哈工程振动噪声一一第6章 噪声控制的声学基础.ppt

Dipole source: Two closed small oscillating sphere sources with same vibration amplitude and opposite phase Sound pressure radiated from the dipole source may be expressed as: Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source r1 r r2 l P θ If is much less than r ,then one may get Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source So Consider , that means So we have r1 r r2 l P θ Sound pressure radiated from the dipole source in the far field is lowered as the distance increasing, and is dependent on the angle. Defining of Directivity Character (指向性特性：任意θ方向的声压幅值与θ=0度轴上相同距离处的声压幅值之比) θ Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source So Particle velocity in the radial direction If kr?1，Sound intensity radiated from the dipole source is In view of , Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source It is still the same as we met in plane sound fields and in sphere source sound fields. Sound power radiated from the dipole source Sound power radiated from the monopole source Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source For kl?1 which means that in lower frequency field, the sound radiated by a dipole source is not as effective as a monopole source. Directivity Factor 指向性因子：设偶极子声场中，距离声源r处 的远声场点均方声压为 ，并设以 r 为半径的球面上的均方声压的均值为 ，则两者比值定义为声源辐射声场的指向性因子。 Directivity Index (指向性指数 ) Chapter 6 Fundamentals of Acoustics for Noise Control 6. 5 Radiation of Sound Source Home Works Page 195 Questions: 7-3～7-8 Chapter 6 Fundamentals of Acoustics for Noise Control * page * 授课人——柳贡民 * 动力与能源工程学院 College of Power and Energy Engineering 第6章 噪声控制的声学基础 Chapter 6 Fundamentals of Acoustics for Noise Control 6. 1 The Wave Equation 6. 2 Basic Characteristics of Plane Sound Wave 6. 3 Acoustic Energy in Sound Field 6. 4 Sound Levels 6. 5 Rad