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The effectiveness of the helmet-mounted Squad Radio AN/PRR-9 in a battlefield environment is largely determined by the capability of the receiver to deliver adequate sound power to the ear of the user without impairing his ability to hear sounds around him. During the development of the Squad Radio receiver conducted by the United States Army Electronic Research and Development Laboratories in conjunction with the Delco Radio Division of General Motors, emphasis was placed on finding a solution to this problem. High audio power could not be used to provide necessary sound power levels due to the size, weight, and battery drain limitations of the receiver. Therefore, effort was placed in optimizing the efficiency of conversion of electrical audio power to acoustical power. The result of this effort is a low-cost, compact, lightweight exponential horn-driver unit that will provide enough sound power to the user's ear to overcome anticipated battlefield noise. A computer program was used to analyze and optimize the driver and horn parameters for this application. This paper is a discussion of the detailed requirements of the horn-driver unit, the methods used in its development, and the performance of the final units.