Low-Frequency Noise Reduction by Earmuffs with Flax Fibre-Reinforced Polypropylene Ear Cups

Figure 6

(a) Averaged sound pressure level of the firing 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%.

(a)

(b)

(c)

(d)