The aim of this paper is to present a method of determining the Reverberation Time (RT) of an enclosed area. The Main Hall or auditorium in the Institute at ITTHO was used for this purpose as it has been investigated in detail over some 18 months for its RT and other acoustic properties. The hall is large and has a uniform rectangular planform area of 35 m x 30 m and a height of 12 m. Its acoustic properties are therefore measureable and repeatable. A description of the acoustic properties and the measures taken to obtain an accurate acoustic knowledge of the enclosure* is presented. The dominant feature in the determination of acoustic properties is the absorption coefficient and a novel technique is devised which is shown to obviate the tranditional method of impulsive sound. Much work has been carried out on the decay of sound in enclosures [1-3] where the statistical averaging of decay curves and the [surface reflection laws were considered in some detail. However, there has been no systematic work done on an actual invetigation of measuring the decay and matching with a well established set of decay curves to fit the absorption cefficient. Thus the aim of this paper is to determine the absorption cefficient by matching the measured decay in the enclosure to a predicted value of absorption froma family decay curves. The results from this method show a close agreement with those obtained from the traditional RT measurements in the Hall.