环境影响评价11噪声

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1、环境影响评价第七章噪声环境影响评价7.1噪声和噪声评价量7.1.1环境噪声和噪声源Whataresoundandnoise?Soundiswhatwehear.Noiseisunwantedsound.Thedifferencebetweensoundandnoisedependsuponthelistenerandthecircumstances.Rockmusiccanbepleasurablesoundtoonepersonandanannoyingnoisetoanother.Ineithercase,itcanbeh

2、azardoustoaperson'shearingifthesoundisloudandifheorsheisexposedlongandoftenenough.噪声指人们不需要的频率在20~20000Hz范围内的可听声。环境噪声源的分类工厂噪声鼓风机、气轮机、织布机、冲床建筑施工噪声打桩机、混凝土搅拌机、卷扬机和推土机交通噪声汽车、火车、船舶汽笛和飞机社会生活噪声人群大声喧闹、高音喇叭和收放机等发出的过强的声音7.1.2声音的频率、波长和声速Soundisproducedbyvibratingobjectsandreach

3、esthelistener'searsaswavesintheairorothermedia.Whenanobjectvibrates,itcausesslightchangesinairpressure.Theseairpressurechangestravelaswavesthroughtheairandproducesound.单位时间内空气分子发生的密-疏变化的周期称频率。每秒钟密-疏变化一次称1赫（Hz）。人耳所能觉察的频率在20~20000Hz间。声波中两个相邻压缩区或膨胀区之间距离称为波长。c=λf；f=1/T；

4、c=λ/Tc≈331.4+0.607tGenerationofSoundWavesTable1ApproximateSpeedofSoundinCommonMaterialsMediumSoundVelocity(ft/s)m/sAir,dry(0Cand0.76mmHg)1,100330Wood(soft-alongthefibre)11,1003400Water(15C)4,7001400Concrete10,2003100Steel16,0005000Lead3,7001200Glass18,5005500Hydro

5、gen(0Cand0.76m)4,1007.1.3噪声的基本评价量7.1.3.1分贝Whatisadecibel是指两个相同的物理量（例如A1和A0）之比取以10为底的对数并乘以10（或20），即N=10log(A1/A0)dBwherethelogistobase10Ifthesecondproducestwiceasmuchpowerthanthefirst,thedifferenceindBis10log(P2/P1)=10log2=3dB.Ifthesecondhad10timesthepowerofthefirst,

6、thedifferenceindBwouldbe10log(P2/P1)=10log10=10dB.Ifthesecondhadamilliontimesthepowerofthefirst,thedifferenceindBwouldbe10log(P2/P1)=10log1000000=60dB.Plotof10log(P2/P1)7.1.3.2声压和声压级Whatissoundpressure?Soundpressureistheamountofairpressurefluctuationanoisesourcecrea

7、tes.Whatisasoundpressurelevel?Soundpressureconvertedtothedecibelscaleiscalledsoundpressurelevel(Lp).Thezeroofthedecibelscale(0dB)isthesoundpressureof0.00002Pa.Thismeansthat0.00002PaisthereferencesoundpressuretowhichallothersoundpressuresarecomparedonthedBscale.Thisi

8、sthereasonthedecibelsofsoundareoftenindicatedasdBre0.00002Pa.Lp=10lg(p22/p12)=20lg(p/p0)ComparisonofSoundPressureLevelandSoundPressure7.1.