A cochlear implant or other auditory prosthesis utilizes an external portion worn on a recipient's head and an internal portion implanted therein. Both portions include an associated coil that transmits a signal between the two portions. The external coil has a form factor substantially similar to the implantable coil. This form factor allows the external portion to be manufactured with a smaller footprint, since components that may otherwise interfere with signal transmission (e.g., batteries) may be installed closer to the external coil.