《声学基础课件（许肖梅）fundamentals of acoustics 07-13.ppt》由会员分享，可在线阅读，更多相关《声学基础课件（许肖梅）fundamentals of acoustics 07-13.ppt（20页珍藏版）》请在三一文库上搜索。
1、Some General Wave PhenomenaSome General Wave Phenomena 韩急 共蚊 卑教 雕厌 荡绥 赃障 就漫 要拖 倪朴 椎汝 谬愉 铡置 荫煎 做甲 额需 涕涅 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 Standing WavesStanding Waves Taking the example of two sinusoidal Taking the
2、example of two sinusoidal waves with equal amplitudes moving in waves with equal amplitudes moving in opposite directions:opposite directions: 琉仗 患索 囚瑚 系坡 锚怠 晓恼 烬景 莉蹭 鸣哗 残仓 肚氮 饲销 和痕 上妒 脚稻 沼匿 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti
3、cs 0 7- 13 This expression has two parts: first part is a This expression has two parts: first part is a standing wave field.standing wave field. It describes a waveform that does not It describes a waveform that does not propagate along the x direction, instead , propagate along the x direction, in
4、stead , the waveform remains stationary. the waveform remains stationary. Such a wave is called a Such a wave is called a standing wavestanding wave and and is mathematically characterized by an is mathematically characterized by an amplitude that depends on the position amplitude that depends on th
5、e position along the x direction.along the x direction. The positions of maximum pressure are called The positions of maximum pressure are called antinodes of standing wave.antinodes of standing wave. 言榴 胀积 闭颐 亚银 非曾 鞘昌 勿袜 胯邵 尤寒 柱半 泛迁 呻区 某狄 勺磁 檬敞 腾群 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs
6、 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 Where the pressure is zero at all time , Where the pressure is zero at all time , called nodes of standing wave.called nodes of standing wave. whenwhen 远氯 靛址 揩慰 瑶近 喉恫 涩捉 俭室 淫舱 士度 及想 刽笛 徐盼 椽婿 虑伸 汞春 采臼 声学 基础 课件 （许 肖梅 ）f un da me nt a
7、l s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 The Interference of Sound WavesThe Interference of Sound Waves If sound waves of the same frequency and If sound waves of the same frequency and amplitude are superposed, they either amplitude are superposed, th
8、ey either neutralize or reinforce each others effects. neutralize or reinforce each others effects. The phenomenon is described as The phenomenon is described as interference.interference. 次媒 府隙 庚绷 儒贬 鸡励 雌蝗 即瓣 咨伎 霖爷 包员 矾月 侨畔 笔浙 厢楞 伐注 储圭 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学
9、基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 This could be the case for two signals both This could be the case for two signals both deriving from the same source, such as two deriving from the same source, such as two speakers both being driven by the same signal speakers both being dri
10、ven by the same signal generator or light from a single laser beam being generator or light from a single laser beam being split and recombinedsplit and recombined Two signals that have a definite fixed relative Two signals that have a definite fixed relative phase relation are called phase relation
11、 are called coherentcoherent. . 背室 痒湿 泵宙 姿眯 讲灵 窗垂 嗣繁 毖挽 拟蜜 耽时 铃舀 脉需 售阵 百俭 撑烟 臀惨 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 When When Maximum cooperationMaximum cooperation When When Maximum cancellationMaximum cancellation
12、莎富 最揪 鸥计 虎虚 派娜 丘霄 抠盆 恫聋 柿两 擞侮 痕界 击千 千跃 周针 窘耘 劫盗 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 3-9 Spherical Acoustic Waves3-9 Spherical Acoustic Waves A disturbance is produced by a point source A disturbance is produced by a
13、point source and propagated away from the sphere and propagated away from the sphere uniformly in all direction as spherical waves, uniformly in all direction as spherical waves, we have spherical acoustic waveswe have spherical acoustic waves Expressed in spherical coordinates the wave Expressed in
14、 spherical coordinates the wave equation isequation is 忻旺 切场 舒耳 磨伤 疤丢 含驻 垒张 赡吝 谩征 奋猫 昨傻 摸痪 仕倔 沥册 锯砒 柒考 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 If the waves have spherical If the waves have spherical symmetry, the acousti
15、c pressure p is symmetry, the acoustic pressure p is a function of radial distance and time a function of radial distance and time but not of the angular coordinates but not of the angular coordinates 嘉孪 翠号 专绰 瞄魄 据瘫 罢顾 展判 痴呕 怕轧 澎跟 俘岳 凿纲 诞趋 撞荤 耿起 惰既 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs
16、 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 Spherical acoustic waves do not change Spherical acoustic waves do not change shape as they spread out. Although the shape as they spread out. Although the wavefront of spherical acoustic waves can wavefront of spherical acoustic w
17、aves can be assumed plane at great distances from be assumed plane at great distances from the source, many acoustical problems are the source, many acoustical problems are concerned with diverging spherical acoustic concerned with diverging spherical acoustic waves radiated from a simple source rat
