朗德科技声学测试培训PPT幻灯片

1,噪声测量第一部分:声学基础,2,Whatisasound?声音是什么?1-Physicalphenomenon物理现象,Soundisaphenomenondefinedasatimevaryingdisturbanceofthedensityofafluidmediumassociatedwithverysmallvibrationnalmovementsoffluidparticles.声音是一种物理现象，是描述由于媒体质点振动运动引起的质点密度随时间变化的情况。Particles:continuousmatterwith:质点：具有连续相同的：mass质量density密度temperature温度associatedwithverysmallchangesofpressureandtemperature.随压力、温度有微小变化Particle=smallbitofcontinuousmediumthemoleculesofthemedium.质点=少量连续的媒质颗粒媒质的化学分子Densitychange:compressibility=changeofvolume密度变化：压缩比例=颗粒数量变化,3,Equilibriumstateoffluidarticles平衡状态,Beginningofthedisturbance干扰开始,Propagationofthedisturbance扰动传播方向,P0,v0,r0,Time时间,Thesmallcompression(duetothedisturbance)isfollowedbyacompensatingrarefaction.Thelocalparticledisplacementisfirstinthedirectionofpropagationthenitreturnstoitsinitialpositionafterpassageofthedisturbance.Whentheassociatedparticlevelocityis/tothedirectionofpropagationofthedisturbance=compressionalorlongitudinalwave.Iftheassociatedparticlevelocityisnormaltothedirectionofpropagationofthedisturbance=shearwave.质点沿声波传播的方向产生位移，往返运动，并将位移传递到下一个质点，这样就形成了波的传递。纵波-媒质质点的振动方向与声波的传播方向一致。横波-媒质质点的振动方向与声波的传播方向相互垂直。,4,S,propagationvelocityC传播速度C,Thedisturbancepropagatesthroughoutthemediumintheformofwaveatacharacteristicspeedc.声波在媒质中的传播速度为CC=340ms-1aboutinair空气C=1450ms-1aboutinwater水C=5200ms-1aboutinsteel钢铁C=3400ms-1aboutinconcrete混凝土,5,WavescanpropagateinFluids:fluidbornenoiseortransmissions(ex:incar:steeringsystems,pumps.Inhouses:pipingsystems)Air:airbornenoiseortransmission(motorofthecarorinhouseinsidetheroom.)Solids:solidbornenoiseortransmission(ex:radiatednoisefromwindscreenordoorsinhouse:radiatednoisefromwalls)液体、气体、固体都可以传递声波。,空气动力噪声由气体振动产生。气体的压力产生突变，从而引起噪声，空气压缩机、电风扇的噪声属此类。机械噪声由固体振动产生。金属板、齿轮、轴承等设备运行时，受到撞击摩擦及各种突变机械力的作用，会产生振动，引起噪声。液体流动噪声液体流动中，由于液体内部的摩擦，液体与管壁的摩擦，或流体的冲击，都会引起液体和管壁的振动，产生噪声。,6,Inliquidsandgas=predominantlylongitudinalandcompressionalwaves液体和气体中=主要是纵波Insolids=longitudinalwavesandtransverseshearwavestorsionalwaves.固体中=纵波、横波、声扭波(bendingwavesareacombinationoflongitudinalandshearwaves).（弯曲波是纵波和剪切波的结合）Insolidsthetypesofwavespropagatingstronglydependontheboundarycondition.在固体中，波的传播类型依赖于边界条件。,Planewave:onlyonelengthdimensionisrequiredtodescribetheacousticfield平面波：采用一维空间来描述声场,7,1-Subjectivephenomenon.Sound/noise声音/噪声的主观现象,Soundaffectdifferentpeopleindifferentways.Theperceptionofsoundissubjectivelyinterpreteddependingonthemoonofeachandthestateoftiredness.声音以各种方式影响着人们，声音的感知主观上依赖于人们自身的心理、生理状态，愉快、疲劳,Communication/warn交谈/报警声,8,Thereforeanindividualwillmakesubjectivejudgmentaboutvariousnoiseswhichimpingehim.因此，每个人都会对噪声作出自己的主观判断。Soundallowhumanbeingtomakequalityevaluationsanddiagnoses.人们可以通过声音对品质作出评价和诊断。Howcanweobtainobjectivemeasuresofthesesubjectiveeffects?