Theoretical and Experimental Considerations on Acoustic Attenuation of Plenum Boxes Lined with Different Materials

Plenum boxes are used for supply and exhaust of air through diffusers and grilles from heating and ventilating air conditioning (HVAC) systems. The plenum boxes ensure a continuous flow and moreover, they are usually lined with different materials in order to realize an acoustic insulation. These silencers/attenuators are of great importance in realizing a comfortable acoustical environment. The paper presents a theoretical and experimental investigation on some commercial plenum boxes with various sizes and lined with different sound absorbing materials. The sound transmission loss TL is the performance criterion for the silencers acoustical behaviour. The test procedure agrees the requirements of ISO 7235:2010 and the measurements were made in an anechoic room. Third-octave band analysis of experimental data is compared with theoretical ones. The results evidence the importance of silencer design which must take account of its geometry and the proper sound absorbing material as a function of frequency in order to optimize its acoustic efficiency.