噪声分析与测量

噪声分析与测量第一页，共十七页，编辑于2023年，星期二Theroot-meansquare(rms)soundpressure

Combinedsoundpressureofp1andp2Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第二页，共十七页，编辑于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels(1)两列频率相同且以恒定相位差相交的单频率噪声声波的叠加

相干波：频率相同、相位差固定不变的波称为相干波。第三页，共十七页，编辑于2023年，星期二ififChapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels这两种情况下的平均声能密度分别为第四页，共十七页，编辑于2023年，星期二(2)两列不相干噪声声波的叠加orthefrequencyissame,butthephaseanglevariationisofrandomTimeislongenough两列具有不同频率，或频率相同但相交时相位差无规律变化的噪声声波叠加后的合成声场，其平均声能量密度等于每列噪声声波平均能量密度之和，这两列噪声波称为不相干波，它们的合成声场将遵守“能量相加法则”。Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第五页，共十七页，编辑于2023年，星期二Noiseisemittedusuallyfrommorethanonesourceoratdifferentfrequencies,anditisnecessarytocalculatethecumulativeoroverallsoundlevels.Obviously,sincethesoundlevelscalesarelogarithmic,theycannotbeaddedalgebraically.Combiningofsoundlevelsmaybeperformedusingtheenergyadditiontheoremandtheoveralllevel

L(OA)isdeterminedbyHere,eachsoundleveltobecombinedmightbethenoisefromnindividualsourcesorthesoundlevelsassociatedwithnoctavebands.Theymaybesoundpowerlevelsorsoundpressurelevels.Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第六页，共十七页，编辑于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第七页，共十七页，编辑于2023年，星期二L1-L2012345678910Lc-L13.02.52.11.81.51.21.00.80.60.50.4Anothereasyandusefulmethodforcombiningsoundlevelsistoutilizethetableasbellow.Thecombinedeffectofsoundsdependsonthedifferenceintheirdecibellevels.实际计算表明，两列声压级相同的噪声叠加后，总声压级仅增加3dB；两列噪声的声压级相差10dB以上，则声压级低的那列噪声对总声压级的贡献可以忽略不计，总声压级近似等于声压级高的那个值.Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第八页，共十七页，编辑于2023年，星期二(1)OctaveBandand1/3OctaveBandSpectralAnalysis

Innoisecontrolengineering,thebandsarerelatedbythefollowingrelationshipn=1,octaveband

n=1/3,one-third-octaveband

ThecenterfrequencyofanysuchbandisdefinedasthegeometricmeanThelowerandupperlimitfrequenciesmaybedeterminedfromthecenterfrequencyasChapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第九页，共十七页，编辑于2023年，星期二OctaveBand1/3OctaveBandLowerLimitFrequency(Hz)CenterFrequency(Hz)UpperLimitFrequency(Hz)LowerLimitFrequency(Hz)CenterFrequency(Hz)UpperLimitFrequency(Hz)2231.54422.42528.228.231.535.535.54044.744638844.75056.256.26370.870.880891100112112125141141160178177250355178200224224250282282315355355500710355400447447500562562630708Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十页，共十七页，编辑于2023年，星期二7101,0001,4207088008918911,0001,1221,1221,2501,4131,4202,0002,8401,4131,6001,7781,7782,0002,2392,2392,5002,8182,8404,0005,6802,8183,1503,5483,5484,0004,4674,4675,0005,6235,6808,00011,3605,6236,3007,0797,0798,0008,9138,91310,00011,22011,36016,00022,720

11,220

12,500

14,130

14,130

16,000

17,780

17,780

20,000

22,390Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十一页，共十七页，编辑于2023年，星期二(1)OctaveBandand1/3OctaveBandSpectralAnalysis

BandNumber12345678CenterFreq.(Hz)631252505001000200040008000SPLat3ft(dB)1261321281191151089890

133134.3134.4OverallSPL134dBChapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise128.5115.898.6115.9L1-L2012345678910Lc-L13.02.52.11.81.51.21.00.80.60.50.4第十二页，共十七页，编辑于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十三页，共十七页，编辑于2023年，星期二(2)ConstantBandwidthNarrowBandSpectralAnalysis在倍频程分析中，中心频率越高，对应的带宽越大，得出的数据越粗糙。在恒定窄带分析中，在高频域仍能保持同样的带宽，可达到很高的分析精度。但其代价是大大增加了分析的工作量。Ifthenoisehasfrequenciesevenlydistributedthroughouttheaudiblefrequencyrangeitisknownaswhitenoise.Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十四页，共十七页，编辑于2023年，星期二Frequency(Hz)Relativeresponse(dB)Frequency(Hz)Relativeresponse(dB)

2531.540

-44.7-39.4-34.6

8001,0001,250

-0.80+0.6

506380

-30.2-26.2-22.5

1,6002,0002,500

+1.0+1.2+1.3

100125160

-19.1-16.1-13.4

3,1504,0005,000

+1.2+1.0+0.5

200250315

-10.9-8.6-6.6

6,3008,00010,000

-0.1-1.1-2.5

400500630

-4.8-3.2-1.9

12,50016,00020,000

-4.3-6.6-9.3Aelectricalweightingnetworksforsoundlevelmeter

Chapter6NoiseAnalysisandMeasurement6.3WeightedSoundLevels第十五页，共十七页，编辑于2023年，星期二BandNumber12345678CenterFreq.(Hz)631252505001000200040008000SPLat3ft(dB)1261321281191151089890A-weighting-26.2-16.1-8.6-3.2+0+1.2+1.0-1.1A-weightedSPL99.8115.9119.4115.8115109.29988.9116121