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1、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
2、：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 ar
3、ticles平衡状态,Beginning of the disturbance干扰开始,Propagation of the disturbance扰动传播方向,P0,v0,r0,Time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 aft
4、er 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
5、就形成了波的传递。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,propagation velocity C 传播速度C,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 空气 C=1450 ms-1 about in water 水 C=5200 ms-1 about in steel 钢铁 C=3400 ms-1 ab
6、out in concrete 混凝土,Waves can propagate inFluids: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 o
7、r doors in house:radiated noise from walls)液体、气体、固体都可以传递声波。,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 体和管壁的振动，产生噪声。,In liquids and gas=predominantly longitudinal and compressional waves液体和气体中=
8、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 oflongitudinal and shear waves).（弯曲波是纵波和剪切波的结合）In solids the types of waves propagatingstrongly depend on the boundary condition.在固体中，波的传播类型依赖于边界条件。,Plane wave:only one length d
9、imension is required to describe the acoustic field平面波：采用一维空间来描述声场,1-Subjective phenomenon.Sound/noise声音/噪声的主观现象,Sound affect different people in different ways.The perception of sound issubjectively interpreted depending on the moon of each and the state of tiredness.声音以各种方式影响着人们，声音的感知主观上依赖于人们自身的心理
10、、生理状态，愉快、疲劳,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
11、?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
12、from any environment(airport,train station,factories.)减少各种环境中的噪声(机场、火车站、工厂),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 r
13、esponds 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。,4-Physical characteristics of sound声音的物理特性,The two basic characteristics of soun
14、d wave are frequency and amplitude声波的两个基本特征量是频率和振幅,distance,Velocity c,Wavelength l,PeriodT,Pressure,Time,f(Hz),Wave number may be thoughtas spatial Frequency波数也被称为空间频率,T is the period of propagating wave.f is the number of pressure variation per second.T=周期 f=频率，即单位时间内振动的次数,Sound wave in a tube,4.1
15、 Frequency频率,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。,High frequency components could go through small holesminimizing any insulation installation!(hole dimension d l).高频成分更容易穿过小孔（d l）,l d,d,l
16、 d,All the sound through the apertureis transmitted.(TL=0,TransmissionLoss,Transmission coefficient t=1)通过小孔的声音被完全传播(TL=0，传播系数t=1),Example:Diffusion of sound(sound passes through holes)例：声音的散射（声音通过小孔传播）,The sound will pass through the hole re-radiated in an omnidirectional way similar to the origina
17、l but TL is not zero.The sound power transmitted is far less(t 1).声音通过小孔发散，像初始声源一样，但是TL0，声能大大减小。,ad,Frequency decomposition of sound is very important because:声音的频率分析非常重要，因为：The auditory system sensitivity varies with frequencies听觉系统的灵敏度会随着频率的不同发生变化,Speech range:200Hz-6000Hz语音频率范围：200Hz-6000HzSpeech
18、 intelligibility range:500Hz-4000Hz清晰语音频率范围：500Hz-4000Hz,Frequency decomposition of sound is very important because:声音的频率分析非常重要，因为：The performance of noise control systems vary with frequencies声音控制系统的性能随频率变化,Typical absorption coefficients for 4 materials 4种典型材料的吸声系数（吸声系数用以表征材料和结构吸声能力的基本参量）,Frequenc
19、y decomposition of sound is very important because:声音的频率分析非常重要，因为：The noise propagation vary with frequencies within a closed space在封闭的空间内，声音的传播随频率变化Propagation of waves inside a room will be different according to frequencies:室内声波的传播随着频率的不同而变化：Some of waves from a source inside an enclosure will re
20、flected on the wall and will be back at any point in phase在密闭空间里，部分声波被墙壁反射，并以不同相位反射amplification of the wave disturbance 对声波的幅值进行增益Normal mode will be resonant 引起固有振荡When frequency of the source=resonance frequency of a normal mode of room当声源频率=室内固有振荡的频率时resonance occurs&room responds strongly(spati
21、al distribution ofpressure characterize by nodes and antinodes).产生共振，（此时质点的振动处于节点和峰值点上）。,x3,x1,x2,Nodal plane,f1,0,0,x3,x1,x2,x1,x2,x3,f2,1,0,f2,1,1,The sound absorption materials will only reduce noise from the reverberantfield of the sound.Absorbent materials have no effect on the direct field.吸声材
