A head-mounted display, comprising: a front rigid body; a strap arm attached to a strap that secures the front rigid body to a user's head, the strap arm including: a body portion defining a boss at a side of the body portion, the boss having an aperture, the boss rotatably connecting the strap arm to the front rigid body, the body portion further defining an audio passage (512A, 512B) to transmit sound and an audio port to output the sound, the audio passage (512A, 512B) being defined along the body portion between the aperture of the boss and the audio port; the strap arm further including: a speaker positioned to emit the sound through the audio passage (512A, 512B) and to the audio port; and a back volume unit including: an enclosure portion; characterized in that the back volume unit further includes a cylindrical column inserted through the aperture of the boss, the cylindrical column defining a second aperture, the speaker being positioned within the second aperture with a back side of the speaker facing an interior surface of the enclosure portion to define a back volume between the interior surface and the back side of the speaker, at least a portion of the sound from the speaker being transmitted from the back volume through the audio passage (512A, 512B). a front rigid body; a strap arm attached to a strap that secures the front rigid body to a user's head, the strap arm including: a body portion defining a boss at a side of the body portion, the boss having an aperture, the boss rotatably connecting the strap arm to the front rigid body, the body portion further defining an audio passage (512A, 512B) to transmit sound and an audio port to output the sound, the audio passage (512A, 512B) being defined along the body portion between the aperture of the boss and the audio port; the strap arm further including: a speaker positioned to emit the sound through the audio passage (512A, 512B) and to the audio port; and a back volume unit including: an enclosure portion; characterized in that the back volume unit further includes a cylindrical column inserted through the aperture of the boss, the cylindrical column defining a second aperture, the speaker being positioned within the second aperture with a back side of the speaker facing an interior surface of the enclosure portion to define a back volume between the interior surface and the back side of the speaker, at least a portion of the sound from the speaker being transmitted from the back volume through the audio passage (512A, 512B). a speaker positioned to emit the sound through the audio passage (512A, 512B) and to the audio port; and a back volume unit including: an enclosure portion; characterized in that the back volume unit further includes a cylindrical column inserted through the aperture of the boss, the cylindrical column defining a second aperture, the speaker being positioned within the second aperture with a back side of the speaker facing an interior surface of the enclosure portion to define a back volume between the interior surface and the back side of the speaker, at least a portion of the sound from the speaker being transmitted from the back volume through the audio passage (512A, 512B).