The worshippers’ different postures and their orientation in relation to the Imam in the two religious modes, ͑ a ͒ sections showing congregations listening to the Friday speech ͑ i.e., the preaching mode ͒ and performing Daily individual or group prayer ͑ i.e., the prayer-performing mode ͒ , and ͑ b ͒ a top-view plan showing the source–receiver path ͑ i.e., Imam worshippers ͒ in group prayer performing. 

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... the first mosque built in Al-Madinah Al- Monawarah city, Saudi Arabia formed the model for subsequent mosques throughout the Islamic world 13 in its combination of basic elements. It was a simple rectangular, walled enclosure with a roofed prayer hall. The long side of the rectangle is oriented toward the direction of the holy mosque in Makkah city. This wall is usually described as the qibla wall. The wall contains a recess in its center in the form of a wall niche called the mihrab . This wall also includes the minbar which is commonly an elevated floor, to the right of the mihrab , from which the Imam preaches or delivers the Friday sermon, the khutba . These basic elements are the essentials of mosque design in Saudi Arabia, as they are elsewhere in the Islamic world. Figure 1 illustrates the plan and isometric of a simple, typical mosque design. The basic design elements are emphasized. Since the construction of the first mosque, the functions of every mosque have remained unchanged. However, the mosque architectural form, space, construction system, and building materials have evolved and developed to a significant and variable extent in different parts of the Islamic world, influenced by many factors men- tioned elsewhere. 13,14 The mosque design is mainly influenced by worship considerations. Worship in a mosque consists of two major modes. The first mode, namely the prayer mode , involves performing prayers either individually or in a group, as reli- giously prescribed. Group prayer must be performed with worshippers standing, bowing, prostrating, or sitting behind the Imam , on the same floor level, aligned in rows parallel to the qibla wall with distances around 1.2 m apart. The second mode is the preaching mode , where worshippers are directly seated on the floor in random rows listening to the Imam preaching or delivering the khutba while standing on the elevated minbar floor. The minbar floor height varies from one mosque to the other but usually is in the range of one to three meters above the mosque floor. Figure 2 shows the worshippers’ different postures and their orientation in relation to the Imam while performing the two different religious activities in the mosque. The congregational capacity of the mosque is usually determined by the floor area divided by the area required for a worshipper to perform the prayer, i.e., approximately 0.80 ϫ 1.2 ϭ 0.96 m 2 . While, in general, traditional mosques can be classified according to their architectural form and configuration, contemporary mosques may be broadly classified according to their size and location in relation to the community. 14,15 Large mosques are located in large cities as public landmarks. They are usually built by the government expressing the state’s commitment to Islam. They are generally grand in size and of large congregational capacity. Community mosques i.e., Jamma mosques, where Friday prayer, pre- ceded by Friday speech, can be performed ͒ are distributed throughout urban and rural communities and may house additional functions ͑ e.g., a library, meeting rooms, clinic, etc. ͒ , in addition to the prime function of a space for performing prayers. They are usually utilized for both daily prayers as well as the Friday prayer and occasionally are supplemented with a separate annex on the same floor level or in a mezza- nine floor for female worshippers. Small local mosques are located in small neighborhoods, and are of modest dimensions and congregational capacity. The planning and design guidelines for the above three types of mosque are available in Ref. 15. In Saudi Arabia, many prototypes of mosque design exist. 16 Mosques are built in various sizes ranging from small and medium to large types. They are usually typical in lay- out, shape, construction system, and building material, but with different types of air conditioning and electroacoustic sound systems. From a field survey of 90 mosques, it was observed from site visits, design drawings, and ‘‘as built’’ sketches that mosques are fairly similar with respect to their construction systems. They are commonly constructed of re- inforced concrete skeletal structures with flat roofs. The flat roof is commonly supported on columns that are arranged on a regular grid ͑ i.e., structural unit ͒ . A dome is sometimes constructed spanning the central part of the roof to eliminate intermediate columns. The shape represented by the aspect ratio ͑ i.e., the mosque length over width ͒ , and the floor area of each mosque type is mainly controlled by the size and proportion of the structural unit dimensions as well as the total number of units ͑ e.g., 5 ϫ 3 units ͒ . Interior materials of these typical contemporary mosques vary. Walls are mostly finished with reflecting materials such as painted plaster. They usually contain a wainscot, around 1.0 m high, made of marble tiles. The floor area is always covered with heavy carpet. Hard, painted concrete ceilings with simple to elabo- rate decorations are commonly used. Due to the harsh cli- matic conditions in most of Saudi Arabia’s regions, air- conditioners are virtually a necessity. Therefore, almost all types of mosques are equipped with either a central, or a split unit air-conditioning system or window-type unit, in concert with ceiling fans for air circulation. Electroacoustic SRS have also been implemented in mosques of all sizes to en- hance the listening conditions in the mosque space, particularly after the introduction of the air-conditioning systems and the anticipated subsequent increase of ambient noise in the mosque. Nowadays, numerous subjective attributes of the listening experience in enclosures can be described by the many available contemporary room-acoustic indicators. A comprehensive listing of these contemporary indicators, definitions, corresponding subjective attributes, and suggested tolerance range values can be found in Ref. 17. In mosques, the major acoustical concern is verbal communication. All activities in the mosque are dependent on speech audibility and intelligibility. Speech intelligibility ͑ SI ͒ is the percentage of speech material that is correctly identified by the average listener. The intelligibility of speech in rooms is related to both the speech signal-to-noise ratio and to the acoustic characteristics of the enclosure. That is, it can be influenced by the speech sound level, ambient background noise ͑ BN ͒ , and the reverberation time ͑ RT ͒ of the enclosure. Reverberation affects SI by affecting the early-to-late arriving sound energies. SI is directly related to the early-to-late energy fraction, namely sound definition. In summary, in order to measure or predict speech intelligibility, various objective-based measures can be used. Definition (D 50 ) which is related to sound clarity (C 50 ), useful-to-detrimental sound ratios ͑ e.g., SNR 95 , 18 U 50 , and U 8019,20 ͒ , Speech transmission index ͑ STI ͒ , 21 rapid speech transmission index ͑ RASTI ͒ , 22,23 and the articulation loss of consonants ...