An ear unit for stably fitting in an ear includes a first surface facing inwardly toward the ear, a second, opposite surface facing outwardly from the ear and an outer circumferential surface formed between the first and second surfaces. The outer circumferential surface is shaped as a decremental curve. The distance between the ends of the decremental curve is approximately equal to the distance between a first cavity formed under the tragus of the ear and second cavity covered by the lower node of the antihelix of the ear. The first surface is provided with a curvature that provides a contact surface that substantially conforms to the concha, providing an improved attachment, thereby enabling the ear unit to fit closely against the concha when the ear unit is positioned into the ear.