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Speech-reinforcement systems in six large auditoriums were evaluated, using subjective rating tests, word-articulation tests, and, in two cases, a new test method. This method, called the "terminal-word test," makes possible the quantitative measurement of speech intelligibility for a sound system in actual use. A graphical method is presented for calculating the performance of a sound system in which account is taken of the frequency response of the system, the reverberation time of the room, the directivity index of the loudspeaker, and the room noise. Test results indicate that a flat frequency response in the range between 400 and 4,000 cps is required for good intelligibility. The graphical method indicates that little further increase in intelligibility would result from extending this range upward or downward. If the loudspeaker system is sufficiently directive in this frequency range and properly located in the room, room reverberation has little effect on speech intelligibility.