An Electrically Switchable Bragg Grating despeckler device comprising at least one ESBG element recorded in a hPDLC sandwiched between transparent substrates to which transparent conductive coatings have been applied. The auxiliary lobes are defined, at least in part, by the discharge end of the duct. The operating mode is controlled in conformity with the audio signal level, which may be determined from a volume control setting of the device andor from a signal level detector that determines the amplitude of the signal being amplified. NA1\u2267NA2 is satisfied, where NA1 represents a numerical aperture for the first optical disc, and NA2 the numerical aperture for the second optical disc. Further, both ram or flush inlets may be used with the ram inlet being, at least in its majority, positioned above the marine vehicle forward of it.