Application of the edge-constraint effect to nearly-realistic barrier treatments

It was shown in earlier work that when internal constraint planes are used to segment a fibrous lining, the normal incidence transmission loss of the lining can be substantially enhanced at low frequencies by an edge-constraint effect. Here it is shown in three examples that internal constraints can enhance the transmission loss of fibrous lining materials both under random incidence conditions and in an interior noise control application. First, sound transmission through a circular duct, part of whose length was filled with fibrous material constrained within radially separated, circumferential constraints was considered. Next, sound transmission through a square aperture filled by a fibrous lining constrained within a honeycomb lattice was studied. The performance of the honeycomb lining both by itself and when used in combination with a single limp panel to form a two element barrier system was measured. Finally, the use of a fibrous lining constrained within a rectangular honeycomb lattice to line an interior space driven by a structure-borne noise source was considered. In all cases, a transmission loss enhancement attributable to the internal constraints was identified. In addition, finite element predictions were found to be in good agreement with measured results, indicating that the effect can be modeled successfully.