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A time-averaging transient testing technique has been developed to allow for a rapid measurement of the matrix parameters and other frequency-dependent characteristics of acoustical systems with or without mean flow. The technique is applicable to systems with substantial flow noise contamination which is either random or periodic in nature. Flow and noflow experiments were conducted on laboratory models of exhaust mufflers, variable area ducts, and complex piping networks. Excellent agreement between theoretical and experimental results was obtained. This success not only demonstrated the feasibility of the experimental technique for a range of practical industrial applications but also confirmed certain theoretical postulations that have not yet been verified adequately through comparison with experimental results. PACS numbers: 42.50. Gf, 43.50.Ed, 43.20.Mv LIST OF SYMBOLS B C c D f J k0 L 1 M P p s S/N Subscripts d enh exp i{ = 1,2,3,...) j( = 1,2,3,...) u Transmission loss Time Fourier transform of vibratory volume velocity As defined in Eq. (2) As defined in Eq. (2) As defined in Eq. (2) As defined in Eq. (2) Abscissa in the Cartesian coordinate Characteristic impedance Complex propagation constant Angular frequency (2•rf) of the downstream reference pipe enhancement experimental of the ith station; of the ith element of thejth element of the series connection of the upstream reference pipe INTRODUCTION Despite significant progress in the development of acoustical modeling techniques for piping systems and acoustic filters in the past few years, continued efforts are being made to develop experimental methods to allow direct measurement of acoustic properties of unknown systems. A reliable and practical testing method is not only required for the verification of theoretical postulations but also to identify acoustic characteristics of systems for which there is still no adequate theoretical representation.When designing experiments to measure acoustic properties of systems containing a mean flow, two essential aspects must be considered. First, the effect of the Mach number must be accounted for in the formulation of the system equations. Second, flow noise generated within the system must be eliminated or effectively reduced to maintain an acceptable signal-to-noise (S/N) ratio.The techniques used in the past can be classified into three main categories according to the type of excitation used. They are (i) the standing-wave-ratio (SWR) method, (ii) the steady-state random excitation method, and (iii) the transient testing method.The SWR method has been by far the most popular method used for both no-flow and with-flow measure-867

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