The 4000 seat multi-purpose Bilkent Amphitheater is a semi-closed amphitheater with a volume of 90,000 m3, designed to serve the University's and the city's educational and artistic activities. At the beginning, the amphitheater was designed only for open-air performances. Afterwards it was decided it would be roofed with a tensile membrane in order to protect the spectators from atmospheric effects. However, the covered amphitheater was turned into a resounding and a problematic place with a reverberation time of more than 6 s. when the hall is unoccupied. Acoustical interventions were implemented, but these have not been sufficient in decreasing the number of problematic echoes and dead spots. This paper analyzes the hall by means of assessing the fundamental acoustical parameters for both speech and music. Parameters such as reverberation time, early decay time, clarity, definition, lateral fraction, strength and speech transmission index were calculated by the aid of ODEON Room Acoustics Program simul...