22、料吸收混响场的声音，一般不在直达声场中吸收声音。Pressure inside a room is due to:室内某点的声压大小取决于：r is the position in the room室内某点的位置D is the directivity factor方向因数W is the sound power of the source 声源声能R is the room constant depending on the absorption coefficient R是房间常数，与室内平均吸声系数，室内总表面积S有以下关系式：,Direct field,Reverberant fiel
23、dcorresponding to the diffuse field,Look at the problem from outside of a noisy machinery house:室内有噪声源，室外：,The power transmitted WT outsidethe plant is given by:ad the average absorption coefficient平均吸收系数td the transmission coefficient of the walls墙壁反射系数W the inside source power内部声能,For large plants
24、 ignore the direct field and just take into account of the diffuse field:在足够大的工厂里，可以忽略直接声场，当作是扩散场：,Typical transmission loss for 4 materials 4种典型材料的传递损失,Transmission Loss传递损失:,Frequency decomposition of sound is very important because:声音的频率分析非常重要，因为：The source of noise is characterized by its freque
25、ncy contents and any control of it must be done accordingly.频率成分是声源的特征，噪声控制的依据是频率特性。Noise reduction performance can not be specified independently of source frequencies.减振降噪工作如果离开了声源频率特性研究就无从下手。,20 HzAudible range20kHz,Frequency decomposition of sound is very important because:声音的频率分析非常重要，因为：The mat
26、hematical Fourier Transform synthesizes any time history intofrequency information傅立叶变化可以把时间信号的变化在频域上同步体现出来The Fourier Transform function is a mathematical algorithm which transform a signal from time domain into a frequency domain.傅立叶函数是一种数学算法，可以把时域信号转换成频域信号。,Pure tone(for example a air conditionin
27、g turning at a constant speed)contains only one frequency(really seldom in reality)纯音（例如：空调扇匀速转动）只包含一个 频率成分（现实中很少存在）Most of sounds are complex and possess several pure tone of different amplitudes.Energy exists in a number of discrete frequencies.Musical notes possess a fundamental frequency and har
28、monics which will characterize the pitch of instrument.大部分声音是复杂的，包含很多振幅不同的纯音。能量包含在一系列不连续的频率之中。乐器有特定的频率，组合在一起成为音乐。,Different frequency contents for different type of sound:不同的频率对应不同类型的声音,Pure tone,Piano note,Broad band noise consist of a wide mixture of frequencies.It is typically industrial noise or
29、 environmental noise.宽带噪声：由多种频率组成，典型的是工厂噪声、环境噪声。Modulated frequencies.调制频率White noise:frequency components of equal amplitude between 20Hz and 20kHz白噪声：由20Hz-20kHz的等幅频率组成Pink noise is a white noise that each octave is decreased by 6 dB粉红噪声：每个音阶都降低6dB的白噪声,Different frequency contents for different ty
30、pe of sound:不同的频率对应不同类型的声音：,White noise spectrum白噪声频谱,Pink noise spectrum粉红噪声频谱,Harmonic series谐波系列A harmonic series consists of integer multiples of a fundamental frequency,e.g.if the fundamental is 100 Hz,then the harmonic series is:100,200,300,400,500,600 Hz,.etc.谐波系列包含了一系列与基频成整数倍的频率，例如，如果基波频率是10
31、0Hz，谐波系列就是100，200，300，400，500，600HzThe 100 Hz fundamental is the first harmonic,200 Hz is the second harmonic.The fundamental is often denoted by F0.基波频率100Hz是第一级，200Hz则是第二级。基波频率通常由F0表示。Harmonics above the fundamental constitute the overtone series.高于基波频率的声音形成泛音。Sub-harmonics are integer divisions o
32、f the fundamental:e.g.for F0=100 Hz,sub-harmonics are at 50,33,25,20,16.6 Hz etc.Sub-harmonics are also called undertones.分谐波是基波频率除以整数：例如，F0=100Hz，分谐波就是50，33，25，20，16.6Hz,4.2 Amplitude of sound:声音的振幅,The acoustic audible pressure variation(from 20mPas to 100 Pas)is very small compared to the static
33、air pressure(100000 Pas).The ratio between the two extremes is 1 million to 1 for the linear Pas scale.可听到的声压变化（20mPas to 100 Pas）与大气压（1000 Pas）相比非常的小。两者之比是：1百万 比1 Use of a logarithmic scale.Logarithmic ratio between the measured value to a reference value.The ear respond not linearly but logarithmi
34、cally to stimulus.采用取对数的方法，取测量值和参考值的对数之比。人耳的感觉不是成线性的，而是与其对数近似成正比。,Thresholof pain,Quietest sound that can be heard,Sound pressure level in dB scale:声压级（dB）：Pressure reference参考声压:P0=20mPas which is the lowest sound pressure level detected by the human ear.人耳能探测到的最小声压级P0=20*10-6Pas P is in Pascal and
35、 the subscript P points out that sound pressure level is looked at and not sound intensity level(LI)or sound power level(LW)P表示帕斯卡，右下角的P代表该量 是声压级，而不是声强级或声功率级,Low frequencies need more“energy”or sound pressure level to be heard than sound within 1kHz-5kHz.与频率在1kHz-5kHz之间的声音相比，低频声音往往需要具有更高的能量或者更高声压级时，
