An acoustic device comprises a first closed cavity and a second closed cavity, at least a portion of a partition part flexibly deforms, the first closed cavity is adjacent to a vibration diaphragm, and the second closed cavity is far away from the vibration diaphragm; when the vibration diaphragm vibrates, the internal sound pressure of the first closed cavity changes, a flexible deformation part of the partition part deforms with the change, to flexibly adjust the volume of the first closed cavity; the second closed cavity encloses sound waves into the second closed cavity; and the Young's modulus or strength of at least partial region of the flexible deformation part is less than that of the wall of the first and/or the second closed cavity, the Young's modulus of entire region or partial region of the flexible deformation part is less than or equal to 8000 Mpa.