朗德科技 声学测试培训

1 c T
f is the number of pressure variation per second.
Time
T=周期
f =频率，即单位时间内振动的次数
1 c f ( Hz ) T
It can be seen that at high frequency sounds have short wave length and at low frequency sounds have long wavelength. 我们可以看出，高频率的声音对应波长短，低频率的声音对应波长长。
propagation velocity C 传播速度C
Copyright HEADacoustics 1999
Waves can propagate in • Fluids : fluid borne noise or transmissions (ex : in car: steering systems, pumps.. In houses : piping systems…) • Air : air borne noise ortransmission (motor of the car or in house inside the room..) • Solids : solid borne noise or transmission ( ex : radiated noise from wind screen or doors… in house : radiated noise from walls…) 液体、气体、固体都可以传递声波。
Communication/warn交谈/报警声
Therefore an individual will make subjective judgment about various noises which impinge him. 因此，每个人都会对噪声作出自己的主观判断。 Sound allow human being to make quality evaluations and diagnoses. 人们可以通过声音对品质作出评价和诊断。 How can we obtain objective measures of these subjective effects? 那么如何对这些主观影响进行客观测量呢？ • Rating of the sounds in terms of annoying feelings (loudness, sharpness, roughness, tonality….) means of comparing sounds under different conditions.可以根据声音烦恼度不同(评价参数包括: 响度、尖锐度、粗糙度、 音调)或不同条件下各种声音间的对比, 将其划分为不同等级。 • Measurement of the hearing damage (audiometry)测量听力损害度(听力计) Allow to reduce noise from any environment (airport, train station, factories..) 减少各种环境中的噪声(机场、火车站、工厂)
空气动力噪声—由气体振动产生。气体的压力产生突变，从而引起噪声，空气压缩机、电风扇的噪声 属此类。 机械噪声—由固体振动产生。金属板、齿轮、轴承等设备运行时，受到撞击摩擦及各种突变机械 力的作用，会产生振动，引起噪声。 液体流动噪声—液体流动中，由于液体内部的摩擦，液体与管壁的摩擦，或流体的冲击，都会引起液 体和管壁的cteristics of sound声音的物理特性
The two basic characteristics of sound wave are frequency and amplitude 声波的两个基本特征量是频率和振幅
4.1 Frequency频率
f (Hz)
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
Sound is a phenomenon defined as a time varying disturbance of the density of a fluid medium associated with very small vibrationnal movements of fluid particles. 声音是一种物理现象，是描述由于媒体质点振动运动引起的质点密度随时间变化的情况。 Particles : continuous matter with : 质点：具有连续相同的： • mass 质量 • density 密度 • temperature 温度 associated with very small changes of pressure and temperature.随压力、温度有微小变化 Particle = small bit of continuous medium ≠ the molecules of the medium. 质点=少量连续的媒质颗粒≠媒质的化学分子 Density change: compressibility = change of volume 密度变化：压缩比例=颗粒数量变化
Equilibrium state of fluid articles 平衡状态 P0 ,v0, r0
V , P, r
Beginning of the disturbance 干扰开始
时 间
The small compression (due to the disturbance) is followed by a compensating rarefaction. The local particle displacement is first in the direction of propagation then it returns to its initial position after passage of the disturbance. When the associated particle velocity is// to the direction of propagation of the disturbance = compressional or longitudinal wave. If the associated particle velocity is normal to the direction of propagation of the disturbance = shear wave. 质点沿声波传播的方向产生位移，往返运动，并将位移传 递到下一个质点，这样就形成了波的传递。
d
W
S
WT W
WT
t d (1 d ) d
<< d S
d d
>> d

S
d
All the sound through the aperture is transmitted. (TL=0, Transmission Loss, Transmission coefficient t 1) 通过小孔的声音被完全传播 (TL=0， 传播系数t 1)
Water Pipes sys te m
In liquids and gas = predominantly longitudinal and compressional waves 液体和气体中=主要是纵波 In solids = longitudinal waves and transverse shear waves torsional waves. 固体中=纵波、横波、声扭波 (bending waves are a combination of longitudinal and shear waves). （弯曲波是纵波和剪切波的结合） In solids the types of waves propagating strongly depend on the boundary condition. 在固体中，波的传播类型依赖于边界条件。
2-Human hearing system人类的听觉系统
Human hear responds predominantly to airborne noise = pressure changes 人耳主要对空气噪声有响应 =气压变化
Pressure variation is an adequate noise measurement quantity because : 压力变化可用来充分度量噪声的原因是： • The auditory system responds to pressure changes • 听觉系统对声压的变化有响应 • Mechanical structures responds to pressure • • • 机械结构对压力有响应 Easiest acoustic quantity to measure. From pressure, sound intensity and power can be evaluated. 可用于测量最简单的声学量。通过测量声压，可以估计出声强度和声能量。
Time
Propagation of the disturbance 扰动传播方向
纵波----媒质质点的振动方向与声波的传播方向一致。 横波----媒质质点的振动方向与声波的传播方向相互垂直。
S
The disturbance propagates throughout the medium in the form of wave at a characteristic speed c. 声波在媒质中的传播速度为C C = 340 ms-1 about in air C = 1450 ms-1 about in water C= 5200 ms-1 about in steel C = 3400 ms-1 about in concrete 空气 水 钢铁 混凝土