Conventional Hearing Aid Indications and Selection

This article will discuss the indications and selection of conventional hearing aids. Conventional hearing aids are non-invasive (not requiring surgery) and are placed behind the pinna, in the canal, or are body-worn. Invasive hearing aids, including bone-anchored hearing aids and cochlear implants, are excluded from coverage in this chapter. Hearing aids, by definition, are sound-amplifying devices that increase the user's ability to detect noise. The components of a non-invasive hearing aid vary widely but broadly consist of a microphone, amplifier, receiver, and battery. The microphone converts external acoustic energy into electrical energy, which is amplified by the amplifier. The receiver detects this and converts it back into acoustic energy, projecting sound into the ear canal. The amplification is driven by the battery, which can be made from zinc-air batteries, mercury, alkaline, or rechargeable batteries. A non-invasive hearing aid aims to increase the sound levels delivered to and hence detected by the hair cells in the cochlea.