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The major objective is to optimize dimensions of the expansion chamber muffler for enhancing transmission loss thereby increasing efficiency. This is brought about by changing characteristic properties of the muffler viz. the length and ratio of cross sections, both physically and by using simulation routines. An assortment of mufflers is assembled using a range of tube diameters including variable jackets and caps to manipulate the lengths and cross sections, as necessary. Each combination is tested at varying frequencies using the horn driver exciter. The input SPL is maintained constant for each frequency and the corresponding output SPL is recorded at the output port using an acoustic analyzer. The transmission loss for each of the assembled combinations over a range of frequencies is determined. The correction in effective length of the expansion chamber muffler due to extension of inlet and outlet pipes into the chamber is accounted for. A comparison of two distinct cases is presented: Muffler-1 having a variable length provision and a fixed cross section ratio of 7.27, and Muffler-2 having variable length and a fixed ratio of 12.14, both investigated for transmission loss.The data obtained is fitted to appropriate polynomials, and the curves obtained therefrom are compared with characteristic curves obtained using the standard formula for transmission loss. The difference in frequency values corresponding to maximum loss are accounted for using appropriate end-correction models. Furthermore, a comparison of the coefficients of the polynomial fits over variable lengths is also made. The experimentally obtained results are verified using standard end-correction simulation routines.
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