42 Design of Absorption Teruo Obata

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Teikyo University

42.1 Introduction ....................................................................... 42-1

42.2 Fundamentals of Sound Absorption ................................ 42-2

Attenuation of Sound

42.3 Sound-Absorbing Materials .............................................. 42-3

Porous Material † Tubular Material † Membrane

Material † Perforated Plate † Acoustic Resonator

42.4 Acoustic Characteristic Computation of

Compound Wall ................................................................. 42-6

Absorption Coefficient of Combined Plate with Porous

Blanket † Transmission Loss through a Single Porous

Board † Transmission Loss through a Sandwich Board

42.5 Attenuation of Lined Ducts .............................................. 42-10

Computation of Attenuation in a Lined Duct † Attenuation

in a Lined Bend † Attenuation in Splitter Lined Duct

42.6 Attenuation of Dissipative Mufflers ................................. 42-12

Transmission Loss of Lined Expansion Chamber †

Transmission Loss of a Plenum Chamber

42.7 General Considerations ..................................................... 42-15

Surface Treatment with Lining of Acoustic Material † Gas

Flow Velocity † Gas Temperature † Dust and Water

Exposure

42.8 Practical Example of Dissipative Muffler ......................... 42-17

Summary

This chapter presents the basics of designing devices for sound absorption. The absorption coefficient and acoustic

impedance are introduced. Characteristic properties and parameters of sound absorption material and basic

elements are presented. Acoustic modeling, analysis, and design considerations of components, such as ducts, and

noise attenuation devices, such as mufflers, are presented. A practical design example is presented for illustration of

the concepts presented in the chapter.

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