On the Techniques for Measuring Muffling Devices with Flow

ABSTRACT: The characterization of a muffling device used for noise control applications can be given in terms of the attenuation, insertion loss, transmission loss, and the noise reduction. In addition, the four-pole parameters of a muffler can supply important information on the acoustical properties of the device. In certain cases, some of the parameters to measure the performance can be related. It has been commonly accepted that the transmission loss is the most important parameter to characterize the performance of a muffling device. However, there are some discrepancies regarding the most precise method to measure it, in particular, when the effects of a mean flow are needed. In this article some of the techniques used to measure the acoustic performance of muffling devices are described. In particular, the decomposition method, the two-load method, and the two-source method are discussed and its associated errors and limitations are examined. Some numerical and experimental examples on a single expansion chamber are presented. For the numerical results, the finite element method is used to estimate the sound pressure distribution inside each muffling device and, consequently, to predict its properties