机械噪声控制技术详解.ppt

The sound power transmission coefficient of a structure is defined as Chapter 7 Mechanical Noise Control Techniques 7. 2 Noise Insulation 7.2.1 Definitions of Sound Insulation Transmission loss may be expressed as where and are the incident and transmitted sound intensities, respectively. General variation of the transmission loss with frequency for a homogeneous panel. 幻灯片 42 Chapter 7 Mechanical Noise Control Techniques 7. 2 Noise Insulation 7.2.2 Sound Transmission through a Panel (1) Region I: Stiffness-Controlled Region At low frequencies, the panel (provide that the panel is very thin) vibrates as a whole, and sound transmission Chapter 7 Mechanical Noise Control Techniques 7. 2 Noise Insulation 7.2.2 Sound Transmission through a Panel A1 B1 A2 through the panel is determined primarily by the stiffness of the panel. At the surface of the panel (for a very thin panel), the particle velocities are both equal to the instantaneous velocity of the panel . We may write the following expressions from above Equations for : If the panel has a finite stiffness, the net force acting on the panel is equal to the “spring-force” of the panel. The specific mechanical compliance or mechanical compliance per unit area will be denoted by the symbol . Chapter 7 Mechanical Noise Control Techniques 7. 2 Noise Insulation 7.2.2 Sound Transmission through a Panel The sound power transmission coefficient for normal incidence may be determined The transmission loss for normal incidence may be written as follows: where Chapter 7 Mechanical Noise Control Techniques 7. 2 Noise Insulation 7.2.2 Sound Transmission through a Panel For a rectangular panel, the expression for the specific mechanical compliance is given by : The quantities a and b are the width and height of the panel; h is the thickness of the panel; and E and are the Young’s modulus and Poisson’s ratio for the panel material, respectively. Chapter 7 Mechanical Noi