那么如何对这些主观影响进行客观测量呢？Ratingofthesoundsintermsofannoyingfeelings(loudness,sharpness,roughness,tonality.)meansofcomparingsoundsunderdifferentconditions.可以根据声音烦恼度不同(评价参数包括:响度、尖锐度、粗糙度、音调)或不同条件下各种声音间的对比,将其划分为不同等级。Measurementofthehearingdamage(audiometry)测量听力损害度(听力计)Allowtoreducenoisefromanyenvironment(airport,trainstation,factories.)减少各种环境中的噪声(机场、火车站、工厂),9,2-Humanhearingsystem人类的听觉系统,Humanhearrespondspredominantlytoairbornenoise=pressurechanges人耳主要对空气噪声有响应=气压变化,10,Pressurevariationisanadequatenoisemeasurementquantitybecause:压力变化可用来充分度量噪声的原因是：Theauditorysystemrespondstopressurechanges听觉系统对声压的变化有响应Mechanicalstructuresrespondstopressure机械结构对压力有响应Easiestacousticquantitytomeasure.Frompressure,soundintensityandpowercanbeevaluated.可用于测量最简单的声学量。通过测量声压，可以估计出声强度和声能量。,11,4-Physicalcharacteristicsofsound声音的物理特性,Thetwobasiccharacteristicsofsoundwavearefrequencyandamplitude声波的两个基本特征量是频率和振幅,distance,Velocityc,Wavelengthl,PeriodT,Pressure,Time,f(Hz),WavenumbermaybethoughtasspatialFrequency波数也被称为空间频率,Tistheperiodofpropagatingwave.fisthenumberofpressurevariationpersecond.T=周期f=频率，即单位时间内振动的次数,Soundwaveinatube,4.1Frequency频率,12,Itcanbeseenthatathighfrequencysoundshaveshortwavelengthandatlowfrequencysoundshavelongwavelength.我们可以看出，高频率的声音对应波长短，低频率的声音对应波长长。,Highfrequencycomponentscouldgothroughsmallholesminimizinganyinsulationinstallation!(holedimensiondl).高频成分更容易穿过小孔（dl）,13,ld,Allthesoundthroughtheapertureistransmitted.(TL=0,TransmissionLoss,Transmissioncoefficientt=1)通过小孔的声音被完全传播(TL=0，传播系数t=1),Example:Diffusionofsound(soundpassesthroughholes)例：声音的散射（声音通过小孔传播）,Thesoundwillpassthroughtheholere-radiatedinanomnidirectionalwaysimilartotheoriginalbutTLisnotzero.Thesoundpowertransmittedisfarless(t1).声音通过小孔发散，像初始声源一样，但是TL0，声能大大减小。,ad,14,Frequencydecompositionofsoundisveryimportantbecause:声音的频率分析非常重要，因为：Theauditorysystemsensitivityvarieswithfrequencies听觉系统的灵敏度会随着频率的不同发生变化,Speechrange:200Hz-6000Hz语音频率范围：200Hz-6000HzSpeechintelligibilityrange:500Hz-4000Hz清晰语音频率范围：500Hz-4000Hz,15,Frequencydecompositionofsoundisveryimportantbecause:声音的频率分析非常重要，因为：Theperformanceofnoisecontrolsystemsvarywithfrequencies声音控制系统的性能随频率变化,Typicalabsorptioncoefficientsfor4materials4种典型材料的吸声系数（吸声系数用以表征材料和结构吸声能力的基本参量）,16,Frequencydecompositionofsoundisveryimportantbecause:声音的频率分析非常重要，因为：Thenoisepropagationvarywithfrequencieswithinaclosedspace在封闭的空间内，声音的传播随频率变化Propagationofwavesinsidearoomwillbedifferentaccordingtofrequencies:室内声波的传播随着频率的不同而变化：Someofwavesfromasourceinsideanenclosurewillreflectedonthewallandwillbebackatanypointinphase在密闭空间里，部分声波被墙壁反射，并以不同相位反射amplificationofthewavedisturbance对声波的幅值进行增益Normalmodewillberesonant引起固有振荡Whenfrequencyofthesource=resonancefrequencyofanormalmodeofroom当声源频率=室内固有振荡的频率时resonanceoccurs&roomrespondsstrongly(spatialdistributionofpressurecharacterizebynodesandantinodes).