Disclosed by the present invention is an acoustic device, comprising a sound generating unit. A first sealed cavity is formed at the rear side of a vibrating diaphragm of the sound generating unit, a mounting hole is provided on a cavity wall of the first sealed cavity, and a flexible deformation part is provided on the mounting hole. A second sealed cavity is formed at the outer side of the first sealed cavity, and the second sealed cavity encloses the sound wave generated during deformation of the flexible deformation part therein. The mounting hole is located on the first wall, and a groove is provided on the first wall at the periphery of the mounting hole towards the first sealed cavity. The flexible deformation part is fixed on the bottom of the groove, and a through groove is further provided on the first wall.