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1、CHAPTERFIVE ACOUSTICENCLOSURESANDBARRIERS5.1SOUNDTRANSMISSIONLOSSAirborneSTLisdefinedasfollows:Whereis:1.AirborneSTLAbsorptioncoefficient:Transmissioncoefficient:Incident:IiReflected:IrAbsorbed:IaTransmitted:ItSoundInsertionloss(IL)Thedifferenceinsoundpressuremeasuredinasingl
2、elocationwithandwithoutanoise-controldevicelocatedbetweenthesourceandreceiver.ThedifferenceinthesoundpressuremeasuredintheoccupiedspacewiththewallversuswithoutthewallistheILofthewallSoundtransmissionloss(TL)Itequalstotheratiooftheairbornesoundpowerincidentonthepartitiontotheso
3、undpowertransmittedbythepartitionandradiatedontheotherside.ILandTLSourceBarrierInaroomWehaveknown:αi=absorptioncoefficientofithsurfaceForithsurface:Forawholeroom:theroom-averagedsoundabsorptioncoefficient,:Sisthetotalsurfaceareaoftheroom.Also,inaroomAlso,inaroomThecorrespondin
4、gsoundtransmissionlossisgivenby:Weassume:Anotherform:exampleWall:20m2,walldoorwindowsDoor:2m2,Windows:3m2,CalculatetheSTL.exampleWall:20m2,walldoorwindowsDoor:2m2,Windows:3m2,STL=10log105=50dBSTL=10log103=30dBSTL=10log102=20dBAveragetransmissionlossrequiredforvariouslevelsofsp
5、eechprivacyAverageTransmissionlossofwall,dBHearingconditionsRating30orlessNormalspeechcanbeunderstoodquiteeasilyanddistinctlythroughthewall.Poor30-35Loudspeechcanbeunderstoodfairlywell.Normalspeechcanbeheardbutnoteasilyunderstood.Fair35-40Loudspeechcanbeheard,butiseasilyintell
6、igible.Normalspeechcanbeheardonlyfaintly,ifatall.Goodnot40-45Loudspeechcanbefaintlyheardbutnotunderstood.Normalspeechisinaudible.Verygood—recommendedfordividingwallsbetweenapartments.45orgreaterVeryloudsounds,suchasloudsinging,brassmusicalinstruments,oraradioatfullvolumecanbeh
7、eardonlyfaintlyornotatall.Excellent—recommendedforbandrooms,musicpracticerooms,radioandsoundstudios,2.STLinaseparatedroomSoundtransmissionlossiscalculatedby:L1L2Theisobtainedasfollows:ThesoundpowerimpingingonthetestspecimenfromthesourcesideisS=surfaceareaoftestspecimen,m2Inthe
8、sourceroomInthereceiverroomTherateofenergytransmissionintothe
