The hearing aid a device that increases the loudness of sounds in the ear of the wearer. The earliest hearing aid was the ear trumpet, which is characterized by a large mouth at one end for collecting the sound energy from a large area and a gradually tapering tube to a narrow orifice for insertion in the ear.
Modern hearing aids are electronic. Principal components are a microphone that converts sound into a varying electrical current, an amplifier that amplifies this current, and an earphone that converts the amplified current into a sound of greater intensity than the original. Early models were quite large, but when transistors replaced amplifier tubes and smaller magnetic microphones became available in the 1950s, it became possible to build very small hearing aids, some of which were constructed to fit within the frames of eyeglasses and, later, behind the earlobe or within the external ear.
Hearing aids have widely differing characteristics; requirements for suitable aids have been extensively investigated. The two characteristics of a hearing aid that most influence the understanding of speech are the amplification of the various components of speech sounds and the loudness with which the sounds are heard by the wearer. As regards the first characteristic, speech sounds contain many components of different frequencies, which are variously amplified by a hearing aid.
The variation of amplification with frequency is called the frequency response of the hearing aid. An aid need amplify sounds only within the range of 400 to 4,000 hertz, although the components of speech cover a much wider range. With regard to the second characteristic--the loudness with which sounds are heard--too loud a sound can be as difficult to understand as one that is too faint. The loudness range over which speech is understood best is wide for some users and narrow for others.
Hearing aids with automatic volume control vary the amplification of the aid automatically with variations of the input.
A binaural hearing aid consists of two separate aids, one for each ear. Such an arrangement can benefit certain users.
HEARING AIDS AND HOW THEY WORK
A hearing aid is a small, electronic device that amplifies sound. No matter what the size, style or manufacturer, all hearing aids have the same basic components: a microphone, an amplifier, a receiver and a battery for power. Most hearing aids also have internal and external controls.
HOW A HEARING AID WORKS
All parts of the hearing aid work together to amplify sound. The microphone changes sound waves to electrical signals. These signals pass through the amplifier of the aid and are made louder. The amplified electrical signals are changed back into sound waves by the receiver and are channelled into the ear by the earmold or sound bone. The amount of amplification provided by a hearing aid is called "gain".
Hearing aids are powered by ba tteries and feature:
- Internal controls which are set by your audiologist. These controls determine which frequencies are amplified (frequency response) and the loudest sound the hearing aid can make (saturation response).
- External controls which are set by the hearing aid user. They may include a switch that can be set on M (microphone), M-T (microphone + telecoil), T (telecoil), or O (off).
- A Telecoil switch which allows the hearing aid to be used with a telephone and some assistive listening devices.
- A volume control, a small wheel which can be adjusted to increase or decrease the loudness of sound. On some hearing aids the volume control is combined with the on/off switch.
|
As the name suggests, this type of hearing aid fits behind the ear and is connected to a soft plastic earmold which fits inside the ear. As shown, the ear hook curves around the top of the ear and attaches to a small piece of plastic tubing extending from the earmold. Sound is routed through the earmold into the ear. The microphone is located at the top of the hearing aid near the ear hook. The battery, amplifier and receiver are all inside the case that fits behind the ear.
This type of hearing aid fits completely in the outer ear. The hearing aid case is custom made out of a hard plastic material. As shown, the hearing aid case houses all of the miniaturized hearing aid parts.
This type of aid is similar to the in-the-ear hearing aid except that it is smaller and fits mainly in the ear canal. ITC hearing aids are only suitable for milder hearing losses. A completely-in-the-canal (CIC) hearing aid is also available. A CIC aid is smaller yet, fitting entirely in the ear canal. CIC hearing aids may be suitable for mild to moderate hearing losses.