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Itshouldbeemphasizedthatvaluesoftheabsorptioncoecientpresentedin
thispapercandifferfrom'similar'experimentsperformedongranularplastics
[10,11].Thisisobviouslyconnectedtothe problemdescribedinpt. 3.2,which
isthesample'sconstructionandtheintroductionofamembraneinfrontofthe
granular medium. Despite the use of a very thin material to seal the sample,
itsinfluenceontheresultscouldnotbeavoided.Withunderpressuregenerated,
thewallsofthecontainer(aswellasthefront),slightlydeformstickingtothe
granularstructure,astheairistakenoutofthesystemandstaythatwayuntil
relieved.
Fig. 7.
AbsorptioncoecientforgrainsofPOL,ABS,PPandPS,atmosphericpressure
Table 3.
Values of absorption coecient for chosen frequencies of sound for atmo-
sphericpressure
Frequency
[
Hz
]
500 1000 2000 4000 6400
POL
0,4570,5740,5810,571 0,58
ABS
0,2670,4480,4290,5470,464
PP
0,5430,6510,5870,6190,654
PS
0,420,5350,6020,6060,617
Material
5 Conclusions
Resultspresentedinthispaperclearlyprovethattheunderpressurehasacon-
siderableeffectonacousticpropertiesofspecialgranularstructures.Sinceitis
possible to apply this type of engineering solution in a construction of multi-
layered acoustic barriers with controllable properties, additional experiments
willbeconductedtodescribethebehaviorofSGS.Futureresearchwillfocuson
suchaspectsas:
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