A summary is given of the quantitative effects of loudness, reverberation, noise and the shape of an auditorium upon the hearing of speech in auditoriums. The average loudness of speakers is found to be about 50.7 db in small auditoriums (27,200 cu. ft.) and 45.7 db in large auditoriums (240,000 cu. ft.). The loudness of spech in large auditoriums is therefore at a critically low level, so that slight disturbances from reverberation or noise suffice to make hearing conditions unsatisfactory. The percentage articulation in an auditorium is ascertained by means of the formula,Percentage Articulation = 96k1kτknks, wherek1,kτ,knandksare the reduction factors owing to diminution of loudness, reverberation, noise, and shape of auditorium, respectively. Methods and data are given for determining these reduction factors. A study of the combined effects of loudness and reverberation yields the optimal times of reverberation for the hearing of speech in auditoriums of different sizes. Thus, the optimal time for a room of 25,000 cu. ft. is found to be .80 second. The optimal time increases to .90 second for an auditorium of 100,000 cu. ft., and to 1.00 second for an auditorium of 400,000 cu. ft. It is shown that artificial amplification of speech is imperatively needed in auditoriums larger than 400,000 cu. ft., and is desirable in auditoriums larger than 100,000 cu. ft. A series of curves indicates the probable percentage of speech‐articulation in auditoriums varying in size from 25,000 cu. ft. to 1,600,000 cu. ft. and having times of reverberation between .5 and 8.0 seconds. The results of the investigation make it possible to assign a quantitative rating to the acoustic quality (for the hearing of speech) of any auditorium, or to determine the physical requirements of an auditorium which is to attain a specified degree of excellence.