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Fig.5and6itillustratehowvariouslevelsofunderpressureinsidethesample
affect tested the characteristic. For both POL (fig. 5) and ABS (fig. 6) it is
clear that the controlling parameter has a considerable influence on acoustic
absorption.Asimilarresponseisfoundforalltestedmaterials.Thesechanges,
dependingonthematerial,canreachseveralhundredpercent.Forthenextlevels
ofunderpressure,theresponsefixes.Fordifferenttypesofgrains,theinfluence
isnoticeableuptothelimitof0,03MPa(asforABS).Beyondthatthechanges
inabsorptionarehardtoobserve.
Fig. 5.
AbsorptioncoecientforPOLmaterial,pressure0-0,09MPa
Fig. 6.
AbsorptioncoecientforABSmaterial,pressure0-0,09MPa
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