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hearing aid is an electroacoustic device 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 implant.
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:
Body worn aids
This was the first type of hearing aid . Thanks to developments in technology they are now rarely used. These aids consist of a case, an earmold, 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 use of vacuum tubes, body worn aids can provide loud amplification. This made them the first appropriate hearing aid for profound hearing losses. Today, body aids have largely been replaced by Behind-The-Ear (BTE) instruments.
Behind the ear aids (BTE)
BTE aids consist of a case, a tube and an earmold. The case is small and made of plastic. Generally, the case sits behind the pinna (ear) with the tube coming down the front into the earmold. The case contains the amplification system. The sound is routed from the hearing aid case to the earmold via the tube. The sound can be routed acoustically or electrically. If the sound is routed electrically, the speaker (receiver) is located in the earmold, rather than in the case. The earmold is created from an impression taken of the individual's outer ear. This usually ensures a comfortable fit and reduces the possibility of feedback. Earmolds are made from a variety of hard (firm) and soft (pliable) materials. The color of the case and earmold of a BTE aid can be modified and optional decorations can be added.
BTEs can be used for mild to profound hearing loss. Due to the electrical components being located outside the ear, the chance of moisture and earwax damaging the components is reduced. This increases the durability of a BTE aid and with proper care it can last for a number of years. BTEs can be connected to assistive listening devices, such as FM systems. An important aspect of the BTE aid is that the case and earmold are separate which makes it easier to replace the earmold. BTE aids are commonly worn by children who need a durable type of hearing aid. As children get older, they will require new earmolds on a regular basis; for example, babies may need earmolds replacing as often as every two weeks.
In the ear aids (ITE)
These devices fit in the outer ear bowl (called the concha); they are sometimes visible when standing face to face with someone. ITE hearing aids are custom made to fit each individual's ear. They can be used in mild to some severe hearing losses. Feedback, a squealing/whistling caused by sound (particularly high frequency sound) leaking and being amplified again, may be a problem for severe hearing losses.Some modern circuits are able to provide feedback regulation or cancellation to assist with this. Another way to deal with feedback is venting. The vent is a tube primarily placed to offer pressure equalization. However, different vent styles and sizes can be used to influence and prevent feedback . Traditionally, ITEs have not been recommended for young children because their fit could not be as easily modified as the earmold for a BTE, and thus the aid had to be replaced frequently as the child grew. However, there are new ITEs made from a silicone type material that mitigates the need for costly replacements.
Receiver In the Canal/Ear (RIC/RITE)
At a first glance, these devices are similar to the BTE aid. There is however one crucial difference: The speaker ('receiver') of the hearing aid is placed inside the ear canal of the user and thin electrical wires replace the acoustic tube of the BTE aid. There are some advantages with this approach: Firstly, the sound of the hearing aid is arguably smoother than that of a traditional BTE hearing aid. With a traditional BTE hearing aid, the amplified signal is emitted by the speaker (receiver) which is located within the body of the hearing aid (behind the ear). The amplified signal is then directed to the ear canal through an acoustic tube, which creates a peaky frequency response. With a RITE hearing aid, the speaker (receiver) is right in the ear canal and the amplified output of the hearing aid does not need to be pushed through an acoustic tube to get there, and is therefore free of this distortion. Secondly, RITE hearing aids can typically be made with a very small part behind-the-ear and the wire connecting the hearing aid and the speaker (receiver) is extremely inconspicuous. For the majority of people this is one of the most cosmetically acceptable hearing device types.Thirdly, RITE devices are suited to "open fit" technology so they can be fitted without plugging up the ear, offering relief from occlusion.
