Active noise reduction hearing protectors; 50 years of development

Abstract

This paper will review the technology development of active noise reduction (ANR) hearing protectors. Such devices have been in development for close to 50 years. Early studies by Meeker on feedback implementation of ANR identified many of the issues and performance criteria that are still relevant today. These issues include compensation, minimum phase filter design, and out-of-band control stability. Numerous patents and publications since the early developments focused on means to address the issues discussed by Meeker, and, to introduce alternative implementations of ANR hearing protectors or headsets. Such alternatives include feed-forward designs, as well as open-back and closed-back designs (open-back designs rely solely upon active control for noise protection; closed-back designs include passive attenuation from an ear muff). Development has also proceeded on designs which include communication elements; here, the active control system must attenuate the noise, but not the communication. Fifty years on, ANR hearing protectors represent the most successful commercial application of active noise control technology.