A head-mounted display apparatus, comprising: a display device comprising: an outer casing comprising a display portion and a wearing portion connected to the display portion; and a display panel disposed in the display portion; an acoustic device comprising: a speaker disposed in the outer casing, and adjacent to the display panel, the speaker comprising a speaker housing and a diaphragm disposed in the speaker housing, and the speaker housing comprising: an acoustic surface; an acoustic outlet formed on the acoustic surface; and a rear surface opposite to the acoustic surface; and wherein the acoustic device further comprising a resonance box connected to the acoustic surface of the speaker housing; and a waveguide connected to the resonance box and the wearing portion; and and wherein the head-mounted display apparatus further comprising a wearing structure connected to the outer casing, wherein a volume of the waveguide is greater than 2 times a volume of the speaker, and a length of the waveguide which is measured along a wave path is greater than 5 times the thickness of the speaker between the acoustic surface and the rear surface, wherein the waveguide comprises a connection portion connected to the resonance box and an extension portion connected to the connection portion, wherein a maximum length of the connection portion which is measured in an extension direction is about 0.8 times to 5 times the maximum thickness of the extension portion which is measured in the extension direction, wherein the minimum thickness of the extension portion is in a range from about 3 mm to 8 mm, wherein the connection portion extends in the extension direction, and the extension portion extends in a direction that is perpendicular to the extension direction. a display device comprising: an outer casing comprising a display portion and a wearing portion connected to the display portion; and a display panel disposed in the display portion; an outer casing comprising a display portion and a wearing portion connected to the display portion; and a display panel disposed in the display portion; an acoustic device comprising: a speaker disposed in the outer casing, and adjacent to the display panel, the speaker comprising a speaker housing and a diaphragm disposed in the speaker housing, and the speaker housing comprising: an acoustic surface; an acoustic outlet formed on the acoustic surface; and a rear surface opposite to the acoustic surface; and wherein the acoustic device further comprising a resonance box connected to the acoustic surface of the speaker housing; and a waveguide connected to the resonance box and the wearing portion; and a speaker disposed in the outer casing, and adjacent to the display panel, the speaker comprising a speaker housing and a diaphragm disposed in the speaker housing, and the speaker housing comprising: an acoustic surface; an acoustic outlet formed on the acoustic surface; and a rear surface opposite to the acoustic surface; an acoustic surface; an acoustic outlet formed on the acoustic surface; and a rear surface opposite to the acoustic surface; and wherein the acoustic device further comprising a resonance box connected to the acoustic surface of the speaker housing; and a waveguide connected to the resonance box and the wearing portion; and and wherein the head-mounted display apparatus further comprising a wearing structure connected to the outer casing, wherein a volume of the waveguide is greater than 2 times a volume of the speaker, and a length of the waveguide which is measured along a wave path is greater than 5 times the thickness of the speaker between the acoustic surface and the rear surface, wherein the waveguide comprises a connection portion connected to the resonance box and an extension portion connected to the connection portion, wherein a maximum length of the connection portion which is measured in an extension direction is about 0.8 times to 5 times the maximum thickness of the extension portion which is measured in the extension direction, wherein the minimum thickness of the extension portion is in a range from about 3 mm to 8 mm, wherein the connection portion extends in the extension direction, and the extension portion extends in a direction that is perpendicular to the extension direction.