Impact of Mihrab Geometry on The Acoustics of Mosque Hany Hossam Eldien 1 Department of Building Engineering, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia Umaru Mohammed Bongwirnso 2 Department of Building Engineering, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia Emad Hammad 3 Department of Interior Architecture, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia

ABSTRACT Mihrab is a niche in the wall of a mosque that indicates the qibla, the direction of the Kaaba in Mecca towards which Muslims should face when praying. The wall in which a mihrab appears is thus the "qibla wall”. Mihrab geometry has an impact on daily prayer recitation and others. This paper investigates the impact of new type of the Mihrab geometry on the acoustics of the mosque. Flat wall and 7 types of mihrab were modeled. Polar response measurements were carried out using 1:10 scale model. Sound Transmission Index had been measured. Measurements had been realized using 1:10 omni-directional sound source and Dirac room acoustics software. It is found that, the flat wall and Mihrab with trapezium shape can generate a uniform polar response over the frequency range we are interested in (250-4000 Hz). 1. INTRODUCTION

1.1 General Background The mosque as an important building type of Muslim architecture has evolved to meet Islamic needs. Different varieties of worship activities happen within these multifunctional public spaces; these different uses have different acoustical requirements. Masjid is a place for prostration. They are structures available in every Muslim community around the world. There are characterized by size and location depending on the public. They are classified as large masjid, major landmark building and focal point for communities likewise small masjid for local neighborhoods. Even though their uses are undoubtedly varied, they have several dependable characteristics. The prayer niche (or mihrab in Arabic) is the focal point in the interior of a mosque, located in the qibla wall that faces Mecca, the holy city of Islam [1]. Topaktas et al. have studied most acoustics in what can be divided into three main tracks viz; track on focuses on academic works such as, analysis of existing mosques cases, comparisons of Mosque to another Mosque, or comparisons of Mosques to churches or chapels around the world. The second track tackles acoustical renovation and modifications of mosque from

1 hehassam@iau.edu.sa 2 mbumaru@iau.edu.sa 3 ehammad@iau.edu.sa

20-24 august

a material and geometric and lastly the third track with deals on developing acoustical frameworks and guidelines for virtual and real mosque [2].

1.2 Acoustics studies on existing Mosques. A group of research indicates studies on the assessment of single Mosque or church cases, likewise comparisons between Mosques and comparisons of Mosques to churches or chapels. António and Carina [3] studied the acoustic performance of central Mosque of Lisbon, Portugal. In which, Reverberation Time (RT), Rapid Speech Transmission Index (RSTI) and Background Noise (BN) were measure for both unoccupied situation in male and female prayer halls. A comparison was done for similar mosque volume and other religious building such as Catholic Church; the RT was within 500 – 1 KHz relatively high from the recommended value. El-khateeb and Ismail [4] on the other hand explored the speech intelligibility and RT in Sultan Hassan Mosque and Madrasa situated in Cairo, Egypt, by field measurements and ODEON simulation for both occupied and unoccupied cases. It was found that Sultan Hassan Mosque and Madrasa had high RT and echoes at some examined points; despite not having impact worshippers understanding of Imam either in Friday Speech or Daily prayers. In a similar study, Zühre and Yilmazer [5] investigated the acoustical characteristics of Kocatepe mosque in Ankara, Turkey, and compared them with Masjid in the ancient Othman period. Kocatepe had a long RT in low frequencies due to central dome which was the aim of the study. A simulation by ODEON 6.05version were done on parameters such as RT, early decay time (EDT), clarity (C80), sound definition (D50), lateral fraction (LF), STI and strength (G). They tested three scenarios: the empty Mosque, prayer mode when Mosque was one third full (1/3), and fully occupied, for daily and Friday speech. The acoustic performance of Kocatepe mosque was below average when empty but was acceptable when entirely occupied. Similarities and differences base on architectural and acoustical features were investigated considering, RT, C50/C80 and STI/ RSTI for unoccupied spaces by António and Cândido [6]. The architectural features considered, volume, length, area, height, and width. From measurements on Churches (41 buildings in Portugal) and Mosques (21 buildings in Saudi Arabia), they concluded that Mosques in general had an overall better acoustic performance due to floor surface absorption value António and José [8] investigated the acoustics of Mekor Haim Synagogue (Jewish worship place), Portugal. The aim of this study was to compare the acoustic behavior of the Synagogue with Catholic churches in Portugal and Mosques in Saudi Arabia with comparable volume. It was suggested through findings that reducing RT only at dome could enhance the Synagogue acoustics. Also, David and Paulo [7] evaluated the acoustical performance (of a contemporary church in Curitiba, Brazil, to study its compliance with NBR 12179 Brazilian National Standard, ISO 3382-1 international standard and IEC 60268-16 standard. They measured RT and D50 in accordance with ISO 3382 and ISO 3382-1, and calculated STI by ODEON software. It was found that the overall performance of the church exceeded the recommended values of some standards and was satisfactory for some parameters in a specific standard. A similar result was found by Zerhan and Sevda [8] in which acoustical parameters were compared between modern and ancient mosques.

