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1、1FUNDAMENTALSOFACOUSTICSProfessorColinHHansenDepartmentofMechanicalEngineeringUniversityofAdelaideSouthAustralia5005AUSTRALIAchansen@mecheng.adelaide.edu.auFundamentalaspectsofacousticsarepresented,astheyrelatetotheunderstandingandapplicationofamethodolo
2、gyfortherecognition,evaluationandpreventionorcontrolofnoiseasanoccupationalhazard.Furtherinformationcanbefoundinthespecialisedliteraturelistedattheendofthechapter.1.1.PHYSICSOFSOUNDToprovidethenecessarybackgroundfortheunderstandingofthetopicscoveredinthi
3、sdocument,basicdefinitionsandotheraspectsrelatedtothephysicsofsoundandnoisearepresented.MostdefinitionshavebeeninternationallystandardisedandarelistedinstandardspublicationssuchasIEC60050-801(1994).Noisecanbedefinedas"disagreeableorundesiredsound"orother
4、disturbance.Fromtheacousticspointofview,soundandnoiseconstitutethesamephenomenonofatmosphericpressurefluctuationsaboutthemeanatmosphericpressure;thedifferentiationisgreatlysubjective.Whatissoundtoonepersoncanverywellbenoisetosomebodyelse.Therecognitionof
5、noiseasaserioushealthhazardisadevelopmentofmoderntimes.Withmodernindustrythemultitudeofsourceshasacceleratednoise-inducedhearingloss;amplifiedmusicalsotakesitstoll.Whileamplifiedmusicmaybeconsideredassound(notnoise)andtogivepleasuretomany,theexcessivenoi
6、seofmuchofmodernindustryprobablygivespleasuretoveryfew,ornoneatall.Sound(ornoise)istheresultofpressurevariations,oroscillations,inanelasticmedium(e.g.,air,water,solids),generatedbyavibratingsurface,orturbulentfluidflow.Soundpropagatesintheformoflongitudi
7、nal(asopposedtotransverse)waves,involvingasuccessionofcompressionsandrarefactionsintheelasticmedium,asillustratedbyFigure1.1(a).Whenasoundwavepropagatesinair(whichisthemediumconsideredinthisdocument),theoscillationsinpressureareaboveandbelowtheambientatm
8、osphericpressure.1.1.1.Amplitude,Frequency,WavelengthAndVelocitySoundwaveswhichconsistofapuretoneonlyarecharacterisedby:theamplitudeofpressurechanges,whichcanbedescribedbythemaximumpressureamplitude,pM,ortheroot-mean-squa
