• A S Wagstaff, O Tvete, and B Ludvigsen.
• Royal Norwegian Air Force Institute of Aviation Medicine, Oslo, Norway.
• Aviat Space Envir Md. 1996 Nov 1;67(11):1034-8.

IntroductionSpeech intelligibility tests in recorded helicopter noise were performed on 10 subjects with normal hearing, using a Peltor aviation headset. The subjects acted as their own controls, a pair of sunglasses being the only variable factor.MethodsNoise levels were also measured at the tympanic membrane in one of the test subjects for 7 consecutive fittings of the headset, with and without glasses.ResultsResults showed a substantial decrease in speech intelligibility when wearing glasses, being most marked for critical signal-to-noise ratios and the most difficult speech material. Changes were statistically highly significant. Average speech intelligibility scores decreased from 68% to 29% for one-syllable words when wearing glasses at critical signal-to-noise ratios. Noise measurements at the tympanic membrane in one subject showed a low-frequency leakage varying between consecutive fittings.ConclusionOur findings show that even small leakages due to fitting of the headset or helmet should be avoided, particularly in noisy aircraft with communication-demanding mission profiles.

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