1.3 Acoustic studies on geometry and renovations Limited studies solely applied electronic sound reinforcement systems (SRS) without considering the interior design, nevertheless some were considered as Abdou [9] made a wide analysis of the most common Mosque floor plan geometries to measure the effect of the floor plan geometry on acoustic performance, particularly on the spatial distribution patterns of speech intelligibility without SRS. A simulation has been done of sound fields of five common forms of Muslims worship activities and level of occupancy. It was concluded that the square floor plan was the best in terms of acoustics performance. Similarly focused on Mihrab design and its basic acoustical characteristics of traditional vernacular Mosques in Malaysia aiming at reviewing the acoustic performance of the investigated Mosques, and also to evaluate the acoustic performance of Mihrabs. Thirty-seven (37) old Mosques built within the period 1728 to 1830 in Malaysia; all these Mosques had either square or rectangular floor plan geometry. The Mihrabs of the investigated Mosques had circular niche with flat ceiling to rectangular shape with slanting ceiling and semi-circular concaved niched forms. They utilized a PC-

based acoustics measuring system and analyzer, and data from previous five case studies were analyzed and compared. They concluded that Mosque Mihrabs offered a good feature to confirm the trend of reasonable acoustical performance with a maximum variance of T4.0dB [10]. Utami [11] explored studies on domes coupled to rooms in Mosques to identify the impact of centralized ceiling domes on acoustic performance of Mosque buildings. By using a computer model, it was easy to compare the outcomes derived from analytical, numerical, and experimental (scale modeling) methods. Moreover, statistical techniques such as ANOVA and t-tests were utilized to compare the experimental results. The conclusion was based on comparisons and on realization listening tests in order to discover Mosque components that produced the major acoustics impact. As a recommendation, the findings could be used as a guide for Mosque acoustical performance with domed ceiling. Throughout the history in Othman period Kayili [12] examined the applied acoustics systems; especially the elaborated domes and cavity resonator technology made of bronze as well. It was found that a variety of plaster types on internal surfaces of the investigated Mosque (Selimiye Mosque in Istanbul, Turkey). A study about the influence of SRS on acoustic performance in churches analyzed the sound field and its influence on speech intelligibility and clarity of music and recitation. The acoustical parameters such as RT, EDT, D50, C80 and STI were measured with the impulse response technique and compared the outcome with and without SRS. It was shown that SRS improved D50 and C80 for sound receivers. Also, for EDT the reverberance sensation decreased by distance reduction between sound receiver and source. The study showed that, SRS could provide slight enhancement in speech and music/recitation perception; however, it did not solve the issue originated by poor acoustic design [13]. Likewise, a study aiming at developing and optimizing control algorithms for Digital Signal Processing (DSP) was reported on acoustics in worship spaces particularly Mosques containing existing or newer computer-supported SRS. The required radiation properties were reached by use of controlled electro-acoustic devices and computer-based system [14]. Taking account to floor plan geometry, Eldien and Al Qahtani [15] studied the most common two geometries of Mosques, which are rectangular and square. They excluded the dome, worshippers, and sound reinforcement system, and used the same finishing materials for both shapes for proper and fair simulation. They measured Reverberation time (RT), early decay time (EDT) and Sound Transmission Index (STI). This study found that the square floor plan has better overall sound qualities.

