several fascinating difficulties in acoustics involve the propagation of sound in ducts. moreover, several purposes of acoustics to ventilation / exhaust programs in buildings and cars use mufflers and acoustic filters to lessen the level of noise propagating down a duct or radiating from the finish of a duct. on this laboratory physical exercise you will investigate the conduct of acoustic waves in a very duct with changes in cross-sectional location, side branches, and resonators. in the process you will observe the conduct of acoustic low-pass, high-pass,
Office 2007 Key, and band-stop filters as they are utilized in a duct technique. ii. the concept of acoustic transmission lines
a instead total theoretical development of acoustic waveguides, transmission lines, and filters might be found in chapters nine & 10 of fundamentals of acoustics, 3rd ed.,
Office 2010 Home And Business, kinsler, frey,
Office Professional 2010, coppens, and sanders,
Office 2007, (j. wiley & sons, 1982). a. waveguides and transmission lines
a waveguide is a structure which forces wave propagation along a path parallel to its longest dimension. acoustic wavequides are structures with constant cross-sectional region and shape. simple examples of such structures include hoses, tubes, and pipes, referred to hereafter as ducts. if a duct is excited by a pressure disturbance with a wavelength larger than twice the duct's largest cross-sectional dimension, then only plane waves will propagate down the duct. for a circular duct containing air at room temperature,
Office 2010 Standard Key, the highest frequency at which only plane waves will propagate is given by f = 100/a where a is the radius of the duct cross-section. once plane waves are generated inside the duct, they will propagate down the duct, even if the duct has bends or turns in it. a propagating plane wave might encounter a change in the acoustic impedance of the duct when the duct (i) opens into free space, (ii) is connected to another section of duct with a different cross-section, (iii) branches off into two ducts, or (iv) is terminated in some other way. this impedance change causes partial reflection and partial transmission of the incident plane waves.