朗德科技--声学测试培训

噪声测量第一部分:声学基础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=smallbitofcontinuousmedium≠themoleculesofthemedium.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Equilibriumstateoffluidarticles平衡状态Beginningofthedisturbance干扰开始Propagationofthedisturbance扰动传播方向P0,v0,r0Time时间r,,PVThesmallcompression(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。SpropagationvelocityC传播速度CThedisturbancepropagatesthroughoutthemediumintheformofwaveatacharacteristicspeedc.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CopyrightHEADacoustics1999Wavescanpropagatein•Fluids:fluidbornenoiseortransmissions(ex:incar:steeringsystems,pumps..Inhouses:pipingsystems…)•Air:airbornenoiseortransmission(motorofthecarorinhouseinsidetheroom..)•Solids:solidbornenoiseortransmission(ex:radiatednoisefromwindscreenordoors…inhouse: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。WaterPipessystemInliquidsandgas=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……Enjoyablesound令人愉悦的声音Unwantedsound让人反感的声音Communication/warn交谈/报警声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)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。4-Physicalcharacteristicsofsound声音的物理特性cTHzf1)(Thetwobasiccharacteristicsofsoundwavearefrequencyandamplitude声波的两个基本特征量是频率和振幅distanceVelocitycWavelengthPeriodTPressureTimef(Hz)2ckWavenumbermaybethoughtasspatialFrequency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Soundwaveinatube4.1Frequency频率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!!(holedimensiond).高频成分更容易穿过小孔（d）cTHzf1)(ddSddSdAllthesoundthroughtheapertureistransmitted.(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TL≠0，声能大大减小。dddTWWt)1(dSWWTFrequencydecompositionofsoundisveryimportantbecause: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---4000HzFrequencydecompositionofsoundisveryimportantbecause: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MaterialThicknessIncludinganyairspace(mm)Frequency(Hz)63125250