High Noise Reduction Ear Enclosures

Abstract

Personnel associated with operation and maintenance of combat vehicles and military aircraft are subject to noise environments so severe that the available ear protective devices do not provide adequate noise reduction. A study and development program has been conducted to improve available noise reduction by (1) design of an ear enclosure cushion to provide a better seal at low frequencies; (2) provision of a secondary seal inside the earcup between the communications earphone and the ear canal, and (3) utilization of electronic noise cancellation to improve further the noise reduction at low frequencies. The design evolved from this study features a low-profile ear enclosure in which the earcup and cushion form a smooth continuous shell that is curved inward to rest behind the pinna. The cushion is fabricated from material which has frequency-dependent viscoelastic properties. It is compliant at low frequencies to provide a good seal, but stiff at autio frequencies to act as an extension of the earcup wall. The design requirements that have been met provide for better than 20 dB noise reduction at low frequencies and better than 45 dB at high frequencies. [Supported by the U. S. Army, under contract.]