产生共振，（此时质点的振动处于节点和峰值点上）。,17,x3,x1,x2,Nodalplane,f1,0,0,x3,x1,x2,x1,x2,x3,f2,1,0,f2,1,1,18,Thesoundabsorptionmaterialswillonlyreducenoisefromthereverberantfieldofthesound.Absorbentmaterialshavenoeffectonthedirectfield.吸声材料吸收混响场的声音，一般不在直达声场中吸收声音。Pressureinsidearoomisdueto:室内某点的声压大小取决于：risthepositionintheroom室内某点的位置Disthedirectivityfactor方向因数Wisthesoundpowerofthesource声源声能RistheroomconstantdependingontheabsorptioncoefficientR是房间常数，与室内平均吸声系数，室内总表面积S有以下关系式：,Directfield,Reverberantfieldcorrespondingtothediffusefield,19,Lookattheproblemfromoutsideofanoisymachineryhouse:室内有噪声源，室外：,ThepowertransmittedWToutsidetheplantisgivenby:adtheaverageabsorptioncoefficient平均吸收系数tdthetransmissioncoefficientofthewalls墙壁反射系数Wtheinsidesourcepower内部声能,Forlargeplantsignorethedirectfieldandjusttakeintoaccountofthediffusefield:在足够大的工厂里，可以忽略直接声场，当作是扩散场：,20,Typicaltransmissionlossfor4materials4种典型材料的传递损失,TransmissionLoss传递损失:,21,Frequencydecompositionofsoundisveryimportantbecause:声音的频率分析非常重要，因为：Thesourceofnoiseischaracterizedbyitsfrequencycontentsandanycontrolofitmustbedoneaccordingly.频率成分是声源的特征，噪声控制的依据是频率特性。Noisereductionperformancecannotbespecifiedindependentlyofsourcefrequencies.减振降噪工作如果离开了声源频率特性研究就无从下手。,20HzAudiblerange20kHz,22,Frequencydecompositionofsoundisveryimportantbecause:声音的频率分析非常重要，因为：ThemathematicalFourierTransformsynthesizesanytimehistoryintofrequencyinformation傅立叶变化可以把时间信号的变化在频域上同步体现出来TheFourierTransformfunctionisamathematicalalgorithmwhichtransformasignalfromtimedomainintoafrequencydomain.傅立叶函数是一种数学算法，可以把时域信号转换成频域信号。,23,Puretone(forexampleaairconditioningturningataconstantspeed)containsonlyonefrequency(reallyseldominreality)纯音（例如：空调扇匀速转动）只包含一个频率成分（现实中很少存在）Mostofsoundsarecomplexandpossessseveralpuretoneofdifferentamplitudes.Energyexistsinanumberofdiscretefrequencies.Musicalnotespossessafundamentalfrequencyandharmonicswhichwillcharacterizethepitchofinstrument.大部分声音是复杂的，包含很多振幅不同的纯音。能量包含在一系列不连续的频率之中。乐器有特定的频率，组合在一起成为音乐。,Differentfrequencycontentsfordifferenttypeofsound:不同的频率对应不同类型的声音,Puretone,Pianonote,24,Broadbandnoiseconsistofawidemixtureoffrequencies.Itistypicallyindustrialnoiseorenvironmentalnoise.宽带噪声：由多种频率组成，典型的是工厂噪声、环境噪声。Modulatedfrequencies.调制频率Whitenoise:frequencycomponentsofequalamplitudebetween20Hzand20kHz白噪声：由20Hz-20kHz的等幅频率组成Pinknoiseisawhitenoisethateachoctaveisdecreasedby6dB粉红噪声：每个音阶都降低6dB的白噪声,Differentfrequencycontentsfordifferenttypeofsound:不同的频率对应不同类型的声音：,Whitenoisespectrum白噪声频谱,Pinknoisespectrum粉红噪声频谱,25,Harmonicseries谐波系列Aharmonicseriesconsistsofintegermultiplesofafundamentalfrequency,e.g.ifthefundamentalis100Hz,thentheharmonicseriesis:100,200,300,400,500,600Hz,.etc.