声学基础课件(许肖梅)fundamentals of acoustics 07-6-PPT课件
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声学基础课件(许肖梅)fundamentals of acoustics 07-9-26页精选文档
VE0 120u212p0c22
The instantaneous particle speed and acoustic pressure are functions of both position and time, and consequently the instantaneous energy density is not constant throughout the fluid.
3.5 Pressure and Intensity Level
• The average power produced by a person talking in an ordinary conversational tone is about 10-5 watt, or 100 ergs per sec.
• The range of power that can be produced by the voice varies from about 1 erg per sec for very weak speech to about 104ergs per sec for loud speech.
3.4.1 Sound Energy Density
The energy transported by acoustic waves through a fluid medium is of two forms:
• The kinetic energy of the moving particles ; • The potential energy of the compressed
The total acoustic energy of the volume element is:
The instantaneous particle speed and acoustic pressure are functions of both position and time, and consequently the instantaneous energy density is not constant throughout the fluid.
3.5 Pressure and Intensity Level
• The average power produced by a person talking in an ordinary conversational tone is about 10-5 watt, or 100 ergs per sec.
• The range of power that can be produced by the voice varies from about 1 erg per sec for very weak speech to about 104ergs per sec for loud speech.
3.4.1 Sound Energy Density
The energy transported by acoustic waves through a fluid medium is of two forms:
• The kinetic energy of the moving particles ; • The potential energy of the compressed
The total acoustic energy of the volume element is:
FUNDAMENTALS OF ACOUSTICS(10) 声学基础(英文版教学课件)
• The simplest solutions to the wave
equation (3-4) are those that depend
on only one of the three spatial
coordinates.
2t2pc22p
(34)
We may as well call that one x. the equation (3-4)reduces to follow equation
the negative x direction
(x,t)Aej(tkx)
Now acoustic pressure
p 0 c 0 u j0 c 0A e j( t k x ) j0 c 0
Therefore the acoustic pressure legs the particle displacement by 900
uumcos(tkx)
0um 2co 2( stk)x
Average energy density
1
T
dt
T0
120um 2 1202m 2p0ce202
Acoustic intensity
I 1
T
pudt
T0
1
T
T 0
pm
cos(t
kx)
pm
0c0
cos(t
kx)dt
pm2
20c0
j(tx)
j(tx)
pA1e c0 A2e c0
pA 1 ei( t k)xA 2 ei( t k)x
• Where the wave number k is defined by
k 2 c0
A1,A2 are two arbitrary constants
《声学基础知识》课件
《声学基础知识》PPT课件
让我们一起探索声学的奥秘吧。从声学基础概述开始，深入了解声音的产生 机制、声音的特性和参数，以及声学波动的基本概念。
声学基础概述
声学是研究声音在空气、固体和液体中的传播和变化的学科。它涵盖了声音的起源、传播和感知等方面的内容。
声音的产生机制
声音的产生涉及物体振动，从声源传递到介质中形成声波。声波通过空气、固体或液体的震动传递，最终被我 们的耳朵接收。
声音的特性和参数
声音具有许多特性和参数，包括频率、振幅、声压级和声色。这些特性决定 了声音的音调、响度和音质。
声学波动的本概念
声学波动是指声音在空气、固体或液体介质中传播的过程。了解波动的基本概念可以帮助我们理解声音的行为 和传播规律。
声场的传播和测量
声场是声波在空间中的分布情况。了解声场的传播和测量方法有助于我们优 化声音的传递和改善声学环境。
声学信号的处理和分析
声学信号的处理和分析可以帮助我们理解和改善声音的质量。通过采用数字信号处理等技术，我们可以对声音 进行精确的控制和调整。
声学应用的案例研究
通过案例研究，我们可以了解声学在不同领域的应用，包括音乐演奏、建筑 设计、噪声控制等。这些案例可以帮助我们更好地理解声学的实际应用。
让我们一起探索声学的奥秘吧。从声学基础概述开始，深入了解声音的产生 机制、声音的特性和参数，以及声学波动的基本概念。
声学基础概述
声学是研究声音在空气、固体和液体中的传播和变化的学科。它涵盖了声音的起源、传播和感知等方面的内容。
声音的产生机制
声音的产生涉及物体振动，从声源传递到介质中形成声波。声波通过空气、固体或液体的震动传递，最终被我 们的耳朵接收。
声音的特性和参数
声音具有许多特性和参数，包括频率、振幅、声压级和声色。这些特性决定 了声音的音调、响度和音质。
声学波动的本概念
声学波动是指声音在空气、固体或液体介质中传播的过程。了解波动的基本概念可以帮助我们理解声音的行为 和传播规律。
声场的传播和测量
声场是声波在空间中的分布情况。了解声场的传播和测量方法有助于我们优 化声音的传递和改善声学环境。
声学信号的处理和分析
声学信号的处理和分析可以帮助我们理解和改善声音的质量。通过采用数字信号处理等技术，我们可以对声音 进行精确的控制和调整。
声学应用的案例研究
通过案例研究，我们可以了解声学在不同领域的应用，包括音乐演奏、建筑 设计、噪声控制等。这些案例可以帮助我们更好地理解声学的实际应用。
声学基础课件(许肖梅)fundamentals of acoustics 07-2-38页精选文档
Sound waves (in fluids) are longitudinal waves: the particles move in the direction of the wave motion. Propagation of sound waves involves the transfer of energy through space. While sound waves spread out in all directions from the source, they may be reflected and refracted, scattered and diffracted, interfered and absorbed. A medium is required for the propagation of sound wave, the speed of which depends on the density and temperature of the medium.
