The Architectural Development Of The Historic Masjids In Cairo And Its Acoustical Impact

摘要

This work examines the acoustical characteristics of the four patterns that represent the architectural development of the historic Masjids (Mosques) in Cairo: the semi-closed Rewaq pattern; the semi-closed Iwan pattern; the closed Iwan pattern and the closed simple geometrical pattern. Detailed architectural and acoustical analyses were performed on samples collected through a comprehensive historical survey of Masjids that were built between the ninth and eighteenth centuries. The architectural analysis included consideration of: room area; volume; shape; form; finishing materials; roof type and room aspect ratio. The acoustical analysis involved the application of geometrical acoustics using the RAYNOISE program ver3.1 to investigate the acoustical qualities of two Mamluk Masjids. The acoustics of two other Masjids are also briefly discussed. Results of the computer simulations showed that the semi-closed Rewaq pattern has the most problematic acoustic environment due to its enormous volume and the use of massive pillars that tend to confine the sound rays in a limited area around the source. The semi-closed Iwan pattern yields the best acoustical qualities relative to the other three patterns with high values of speech SPL (65-70dB(A)) and a D_(50) value that is equates to speech intelligibility of 70% or higher. In the closed Iwan pattern, only the worshipers in the Qibla Iwan experience a good acoustic environment whereas the other worshipers may experience some difficulties in hearing and understanding clearly the voice of the Imam. The closed simple pattern has fair acoustical qualities with most of the worshipers receiving a speech SPL equal to or higher than 50dB(A). This is due to its excessive height and the resulting long distance travelled by the rays reflected from the ceiling (about 42m) before reaching the plane of the worshipers. This results in their intensity being severely diminished. The three patterns for which simulations were carried out all have long reverberation times (RT) at the low and mid frequencies. This long RT is considered appropriate for the spiritual nature of these places and in addition in some cases it helps in increasing the speech SPL in the room.