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Schematic diagram of the apparatus for measuring the sound absorption coefficient (a) and a schematic of the impedance tube equipment (b). Legend of the abbreviations: a—air gap size; EA—absorbed acoustic energy; EI—incident acoustic energy; ER—reflected acoustic energy; M1, M2—measuring microphones; t—sample thickness; W—solid wall; x1, x2—microphone distances from the tested ABS sample.
