A coupling element for establishing acoustic connection between a cylindrical hearing aid placed in the concha and a custom made ear plug placed in the auditory canal is formed by a disc-shaped element, which can be rotatably mounted a sound exit nipple on the hearing aid and an angularly bent tube section rotatably mounted on a laterally directed spout on the disc-shaped part. Because the hearing aid housing can rotate about its own axis in the concha and the coupling element can rotate about the nipple of the hearing aid, and because the tube section can rotate about the spout of the disc-shaped part, the tube section may be placed with respect to the auditory canal such that the sound channel in the ear plug can be established by a single, straight bore.