噪聲分析與測量第一頁，共十七頁，編輯于2023年，星期二Theroot-meansquare(rms)soundpressure

Combinedsoundpressureofp1andp2Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第二頁，共十七頁，編輯于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels(1)兩列頻率相同且以恒定相位差相交的單頻率噪聲聲波的疊加

相干波：頻率相同、相位差固定不變的波稱為相干波。第三頁，共十七頁，編輯于2023年，星期二ififChapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels這兩種情況下的平均聲能密度分別為第四頁，共十七頁，編輯于2023年，星期二(2)兩列不相干噪聲聲波的疊加orthefrequencyissame,butthephaseanglevariationisofrandomTimeislongenough兩列具有不同頻率，或頻率相同但相交時(shí)相位差無規(guī)律變化的噪聲聲波疊加后的合成聲場，其平均聲能量密度等于每列噪聲聲波平均能量密度之和，這兩列噪聲波稱為不相干波，它們的合成聲場將遵守“能量相加法則”。Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第五頁，共十七頁，編輯于2023年，星期二Noiseisemittedusuallyfrommorethanonesourceoratdifferentfrequencies,anditisnecessarytocalculatethecumulativeoroverallsoundlevels.Obviously,sincethesoundlevelscalesarelogarithmic,theycannotbeaddedalgebraically.Combiningofsoundlevelsmaybeperformedusingtheenergyadditiontheoremandtheoveralllevel

L(OA)isdeterminedbyHere,eachsoundleveltobecombinedmightbethenoisefromnindividualsourcesorthesoundlevelsassociatedwithnoctavebands.Theymaybesoundpowerlevelsorsoundpressurelevels.Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第六頁，共十七頁，編輯于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第七頁，共十七頁，編輯于2023年，星期二L1-L2012345678910Lc-L13.02.52.11.81.51.21.00.80.60.50.4Anothereasyandusefulmethodforcombiningsoundlevelsistoutilizethetableasbellow.Thecombinedeffectofsoundsdependsonthedifferenceintheirdecibellevels.實(shí)際計(jì)算表明，兩列聲壓級相同的噪聲疊加后，總聲壓級僅增加3dB；兩列噪聲的聲壓級相差10dB以上，則聲壓級低的那列噪聲對總聲壓級的貢獻(xiàn)可以忽略不計(jì)，總聲壓級近似等于聲壓級高的那個(gè)值.Chapter6NoiseAnalysisandMeasurement6.1CombinationofSoundLevels第八頁，共十七頁，編輯于2023年，星期二(1)OctaveBandand1/3OctaveBandSpectralAnalysis

Innoisecontrolengineering,thebandsarerelatedbythefollowingrelationshipn=1,octaveband

n=1/3,one-third-octaveband

ThecenterfrequencyofanysuchbandisdefinedasthegeometricmeanThelowerandupperlimitfrequenciesmaybedeterminedfromthecenterfrequencyasChapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第九頁，共十七頁，編輯于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第十頁，共十七頁，編輯于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第十一頁，共十七頁，編輯于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第十二頁，共十七頁，編輯于2023年，星期二Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十三頁，共十七頁，編輯于2023年，星期二(2)ConstantBandwidthNarrowBandSpectralAnalysis在倍頻程分析中，中心頻率越高，對應(yīng)的帶寬越大，得出的數(shù)據(jù)越粗糙。在恒定窄帶分析中，在高頻域仍能保持同樣的帶寬，可達(dá)到很高的分析精度。但其代價(jià)是大大增加了分析的工作量。Ifthenoisehasfrequenciesevenlydistributedthroughouttheaudiblefrequencyrangeitisknownaswhitenoise.Chapter6NoiseAnalysisandMeasurement6.2SpectralAnalysisofNoise第十四頁，共十七頁，編輯于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第十五頁，共十七頁，編輯于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