The Sound Wave Produces Sound Pressure Changes
The pressure changes produced by a sound wave are known as the sound pressure. Compared with atmospheric pressure (about 100 000 pascals(1Pa=1N/m2) they are very small (between 20 micropascals and 200 pascals) and are superimposed on it
• The acoustical engineer is interested in the fidelity of reproduction of sound • The conversion of mechanical and electrical energy into acoustical energy, • The design of acoustical transducers. • The architect is more interested in the absorption and isolation of sound in buildings, and in controlled reverberation and echo prevention in auditoriums. • The musician likes to know how to obtain rhythmic combinations of tones through vibrations of strings ,air columns.
FUNDAMENTALS OF ACOUSTICS(18) 声学基础(英文版教学课件)
• 3.When kb＜＜ 1
k b sin ＜＜1
2
sin(2 b sin)
R(
)
2 sin( b
sin
)
1
We can obtain a polar plot of pressure( in dB) versus angular displacements as shown in the following Fig., which is the radiation pattern or directivity of this particular arrangement of two point sources.
be the major lobe and the greater the number of side
The simple line array
• Consider a line of N simple sources with
adjacent elements spaced distance b apart, as shown in Fig.
can approximate by assuming all ri are parallel.
• In far field ,ri in amplitude can be replaced
2 sin( b
sin
)
1.When b s in m , b s in m (m 0 ,1 ,2 )
sin1m (m0,1,2,),
b
In these direction, We have two sound waves
of same magnitude and phase , hence R( ) 1
《声学基础》课件
声学与音乐学
声学研究为音乐学提供了 科学基础，有助于理解声 音在音乐中的产生、传播 和感知。
声学与医学
声学应用于医学领域，如 超声波成像、听力研究等， 为医学诊断与治疗提供了 重要工具。
结论
1 声音是什么？
声音是声波的感知，是人类与世界沟通的重要方式。
2 声学在生活中的应用
声学研究为我们提供了许多实用的应用，如语音识别、音乐欣赏、医学诊断等。
声波传播
1
声音的产生和传播方式
声音可以通过声源的振动产生，并在空气中以波的形式传播。了解声音传播的方 式对声学研究至关重要。
2
空气中声波传播的特性
空气中声波的传播速度、衰减和传播路径都受到温度、湿度和空气密度等因素的 影响。
3
物体表面反射和衍射
声波在物体表面上反射和衍射，这些现象会引起声音的反射、散射和聚焦。
《声学基础》PPT课件
# 声学基础 ## 概述 - 声波与声音的区别 - 声学基础概念 - 声学研究领域 ## 声波传播 - 声音的产生和传播方式 - 空气中声波传播的特性 - 物体表面反射和衍射 ## 声音特性 - 频率、波长及周期 - 振幅、声压和声强 - 速度和能量传播 ## 声学应用 - 声学与语音识别 - 声学与音乐学
3 声学的未来发展方向
随着科技的不断进步，声学研究将继续发展并为我们带来更多惊喜与可能。
声音特性
频率、波长及周期
声音的频率决定了它的音高； 波长和周期是描述声音波动特 征的声音的音量；声压和 声强是描述声音强度的指标。
速度和能量传播
声音传播速度的了解有助于研 究声音如何在空间中传递和传 播能量。
声学应用
声学与语音识别
声学在语音识别技术中发 挥着重要作用，帮助计算 机理解和转换人类的声音 信息。
声学基础课件fundamentals of acoustics 07-7
2020/4/28
The Nature of Sound
• Sound is a wave phenomenon • In gas or liquid , sound waves are
classified as longitudinal waves — the vibration is always parallel to the direction of wave travel • The speed of sound in air is roughly 340 meter per second; in water is roughly 1500 meter per second
• Although nonlinearity does occur for sound waves of very large amplitude, the approximation that sound waves behave linearly is generally in excellent one for many uses.
