ASHRAE 06-1999 Noise Pollution

Liu,D.H.F.&Roberts,H.C.“NoisePollution”EnvironmentalEngineer'sHandbookEd.DavidH.F.Liu&BelaG.LiptakBocaRaton:CRCPressLLC,1999c1999byCRCPressLLC6.1THEPHYSICSOFSOUNDANDHEARINGSoundProductionandPropagationReflection,Dispersion,Absorption,andRefractionWaveCharacterEnergyRelationshipsinSoundTheHearingMechanismHearingImpairmentAudiometryPrinciplesAudiometricPracticesHearingAids6.2NOISESOURCESTypicalRangeofNoiseLevelsCharacteristicsofIndustrialNoiseIndustrialNoiseSourcesMiningandConstructionNoiseTransportationNoiseUrbanNoiseSpecificNoiseSources6.3THEEFFECTSOFNOISEReactionstoNoiseAuditoryEffectsPTS467AcousticTraumaDamage-RiskCriteriaPsychologicalEffectsofNoisePollutionSpeechInterferenceAnnoyanceSleepInterferenceEffectsonPerformanceAcousticPrivacySubjectiveResponses6.4NOISEMEASUREMENTSBasicDefinitionsandTerminologyFrequencySensitivityandEqualLoudnessCharacteristicsObjectiveandSubjectiveValuesWeightingNetworksFrequencyAnalysisofNoiseSpeechInterferenceandNoiseCriteria(NC)CurvesVibrationandVibrationMeasure-mentMeasuringNoiseBackgroundCorrectionsInstrumentsforMeasuringNoiseImpactandImpulseMagnitudesMonitoringDevices(NoiseDosi-meters)FieldMeasurementsPracticalProblems6.5NOISEASSESSMENTANDEVALUATIONWorkplaceNoiseNoiseDosimetersSoundLevelMetersCommunityNoiseNoiseRatingSystemsInstrumentationNoisePollutionDavidH.F.Liu|HowardC.Roberts©1999CRCPressLLCTrafficNoisePredictionPlantNoiseSurvey6.6NOISECONTROLATTHESOURCESource-Path-ReceiverConceptNoise-LevelSpecificationsProcessSubstitutionMachineSubstitutionSystemsDesignControlofNoiseSourcebyDesignReducingImpactForcesReducingSpeedsandPressuresReducingFrictionalResistanceReducingRadiatingAreaReducingNoiseLeakageIsolatingandDampingVibratingElementsControlofNoiseSourcebyRedressBalancingRotatingPartsReducingFrictionalResistanceApplyingDampingMaterialsSealingNoiseLeaksPerformingRoutineMaintenance6.7NOISECONTROLINTHETRANSMISSIONPATHAcousticalSeparationAbsorbentMaterialsAcousticalLiningsPhysicalBarriersBarriersandPanelsEnclosuresIsolatorsandSilencersVibrationIsolatorsandFlexibleCouplersMufflersandSilencers6.8PROTECTINGTHERECEIVERWorkSchedulesEquipmentandShelters©1999CRCPressLLCSoundcanbedefinedasatmosphericorairbornevibra-tionperceptibletotheear.Noiseisusuallyunwantedorundesiredsound.Consequently,aparticularsoundcanbenoisetoonepersonandnottoothers,ornoiseatonetimeandnotatothertimes.Soundloudenoughtobeharmfuliscallednoisewithoutregardtoitsothercharacteristics.Noiseisaformofpollutionbecauseitcancausehearingimpairmentandpsychologicalstress.Thissectionintroducesthesubjectofsoundinengi-neeringtermsandincludesappendedreferenceswhichpro-videdetailedback-upmaterial.Itincludesthegeneralprin-ciplesofsoundproductionandpropagation,adescriptionoftheearanditsfunctions,adescriptionoftheeffectsofnoiseonthehearingapparatusandontheperson,andanintroductiontohearingmeasurementandhearingaids.SoundProductionandPropagationAudiblesoundisanyvibratorymotionatfrequenciesbe-tweenabout16and20,000Hz;normallyitreachestheearthroughpressurewavesinair.Soundisalsoreadilytransmissiblethroughothergases,liquids,orsolids;itsve-locitydependsonthedensityandtheelasticityofthemedium,whileattenuationdependslargelyonfrictionaldamping.Formostengineeringwork,adiabaticconditionsareassumed.Soundisinitiallyproducedbyvibrationofsolidobjects,byturbulentmotionoffluids,byexplosiveexpansionofgases,orbyothermeans.Thepressures,amplitudes,andvelocitiesofthecomponentsofthesoundwavewithintherangeofhearingarequitesmall.Table6.1.1givestypicalvalues;thesoundpressuresreferencedarethedynamicex-cursionsimposedontherelativelyconstantatmosphericpressure.Inafreefield(definedasanisotropichomogeneousfieldwithnoboundarysurfaces),apointsource°ofsoundproducesspherical(Beranek1954)soundwaves(seeFigure6.1.1).Ifthesewavesareatasinglefrequency,theinstantaneoussoundpressure(Pr,t)atadistancerandatimetisPr,t5[(V2wP)/r]cos[v(t2r/t)]dynes/cm26.1(1)wherethetermv2wPwdenotesthemagnitudeofpeakpres-sureataunitdistancefromthesource,andthecosinetermrepresentsphaseangle.Ingeneral,instantaneouspressuresarenotusedinnoisecontrolengineering(thoughpeakpressuresandsomenon-sinusoidalpulsepressuresare,asisshownlater),butmostsoundpressuresaremeasuredinroot-mean-square(RMS)values—thesquarerootofthearithmeticmeanofthesquaredinstantaneousvaluestakenoverasuitableperiod.ThefollowingdescriptionreferstoRMSvalues.Forsphericalsoundwavesinair,inafreefield,RMSpressurevaluesaredescribedbyPr5Po/rdynes/cm26.1(2)wherePrdenotesRMSsoundpressureatadistancerfromthesource,andPoisRMSpressureatunitdistancefromthesource.(Metersinmetricunits,feetinEnglishunits.)Acousticterminologyisbasedonmetricunits,ingeneral,thoughtheEnglishunitsoffeetandpoundsareusedinengineeringdescriptions.Afewothertermsshouldbedefined,andtheirmathe-maticalrelationshipsnoted.SoundintensityIisdefinedastheacousticpowerWpassingthroughasurfacehavingunitarea;andforspher-icalwaves(seeFigure6.1.1),thisunitareaisaportionofasphericalsurface.SoundintensityatadistancerfromasourceofpowerWisgivenbyIr5W/4pr2watts/cm26.1(3)SoundintensityisalsogivenbyIr5P2