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2
Application-orienteddesignofactivenoisecontrolsystems
Therearedifferentpassivemethodstoprotectusersagainstexpositionto
excessivenoise.Theyinclude[Crocker,2007]:
1)reductionofmechanicalplaysandprecisefittingofmachineparts;
2)usingvibrationabsorbingmats;
3)soundisolationofworkingnoisymechanisms;
4)soundisolationofworkers;
5)acousticbarriersandscreens;
6)personalhearingprotectors.
Evenalthoughmethods1)and2)arebelievedtobeundertakenbymanufacturers
andinstallersofthemachinery,therearestillenvironments,whichduetothe
technologicalprocessofmaterialtreatmentareinsufficientlyquiet.Inmajorityof
casesthestaffneedstomovearoundthedevicestomonitortheprocess,maintain
neighboringmachines,etc.Therefore,theisolationsolutionspresentedinitems
3)-5)cannotbeapplied.Ontheotherhand,commonlyusedpassivebarriersare
practicallyunfeasibleforlow-frequencynoise,becauseofthedependencebetween
acousticwavelengthofthenoiseandthicknessofthebarriersrequiredfor
absorption[NelsonandElliott,1991].Therefore,personalprotectorsintheformof
headsetsandearplugsarecommonlyused.Theyareusuallythecheapestprotection
mean,butnoiseattenuationforlowfrequenciesisnotsatisfactory.Ontheother
hand,theyarenotacceptedforsomeenvironments,e.g.inhouseholdstoprotect
againstnoisegeneratedbyhomeappliances.
1.2ACTIVENOISECONTROLANDACTIVESTRUCTURAL
ACOUSTICCONTROL
Inactivenoisecontrol(ANC)anadditionalsecondarysoundsourceisusedto
cancelnoisefromtheoriginalprimarysource.Thecommonphysicaljustification
isgivenbyYoung’sinterferenceprinciple.Accordingtothisprinciple,interference
