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1、page 1授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringChapter 6 Noise Analysis and Measurement 第6章 噪声分析与测量6. 1 Combination of Sound Levels6. 2 Spectral Analysis of Noise6. 3 Weighted Sound Levels6. 4 Noise Measurements6. 5 Noise Source Identificationpage 2授课人柳贡民*动力与能源工程学院College of Power and
2、Energy EngineeringThe root-mean square (rms) sound pressure Combined sound pressure of p1 and p2Chapter 6 Noise Analysis and Measurement 6. 1 Combination of Sound Levelspage 3授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringChapter 6 Noise Analysis and Measurement 6. 1 Combination of Sound Lev
3、els(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。page 4授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringififChapter 6 Noise Analysis and Measurement 6. 1 Combination of Sound Levels这两种情况下的平均声能密度分别为page 5授课人柳贡民*动力与能源工程学院College of Power and Energy Engineering(2) 两列不相干噪声声波的叠加or the freq
4、uency is same, but the phase angle variation is of randomTime is long enough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”。Chapter 6 Noise Analysis and Measurement 6. 1 Combination of Sound Levelspage 6授课人柳贡民*动力与能源工程学院College of Power and Energy E
5、ngineeringNoise is emitted usually from more than one source or at different frequencies, and it is necessary to calculate the cumulative or overall sound levels. Obviously, since the sound level scales are logarithmic, they cannot be added algebraically. Combining of sound levels may be performed u
6、sing the energy addition theorem and the overall level L(OA) is determined by Here, each sound level to be combined might be the noise from n individual sources or the sound levels associated with n octave bands. They may be sound power levels or sound pressure levels. Chapter 6 Noise Analysis and M
7、easurement 6. 1 Combination of Sound Levelspage 7授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringChapter 6 Noise Analysis and Measurement 6. 1 Combination of Sound Levelspage 8授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringL1-L2012345678910 Lc-L13.02.52.11.81.51.21.00.80.60.50.4Anothe
8、r easy and useful method for combining sound levels is to utilize the table as bellow. The combined effect of sounds depends on the difference in their decibel levels. 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. Chapter 6 Noise Analysis and Measureme
9、nt 6. 1 Combination of Sound Levelspage 9授课人柳贡民*动力与能源工程学院College of Power and Energy Engineering(1) Octave Band and 1/3 Octave Band Spectral Analysis In noise control engineering, the bands are related by the following relationship n=1, octave band n=1/3, one-third-octave band The center frequency o
10、f any such band is defined as the geometric mean The lower and upper limit frequencies may be determined from the center frequency as Chapter 6 Noise Analysis and Measurement6. 2 Spectral Analysis of Noisepage 10授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringOctave Band1/3 Octave Band Lower
11、Limit Frequency (Hz)Center Frequency (Hz)Upper Limit Frequency (Hz)Lower Limit Frequency (Hz)Center Frequency (Hz)Upper Limit Frequency (Hz) 2231.54422.42528.2 28.231.535.5 35.54044.7 44638844.75056.2 56.26370.8 70.88089.1 8812517789.1100112 112125141 141160178 177250355178200224 224250282 282315355
12、 355500710355400447 447500562 562630708Chapter 6 Noise Analysis and Measurement 6. 2 Spectral Analysis of Noisepage 11授课人柳贡民*动力与能源工程学院College of Power and Energy Engineering7101,0001,4207088008918911,0001,1221,1221,2501,4131,4202,0002,8401,4131,6001,7781,7782,0002,2392,2392,5002,8182,8404,0005,6802,
13、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 14,13014,130 16,000 17,78017,780 20,000 22,390Chapter 6 Noise Analysis and Measurement6. 2 Spectral Analysis of Noisepage 12授课人柳贡民*动力与能源工程学院College of Power and
14、Energy Engineering(1) Octave Band and 1/3 Octave Band Spectral Analysis Band Number 1 2 3 4 5 6 7 8 Center Freq. (Hz) 63 125 250 500 1000 2000 4000 8000 SPL at 3 ft (dB) 126 132 128 119 115 108 98 90133134.3134.4Overall SPL 134 dB Chapter 6 Noise Analysis and Measurement6. 2 Spectral Analysis of Noi
15、se128.5115.898.6115.9L1-L2012345678910Lc-L13.02.52.11.81.51.21.00.80.60.50.4page 13授课人柳贡民*动力与能源工程学院College of Power and Energy EngineeringChapter 6 Noise Analysis and Measurement6. 2 Spectral Analysis of Noisepage 14授课人柳贡民*动力与能源工程学院College of Power and Energy Engineering(2) Constant Bandwidth Narrow Band Spectral Analysis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。 If the noise has frequencies evenly distributed throughout the audible frequency range it is known as white noise. Chapter 6 Noise Analysis and Measurement6. 2 Spectral Analysis of Noi