2020/4/28
• Many physical phenomena have a property called linearity. This means that the forces acting on the medium produce motions in exact proportion; doubling the cause will double the effect.
pe
1 T P2dt T0
For harmonic vibration:
ppmcost, so,
2020/4/28
pepm 2
• Under the sound pressure, the displacement
The Nature of Sound
• Sound is a wave phenomenon • In gas or liquid , sound waves are
classified as longitudinal waves — the vibration is always parallel to the direction of wave travel • The speed of sound in air is roughly 340 meter per second; in water is roughly 1500 meter per second
• Although nonlinearity does occur for sound waves of very large amplitude, the approximation that sound waves behave linearly is generally in excellent one for many uses.
2020/4/28
• Many physical phenomena have a property called linearity. This means that the forces acting on the medium produce motions in exact proportion; doubling the cause will double the effect.
pe
1 T P2dt T0
For harmonic vibration:
ppmcost, so,
2020/4/28
pepm 2
• Under the sound pressure, the displacement
声学基础课件(许肖梅)fundamentals of acoustics 07-11.ppt
Reflection, Refraction and Transmission of Plane Waves
When sound waves are traveling through a medium, they may be reflected or refracted, diffracted or scattered, interfered or absorbed. The transmission of sound involves the transfer of acoustic energy through the medium in which sound waves travel.
Transmission From One Fluid to Another: Normal Incidence
• As suggested in Fig. let the plane x=0 be the boundary between fluid I of characteristic acoustic impedance Z1 and fluid II of characteristic acoustic impedance Z2.
The first condition , continuity of pressure , means that there can be no net force on the (massless) plane separating the fluid.
In complex exponential form, the general solution can be written as
j (t x )
j (t x )
p A1e c0 A2e c0
When sound waves are traveling through a medium, they may be reflected or refracted, diffracted or scattered, interfered or absorbed. The transmission of sound involves the transfer of acoustic energy through the medium in which sound waves travel.
Transmission From One Fluid to Another: Normal Incidence
• As suggested in Fig. let the plane x=0 be the boundary between fluid I of characteristic acoustic impedance Z1 and fluid II of characteristic acoustic impedance Z2.
The first condition , continuity of pressure , means that there can be no net force on the (massless) plane separating the fluid.
