Development of Audio Transducer Helmet Assembly

摘要

The program objective is the development of an Audio Transducer Helmet Assembly to be used in the Army Air Crewman Helmet. The Assembly includes earphones mounted in attenuating earcups along with auxiliary hardware, wiring and ancillary devices. A further goal is the development of a miniature moving-coil noise-cancelling microphone having improved noise-cancellation characteristics. Study of Mutual Stiffness Coupled (MSC) and Bellows Coupled Enclosures was initiated with an assessment of helmet stiffness requirements. It was found that an APH-5 helmet could be made adequately stiff by attaching two yokes fitting within the helmet. An experimental MSC enclosure was installed and noise attenuation measurements confirmed that the helmet was sufficiently rigid for this purpose. Designs for a practical method of assembling the ear enclosures into the helmet were conceived and evaluated. Work on the Low Frequency Coupled Volume (LFC) included further study of the spring design for mounting the LFC enclosures into the helmet. Several spring types were fabricated and of these, spiral springs appeared most practical and simple to produce. Initial models of the noise-cancelling microphone magnetic circuit were constructed and tested. They indicated the potentiality of considerably higher flux densities. Diaphragm dimensions were computed, a coil design was generated, and calculations of the predicted microphone sensitivity were performed. (Author)