谐波系列包含了一系列与基频成整数倍的频率，例如，如果基波频率是100Hz，谐波系列就是100，200，300，400，500，600HzThe100Hzfundamentalisthefirstharmonic,200Hzisthesecondharmonic.ThefundamentalisoftendenotedbyF0.基波频率100Hz是第一级，200Hz则是第二级。基波频率通常由F0表示。Harmonicsabovethefundamentalconstitutetheovertoneseries.高于基波频率的声音形成泛音。Sub-harmonicsareintegerdivisionsofthefundamental:e.g.forF0=100Hz,sub-harmonicsareat50,33,25,20,16.6Hzetc.Sub-harmonicsarealsocalledundertones.分谐波是基波频率除以整数：例如，F0=100Hz，分谐波就是50，33，25，20，16.6Hz,26,4.2Amplitudeofsound:声音的振幅,Theacousticaudiblepressurevariation(from20mPasto100Pas)isverysmallcomparedtothestaticairpressure(100000Pas).Theratiobetweenthetwoextremesis1millionto1forthelinearPasscale.可听到的声压变化（20mPasto100Pas）与大气压（1000Pas）相比非常的小。两者之比是：1百万比1Useofalogarithmicscale.Logarithmicratiobetweenthemeasuredvaluetoareferencevalue.Theearrespondnotlinearlybutlogarithmicallytostimulus.采用取对数的方法，取测量值和参考值的对数之比。人耳的感觉不是成线性的，而是与其对数近似成正比。,Thresholofpain,Quietestsoundthatcanbeheard,27,SoundpressurelevelindBscale:声压级（dB）：Pressurereference参考声压:P0=20mPaswhichisthelowestsoundpressureleveldetectedbythehumanear.人耳能探测到的最小声压级P0=20*10-6PasPisinPascalandthesubscriptPpointsoutthatsoundpressurelevelislookedatandnotsoundintensitylevel(LI)orsoundpowerlevel(LW)P表示帕斯卡，右下角的P代表该量是声压级，而不是声强级或声功率级,28,Lowfrequenciesneedmore“energy”orsoundpressureleveltobeheardthansoundwithin1kHz-5kHz.与频率在1kHz-5kHz之间的声音相比，低频声音往往需要具有更高的能量或者更高声压级时，才能被人们听见。TotakeintoaccountofthenonlinearityoftheearresponseatlowfrequenciestheA-weightingcurveisoftenused.通常用A计权曲线来更好地说明人耳在低频段的非线性响应特性。,29,AweightingcurveA计权曲线,30,ButA-weightingcurvesimulatestheresponseonlyoftheearforlowlevelsound.TheA-weightingcurvefollowsapproximatelytheequalloudnesscurveof40phons.但A计权曲线只能模拟人耳对低声压声音的响应特性。下图所示，A计权曲线对应于40宋等响度曲线。,Eachcurvecorrespondstotheequalsensationofloudnessperceptionfordifferentpuretonesfrequencies.每条曲线都是不同频率纯音的等响度曲线。ToneofdifferentfrequencybutsameSPLarenotperceivedequal.声压级相同但频率不同的纯音，其对应感知度并不相同。Atoneof10dB200Hzhasthesameloudnessperceptionthanatoneof0dB2kHz.10dB200Hz与0dB2kHz的声音拥有相同的响度感知度。Atlowlevelapurehighfrequencytonewilleasilymasklowfrequencypuretone.在低声压级段，高频纯音可以轻易掩蔽低频纯音。,31,LookingatthesecurvesthenoiseengineertaskwillneedtodecreasemoreSPLathighfrequenciesthanatlowfrequenciestogetthesamesubjectiveperceptionofloudness.从曲线中可看出，为了使高频和低频声音响度的主观感知度一致，噪声工程师需要更多地降低高频声音的声压级。,32,Totakeintoaccountoftheearresponsefordifferentlevelofsoundseveralweightinghasbeendeveloped:考虑到人耳对不同等级声音的响应，人们提出了几种不同计权方法：B-weightingcurveapproximatelyfollowsthe70phonsequalloudnesscurveB计权曲线约对应于70宋等响度曲线C-weightingcurveapproximatelyequalloudnessfollowsthe100phonscurveC计权曲线约对应于100宋等响度曲线,D-weightingcurvefollowsaspecialcurvewhichemphasizesfrequenciesbetween1kHz-10kHz.Usedforaircraftapplications.D计权曲线对应于一条主频在1kHz-10kHz内的特殊曲线，主要应用于机场噪声评价。