In complex exponential form, the general solution can be written as
j (t x )
j (t x )
p A1e c0 A2e c0
FUNDAMENTALS OF ACOUSTICS(16) 声学基础(英文版教学课件)
FUNDAMENTALS OF ACOUSTICS (16)
Sound waves travel in the pipe
3. The nx, ny mode
• 1. (0,0) order mode • 2. (nx ny) order mode
For (0,0) order, the pressure is
n x 0n y 0
n x 0n y 0
f fnx ,ny
f fnx,ny
Corresponding high order waves can travel in z direction
• Corresponding high order waves can not
travel in z direction, these waves decay in z direction
x
c0
lx
jt
x
x
cos nxc0 lx
z
cos1, 00
Which means there are not high order
waves travel in the z direction (except nx 0,ny 0)
cos nx c0 nx 1
lx
2lx
so
fc
nxc0 2lx
kr k2 kz2
B=0
uz 0
z=0, z=l
ur 0
r=a
pp0cosm Jm ( c0 rr)cos c0 zzejt
z
(nz
l
)c0
r
(mn
a
)c0
m n is the solutions of
(
dJm dr
Sound waves travel in the pipe
3. The nx, ny mode
• 1. (0,0) order mode • 2. (nx ny) order mode
For (0,0) order, the pressure is
n x 0n y 0
n x 0n y 0
f fnx ,ny
f fnx,ny
Corresponding high order waves can travel in z direction
• Corresponding high order waves can not
travel in z direction, these waves decay in z direction
x
c0
lx
jt
x
x
cos nxc0 lx
z
cos1, 00
Which means there are not high order
waves travel in the z direction (except nx 0,ny 0)
cos nx c0 nx 1
lx
2lx
so
fc
nxc0 2lx
kr k2 kz2
B=0
uz 0
z=0, z=l
ur 0
r=a
pp0cosm Jm ( c0 rr)cos c0 zzejt
z
(nz
l
)c0
r
(mn
a
)c0
m n is the solutions of
(
dJm dr
FUNDAMENTALS OF ACOUSTICS(14) 声学基础(英文版教学课件)
WaIS4r2I
Since
I
1 pm 2
2 0c0
A2
20c0r2
2 A 2 Wa 0c0
The average rate of energy flow through any spherical surface surrounding the origin is independent of the radius of the surface, a conclusion that is consistent with conservation of energy in a lossless medium
function
• N0(kr) is the zero order Neumann function
Introduce Hankel function
H 0 1(z)J0(z)jN 0(z)
H 0 2(z)J0(z)jN 0(z)
For the diverging waves
R(r)AH 0(2)(kr)
• For kr >>1, Za is predominantly resistive,
meaning that energy fed into such waves propagates away from the source, never to return.
• The larger the value of kr, the less curved are
I 1
T
RepReudt
T0
1 T
T 0
pmcos(t
kx)
pm
0c0
cos(tkx)dt
I
1
20c0
p2 m
Since
I
1 pm 2
2 0c0
A2
20c0r2
2 A 2 Wa 0c0
The average rate of energy flow through any spherical surface surrounding the origin is independent of the radius of the surface, a conclusion that is consistent with conservation of energy in a lossless medium
function
• N0(kr) is the zero order Neumann function
Introduce Hankel function
H 0 1(z)J0(z)jN 0(z)
H 0 2(z)J0(z)jN 0(z)
For the diverging waves
R(r)AH 0(2)(kr)
• For kr >>1, Za is predominantly resistive,
meaning that energy fed into such waves propagates away from the source, never to return.
• The larger the value of kr, the less curved are
I 1
T
RepReudt
T0
1 T
T 0
pmcos(t
kx)
pm
0c0
cos(tkx)dt
I
1
20c0
p2 m
声学基础课件fundamentals of acoustics 07-1精品文档
Objective: Throughout the course, emphasis is placed on the fundamental of acoustics, with discussions and problems extending into some phases and applications of acoustics
The Generation, Transmission and Reception of Acoustic Waves
On completion of this course, students will be able to understand:
• the terms used to describe sound waves, the
Absorption occurs as the sound enters a porous material and gets trapped in the air pockets. The trapped sound energy is converted to other forms of energy.
Any sound, whatever it might be, is caused by something vibrating. Without vibration there can be no sound. The vibrating body causes the air particles next to it to vibrate. Those air particles, in turn, cause the particles next to them to vibrate. In this way a disturbance of the air moves out from the source of the sound and may eventually reach the ears of a listener.
The Generation, Transmission and Reception of Acoustic Waves
On completion of this course, students will be able to understand:
• the terms used to describe sound waves, the
Absorption occurs as the sound enters a porous material and gets trapped in the air pockets. The trapped sound energy is converted to other forms of energy.
Any sound, whatever it might be, is caused by something vibrating. Without vibration there can be no sound. The vibrating body causes the air particles next to it to vibrate. Those air particles, in turn, cause the particles next to them to vibrate. In this way a disturbance of the air moves out from the source of the sound and may eventually reach the ears of a listener.
声学基础课件(许肖梅)fundamentals of acoustics 07-6-文档资料
Standing Waves • Consider now a string of finite length L. Describing all motions of this string in terms of traveling waves remains possible in principle. • Because of repeated reflections between the two ends, that is usually not the most helpful description. • We find it more convenient to study standing waves.
l
General Solution of The Equation of Motion Equation (2-1) is a second-order, partial differential equation. Its complete solution contains two arbitrary functions. The most general solution is
Component of the tension at the two ends of the element is:
Fx (T sin 1 ) x
Fx dx (T sin 2 ) x dx
dFx (T sin 2 ) xdx (T sin 1 ) x
η is small, We get:
Transverse Motion - The Vibrating String
Vibrations of Extended Systems • In the previous chapter it was assumed that the mass moves as a rigid body so that it could be considered concentrated at a single point. • However, most vibrating bodies are not so simple. A loudspeaker has its mass distributed over its surface so that the cone does move as a unit .
