The anechoic assumption has long been used for the modeling of long exit pipes or ducts of acoustic elements [1, 2, 3, 4, 5, 6, 7]. Especially in compressor discharge line modeling, the exhaust pipe from the compressor manifold leading all the way to the condenser is usually assumed to be anechoic since it is very long. Also, experimental efforts have been made by investigators using different acoustical testing rigs to simulate anechoic terminations. In this study, the effect of the discharge pipe length of a muffler model on the transfer function is discussed on a theoretical basis. The transfer functions of a muffler model with different discharge pipe lengths and dampings are simulated and compared. The results mimic actual data which would be measured experimentally if the pipe length is finite instead of infinitely long or if absorption material is used. Furthermore, a horn type exit is investigated. The permissibility of the anechoic termination assumption in realistic modeling is also discussed.
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