One embodiment of the invention discloses an acoustic device having a housing having an accommodating space with a sound hole formed thereon and communicating with the accommodating space; a speaker unit received in the accommodating space having a diaphragm including a first area away from the sound hole and a second area close to the through window; wherein, the diaphragm has a plurality of corrugations formed on the first area and the second area, respectively, and the amount of the corrugations on the first area is less than that on the second area.