Generation of Sound Waves
Table 1 Approximate Speed of Sound in Common Materials
Sound Velocity (ft/s) 1,100
Medium Air, dry (0C and 0.76 mm Hg)
m/s 330
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.
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