文档介绍：环境影响评价
第七章噪声环境影响评价
噪声和噪声评价量

What are sound and noise?
Sound is what we hear. Noise is unwanted sound. The difference between sound and noise depends upon the listener and the circumstances. Rock music can be pleasurable sound to one person and an annoying noise to another. In either case, it can be hazardous to a person's hearing if the sound is loud and if he or she is exposed long and often enough.
噪声指人们不需要的频率在20~20000 Hz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
声音的频率、波长和声速
Sound is produced by vibrating objects and reaches the listener's ears as waves in the air or other media. When an object vibrates, it causes slight changes in air pressure. These air pressure changes travel as waves through the air and produce sound.
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 ; c =λ/ T
c≈ + t
Generation of Sound Waves
Table 1Approximate Speed of Sound mon Materials
Medium
Sound Velocity (ft/s)
m/s
Air, dry (0C and mm Hg)
1,100
330
Wood (soft - along the fibre)
11,100
3400
Water (15C)
4,700
1400
Concrete
10,200
3100
Steel
16,000
5000
Lead
3,700
1200
Glass
18,500
5500
Hydrogen (0C and m)
4,100
声压和声压级
What is sound pressure?
Sound pressure is the amount of air pressure fluctuation a noise source creates.
What is a sound pressure level?
Sound pressure converted to the decibel scale is called sound pressure level (Lp). The zero of the decibel scale (0 dB) is the sound pressure of Pa. This means that Pa is the reference sound pressure to which all other sound pressures pared on the dB scale. This is the reason the decibels of sound are often indicated as dB re Pa.
Lp = 10 lg (p22/p12) = 20 lg (p /p0)
Comparison of Sound Pressure Level and Sound Pressure