A Comparison of STI Measured by Direct and Indirect Methods for Interiors Coupled with Sound Reinforcement Systems

This paper presents a comparison of STI (Speech Transmission Index) coefficient measurement results carried out by direct and indirect methods. First, acoustic parameters important in the context of public address and sound reinforcement systems are recalled. A measurement methodology is presented that employs various test signals to determine impulse responses. The process of evaluating sound system performance, signals enabling direct objective measurement of the STI (Speech Transmission Index) coefficient, and in particular the STI-PA (STI for Public Address systems) ratio, are employed in accordance with the measurement standards. Sound systems installed in two acoustic interiors are used in the measurements. A comparison of the results obtained for different length of swept sine stimuli is made that enabled to recommend this test signal as more suitable for interiors coupled with sound reinforcement systems.