques. A

real mosque located in the Eastern Province of Saudi Arabia has been chosen for the simulation

and in-situ measurements. The simulations were performed using ODEON (version 11s) for

four typical dome-shapes, namely Saucer, Drum, Onion, and Pointed. The acoustic parameters

studied were Reverberation Time (T30), Early Decay Time (EDT), Clarity (C80), Center time

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(Ts), Sound Pressure Level (SPL), and Speech Transmission Index (STI). The acoustic

characteristics were measured by considering Imam position as the sound source. The

simulation models were calibrated on the basis of the best match between the simulated and

measured parameter values. The majority of simulated and measured results were found to be

within the acceptable limits of the Just Noticeable Differences (JNDs). The main findings are

summarized as follows:

- Saucer and Pointed domes achieved optimal and homogenous T30 values, while the

other domes yielded T30 values greater than the optimal.

- Saucer and Pointed domes achieved better BR values compared to the other domes.

- Saucer and Pointed domes achieved short EDT values and kept the early sound strong

and clear.

- Saucer and Pointed domes caused C80 values to increase positively (creating large

reverberated spaces), while Onion and Drum domes caused C80 to increase negatively

(creating small reverberated spaces).

- The best choral and speech Ts were obtained by Saucer and Pointed domes.

- For all domes, the majority of points located at the front half of the mosque’s main hall

provided acceptable C80 and Ts.

- For A-weighted SPL, the impact of all dome-shape could be found at the middle area of

the mosque.

- Regarding STI, Saucer and Pointed domes achieved better performance compared to the

other types.

In general, the results indicate that the optimum acoustic performance could be achieved by

Saucer and Pointed domes as they meet the recommended values. The coefficient of variation

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was used for comparing the variations between the results and to study their distributions; the

Drum and Onion domes achieve better distributions of all the acoustic parameters.

It could thus be deduced that domes can have a direct positive or negative impact on the acoustic

performance of mosques, which would vary according to the size and architectural features of

the mosque. Therefore, the impact of dome-shape on the acoustical performance should be

studied at the early design stage of a mosque.

The present study has done by considering imam position as the sound source, and the findings

might be different if the Khatib position would be the sound source. Therefore, considering the

Khatib position as the sound source is important if the mosque’s function includes the

congregational Friday prayer, which is being considered in the authors future work.

References

[1] N. Davies, Architect’s Illustrated Pocket Dictionary. 2012.

[2] A. A. El-Khateeb and M. R. Ismail, “Sounds From the Past: The Acoustics of SULTAN

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