1.4 Acoustical parameters and framework studies Several studies on particular architectural parameters/features that affect the acoustics of the Mosque /worship spaces’ typology and/or specifying acoustical parameter limits specifically to be applied for Mosque typology, are included. Abdou [16] studied the acoustic characteristics of existing Saudi Arabian Mosques, by conducting field measurements (for parameters such as RT and C50) in twenty- one (21) typical Mosques which had diverse sizes and architectural features. The aim was to list down or specify their acoustical performance and to clarify air cooling system, ceiling fans, and sound systems’ acoustic effect. BN was measured with and without air conditioning system operation, while STI was evaluated with and without SRS. It was deduced that the acoustical qualities of the investigated Mosques deviated from optimum conditions when it was empty, but the acoustic performance improved in the occupied condition. Similar study on measuring STI with and without SRS was also reported by Cunha [14] for a church . Acoustical recommendations for the construction and renovation of churches and chapels were provided by the Diocese of Columbus [17], in which it clarifies the most important factors accounting for acoustical design viz :

• Basic requirements for good acoustics in churches • Elements of good natural acoustics for worship • Physical provisions for sound sources sound isolation

• Mechanical system noise control • Sound reinforcement systems acoustics and the design/building process • An acoustics checklist for a typical church building process

Also, guidelines were suggested for an appropriate natural acoustics in the architectural and acoustical design of churches and chapels, to maintain RT of at least 2 to 3s and to minimize the amount of sound absorbing materials. In all cases, sound absorbing materials should not be situated nearby the important sources of sound: the assembly, the music ministry, and the presiders and readers. Since all of these sound sources are at floor level, floors cannot be carpeted in churches and pews cannot be covered with upholstery or cushions. Additional suggestions included providing sufficient room volume to allow the natural development and support of sound. A volume of 300-400 cubic feet per seat was recommended for churches with seating capacities up to about 800 seats. Larger churches might require greater volume, but smaller churches should not fall substantially below this range. In providing sufficient room volume for acoustics, height is a more important factor than floor area. It was also suggested to provide properly oriented, hard-surfaced materials around sound sources. All surfaces (including floors, walls, and ceilings) near and around presiders, cantors, readers, musicians, and the assembly must have hard surfaces. The study concluded that the acoustics effort includes the four essential facets of church acoustics: (1) Natural/Architectural Acoustics; (2) Sound Isolation; (3) Mechanical System Noise and Vibration Control; (4) Sound Reinforcement System Design and Specification. Nevertheless, acoustic checkpoints were provided for acoustic consultants: • Pre-Design and Programming Phases • Schematic Design Phase • Design Development Phase • Construction Documents Phase • Construction Phase • Final Construction Evaluation Each step of the above checklist has its own requirement that helps any designer to generally manage the acoustic requirements from project designing phase. Besides, the study gave general instructions that could be used for any building without parametric specification or limitations. Francesco et al. [18] in a similar study, provided guidelines for acoustical measurements in churches, with the motive of preserving the architectural features of this category of cultural heritage buildings. A team of three Italian universities was formed to provide technical and operative supports to perform measurements inside different churches. They collected detailed data of acoustical features of most important cultural heritages in order to improve the knowledge of sound propagation, preserve the architectural aspects in case of renovation and to determine best approaches to improve the acoustic performance in existing buildings. A set of guidelines was proposed to simplify and normalize the choice of source and receiver locations and to suggest suitable hardware for acoustic measurement in churches. Ismail [19] highlighted that designer do not pay enough attention to the acoustic performance in prayer halls due to projects’ time limitation, insufficient basic guidelines for better acoustic performance during the early design stage. He investigated the acoustical performance of contemporary mosques by using computer model based on ray tracing theory. He considered three most common mosque design topologies, which had different size, shape, and internal surface materials. Diverse acoustical treatments were studied to the geometric nature. The outcome of the work provided design recommendations and guidelines that could help architects in conceptual design. Moreover, in a case study work by Zuhre [2] in Dogramacızade Ali Pasa Mosque (Ankara, Turkey) which focused on the impact of design decisions on acoustical comfort parameters. The selected Mosque had unique design that was intensively studied at all design phases. Simulations were done by ODEON v10.13, and results (RT C50, C80, STI and Sound Pressure Level (SPL) were validated by site measurement in the studied space. Despite the various research done on mosques, there’s still a potential for more works regarding scale models. Exploration of various existing mihrab shape and materials enclosure have been studied regarding the acoustic performance with some recommendations derived. However, this work seeks to introduce new Mihrab shape and to test its acoustic performance via scale model with other available Mihrab shapes. There has been a significant development of the Islamic architecture throughout Islamic empire expansion, the massive Islamic land from Eastern

Asia toward Africa and some parts of Europe, has influenced mosque component architecture such as Mihrab, Minarat, and Quba [20]. Table 1: Evolution of Mihrab shape [21].

