A　theoretical　model　is　developed　to　predict　sound　transmission　loss　(STL)　across　periodically　and　orthogonally　stiffened　composite　laminate　sandwich　structures.　The　first　order　shear　deformation　theory　(FSDT)　is　employed　to　describe　the　top　and　bottom　composite　laminate　plates　whilst　the　longitudinal　and　rotational　motion　equations　are　utilized　to　characterize　the　reaction　forces　and　moments　of　the　stiffeners.　By　taking　advantage　of　the　periodicity　of　the　sandwich,　the　governing　vibroacoustic　equations　are　favorably　solved　by　employing　the　method　of　space　harmonic　expansion.　The　validity　and　feasibility　of　the　proposed　theoretical　model　is　qualified　through　comparisons　with　finite　element　simulation　results.　It　is　demonstrated　that　both　the　stiffeners　and　laminate　layup　have　significant　effects　on　the　vibration　and　sound　radiation　behaviors　of　the　structure,　especially　in　the　mid　and　high　frequency　regimes,　enabling　further　acoustic　optimization　design.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.