36、才能被人们听见。To take into account of the non linearity of the ear response at lowfrequencies the A-weighting curve is often used.通常用A计权曲线来更好地说明人耳在低频段的非线性响应特性。,A weighting curve A计权曲线,But A-weighting curve simulates the response only of the ear for low level sound.The A-weighting curve follows approximate
37、ly the equal loudness curve of 40phons.但A计权曲线只能模拟人耳对低声压声音的响应特性。下图所示，A计权曲线对应于40宋等响度曲线。,Each curve corresponds to the equal sensation of loudness perception for different pure tones frequencies.每条曲线都是不同频率纯音的等响度曲线。Tone of different frequency but same SPL are not perceived equal.声压级相同但频率不同的纯音，其对应感知度并不相同
38、。A tone of 10 dB 200Hz has the same loudness perception than a tone of 0 dB2kHz.10dB 200Hz与0dB 2kHz的声音拥有相同的响度感知度。At low level a pure high frequency tone will easilymask low frequency pure tone.在低声压级段，高频纯音可以轻易掩蔽低频纯音。,Looking at these curvesthe noise engineertask will need to decreasemore SPL at high
39、frequenciesthan at low frequenciesto get the same subjectiveperception of loudness.从曲线中可看出，为了使高频和低频声音响度的主观感知度一致，噪声工程师需要更多地降低高频声音的声压级。,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 approximate
40、ly 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,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-10k
41、Hz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,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 SPLneed 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。,How
42、 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 logarithmicvalues.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+55dB105dB!,50dB+55dB=56.19 dB,Assumption for operation on levels:假设：In general the diffe
43、rent sources of noise are not in phase通常不同声源的噪声有不同的相位 they are incoherent sources.Incoherent sounds add together on a linear energy(pressure square)basis.它们是互不相干的声源，不会发生干涉现象，可以进行能量叠加。When sources of the same frequency are combined,phase angle between the sounds must be taken into account.当同频率的声源相结合，
44、两者之间的角相位就可以被计算。When the phases are random,the equation reduces to the incoherent case:当这个相位是任意的时候：,dB addition chart:分贝相加曲线 To simplify and not play with dB and linear values of each noise contributors the following curves can be used to directly calculate the sound pressure level due to several sou
45、rces of noise.从曲线中可以直接计算出两个声压级叠加后的总声压级。,1.19,Note that:Two sources of noise with the same sound pressure levels is equivalent to add 3dB.两个相同声压级的叠加是增加3dBAs long as there is more than 10 dB difference between two source of noise the quietest can be forget.如果两个声压级的差值大于10dB，那么小声压级对总声压级的贡献可以忽略，总声压级近似等于大
46、声压级。,Influence of more than 2 sources of noise:两个以上声源的影响：If more than two sources contribute to the noise level at a point,use the previous curve first for the two first sources of noise,get the total result of them,and add to this result the next source of noise如果有两个以上的声源进行叠加，那么就利用之前的曲线先对两个声源进行叠加，得
47、到的值再与第三个声源进行叠加，依次类推,If P1=P2=P3=PN,Source of noise to be evaluated Ls,dB subtraction:分贝相减：If measurements are performed in noisy environment the background noise must be evaluated(switch off the source of noise under investigation)and subtract it from the total level to get just the source level und
48、er interest.在环境嘈杂的地方进行噪声测试时，受背景噪声影响，需要先把被测声源关闭，测得背景噪声量，再从总噪声量中减去背景噪声，最后获得真实的声源噪声。,LS+N,95dB-90dB5dB!,95dB-90dB=93.3 dB=Ls,LN Background noise,dB subtraction chart:分贝相减曲线：The following curve can be used to directly calculate the sound pressure level due to source under background noise.从曲线中可以直接计算出排除背
49、景噪声影响的声源声压级。,Note that:If the delta is smaller than 3dB then the background noise is to high to perform accurate noise measurements.First the background noise must be reduced.当声压级差小于3dB，就要尽量减小背景噪声，否则会给测量带来严重影响。If delta between 3 and 10 dB noise measurements must be corrected with the following curve
50、.当声压级差在3dB-10dB间，就按照曲线严格计算。If delta greater than 10 dB then the background noise is negligible and sound measurements can directly be estimated.当声压级差大于10dB时，背景噪声可以忽略不计。,5.Noise source quantification and identification噪声源的量化和识别 Now we know how a sound can be characterized.We must objectively measure
