Performance of a dual-cup-dual-cushion earmuff design

Traditionally, earmuffs have been constructed consisting of a single-walled cup seated on a flexible ear cushion, forming a single-cup-single-cushion (SCSC) structure. The average noise attenuation levels provided by SCSC earmuffs typically range from 15 dB at low frequencies to 40 dB at high frequencies. It is difficult to further improve the attenuation of SCSC earmuffs beyond this level in practice unless the structural design is modified radically. One candidate design that is substantially different from the SCSC structure is a dual-cup-dual-cushion (DCDC) structure, where the earmuff consists of two independent earcup shells that are resiliently coupled together. This DCDC structure is based on a concept originally introduced by Shaw and Thiessen in an earlier study [J. Acoust. Soc. Am. 34, 1233-1246]. The present study further explores the dynamic characteristics of the DCDC design by extending the theoretical investigation to higher frequencies using a finite element model, which complements the classical lumped parameter model for low frequency analysis. Furthermore, a laboratory DCDC earmuff prototype is constructed and compared experimentally to a commercial SCSC earmuff. The attenuation data obtained from the acoustic test fixture test indicate significant performance improvement of the DCDC earmuff over the SCSC earmuff. The Real-Ear-Attenuation-at-Threshold test results show attenuation gains ranging from several dB at 125 Hz, up to 10 dB at 250, 500 and 1000 Hz, and slightly more than 10 dB above 2000 Hz. (C) 2009 Institute of Noise Control Engineering.