The use of microperforated materials as duct liners

The acoustical performance of a microperforated panel and a fibrous material are compared to confirm that a microperforated panel lining can be used to replace a fibrous lining as a sound absorber in a duct. Fibrous materials are often used to line ducts in order to attenuate HVAC noise, for example. These treatments are often primarily useful in a limited frequency range owing to the characteristics of non-planar wave propagation in ducts. At the same time, microperforated materials backed by a finite-depth air space are effective in a limited frequency range owing to the nature of the reactive impedance of this combination. Here it will be shown that microperforated materials may be used to create duct linings that produce attenuation comparable with that of fibrous materials. The characteristics of the microperforated panel were studied based on the Maa model. To compare the performance of these two linings, theoretical, numerical and experimental cases were studied. In the case studies, both extended reaction and locally-reacting treatments are considered. For the analytical approach, Morse\u27s theory was applied in the local reaction case. On the other hand, Scott\u27s analysis was used to study the extended reaction case. In the experimental work, the transmission losses of various samples were measured in the square impedance tube. To tune these performance of a microperforated sheet to reproduce that of a fibrous material, the hole size, porosity, thickness, density, and air-backing depth were modified. To validate the experimental and analytical data and to handle situations that are not easily modeled using an analytical approach, a finite element model was used for the calculation. For the finite element model analysis, COMET/VISION and SAFE were used. Since the software does not include explicit microperforated material models, an alternative approach was used. The alternative model was based on the Attala and Sgard model in which the microperforated material is replaced by rigid porous material: that model was formed to represent the microperforated panel in the finite element model. Furthermore, it was demonstrated that the microperforated panel can successfully reproduce the acoustical performance of glass fiber as a duct lining material cover the desired frequency range