The impedance of a simple artificial ear occluded with an earplug and bypassed with narrow air leaks was measured along with the attenuation of sound through the air leaks. A lumped element model is suggested for the simple occluded artificial ear with an air leak. The suggested model was adapted to the impedance measurements and the attenuation was predicted from the model. The attenuation predictions were compared to the attenuation measurements and were found to be within [-3.5,+3] dB of the measured attenuation over the frequency range of 50-1000 Hz and an attenuation range of -2-38 dB. The average difference between the measured and predicted attenuation for four different leaks in the frequency range of 50-1000 Hz was -0.7 dB, indicating a very slight underestimation of the attenuation.
During the development of an intelligent hearing protection and communication system the attenuation of two different earplugs were measured. Both earplugs were measured separately and in combination with earmuffs. Foam earplugs and custom-moulded silicone earplugs were both used. The hearing protection system in question is able to measure the ear canal with respect to leaks. If a leak is detected, the system will warn the user.The measurements show that the foam plug gives higher attenuation than the silicone plug at all frequencies, but particularly at frequencies below 2 kHz. It has a steadily increasing attenuation from 30 dB -43 dB over the frequency range 125 Hz -8 kHz. The silicone plug attenuates around 26 dB, from 125 Hz -1 kHz. Above this range, the attenuation increases to approximately 40 dB. With extra earmuffs added, the attenuation is 40 dB or better at all frequencies except 125 Hz, and the two plugs offer nearly identical protection.The results show that the mean and standard deviation of the attenuation for the foam earplug is as good as for an optimally fitted earplug. In the case of the silicone earplug, the mean attenuation is comparable to a typical custom earplug, but the standard deviation is better than comparable earplug. This finding is a result of the leakage control acting as a 'supervisor' in the fitting of the earplugs.
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