MODEL RELEASED. Hearing aid. Elderly man wearing a hearing aid. This battery powered device is worn behind the ear. It contains a wheel dial to control the volume of incoming sound and a tiny microphone, amplifier and receiver. The microphone converts sound into an electrical signal, which can then be amplified before being sent to the receiver, which converts the amplified electrical signal back into sound. The sound is then transmitted into the ear canal by a thin, transparent tube. Hearing aids improve hearing in people with partial deafness. A hearing aid can be fine-tuned to amplify the range of frequencies most needed by the patient.