Abstract: Among all the criteria used for assessing the acoustical quality of an auditorium, the overall strength, or the loudness, is one of the most essential attributes. But little had been done on this criterion in the past owing to the lack of appropriate measure to describe and quantify such a criterion, therefore it is hard to predict the overall strength in a hall during the design stage, and also cannot check it when the hall is completed. A new measure so called strength index G (Starkemsas) developed by Lehmann gives a good proposal to quantify the overall strength in an auditorium. He found that the impression of the strength is not produced only by the direct Sound,nor by the early ‘useful’ sound, but all of the reflechons arriving at the listener's position. But our experience, also from other authors, shows the direct sound and early reflections playing the main role in determination of loudness impression due to the ‘licit of Perceptibility’ or ‘the inertia of hearing’. Therefore it is more reasonable to set an integrating time of the useful reflections for determining the strength index, say 50ms for speech and 80ms for music. The strength index G hence should be written as G₅₀ for speech and G₈₀ for music.