Zerhan Karabiber - karabi@yildiz.edu.tr
Yildiz Tech. Univ.
Fac. of Arch.
Dept. of Bldg. Phys.
80750 Istanbul/Turkey
Popular version of paper 2pAAa6
Presented Tuesday afternoon, March 16, 1999
ASA/EAA/DAGA '99 Meeting, Berlin, Germany
In acoustically important rooms and spaces - concert and conference halls, opera houses, churches, for example - much work has been done since the 1900s to determine ideal acoustical conditions. The main effort of this type of work is to match subjective judgments with scientific means such as calculations, measurements and statistics. There is a great amount of data on such spaces, and this considerably helps the proper design of a new hall or improvement of an older one. Almost no specific acoustical data exists, however, on mosques. Thus, a study aimed at assessing the acoustical properties of ancient mosques has been started, with the aim of aiding in the acoustical design of future mosques.
Every single building type has its own acoustical requirements. To determine the acoustical requirements in a proper way, we should know the different types of uses of the buildings and spaces. When a single space is used for many different functions, it is very difficult to create the suitable environment. The design of such spaces requires great care.
Mosques are multi-function public halls with a wide range of worshipping activities having different acoustical requirements. As in many other religions, worshippers sometimes need solitude while at other times they must feel themselves in absolute unity with the community. Acoustics is one of the main means to create these effects.
There are three distinct acoustical requirements for mosques:
Thus, intelligibility of both speech and sound is paramount. This is especially important for musical sounds, which must be both spacious and effective.
Mosques, which are one of the most important building types of Muslim architecture, have evolved to meet Islamic needs. Big mosques are separated from residential zones by a large exterior court. There is an inner court between the exterior court and the main space. Mosque masses are directed towards Qiblah at Mekke, and the wall at this side is called the "Qiblah wall." Occupants are aligned in parallel rows, sitting or standing on the floor, facing the Qiblah wall while praying. On the middle of the Qiblah wall, there is a raised niche called the "mihrab," where the prayer leader (Imam) stands. At the right side of the mihrab, there is a high pulpit ("minbar"), where the Imam delivers his sermons.
Figure1. Plan and Section of the Haseki Mosque at Istanbul (Ali S. lgen, 1989).
In Turkish-Ottoman architecture, mosques have generally square or rectangular plans, covered mainly with a big dome and sometimes several smaller ones. Mosque volumes vary greatly; the smallest begin at approximately 700m, and the biggest go up to 90000m, serving up to 150 and 6000 persons respectively. Most older mosques which have survived until now are made of stone and brick.
Floors are generally covered with thick carpets,and thus are highly absorbent, especially of high frequencies like audience sounds. Mosques are used at very levels of occupancy, so carpeted floors, one of the important characteristics that distinguish mosques from churches, convey the advantage of compensating the difference of absorption to some degree.
Walls have acoustically reflecting finishing materials like plaster, Turkish decorated faience, marble, brick and stone. But in some mosques known for their good acoustics, a special plaster works as a kind of a "panel resonator." Many walls have lots of irregularities like window niches and different types of ornaments which help reflect and diffuse sounds.
In Turkish-Ottoman architecture, vaults and domes are used more frequently than flat ceilings. Although these concave surfaces are potentially problematic because of the great probability of focusing sound waves, acoustics are generally good, especially in ancient mosques. But in many new mosques, focusing is a serious problem. Some of the rare studies on ancient mosque acoustics show that there are differently dimensioned jugs buried in domes to absorb sounds. In a sense, they are ancient versions of Helmholtz resonators--essentially, bottles with narrow necks that can produce or absorb sounds with a frequency proportional to the width of the neck.
To examine ancient mosques in a proper way, a consistent plan should be developed. The first step is to select the mosques to be evaluated. Second, one must determine the acoustical criteria to evaluate. Third, calculations, using suitable computer programs as well as in situ measurements, should be carried out to obtain objective data. Finally, by means of surveys, one must verify all objective and subjective data.
Early results that include only a portion of objective evaluations of smaller mosques, demonstrate that mosques are in good condition according to some acoustical criteria, such as total sound pressure levels and room modes, but in inadequate condition according to the others, such as reverberation time. This fact illustrates once more the necessity to establish specific acoustical criteria and parameters to be used for the acoustical evaluation of mosques.