Hearing aid is a small amplifier that amplifies the sound that was originally inaudible, and then uses the residual hearing of the hearing-impaired person to send the sound to the auditory center of the brain and feel the sound. Great convenience for the hearing impaired.

There are several types as follows, but the function and principle are the same.
(1) From the external structure, it can be divided into: box type, behind-the-ear type, in-ear type, and in-ear type can be divided into ordinary in-ear type, ear canal type, and deep-ear canal type.
(2) From the electronic principle, it can be divided into: analog hearing aids; programmable hearing aids, all-digital hearing aids, wide dynamic language technology hearing aids, etc.
(3) Hearing aids are divided into air conduction hearing aids and bone conduction hearing aids according to the conduction mode. Box type, behind-the-ear type, and in-the-ear type are all air conduction hearing aids.