A Review of Current Techniques for Measuring Muffler Transmission Loss

Abstract

The most common approach for measuring the transmission loss of a muffler is to determine the incident power by decomposition theory and the transmitted power by the plane wave approximation assuming an anechoic termination. Unfortunately, it is difficult to construct a fully anechoic termination. Thus, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the twosource method. Both methods are demonstrated on two muffler types: (1) a simple expansion chamber and (2) a double expansion chamber with an internal connecting tube. For both cases, the measured transmission losses were compared to those obtained from the boundary element method. The measured transmission losses compared well for both cases demonstrating that transmission losses can be determined reliably without an anechoic termination. It should be noted that the two-load method is the easier to employ for measuring transmission loss. However, the two-source method can be used to measure both transmission loss and the fourpole parameters of a muffler.

Development of Acoustical Simulation Model for Muffler

“…On the other hand, FEM results show good agreement with experimental result for the frequency range 0-2500 Hz. Frequency 2500 Hz and above, the result deviates from each other, it is most probably caused by insufficient anechoic termination [6]. Based on the observation in Fig.…”

“…Figure 2 shows the geometry of the modeled muffler and isometric view for the simulation analysis. [6]. 50-3000 Hz frequency range was chose in the simulation.…”

“…Fig. 1 Two-load method [6,8] The two load method is based on the transfer matrix approach [8]. This method is used four-pole equation to obtain the TL of muffler, so the formulae almost similar with four-pole method and it easier to be used compare with four-pole method.…”

“…Normally, the TL of muffler obtained by using two-load method, three-point method [4], and four-pole method [5]. TL is considered the discrepancy in the sound power between the incident wave entering and the transmitted wave exiting the muffler when the muffler termination is anechoic [6].…”

Enhancing Noise Attenuation in Exhaust Mufflers on Response to Baffle Configuration

“…Transmission loss (TL) is usually measured using the three-point approach (decomposition method) or four pole methods; the four pole method is carried out by a two-source method and two-load method [1]. Several numerical approaches have been used to model TL in exhaust mufflers such as finite element software: Actran [2] and COMSOL Multiphysics [3], Boundary element methods (BEM) using Coustyx [4], and transfer matrix approach using Ricardo wave [5;6;7].…”