In the present study, it could be shown that by integration of a piezoceramic transducer in a fiber-reinforced door side panel, a flat loudspeaker can be realized. Taking into account the given restrictions, the integration position has been identified, where the geometry decouples the vibrating membrane from the supporting surface. With the help of an acoustic finite-element simulation, the main design variables of the integration position were found and the relevant effects for sound radiation were made visible. The manufacturing of the test specimen with piezoceramic transducers was performed using vacuum-assisted resin infusion and the long fiber injection procedure. The effect on the real sound radiation behavior of the door side panel with a material-immanent loudspeaker was experimentally determined using laser scanning vibrometry and sound pressure measurements. The presented work shows, for the first time, the high potential of acoustic functionalization of lightweight structures during the manufacturing process for the realization of lightweight and space-saving loudspeakers in a production-ready process.