A port tube for an earphone, wherein the port tube is configured to acoustically couple a rear acoustic cavity of the earphone to an external environment, includes a first section that is proximate the rear cavity and defines a first cross-sectional area, a second, transitional, section that is coupled to the first section and defines a gradually increasing cross-sectional area, a third, curved and banked, section that is coupled to the second section and defines a second cross-sectional area that is greater than the first cross-sectional area, a fourth, transitional, section that is coupled to the third section and defines a gradually decreasing cross-sectional area, and a fifth section that is coupled to the fourth section and defines a third cross-sectional area that it less than the second cross-sectional area.