Research of Muffler with Perforated Tube and Its Acoustic Properties Measurement

The perforated rate is a key parameter for the acoustical properties of muffler. To control the transmission loss of the muffler without replacing the chamber volume, an assembled muffler structure is supposed by inserting perforated tubes with different rate into the chamber. The transmission loss of the designed muffler is solved numerically with the finite element method (FEM). The simulation indicates that the acoustic properties of muffler with perforated tube share both the expansion chamber muffler and Helmholtz resonators. When the perforated rates close to zero, the TL curves exhibited resonated peak and the frequency band of the attenuated noise is limited. Increasing the perforated rate, the TL curves exhibit as arches. The bigger the perforated rate is, the closer to the expansion muffler. An impedance tube testing system is designed for measuring the mufflers. The data acquisition and analyzing program were compelled with LABVIEW. Experiments performed with the designed muffler show that in the low frequency band, the transmission loss can be controlled by the perforated rate of tube, which coincides with the simulation.