,33,Perceptionofsoundpressurelevelvariation对声压级变化的感知度,Resultsappliedforfrequencyaround1000Hz.以上结果适用于频率约1kHz的情况。AthigherorlowerfrequenciesmuchlargerdifferenceofSPLneedtobeappliedtoperceivedthedifferenceinloudness.当声音频率明显高于或低于1kHz时，相差相同的响度对应的声压级的变化更大。,34,HowtoaddorsubtractdBvalues:怎样增加或减少分贝值：dBvaluescannotbedirectlysubtractedoraddedastheyarelogarithmicvalues.Onlylinearvaluescanbesummedorsubtracted.dB值是对数量度，不是线性量度，因此不能简单地进行算数加减运算。,LPtot,50dB+55dB105dB!,50dB+55dB=56.19dB,35,Assumptionforoperationonlevels:假设：Ingeneralthedifferentsourcesofnoisearenotinphase通常不同声源的噪声有不同的相位theyareincoherentsources.Incoherentsoundsaddtogetheronalinearenergy(pressuresquare)basis.它们是互不相干的声源，不会发生干涉现象，可以进行能量叠加。Whensourcesofthesamefrequencyarecombined,phaseanglebetweenthesoundsmustbetakenintoaccount.当同频率的声源相结合，两者之间的角相位就可以被计算。Whenthephasesarerandom,theequationreducestotheincoherentcase:当这个相位是任意的时候：,36,dBadditionchart:分贝相加曲线TosimplifyandnotplaywithdBandlinearvaluesofeachnoisecontributorsthefollowingcurvescanbeusedtodirectlycalculatethesoundpressurelevelduetoseveralsourcesofnoise.从曲线中可以直接计算出两个声压级叠加后的总声压级。,1.19,Notethat:Twosourcesofnoisewiththesamesoundpressurelevelsisequivalenttoadd3dB.两个相同声压级的叠加是增加3dBAslongasthereismorethan10dBdifferencebetweentwosourceofnoisethequietestcanbeforget.如果两个声压级的差值大于10dB，那么小声压级对总声压级的贡献可以忽略，总声压级近似等于大声压级。,37,Influenceofmorethan2sourcesofnoise:两个以上声源的影响：Ifmorethantwosourcescontributetothenoiselevelatapoint,usethepreviouscurvefirstforthetwofirstsourcesofnoise,getthetotalresultofthem,andaddtothisresultthenextsourceofnoise如果有两个以上的声源进行叠加，那么就利用之前的曲线先对两个声源进行叠加，得到的值再与第三个声源进行叠加，依次类推,IfP1=P2=P3=PN,38,SourceofnoisetobeevaluatedLs,dBsubtraction:分贝相减：Ifmeasurementsareperformedinnoisyenvironmentthebackgroundnoisemustbeevaluated(switchoffthesourceofnoiseunderinvestigation)andsubtractitfromthetotalleveltogetjustthesourcelevelunderinterest.在环境嘈杂的地方进行噪声测试时，受背景噪声影响，需要先把被测声源关闭，测得背景噪声量，再从总噪声量中减去背景噪声，最后获得真实的声源噪声。,LS+N,95dB-90dB5dB!,95dB-90dB=93.3dB=Ls,LNBackgroundnoise,39,dBsubtractionchart:分贝相减曲线：Thefollowingcurvecanbeusedtodirectlycalculatethesoundpressurelevelduetosourceunderbackgroundnoise.从曲线中可以直接计算出排除背景噪声影响的声源声压级。,Notethat:Ifthedeltaissmallerthan3dBthenthebackgroundnoiseistohightoperformaccuratenoisemeasurements.Firstthebackgroundnoisemustbereduced.当声压级差小于3dB，就要尽量减小背景噪声，否则会给测量带来严重影响。Ifdeltabetween3and10dBnoisemeasurementsmustbecorrectedwiththefollowingcurve.当声压级差在3dB-10dB间，就按照曲线严格计算。Ifdeltagreaterthan10dBthenthebackgroundnoiseisnegligibleandsoundmeasurementscandirectlybeestimated.当声压级差大于10dB时，背景噪声可以忽略不计。,40,5.Noisesourcequantificationandidentification噪声源的量化和识别Nowweknowhowasoundcanbecharacterized.Wemustobjectivelymeasureit.我们现在已经了解了声音的特性，接下来我们就要进行客观测量。