声学基础 教学大纲
三、主要内容及学时安排
章或节 绪论 第1章 第2章
主要内容 声学的科学、技术和艺术
质点振动系统 弹性体的振动
学时安排 1 6 2
习题及讨论课
2
第3章
理想流体介质中声波的传播
6
球面声波的波动方程及其声阻抗率
6
声波在管中的传播
5
期中考试
2
第4章
声波的辐射
10
第5章
声波的散射
4
第6章
声波的吸收
2
第7章
声波的接收
的振动方程及其解，理解三种振动状态下的振动能量，掌握振动系统的 固有频率以及振动系统对固有频率的影响，理解谐振现象、强迫振动过 渡过程的物理意义；掌握机电类比方法。 (2) 弹性体的振动：理解弦的振动，建立弦的振动方程，求解弦振动方程的 一般解，理解弦自由振动的一般规律 — 弦振动的驻波解并理解解的物 理意义；了解棒的纵振动，建立棒的振动方程并求解；了解膜的振动及 膜振动方程。 (3) 声场的声学量：理解声压、质点振速、质点位移和声速的物理概念，推 导出理想流体介质中的三个基本方程；推导小振幅声波传播的波动方程， 理解声能密度、声能流密度、声强、声功率、声压级和声强级的物理概 念； (4) 建立平面波波动方程并求其解，掌握振速和声压的关系，明确声阻抗率 与介质特征阻抗的概念；了解声学边界条件，理解平面声波的反射、折
6
习题及讨论
2
期末考试
四、考核方式： 平时作业，期中、期末闭卷笔试
五、开课专业： 海洋技术
六、其它信息： 双语教学课程
主要 1. 何祚镰、赵玉芳，声学理论基础，北京：国防工业出版社，1981 参考书 2. 杜功焕、朱哲民、龚秀芬，声学基础， 南京大学出版社， 2002
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Transverse Waves on a String Let us consider a long, uniform string whose total mass is m , and length is L. What is important for the local behavior of each part is the linear mass density:
• A flexible string under tension provides the easiest example for visualizing how waves work and developing physical concepts and techniques for their study. • The vibrating string is interesting both for its own sake (as a source of sound on a guitar or violin) and as a model for the motion of other systems. • We study free motion of a string. The procedures we use will apply in our later study of other kinds of waves.
• Fig. A isolates an infinitesimal element of the string with equilibrium position x and equilibrium length dx. • When the string is at rest, the tensions at x and at x+dx are precisely equal in magnitude and opposite in direction, making zero total force.
2
F x dxΒιβλιοθήκη d sT2
1
F
x
x
x dx
x
Fig. A
If η (the transverse displacement of this element from its equilibrium position ) is small, the tension T remains constant along the string and the difference between the η.
l m / L
If a portion of the string is suddenly displaced from its equilibrium position and released , it is observed that the displacement does not remain fixed in its initial position, but instead breaks up into two separate disturbances that propagate along the string, one moving to the right and the other to the left with equal speed.
c T / l
Where c is in m / s, T is the tension in N and pl is the mass per unit length of the string in kg/m.
The Equation of Motion • Assume a string of uniform linear density pl and negligible stiffness, stretched to a tension T great enough that the effects of gravity can be neglected. • Also assume that there are no dissipative forces (such as those associated with friction or with the radiation of acoustic energy)
Transverse Motion - The Vibrating String
Vibrations of Extended Systems • In the previous chapter it was assumed that the mass moves as a rigid body so that it could be considered concentrated at a single point. • However, most vibrating bodies are not so simple. A loudspeaker has its mass distributed over its surface so that the cone does move as a unit .
• It is observed that the speed of propagation of all small displacements is independent of the shape and amplitude of the initial displacement and depends only on the mass per unit length of the string and its tension • Experiment and theory show that this seed is given by
Propagation of a transverse disturbance along a stretched string:
Initial disturbance at t=0
Separate disturbance at t1>>0
Separate disturbance at t2>t1