朗德科技--声学测试培训.ppt

噪声 测量 第一部分: 声学基础 What is a sound? 声音是什么? 1-Physical phenomenon物理现象 1-Subjective phenomenon. Sound/noise声音/噪声的主观现象 2-Human hearing system人类的听觉系统 4-Physical characteristics of sound声音的物理特性 To take into account of the ear response for different level of sound several weighting has been developed:考虑到人耳对不同等级声音的响应，人们提出了几种不同计权方法： B-weighting curve approximately follows the 70 phons equal loudness curve B计权曲线约对应于70宋等响度曲线 C-weighting curve approximately equal loudness follows the 100 phons curve C计权曲线约对应于100宋等响度曲线 where WB = weighting to be applied, dB f = frequency, Hz where WC = weighting to be applied, dB f = frequency, Hz D-weighting curve follows a special curve which emphasizes frequencies between 1kHz-10kHz. Used for air craft applications. D计权曲线对应于一条主频在1kHz-10kHz内的特殊曲线，主要应用于机场噪声评价。 Perception of sound pressure level variation 对声压级变化的感知度 1/100 100 Much quieter or louder 10 times amplitude 20 dB 1/10 10 Half or twice as loud 10 dB 1/4 4 Clearly noticeable Double amplitude 6 dB 1/3 3 Clearly noticeable 5 dB 1/2 2 Just perceptible 3 dB Change in power decrease Change in power increase Human perception Change in sound level Results applied for frequency around 1000Hz.以上结果适用于频率约1kHz的情况。 At higher or lower frequencies much larger difference of SPL need to be applied to perceived the difference in loudness. 当声音频率明显高于或低于1kHz时，相差相同的响度对应的声压级的变化更大。 Lp1 LP2 How to add or subtract dB values :怎样增加或减少分贝值： dB values can not be directly subtracted or added as they are logarithmic values. Only linear values can be summed or subtracted. dB值是对数量度，不是线性量度，因此不能简单地进行算数加减运算。 LPtot 50dB+55dB≠105dB !!! 50dB + 55dB = 56.19 dB Assumption for operation on levels :假设： In general the different