2. METHODOLOGY

2.1. Geometric parameters A 1:10 scale model of a mosque with 4.00m height, 12.00m width and 12.00m length was carried out. The mosque was simulated by half-inch thick plywood with varnished surfaces, which is acoustically hard enough to simulate the concrete blocks. All the surfaces in the model are initially defined as quasi-specular surfaces with absorption coefficient α = 0.07 at 1 kHz). The sound absorption is presented in Table 2. Table 2: Sound absorption c oefficient in octave bands [22].

Frequency 125 Hz 250 Hz 500 Hz 1 kHz 2kHz 4 kHz Painted concrete block 0.1 0.05 0.06 0.07 0.09 0.08 Varnished wood 0.15 0.1 0 0.1 0 0.07 0.06 0.07 Flat wall and 7 types of Mihrab were modelled. Figure 1 presents the geometric configuration for all proposed types.

Flat Wall Mihrab Case 1: Rectangular Mihrab Case 2: Circular Mihrab

Case 3: Inverted Circular

Case 4: Trapezium Mihrab Case 5: Expanded Trapezium

Mihrab

Mihrab

Case 6: Semi Hexagon

Case 7: Triangular Mihrab

Mihrab

Figure 1: Mihrabs geometric configurations.

2.1. Experimental measurements The proposed mihrab forms were modeled and the experimental measurements were carried out using DIRAC PC software. The mihrabs performance can be determined through its spatial distribution, which can be characterized by measuring the polar responses in one-third octaves. The single plane method was adopted. The measuring system of this method comprises a source and microphone located on radial positions in front of the surface to record the sound pressure impulse response (see Figure 2). The impulse response was analyzed by DIRAC software to measure the acoustic parameters.

Figure 2: Sound source and microphone positions

1/10 scale model of an omni-directional source, developed by LCPC [23] was used. It was realized by a cluster of 12 loudspeakers, SRH292HX (3/4" pure silk dome tweeter), in a dodecahedral configuration that radiates sound evenly with a spherical distribution. All twelve speakers were connected in a series parallel network to ensure both in-phase operation and an impedance that matches the power amplifier and filtered to obtain a frequency response from 2 KHz to 120 KHz. Sound source was connected to Brüel & Kjær amplifier (Type 2734) Figure 3 illustrates the dimensions of the used sound source. The sound source situated in front of the mihrab and at 1.65m height.

aes § A

Figure 3: Configuration of the 1:10 sound source. Directivity measurement was carried out using B&K DIRAC system in Imam Abdulrahman Bin Faisal University acoustic lab. 1/4" free field microphone type 4939, with a Frequency Range up to 100 kHz (±2 dB) and a sensitivity 4 mV/Pa, connected to a 1/4" preamplifier type 2670, was used. B&K CCLD Signal Conditioners Type 1704-A was used to connect the microphone with the audio device. The microphone was located at 19 points at equal intervals in a half-circle of 1.20m, 2.40m, 3.60m, and 4.80m radius. The receiver was moved by 10° on each occasion, starting from the angle

4) Ze gic) a

that equals 0° degrees to the angle 180°. Both of sound source and microphone were connected to Terratec DMX 6Fire USB device. This USB audio device supports a 192 kHz sample rate (and a corresponding bandwidth), which is a requirement for scale model measurements. 3. RESULT AND DISCUSSION

In order to investigate the efficiency of the proposed mihrab forms, the polar response was measured and compared with the polar response of the flat panel. After that, STI was used to compare the acoustic behavior of all proposed forms. By examining the polar response, the spatial dispersion in all directions in one-third octave bands had been studied. The ideal Mihrab form should distribute sound energy evenly in all directions: this means that the perfect polar response should look like a semicircle. Figure 4 shows the polar response for all Mihrab forms at the first row (1.20m from the source). The different lines indicate the sound level polar distribution varying with the receiver angle. Every line is characterized by a form. It can be found that at low frequencies the polar response obtained by flat wall and cases 4, 5, and 7 are better than the other cases. It can be found that at low frequencies the high reflection at 250 Hz is obvious, especially when using the flat panel. The sound energy then started to distribute in a more even way at the usable frequency range (2000–4000 Hz), and it tends to be more like a semicircle. Inverted Circular Mihrab causes decreasing of sound energy in front of the sound source. Generally, flat wall, trapezium, expended trapezium, and triangle forms achieve uniform sound polar distribution.

