Purpose <p>Laminated composites are used to build light vehicular cabin structures due to higher weight-specific strength and stiffness. The thin and flexible composite cabin walls interact with the confined acoustic domain producing a complex audio output at various working frequencies. In a large cavity with thin walls, stiffeners are added to enhance structural stability which can further alter the acoustic output. In this study, the response of a thin acoustic cavity comprising of four rigid and two thin laminated composite interacting walls is reported by harmonically exciting one of the rigid walls.</p> Methods <p>This vibroacoustic problem is analyzed by finite element free vibration analysis of the enclosure to extract the mobility relationship between pressure and velocity at the interacting walls and apply that to the pressure–velocity formulation of the interior acoustic domain using the boundary element method to eliminate the velocity terms at the interacting flexible walls and obtain the acoustic pressures at the boundary.</p> Results <p>A series of numerical results are provided to establish the performance of the stiffened cavity over the unstiffened one. The study also shows the effect of increased damping and different stiffener arrangements along with their thicknesses and widths on the acoustic sound pressure and structural displacement of the stiffened cavity.</p> Conclusions <p>The study shows that the structural modes can be regulated without much increase of mass by judiciously adding exterior stiffeners to the containing structures. Examples reveal that one can restrict the acoustic output in any intended working frequency band by carefully planning the stiffeners.</p>