环境影响评价11噪声.ppt

环境影响评价 第七章 噪声环境影响评价 7.1 噪声和噪声评价量 7.1.1环境噪声和噪声源 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 persons 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 7.1.2 声音的频率、波长和声速 Sound is produced by vibrating objects and reaches the listeners 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≈ 331.4 + 0.607 t Generation of Sound Waves Table 1Approximate Speed of Sound in Common Materials 7.1.3 噪声的基本评价量 7.1.3.1分贝 What is a decibel 是指两个相同的物理量（例如A1和A0 ）之比取以10为底的对数并乘以10（或20），即 N=10 log (A1/ A0) dB ?????? where the log is to base 10 If the second produces twice as much power than the first, the difference in dB is 10 log (P2/P1) = 10 log 2 = 3 dB. If the second had 10 times the power of the first, the difference in dB would be 10 log (P2/P1)= 10 log 10 = 10 dB. If the second had a million times the power of the first, the difference in dB would be 10 log (P2/P1) = 10 log 1000000 = 60 dB. Plot of 10 log (P2/P1) 7.1.3.2 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 0.00002