A regulator assembly is provided for use in a respirator system to supply a regulated flow of air to a respirator head piece. The respirator assembly comprises a housing (15) having an air inlet port (17) for connection to a source of air at comparatively high pressure, and an air outlet port (23) for connection to the respirator head piece. The housing (15) contains an air pressure-reduction stage (19) in communication with the inlet port (17), and a noise-reduction stage (21) between the pressure-reduction stage and the outlet port (23). The noise reduction stage (21) comprises two, spaced, muffler discs (41, 43) the first of which is positioned adjacent the air outlet (39) of the pressure-reduction stage (19). A deflector plate (47) deflects the airflow from the pressure-reduction stage (19) through the first muffler disc (41), and thereby diffuses the air flow before it reaches the second muffler disc (43).