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Figure 4: 1 st Row measured polar response at 250Hz, 500Hz, 1000Hz, 2000Hz, and 4000Hz.

Figure 5: 1 st Row measured STI.

Figure 5 presents the Sound Transmission Index (STI) for all cases. It is noted that cases 4, 5, and 7 achieve a good distribution of STI values where the difference between the higher and lower values is negligible. The worst STI distribution was obtained by Case 3: Inverted Circular Mihrab. The polar response for all Mihrab forms at the second row (2.40m from the source) is demonstrated by Figure 6. As the 1 st row the best results obtained by the flat wall, Case 4, Case 5, and Case 7. The polar response obtained by the flat wall could be considered a semicircle at proposed frequencies. As the previous results, Inverted Circular Mihrab caused increasing of sound energy at the two sides of the mosque while it reduced the sound energy at the points located in front of the sound source. This is due to the inverted form of the circle.

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Figure 6: 2 nd Row measured polar response distribution at 250Hz, 500Hz, 1000Hz, 2000Hz, and

4000Hz.

Figure 7 shows the Sound Transmission Index (STI) at the 2 nd row and for all cases. We can observe a good distribution of STI values in flat wall and cases 4, 5, and 7. Rectangular and Semi- Hexagon forms achieved the worst distribution of STI values.

Figure 7: 2 nd Row measured STI.

The polar response for obtained at the 3 rd row (3.60m from the source) is presented in Figure 8. We can note a good performance for the flat wall at all proposed frequencies. Cases 1 and 7 achieved a

uniform polar response at the higher frequencies. Case 5 (Expanded Trapezium Mihrab) causes increasing of sound energy at the center area in front of the sound source. This is due to the sound reflection from its both sides. Contrary to the previous case and due to its form, the Inverted Circular Mihrab caused increasing of sound energy at the two sides of the mosque and reduced the sound energy at the points located in the center area.

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

Figure 8: 3 rd Row measured polar response distribution at 250Hz, 500Hz, 1000Hz, 2000Hz, and

4000Hz.

The measured Sound Transmission Index (STI) for the points located in the 3rd row is shown in Figure 9. It is noted the best distribution of STI could be obtained by the flat wall and cases 4, 7. It is found that the worst distribution of STI values were obtained by the Inverted Circle, Semi-Hexagon and Expanded Trapezium Mihrab.

Figure 9: 3 rd Row measured STI.

Figure 10 demonstrates the polar response obtained at the 4 th row (4.80m from the source). For Case 7 (Triangular Mihrab), we noted that the increasing the distance from the source the lower the distribution of sound energy. Due to its geometry, Triangular Mihrab caused increasing of the sound energy in both sides of the mosque. As the results obtained in the previous rows, The polar response obtained by Flat wall and Trapezium Mihrab is uniform. The 4 th row Sound Transmission Index (STI) is presented in Figure 11. Case 7 (Triangular Mihrab) achieve the higher STI values while Case 5 (Expended Trapezium) achieve the lower STI values. The best distribution of STI values can be obtained by the Flat wall and the Trapezium Mihrab.

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Figure 10: 4 th Row measured polar response distribution at 250Hz, 500Hz, 1000Hz, 2000Hz, and

4000Hz.

Figure 11: 4 th Row measured STI.

4. CONCLUSIONS

According to the function of the architecture of mosques and its acoustic requirements, Mihrab is one of the main elements which can affect the acoustical environment. Flat wall mihrab and 7 types of mihrab forms were tested. The polar response and the Speech Transmission Index were measured. Polar response results were generally varying. During design processes, architects don’t take into consideration the acoustical impact of Mihrab form. Majority of mosques is designed with Circular form Mihrab. According to this study, the Circular Mihrab didn’t achieve neither a uniform polar response nor a good distribution of STI values. For both polar response and STI, the best results were obtained by the Flat Wall and the Trapezium shape. In order to improve the mosques acoustical environment, further studies are necessary to test the impact of Mihrab shapes on the acoustical parameters as EDT, RT, ...etc.

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