Illustration of a generic hearing aid, where the receiver is placed in the hearing aid shell that sits behind the ear. The feedback loop (green) highlights the receiver vibrations that are picked up by the microphone (purple) and sent back to receiver to be reproduced as sound. Another common configuration is to place the receiver in the “ear dome” that sits in the ear canal. While feedback is reduced by this configuration, it is not eliminated. Here, the vibrations propagate via the sound tube (dot-dashed) and back to the hearing aid shell (dashed) and microphones.