Hearing aid in ear. A full concha hearing aid in a man's ear. This hearing aid fits into the middle of the outer ear (concha). The small dial controls the volume of incoming sound. The plastic flap is the lid of the battery case. Hearing aids improve hearing in people with partial deafness. Sound is picked up by a tiny microphone, amplified, and then transmitted into the ear by a tiny speaker. Each hearing aid is fine-tuned to amplify the range of frequencies most needed by the patient.