Research Article
Low-Frequency Noise Reduction by Earmuffs with Flax Fibre-Reinforced Polypropylene Ear Cups
Figure 4
(a) Averaged sound pressure level of the pink noise in the reverberation room measured by the simulator without any earmuff (open ear); comparison between the insertion loss curve of (b) the reference and the nonwoven composite earmuffs; (c) the reference and the twill weave composite earmuffs; and (d) the reference and the hopsack weave composite earmuffs. Shaded area is bounded by the upper and the lower limits of the expanded uncertainty at a confidence level of 95%.
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