JANE SHEMILT / SCIENCE PHOTO LIBRARY JANE SHEMILT / SCIENCE PHOTO LIBRARY
Canal hearing aid. Close-up of a canal hearing aid. This hearing aid fits inconspicuously into the ear canal. 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 trans- mitted into the ear by a tiny speaker. Each hear- ing aid is fine-tuned to amplify the range of frequencies most needed by the patient.
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