Noise Control, 2nd Edition

8

Muffling Devices

LEARNING OBJECTIVES

In this chapter, the reader is introduced to:

• noise reduction, NR, and Transmission Loss, TL, of muffling devices;

• diffusers as muffling devices;

• classification of muffling devices as reactive and dissipative;

• acoustic impedance for analysis of reactive mufflers;

• acoustic impedance of orifices and expansion chambers;

• analysis of several reactive muffler types;

• pressure drop calculations for reactive mufflers;

• lined duct silencers as dissipative mufflers;

• duct break-out noise transmission calculations;

• lined plenum attenuators; and

• directivity of exhaust stacks.

8.1 Introduction

Muffling devices are commonly used to reduce noise associated with internal combustion engine exhausts, high pressure gas ...