A hearing aid is an electroacoustic body worn apparatus which typically fits in or behind the wearer's ear, and is designed to amplify and modulate sound for the wearer. Earlier devices, known as an "ear trumpet" or "ear horn"[1][2], were passive funnel-like amplification cones designed to gather sound energy and direct it into the ear canal. Similar devices include the bone anchored hearing aid, and cochlear.




Types of hearing aids

There are many types of hearing aids (also known as hearing instruments), which vary in size, power and circuitry. Among the different sizes and models are:




NIH illustration of different hearing aid types.[edit] Body worn aids
This was the first type of hearing aid invented by Harvey Fletcher while working at Bell Laboratories.[3] Thanks to developments in technology they are now rarely used.[citation needed] These aids consist of a case, an ear mold, and a cord. The case contains the amplifier components. The case is about the size of a pack of playing cards and is worn in the pocket or on a belt. The ear mold is connected to the case via a cord. Because of their large size, body worn aids can provide loud amplification. This made them appropriate for profound hearing losses. Today, body aids have largely been replaced by Behind-The-Ear (BTE) instruments.[citation needed]

[edit] Behind the ear aids (BTE)
BTE aids consist of a case, a tube and an earmold. The case is small and made of plastic. It fits behind the pinna (ear). The case contains the amplification system. The tube is used to route the sound from the hearing aid case to the earmold. Typically the sound is routed acoustically. Sometimes the sound is routed electrically. In that case, the speaker is located in the earmold instead of in the case. The earmold is usually custom made or made of other pliable fixture that contours to the individuals ear. The color of the BTE components (case, tube and earmold) range from inconspicuous skin tones to bright colors and optional decorations.

BTEs can be used for mild to profound hearing losses. BTEs have several advantages over other types of hearing aids.[citation needed] One advantage is that they tend to be more durable. This is because the electrical components are located outside the ear. This reduces the amount of earwax and moisture that the electrical components are subjected to. Another advantage is that BTEs can be connected to assistive listening devices, such as classroom FM systems. Lastly, if the earmold no longer fits the user, the earmold can be replaced for a fraction of the price of a new hearing aid. BTE hearing aids are typically prescribed for children. This is because children need a durable hearing aid, often need assistive listening devices, and often outgrow the size of the earmold.

Recent innovations in BTEs include miniature BTEs with thin hair-like sound tubes (see open-fit devices below). These are often less visible than In-The-Ear aids (ITEs). They use a larger vent than other hearing aid types. This keeps the ear canal more open, which allows sound to enter the ear without being amplified. This is helpful for listeners with normal hearing in the lower frequencies. Miniature BTEs are generally used for mild to moderate high frequency losses.