An external acoustic chamber (220) for attachment to a mobile device (200) is provided. The external acoustic chamber (220) optimizes the audio performance of the mobile device (200) thus reducing the need for signal equalization and/or hardware to amplify the sound signal. The mobile device (200) includes a loudspeaker (205) and a first acoustic chamber (207) acoustically coupled to the loudspeaker (205). The external acoustic chamber (220) comprises at feast a second acoustic chamber (222) which penetrates the first acoustic chamber (207) adding volume to the first acoustic chamber (207). The combined greater volume reduces the dampening of loudspeaker (205) caused by the pressure in the first acoustic chamber (207). The result is an improvement in the frequency response of loudspeaker (205) approaching the natural frequency response of loudspeaker (205). The at least second acoustic chamber (222) is sized and shaped so that a first exterior surface portion of the acoustic chamber (220) covers or is flush with the battery (214) installed in the housing (201) of the mobile device (200). The first, exterior surface portion is substantially aligned with a second exterior surface portion enclosing the at least second acoustic chamber (222).