PubMed · 7134394
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S Karmy. 1982. A plan for hearing conservation.. https://doi.org/10.1177/146642408210200415
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In the noisy environment, workers use hearing protectors to protect their hearing organ against adverse effects of noise. Hearing protectors should be well selected according to the spectrum and level of noise. The selection of hearing protectors is based on the sound attenuation values measured in laboratory conditions. Workers usually use hearing protectors provided by employers as long as there are no signs of any physical damage. The aim of this study was to assess the effect of use and storage as well as of atmospheric conditions on sound attenuation of ear-muffs. Four models of ear-muffs popular in the Polish work environment were tested for two years. They fulfilled the PN-EN 352-1 standard requirements and were granted a certification mark. Fifteen samples of each model were used by workers every working day; 10 samples were exposed to natural atmospheric conditions; and 10 samples were stored in accordance with the manufacture's advice. Temperature and humidity were checked each day. After periods of one and two years, sound attenuation was measured according to PN-EN 24869-1 standard. The observed changes in high-frequency attenuation value H. medium-frequency attenuation value M, low-frequency attenuation value L and single number rating calculated according to PN - EN ISO 4869-2, are presented. The quantitative assessment how far the period of use, storage and exposure to natural atmospheric conditions affect protection achieved by the four popular models of ear-muffs is presented.
Active noise-reducing (ANR) headsets are available commercially in applications varying from aviation communication to consumer audio. Current ANR systems use passive attenuation at high frequencies and loudspeaker-based active noise control at low frequencies to achieve broadband noise reduction. This paper presents a novel ANR headset in which the external noise transmitted to the user's ear via earshell vibration is reduced by controlling the vibration of the earshell using force actuators acting against an inertial mass or the earshell headband. Model-based theoretical analysis using velocity feedback control showed that current piezoelectric actuators provide sufficient force but require lower stiffness for improved low-frequency performance. Control simulations based on experimental data from a laboratory headset showed that good performance can potentially be achieved in practice by a robust feedback controller, while a single-frequency real-time control experiment verified that noise reduction can be achieved using earshell vibration control.