In accordance with an embodiment of the present invention, a sound system of a wall-mounted flat panel display apparatus can include a speaker, being mounted in an area except for a display area, which plays back a video, in the flat panel display apparatus and playing back a corresponding sound; and an acoustic resonator, having a box shape including one surface formed with an open area and being mounted such that the surface formed with the open area is closely in contact with an outer side of a case of the flat panel display apparatus, the acoustic resonator being configured to induce a resonance of a sound projected from the speaker and inputted through the open area. With the present invention, it can be possible to adequately improve audio balance by simply mounting a pipe or box shaped acoustic resonator in an outer side of a case of the flat panel display apparatus.