Doctoral Dissertations


"The principal objective of this investigation was to study the feasibility of developing laboratory techniques for automobile-exhaust muffler design in order to reduce the amount of on-vehicle trial-and-error testing currently required. The investigation included (1) improving the capability of existing laboratory equipment to simulate the conditions in automobile exhaust (i.e., high-amplitude pressure waves, steady flow, and elevated temperature), and (2) theoretical and experimental studies of typical acoustic elements (side-branch resonators, expansion chambers, louvered tubes) used in muffler design. The sound fields used for these studies included pure tones, single pulses (tone bursts), random noise, and simulated automobile exhaust noise.

Empirical correction factors, which adequately accounted for the effects of both finite-amplitude waves and flow on the impedance of side-branch resonators under pure-tone excitation, were obtained, Using these empirical correction factors, the theoretical response characteristics (in terms of transmission loss and insertion loss) were calculated; these results were in good agreement with the measured responses under anechoic conditions. Single-pulse excitation was found to substantially increase the resistive portion of the impedance of side-branch resonators. Empirical correction factors, applicable to side-branch resonators under single-pulse excitation were also obtained.

Theoretical calculations of the reflection and transmission characteristics of plane discontinuities in the presence of flow were made using small perturbation theory. The use of these reflection and transmission characteristics gave theoretical expansion chamber response characteristics which were in good agreement with measured values. The response of expansion chambers was found to be independent of pressure amplitude.

Theoretical modeling of acoustic filters terminated with finite tailpipes is presented. Good agreement was observed between theoretical and measured responses.

Sound generation by flow past a side-branch resonator showed a complicated dependence on the tailpipe length and flow Mach number, with regard to both magnitude and frequency. This "self-noise" of resonators, in the presence of flow, was effectively eliminated by placing a wire screen at the resonator neck.

A simple prototype muffler showed some deviations from theoretical predictions when tested with simulated exhaust noise but did show good agreement with theoretical predictions when tested with both pure-tones and random noise. Improvement of the muffler performance was achieved by the use of a dissipative element in the muffler; an insertion loss of 20.5 dBA was obtained. A practical muffler design and testing procedure, using simulated automobile exhaust noise in the laboratory, is described"--Abstract, pages ii-iii.


Gatley, William S.

Committee Member(s)

Koval, Leslie Robert
Cunningham, Floyd M.
Howell, Ronald H. (Ronald Hunter), 1935-
Ho, C. Y. (Chung You), 1933-1988


Mechanical and Aerospace Engineering

Degree Name

Ph. D. in Mechanical Engineering


Ford Motor Company


University of Missouri--Rolla

Publication Date



xix, 207 pages

Note about bibliography

Includes bibliographical references (pages 200-202).


© 1973 Richard Chuka Oboka, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Automobiles -- Motors -- Mufflers -- Acoustic properties
Automobiles -- Motors -- Exhaust systems -- Noise

Thesis Number

T 2775

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