Abstract: A plenum mounted, flat metal panel diaphragm masking loudspeaker includes a flat, stamped sheet metal frame which has a deployed state and an undeployed, flat state well suited to storage or shipping. A large, movable tab at the bottom of the frame is weakened by a series of small apertures and forms a hinge or fold line. Electrical accessories including a transformer, a rotary switch for selecting transformer taps and signal connections are included in an enclosed box mounted on the foldable tab. The flat panel masking loudspeaker is shipped flat in the undeployed state and then the large tab is deployed by being folded outwardly before installing the flat panel masking loudspeaker in a ceiling plenum. During installation, the tab is folded along the hinge or fold line out to approximately 90.degree.