Passive Hearing Protection Systems and Their Performance

While ideally noise should be reduced at the source, in the military environment the most effective solution in terms of both cost and operational effectiveness has been to provide personnel with personal hearing protection. This protection may be in the form of either an earplug that occludes the ear canal or a circumaural protector that inserts a barrier between the ambient noise and the ear. For both devices the level of passive protection provided changes with frequency. A great deal of research was conducted in the 1940/50s to define the mechanisms and parameters that appeared to limit the performance of these types of protectors and this presentation will provide an overview of the findings of this early research. By the 1970s the performance of such devices, particularly those used in military applications, had been best optimized for use with the types of cranial protection being worn by soldiers, sailors, and aircrew. Since that time the major thrust in hearing protection enhancement has been the development and integration of Active Noise Reduction (ANR) systems where an electronic circuit is incorporated into the device to provide additional active attenuation in addition to the passive attenuation. ANR has provided significant benefits in low frequency attenuation and provides complementary performance to the passive device. However, for future military noise environments ANR headsets and ANR earplugs will not individually provide sufficient levels of protection, and passive earplugs and earmuffs may have to be used in some combination to provide adequate hearing protection. Recent research developments have resulted in improved passive earplug and earmuff attenuation performance. Deep inserted custom earplug performance and custom earmuff/earcushion design techniques have provided a substantial increase in hearing protection. Issues associated with the fitting of personal hearing protection and their performance in the field will also be discussed.