Static and dynamic noise transmission over an oxygen mask (military aircrew applications)

A description is given of experimental work investigating the acoustic attenuation of an oxygen mask typical of those worn by military aircrew. Dominant noise transmission paths over the mask are identified, and the behaviour of the expiration valve during speech is reported. This valve, which constitutes the most important noise transmission path, opens and closes at a surprisingly high rate during speech. This introduces a time variance into the mask's noise transmission, which is shown to complicate the application of adaptive cancellation techniques to the aircrew oxygen mask problem. >