The CMM306 is a built-in housing for flush mount installation of loudspeakers in concrete structures. The construction with mineral fiberboard plate allows customized cut-outs in various diameters or shapes for installation of loudspeakers (or lighting fixtures). Cast in-place or integration in precast factories is both possible. The mineral fiberboard plate allows cutouts with diameters up to ~ 280 mm, while a maximum built-in depth of 110 mm guarantees compatibility with a large number of in-ceiling loudspeakers. The synthetic enclosure is made out of halogen free and fire (up to 650°C) resistant materials. Entries for both 2xM20 and 2xM25 cables are provided.