A Transfer Matrix Model for Lined Loudspeaker Ducts

This paper presents a Transfer Matrix Method (TMM) model for transmission-line loudspeaker enclosures partially lined with melamine foam (Basotect® G+). The Johnson–Champoux–Allard–Lafarge (JCAL) parameters of the foam are identified from manufacturer absorption data using literature values as physically informed initial estimates. Munjal’s formulation for symmetrically lined ducts is extended to single-sided liners, showing that the bulk-reacting dispersion relation retains the same analytical form after redefining the clear-air geometry. To account for local 3D effects at the driver–duct junction, an equivalent resistive–reactive correction is introduced and its parameters identified from finite-element simulations, where necessary. The model is validated against 3D COMSOL simulations over variations in liner thickness and geometry. Good agreement is obtained for symmetric liners up to approximately 30 mm per side and for single-sided liners up to about 60 mm; beyond these limits, transverse pressure gradients progressively violate the plane-wave approximation. The resulting model provides a practical design tool for transmission-line loudspeaker enclosures, substantially reducing reliance on computationally intensive 3D finite-element simulations.