DA-13-C024 -- Prediction of Insertion Loss of Plenums above the Plane Wave Cutoff Frequency PDF

The finite element method is utilized to predict the insertion loss of plenums. Insertion loss is determined by comparing the transmitted sound power at the termination with and without a plenum inserted into the duct system. The boundary condition for the duct system on the source side is a diffuse or reverberant field, and a baffled termination is assumed. Simulation results are compared to published measurement results for HVAC plenums with good agreement. Additionally, the results are compared to the ASHRAE Handbook equations and a well-known energy based model. The approach is appropriate both above the plane wave cutoff frequency and at frequencies just below the cutoff, and is demonstrably superior to the Handbook.