Sound attenuation of a circular multi-chamber hybrid muffler

The sound attenuation of perforated dissipative circular mufflers including a folded resonator and a short expansion chamber is investigated in detail by means of a two-dimensional axisymmetrical analytical approach based on the mode matching technique. The acoustical properties of the bulk reacting porous material and the perforated screen are taken into account to obtain the governing eigenequation for the wave propagation through the absorbent material and central perforated passage. Once the solution of the transverse eigenproblem is computed in all regions, the muffler transmission loss is determined by matching the acoustic pressure and axial velocity across each geometrical discontinuity. In addition, finite element results and experimental measurements are utilized for validation. The acoustic attenuation performance is examined considering the effect of the internal geometry of the muffler, the properties of the sound absorbent material and the porosity of the perforated pipe. Comparison is also provided with hybrid mufflers of earlier studies. It is shown that the acoustic contribution of the folded resonator is reinforced by the presence of the short expansion chamber, providing a good noise attenuation performance in the low and mid frequency range, whereas the dissipative effects associated with the central chamber suppress the high frequency noise, thus leading to a broadband attenuation of sound energy.