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The purpose of this study was to evaluate the Purdue Speech Intensity Demonstrator (SID) as a training device. This instrument is designed to give visual indication of speech signal-to-noise ratio, an adequate signal-to-noise ratio being a requirement for intelligible radio-telephone communication. The subjects included 170 male undergraduate students at Purdue University. Fifty of these subjects comprised the experimental population; 120 were used as controls. The experimental procedure was as follows: (A) pre-training intelligibility testing of all subjects, experimental and control; (B) one 50-minute period of training in loudness for experimental subjects only, under three experimental conditions; and (C) post-training intelligibility testing of all subjects. The following results were obtained: (a) Trained subjects achieved intelligibility levels significantly higher than untrained subjects. (b) No one of the three experimental conditions was demonstrated to produce statistically significantly greater intelligibility than the other two. A slight superiority was noted for the method which required subjects to sustain signal strength slightly below maximum, rather than attempt to gain maximum signal strength. (c) Subjects trained for one hour with the SID achieved improved intelligibility comparable to that of subjects trained for two or more hours without a visual device. (Author)