Transmission Loss of Absorptive Mufflers Lined with Expanded Clay Granulates

The article presents the results of tests on sound attenuation by two types of cylindrical absorptive mufflers with the same length and different diameters of chambers filled with expanded clay granulates. Using a laboratory stand for testing acoustic mufflers with an impedance tube, the transmission loss parameter was determined. To compare the effectiveness of sound attenuation, the transmission loss of mufflers without sound absorbing material was also determined. The results of these tests were compared to the results obtained with the use of a known calculation model for reflective mufflers. Using an impedance tube, the normal incidence sound absorption coefficients of the expanded clay granulates with thicknesses of material samples from 10 to 100 mm were determined. The dependence between the sample thickness and the first resonance frequency of the sound absorption coefficient was determined, which was then used in the proposed calculation model of the effectiveness of the cylindrical absorptive mufflers with expanded clay granulates. Using the proposed theoretical model, the results of transmission loss calculations, satisfactory for engineering applications, were obtained.