Respirators speech module

Most respirators have some sort of speech module to help overcome the muffling and attenuating effect and improve speech intelligibility. Speech modules are normally mounted on the respirator mid-line for direct speech, or one cheek of the facepiece for indirect speech, e.g. using telephones or radios. Direct speech modules are usually circular or annular in shape and incorporate a thin sheet of polyester such as Mylar , about 5 cm in diameter (the minimum for acceptable speech intelligibility) tensioned on a frame and protected by grilles inside and outside the respirator. 

The primary speech module of the S10 respirator does not have a diaphragm instead, the exhale valve housing is in the shape of a folded acoustic horn, to serve both as a speech module and a deadspace. The S10 also has a secondary speech module, that does incorporate a small diaphragm, to which radio microphones can be attached. 

Modern-day, air-filtering, military respirators consist of a facepiece (mask), on which are mounted various sub-assembly components such as filters, faceseals, visors/eyepieces, valves, air-guides, speech-enhancing modules and drinking systems. 

Respirators muffle and distort speech because the facepiece material absorbs sound, the face-piece moulding forms resonant cavities and the faceseal restricts movement of the lower jaw (Mozo and Peters, 1984 Johnson and Sleeper, 1985 Nelson andMozo, 1985 Fine and Kobrick, 1987 Taylor and Orlansky, 1987 Wetherell and Gwyther, 1993). Voice modules help, but do not resolve the problem completely. 

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