Near-field speech intelligibility in chemical-biological warfare masks

It is common knowledge among field personnel that poor speech intelligibili ty can occur when chemical-biological warfare (CBW) masks are worn; indeed, many users resort to hand signals for person-to-person communicative purpo ses. This study was conducted in an effort to generate basic information ab out the problem; its focus was on the assessment of, and comparisons among, the communicative efficiency of seven different CBW units. Near-field word intelligibility was assessed by use of rhyming minimal contrast tests; use r and acoustic restrictions were studied by means of diadochokinetic tests and system frequency response. The near-field word intelligibility of six A merican-designed masks varied somewhat, but overall it was reasonably good; however, a Russian unit did not perform well. Second, three of the U.S. ma sks were found to produce less physiological restraint than the others, and the Soviet mask produced the greatest physiological restraint. Finally, a few of the CBW masks also exhibited very low levels of acoustic distortion. Accordingly, it was concluded that two of the several configurations studi ed exhibited superior features. Other factors being equal, they can be reco mmended for field use and as a basis for the development of future generati ons of CBW masks. However, it also should be noted that although these devi ces provided reasonably good speech intelligibility when the listener was c lose to the talker, they do not appear to do so even at minimal distances.