Objectivemeasurementsmustbedonetoquantifyandqualifythesourcesofnoise:量化和评价噪声源Evaluatetheoutputsoundpowerandsoundpressure评价声能和声压Comparedifferentsourcesandbeableto比较不同的声源Label分类Select选择Estimatetheeffects估计影响Meetregulationsandrequirements规则和要求toidentifysourcesmechanismsofnoises识别机械噪声的种类Diagnostictechniques诊断技术Understandthephysics符合物理学Control,modify,redesign控制、改变、设计Machineryhealthmonitoring设备监测keepequipmentingoodworkingconditionduringproductiontime保证机器进行正常的工作生产,41,5.1Quantificationandqualificationofsoundsources量化和评价噪声源Evaluationoftheoutputsoundpressureorpowerorintensity.评价声压、声能和声强Frequencycharacteristicisbettertogivepreciseinformationthanglobalvalue.频率特征能更准确地反映信号特性。Aglobalsoundpressurelevelmaybethesamewhereasthefrequencycontentswillbereallydifferent.相同的声压级可能对应完全不同的频率特征。Theanalysisoffrequencieswillallowtopredictannoyanceforhumanandforvibrationmechanicalpotentialproblem.通过频率分析，可以帮助人们预测噪声品质，发现机器的潜在问题。,42,Valvenoiseismainlyhighfrequencieswithaspectrumrisingwithfrequency.Furnaceburnernoiseisdominatedbylowfrequencies.电噪声是高频率噪声，燃烧的噪声是低噪声。Thefandisplaysapeakinthe125Hzoctavebandduetopuretoneofthebladepassingfrequency(f=RPM*numberofblades/60).风扇在125Hz达到峰值，频率f=转速*叶轮数/60IfonlytheglobalSPLislookedatitwillbeconcludedthatthesethreesourcesofnoiseareequallyloud!单看声压级，这3个噪声源的响度相同！Lookingatthefrequenciesandknowingthehumanresponsetofrequencies,thefanwillbejudgedthemostannoyingbecauseofpuretone,andthesteamvalvewithitshigherfrequencycontentswillbelookedatmorenoisythantheburner.从人们对频率的感觉上看，风扇的噪声是令人烦感的，而电噪声比燃烧噪声更加吵。,43,Thequalificationandquantificationofsounds噪声的量化和评价comparedifferentsourcesandbeabletoselectthebestaccordingtosomecriteriaortoestimatealabel.可根据不同的噪声标准来选择ForexampletwodifferentsteeringpumpswillhaveitsownSPL(measuredinthesamecondition)spectrumandaccordingtocarmanufacturernoisecriteriathequietestwillbeselected.例如：两个不同的转向泵，在相同条件下有不同的声压级和频谱，根据汽车生产标准，只能采用声压级低的。Productssuchaswashingmachinearelabeledwithnoiselevel.洗衣机的声级标准,BoschWFR145,53dB,Samsung1253,59dB,ZFsteeringpump,Delphisteeringpump,?,44,Thequalificationandquantificationofsoundswillbecomparedtonoiserequirementsorregulationsifexisted.根据现有的标准和规范来量化和评价噪声ForexampleNRratingcurveareintendedtodeterminatetheacceptableindoornoiselevelforhearingpreservation,speechcommunicationandannoyance.例如：NR等级曲线，定义了作为听力损伤、会话干扰、烦恼的噪声评价数。,45,Firstmeasurethesoundpressurelevelspectrum.ApplyitontheNRCurvesdiagramandevaluatetheNRofthenoiseunderinvestigation.首先测量出声压级，画在NR曲线图上。TheNRisdeterminedbythehighestweightingcurvewhichjustenvelopesthedata.超过这些值的最低曲线的NR值即所求的值。TheSteamvalveandthefanexhibitedaNRof100.WhereasthevalvehasaNRof90.蒸气机和风扇的噪声都低于100NR值。All2ofthemdonotmeettherecommendationsofNR70inheavyengineeringwork.两者都未达到NR70，不满足重型机械工业标准。,Paddlebladefan,Steamvalve,46,5.2Identifysourcesmechani