噪声分析与测量
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page 2
授课人——柳贡民 2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Noise 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 using the energy addition theorem and the overall level L(OA) is determined by
2 2 2 pe pe p 1 e2
2 T' 0 p1 p2 dt 0 T
1 2
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”。
p p1 p2 p1m cos1t 1 p2m cos2 t 2
The root-mean square (rms) sound pressure
1 T 2 1 T 2 0 p dt 0 p1 p 2 dt T T 2 T 1 T 2 1 T 2 2 T 2 2 p p p dt 0 p 1 dt 0 p 2 dt 0 p1 p 2 dt p e 1 e2 0 1 2 T T T T
page 4
授课人——柳贡民 2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
2 pe
page 1
授课人——柳贡民
2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Combined sound pressure of p1 and p2
p1 p1m cos 1t 1 p2 p2m cos 2t 2
L(OA) 10 lg 10Li /10
i 1
n
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.
2 2 2 pe pe p 1 e 2 2 pe1 pe 2 cos( 2 1 )
if 1 2 0
2 pe
pe1 pe2
2
p1m p2m p1m p2m
p e 2 p e1 pe 0
if 1 2
2 pe pe1 pe2
2
这两种情况下的平均声能密度分别为
1 2 2
1 2 2
pe1 pe 2 2 0c0 pe1 pe 2 2 0c0
1 2 0
1 2
pag百度文库 3
授课人——柳贡民
2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
2 T 2 T p1 p2 dt p1m p2 m cos(1t 1 ) cos(2t 2 )dt 0 T T 0
T 1 p1m p2 m cos(1t 2t 1 2 ) cos(1t 2t 1 2 )dt 0 T
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
(2) 两列不相干噪声声波的叠加 2 T 1 2 0 p1 p2 dt 0 T
or the frequency is same, but the phase angle variation is of random Time is long enough
T 1 p1m p2 m cos[(1 2 )t (1 2 )]dt 0 T
(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。
2 1 2 cons tan t 1 2 pe pm 2 T 2 p1 p2 dt p1m p2 m cos( 2 1 ) 2 pe1 pe2 cos(2 1 ) 0 T
授课人——柳贡民 2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Noise 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 using the energy addition theorem and the overall level L(OA) is determined by
2 2 2 pe pe p 1 e2
2 T' 0 p1 p2 dt 0 T
1 2
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”。
p p1 p2 p1m cos1t 1 p2m cos2 t 2
The root-mean square (rms) sound pressure
1 T 2 1 T 2 0 p dt 0 p1 p 2 dt T T 2 T 1 T 2 1 T 2 2 T 2 2 p p p dt 0 p 1 dt 0 p 2 dt 0 p1 p 2 dt p e 1 e2 0 1 2 T T T T
page 4
授课人——柳贡民 2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
2 pe
page 1
授课人——柳贡民
2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
Combined sound pressure of p1 and p2
p1 p1m cos 1t 1 p2 p2m cos 2t 2
L(OA) 10 lg 10Li /10
i 1
n
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.
2 2 2 pe pe p 1 e 2 2 pe1 pe 2 cos( 2 1 )
if 1 2 0
2 pe
pe1 pe2
2
p1m p2m p1m p2m
p e 2 p e1 pe 0
if 1 2
2 pe pe1 pe2
2
这两种情况下的平均声能密度分别为
1 2 2
1 2 2
pe1 pe 2 2 0c0 pe1 pe 2 2 0c0
1 2 0
1 2
pag百度文库 3
授课人——柳贡民
2018年11月10日星期六
动力与能源工程学院 College of Power and Energy Engineering
2 T 2 T p1 p2 dt p1m p2 m cos(1t 1 ) cos(2t 2 )dt 0 T T 0
T 1 p1m p2 m cos(1t 2t 1 2 ) cos(1t 2t 1 2 )dt 0 T
Chapter 6 Noise Analysis and Measurement
6. 1 Combination of Sound Levels
(2) 两列不相干噪声声波的叠加 2 T 1 2 0 p1 p2 dt 0 T
or the frequency is same, but the phase angle variation is of random Time is long enough
T 1 p1m p2 m cos[(1 2 )t (1 2 )]dt 0 T
(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。
2 1 2 cons tan t 1 2 pe pm 2 T 2 p1 p2 dt p1m p2 m cos( 2 1 ) 2 pe1 pe2 cos(2 1 ) 0 T