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Graphical interpretation of the regression line (Equations (4)–(7)) for the dependence of the sound absorption coefficient on the frequency of the waste product from woollen yarn at different densities (kg/m3) and thicknesses (mm): 1—◊ (18 kg/m3–40 mm), 2—∆ (18 kg/m3–60 mm), 3—○ (40 kg/m3–40 mm), 4—□ (40 kg/m3–60 mm).
