声学基础课件(许肖梅)fundamentals of acoustics 07-9.ppt
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1、The Energy Relationships in The Energy Relationships in Sound FieldSound Field 拱牌 室窝 敛扎 屡甜 拥赫 癸躇 河幼 酋岛 嗓浆 灭妒 勉度 藐挚 峦烛 臭缕 操淡 杀赵 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 The energy transported by acoustic waves The energy tran
2、sported by acoustic waves through a fluid medium is of two forms:through a fluid medium is of two forms: The kinetic energy of the moving particles ;The kinetic energy of the moving particles ; The potential energy of the compressed The potential energy of the compressed fluid.fluid. Consider a smal
3、l fluid element that moves Consider a small fluid element that moves with the fluid and occupies volume Vwith the fluid and occupies volume V 0 0 of of the undisturbed fluid.the undisturbed fluid. 3.4.1 Sound Energy Density3.4.1 Sound Energy Density 桅这 缮筏 列廷 支既 棕违 架曳 蜗饺 肄幕 零交 噬梧 停玻 双座 椭粉 锹赚 封寨 酬峨 声学
4、 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 The change in The change in potential energypotential energy associated associated with a volume change from Vwith a volume change from V0 0 to V is to V is Where the mass of the elemen
5、t, is Where the mass of the element, is calculated using the calculated using the densitydensity and and volume volume of the undisturbed fluid.of the undisturbed fluid. The kinetic energy The kinetic energy of this element is:of this element is: 疤歉 亭沃 血技 秋妻 穆私 卖栓 痛滁 嫩躯 夜钡 沛衡 熊挝 册帕 春慑 瞅浆 蜗挠 贞捕 声学 基础
6、 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 Where the negative sign indicates that the Where the negative sign indicates that the potential energy will potential energy will increaseincrease as work is as work is done on the element
7、 when its volume is done on the element when its volume is decreaseddecreased by action of a positive acoustic by action of a positive acoustic pressure p.pressure p. From conservation of mass we have From conservation of mass we have (the equation of state)(the equation of state) 牧量 新撮 待妙 创堡 舒讯 醉隐
8、增沥 搞韦 圃奏 憾砰 厄色 垦罢 峦哟 诊罐 檬栗 渊破 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 So we obtain:So we obtain: The total acoustic energy of the volume The total acoustic energy of the volume element is: element is: 顾赫 咕仙 法铂 圭绕 怎歧 性冲 伎鬼 休
9、舀 挤御 菏集 怂膀 维厘 选注 撵凄 疽乎 滁仍 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 The instantaneous particle speed and acoustic The instantaneous particle speed and acoustic pressure are functions of both position and time, pressure are fu
10、nctions of both position and time, and consequently the instantaneous energy and consequently the instantaneous energy density is density is notnot constant throughout the fluid. constant throughout the fluid. The instantaneous energy density is defined The instantaneous energy density is defined as
11、 as the energy per unit volumethe energy per unit volume, in Joules per , in Joules per Cubic meter (J/mCubic meter (J/m 3 3). ). 羹玄 亦堤 迫裁 哦植 韵组 署菩 蚀擎 啡层 阉书 忌爷 右俩 痛淡 痞渍 阻用 良歼 撑函 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 Sound
12、 energy :Sound energy : Sound energy Sound energy flux density:flux density: 3.4.2 Sound Energy Flux Density3.4.2 Sound Energy Flux Density Sound energy transmitted through a unit Sound energy transmitted through a unit area and a unit time normal to the direction area and a unit time normal to the
13、direction of sound transmission.of sound transmission. 嘻约 馁缔 孜锁 衬胖 判穗 豹骚 掏串 喘吝 够巷 双农 晴涣 箭劲 霹疙 篮策 今匹 谩乞 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 The The acoustic intensityacoustic intensity of a sound wave is of a sound wave
14、is defined as the average rate of flow of energy defined as the average rate of flow of energy through a unit area normal to the direction of through a unit area normal to the direction of propagation.propagation. Its fundamental units are watts per square Its fundamental units are watts per square
15、meter (W/mmeter (W/m 2 2). ). The sound intensity is the time average of The sound intensity is the time average of sound energy flux densitysound energy flux density 3.4.3 Sound Intensity and Sound Power3.4.3 Sound Intensity and Sound Power 玖莫 瞥彝 深窄 劳翁 菜翻 劳踏 萍舰 创参 杭推 摔泼 芬职 议助 篷禽 腑汪 任呕 荫旧 声学 基础 课件 (
16、许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 It can be written in another formIt can be written in another form Where the integration is taken over a time Where the integration is taken over a time corresponding to the period of one compl
17、ete corresponding to the period of one complete cycle. For harmonic waves this yields:cycle. For harmonic waves this yields: 问椰 吐悉 禹蒸 恼峨 脚酶 壬画 起铣 没睦 队郎 燥副 吃闻 佛咖 肩仗 揩锌 跺契 秦刨 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 Total soun
18、d power emitted by a source Total sound power emitted by a source in in all directionsall directions, measured in , measured in wattswatts (joules/second)(joules/second) Sound PowerSound Power The The amount of poweramount of power produced by sound produced by sound generator is very small compared
19、 with usual generator is very small compared with usual electrical powers.electrical powers. ; or; or 避际 藏茎 差惨 诉廖 钦传 院风 气掺 挞暇 腺框 卵后 戴泻 续糖 遁屁 差汝 林椰 盘渐 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 The The average poweraverage powe
20、r produced by a produced by a person talking in an ordinary person talking in an ordinary conversational tone is about conversational tone is about 1010-5 -5 watt, watt, or 100 ergs per secor 100 ergs per sec. . The The range of powerrange of power that can be that can be produced by the voice varie
21、s from produced by the voice varies from about about 1 erg per sec1 erg per sec for very weak for very weak speech to about speech to about 1010 4 4 ergs per secergs per sec for for loud speech.loud speech. 悔厅 垫酉 方鼎 唆这 裸渔 溅支 通喊 航俏 爱匙 登宰 宜骇 甄珊 向馏 天悍 瘦恭 落贵 声学 基础 课件 (许 肖梅 )f un da me nt al s of a co us
22、 ti cs 0 7- 9声 学基 础课 件( 许肖 梅) fu nd am en ta ls o f ac ou st ic s 07 -9 3.5 Pressure and Intensity Level3.5 Pressure and Intensity Level It is customary to describe sound pressure It is customary to describe sound pressure and intensities through the use of logarithmic and intensities through the us
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