Abstract: A self-contained, hand-held device for testing an aircraft helmet communication system including a microphone and earphones in which a selection switch on the housing of the device is movable from an off position to a talk-through position at which the microphone is connected to both the earphones and a volume indicator on the housing and to a self-test position in which actuation of a pushbutton switch on the housing applies the output of an oscillator both to the volume indicator and a circuit having a voltage divider made up of a potentiometer and a fixed resistance to provide a self-test signal which energizes an illuminable element on the housing if the device is functioning properly and to an earphone impedance test position at which the output of the oscillator is applied to a circuit having a voltage divider made up of the potentiometer and the earphones to produce an earphone impedance-test signal which energizes the illuminable element if the earphone impedance is of the correct value.

Abstract: A throat microphone has an outer resonant diaphragm which is adapted to be secured against the throat of a wearer and which cooperates with a housing to form an outer chamber. An electret microphone element disposed inside the outer chamber includes an electret diaphragm acoustically coupled to the outer diaphragm and an electret housing forming an inner chamber with the electret diaphragm. The electret diaphragm is perforated to provide pressure relief between the two chambers to give the electret microphone element a rising response characteristic, which is enhanced by a differentiating network in the input circuit of a local preamplifier. The outer diaphragm is so formed as to have a principal resonance at about 3 kilohertz to provide a further emphasis to voice frequencies at or near that resonance.

Abstract: A local external communication system for use by a person wearing a mask covering the nose and mouth and in sealing engagement with the face in which an assembly secured to the outer surface of the mask without in any way affecting the integrity of the mask seal generates an output signal in response to the wearer's voice. The output signal is fed to a speaker carried on the wearer's body to produce an output which is audible to other persons in the vicinity of the wearer.