Development of a long range acoustic hail and warning device for maritime applications

Author： Brungart Timothy A. Barnard Andrew R. McDevitt Timothy E. Jenkins David M. Kline Brian L. Nicholas Nicholas C.

Publisher： Institute of Noise Control Engineering

ISSN： 0736-2501

Source： Noise Control Engineering Journal, Vol.57, Iss.1, 2009-01, pp. : 1-9

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Abstract

An Acoustic Hail and Warning Device (AHWD), intended to project intelligible voice warning messages to listeners at 500 yards(457 m) where at least 80% of the words in an unknown message are intelligible, was designed, fabricated and tested. Design was facilitated by a methodology developed to help ensure long range intelligibility in different listener environments. Two intelligibility goals, i.e. listener environments, were evaluated: I) an outdoor listener at a distance of 457 m over water and in the presence of 89 dBA background noise levels, and II) a listener inside a closed watercraft enclosure at 457 m and in the presence of 63 dBA background levels. The 457 m distance corresponds to the radius of the protection zone surrounding U.S. Naval vessels and the background noise levels are representative of those encountered in maritime scenarios. Component testing and analyses indicated that a uniformly phased horizontal line array of 8 horn-loaded compression drivers would satisfy both goals I and II. The array was then fabricated and its voice warning message spectrum was measured. The measured spectrum and subsequent prediction showed that the 8 horn/driver array satisfies both goals I and II with 89% and 94% of the words in an unknown voice warning message being intelligible in those respective scenarios assuming homogeneous, quiescent atmospheric conditions.