Disclosed is a hearing aid assembly wherein the hearing aid is comprised of an acoustic receiver, an acoustic transmitter, and a body, and an annular channel, wherein the acoustic receiver is designed to fit into a external acoustic meatus of an ear, the acoustic transmitter is designed to fit into a inner ear canal, and the generally cylindrical body is disposed between the receiver and the transmitter, the annular channel is disposed on the surface of the body such that it circumscribes the body's circumference. The annular channel is adapted to receive an annular ring which functions as an acoustic seal and which, in one preferred embodiment, has a T-shaped cross-section.