@article{ref1,
title="Noise problems in military helicopters; an evaluation of ear protection in HR2S-1 aircraft",
journal="Journal of aviation medicine",
year="1958",
author="Metcalf, C. W. and Witwer, R. G.",
volume="29",
number="1",
pages="59-65",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0095-991X",
doi="",
url="http://dx.doi.org/"
}