City Research Online

Abstract

Acoustic silencing systems with reactive elements are investigated using an analogy with electrical transmission line theory. Plane wave mode of propagation is assumed and convective effects of the flow on the acoustic transmission in the system are investigated. The one-dimensional wave equation is solved and leads to the representation of a silencing element by a symmetrical four pole. Attenuation-frequency characteristics of entire systems are calculated through matrix multiplication from computer programmes. Two test rigs were constructed for obtaining experimental results, one for systems without flow and the other for systems with an internal air flow up to a Mach number of 0.2. Resonators, expansion chambers with and without internal tubes and combinations of these elements have been investigated within the frequency range of 50 Hz to 3000 Hz with reflection-free inlet and outlet pipe terminations. Both the sound source and the pick-up are connected to the test rigs from the side. Theoretical results have been compared with those obtained by the test rigs, and, in some cases for inlet and cutlet pipes without reflection-free termination, to the results obtained by other workers. The Fast Fourier Transform has been used briefly as a technique for obtaining experimental results. A survey of definitions for attenuation has been undertaken and a comparison between the method of matrix multiplication and the alternative method of continuity has also been made. Computer programmes used for calculating the theoretical curves are presented.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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