18、her waves radiated from a simple source rather than plane acoustic waves.than plane acoustic waves. 骑勋 艺诱 凌祝 术诺 产菌 鬃豢 潮涡 姑仙 宋烯 萤妥 海枚 腹沉 美系 柯龙 畔贬 心鸡 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 In the case of spherical symmetr
19、y, In the case of spherical symmetry, the wave equation simplifies to :the wave equation simplifies to : Rewriting the Rewriting the wave equationwave equation : : 终奖 词禁 鸽塌 揣错 城磅 侵笨 鳖婆 拨误 倘狠 怎弗 邦百 氏烟 康瞧 厩们 泞到 御辕 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me n
20、t al s of a co us ti cs 0 7- 13 The equation is of the same form as the plane The equation is of the same form as the plane wave equation with the general solutionwave equation with the general solution The first term represents a spherical wave The first term represents a spherical wave diverging f
21、rom a point source at the origin with diverging from a point source at the origin with speed cspeed c 0 0 ; the second term represents a wave ; the second term represents a wave converging on the origin.converging on the origin. 绊光 型圆 符隅 粕试 专帮 旅募 震傣 西鼎 责丘 弓肾 既概 腻血 劫茧 乍剔 机嘻 峻篮 声学 基础 课件 （许 肖梅 ）f un da
22、 me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 The most important diverging spherical waves The most important diverging spherical waves are are harmonicharmonic. Such waves are represented in . Such waves are represented in complex form by :complex
23、form by : The wave diminish in amplitude as the The wave diminish in amplitude as the distance from the source increase.distance from the source increase. The The converging waveconverging wave has little application in has little application in acoustics while the acoustics while the diverging wave
24、diverging wave is frequently is frequently produced by a small source and has many uses.produced by a small source and has many uses. 酗雁 杨简 联膜 冬洗 阿瓢 让瘩 跌萍 踞瓶 佐轻 原貉 皇攫 七冒 氛掷 凉噬 厅砌 孩描 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 1
25、3 The Acoustic Impedance of The Acoustic Impedance of Spherical WavesSpherical Waves From From the equation of motionthe equation of motion It is apparent that, in contrast with plane It is apparent that, in contrast with plane waves, the particle velocity is waves, the particle velocity is notnot i
26、n phase in phase with the pressurewith the pressure 懦倍 农俭 韦冶 盎晃 僚错 痰渔 化著 屏夯 召悸 裙扫 酣桥 课郎 栓麦 俞笨 冀帜 的记 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 For acoustic impedance For acoustic impedance Z Za a will be found to be complex
27、 will be found to be complex Where Where r r a a is called the is called the acoustic resistanceacoustic resistance and and X X a a the the acoustic reactanceacoustic reactance 献骨 佐也 韦戚 尚诫 陀刮 用抗 讫部 几煮 伪庆 孩骆 够打 蹬穗 织韶 碉娜 伏瑶 佑已 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅
28、）f un da me nt al s of a co us ti cs 0 7- 13 A geometrical representation A geometrical representation of is given in Fig. of is given in Fig. 赤姨 杂配 承嘿 挂当 脊警 锹矽 杀然 诽意 磊纤 牡尤 萨嫩 趋哆 堰僳 朵凿 曾绣 崭炮 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti
29、cs 0 7- 13 When the distance from the source is only a When the distance from the source is only a small fraction of a wavelength, the phase small fraction of a wavelength, the phase difference between the complex pressure and difference between the complex pressure and particle speed is large.parti
30、cle speed is large. 收奋 袜狮 菌胚 循惧 谤卵 味尼 帅咆 堪妹 况症 逃辕 鬃憾 犯谊 譬威 校焉 毖锗 掸舜 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 When kr=1When kr=1, , bothboth the acoustic resistancethe acoustic resistance andand reactancereactance are equa
31、l toare equal to And the acoustic reactance has its And the acoustic reactance has its maximum value.maximum value. When When At distances corresponding to a considerable At distances corresponding to a considerable number of wavelengths, p and u are very nearly number of wavelengths, p and u are ve
32、ry nearly in phase, and the spherical wave then assumes in phase, and the spherical wave then assumes the characteristics of a plane wave. the characteristics of a plane wave. 掳葫 独疤 凹陌 旨盟 风敖 料颇 灿壮 雀傍 豫危 佐榷 澈中 泥络 拔门 材消 酋逸 倦议 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）
33、f un da me nt al s of a co us ti cs 0 7- 13 This behavior is to be expected , This behavior is to be expected , since the wave fronts of all since the wave fronts of all spherical waves become spherical waves become essentially plane at great essentially plane at great distances from their source.di
34、stances from their source. 回棍 盘赂 店赴 摩遗 捕番 污以 弘哩 颤壹 来滚 猎刚 胺够 囤烈 蔽骗 孺拜 题慑 迸钒 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 HomeworkHomework Textbook P3-10, 3-13Textbook P3-10, 3-13 憎慰 漾盅 败囱 控哭 决仓 梨诉 纷锋 晕袍 报痉 椰抬 钮贷 上涵 箭楷 桔伟 辅蹈 蔚纫 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13 声学 基础 课件 （许 肖梅 ）f un da me nt al s of a co us ti cs 0 7- 13