Hearing aid
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A hearing aid is a device used to help the hard-of-hearing hear sounds better. In the past, a funnel-like amplification cone, called an "ear trumpet" or "ear horn", was used. Now, however, the most common style is a small electronic device that fits into the wearer's ear. The first variety of this device had a rectangular battery pack connected by a thin wire, intended to be held in a pocket. During the mid- to late 20th century, this type of power storage was replaced by a more inconspicuous sort in models in which small, circular batteries were placed in the inserted unit itself.
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Types of hearing aids
There are many types of hearing aids, which vary in size, power and circuitry. Among the different sizes and models are:
Body worn aids
These aids consist of a case containing the components of amplification and an ear mold connected to the case by a cord. The case is about the size of a pack of cards and is worn in the pocket or on a belt. Because of their large size, body worn aids are capable of large amounts of amplification and are used for profound hearing losses.
Behind the ear aids (BTE)
BTE aids have a small case that fits behind the ear and conducts sound to the ear through an earmold that is custom made. BTEs can be used for mild to profound hearing losses and are especially useful for children because of their durability and they can easily connect to assistive listening devices such as FM systems for classroom use. Although they are large, BTEs can range from very inconspicuous skin tones to cheerful colors depending on the users preference.
In the ear aids (ITE)
These devices fit in the outer ear, called the concha, they are usually visible when standing face to face with someone. ITE hearing aids are all custom made to fit each individuals ear. They can be used in mild to severe hearing losses although feedback, a squeal caused by sound leaking out of the aid and being amplified again, may be a problem for severe hearing losses. They are not recommended for young children because they must be replaced frequently as the child grows.
In the canal (ITC), mostly in canal (MIC) and completely in the canal aids (CIC)
ITC aids smaller, filling only the bottom half of the external ear. You usually cannot see very much of this hearing aid when you are face to face with someone. They can be used for mild to moderate hearing loss. MIC and CIC aids are even smaller and often not visible unless you look directly into the wearer's ear. They can be used for mild and sometimes moderate losses.
Open-fit devices
Recently a new device has come on the market, the "Open-fit" Hearing Aid. These are small Behind-the-ear type devices, with a clear tube that runs down to the ear canal. In the ear canal, there is a small soft silicone dome that holds the tube in place. These devices are designed to reduce the "occlusion effect", which is the amplification of your own voice when your ears are plugged up (try sticking your fingers in your ears and talking). Open-fit devices are very useful for High-Frequency hearing losses, and have been introduced by all major hearing aid companies.
Telecoil
Telecoils (T-coils) allow different sound sources to be directly connected to the hearing aid, improving sound quality and allowing the hearing aid wearer to easily perceive the signal of interest in almost any environment, and regardless of background noise. They can be used with telephones, FM systems, induction loop systems and public address systems.
T-coils are comprised of a metal core (or rod) around which ultra-fine wire is coiled. T-coils are also called induction coils because when the coil is placed in an electromagnetic (EM) field, an alternating electrical current is induced in the wire (Ross, 2002b; Ross, 2004). The T-coil detects EM energy and transduces (or converts) it to electrical energy. T-coils can also be used to pick up magnetic signals, just as a microphone picks up an acoustic signal; the T-coil then sends the signal to the hearing aid circuit or processor for amplification.
DAI-direct audio input allows the hearing aid to be connected to an external audio source like a CD player or an assistive listening device (ALD).
Processing
The inside mechanisms of hearing aids vary among devices, even if they are the same style. Three types of circuitry, or electronics, are used:
- Analog/Adjustable: The audiologist determines the volume and other specifications you need in your hearing aid, and then a laboratory builds the aid to meet those specifications. The audiologist retains some flexibility to make adjustments. This type of circuitry is generally the least expensive.
- Analog/Programmable: The audiologist uses a computer to program your hearing aid. The circuitry of analog/programmable hearing aids will accommodate more than one program or setting. If the aid is equipped with a remote control device, the wearer can change the program to accommodate a given listening environment. Analog/programmable circuitry can be used in all types of hearing aids.
- Digital/Programmable: The audiologist programs the hearing aid with a computer and can adjust the sound quality and response time on an individual basis. Digital hearing aids use a microphone, receiver, battery, and computer chip. Digital circuitry provides the most flexibility for the audiologist to make adjustments for the hearing aid. Digital circuitry can be used in all types of hearing aids and is typically the most expensive. However, digital hearing aids can be specially programmed with multiple programs for quiet situations, background noise reduction, music listening and directionality.
Buyer beware
Hearing aids are often advertised on the internet for much lower prices than you can get at an audiologist or hearing aid dispenser. These hearing aids are often substandard in quality, are never custom-fit to your ear, and are rarely adjustible. They may be too powerful for your ears or too weak. The best way to purchase a hearing aid is from a licensed professional who has tested your hearing. Visiting an audiologist or an Ear-Nose-Throat physician (outside of the US, Canada and the UK) is always your best bet.
See also
External links
- American Academy of Audiology (http://www.audiology.org) Find an Audiolgist, and get more information on hearing loss.
- Choosing a Hearing Aid (http://www.fact-sheets.com/health/choosing_hearing_aid/).
- Using hearing aids with bluetooth (hearing aid - cellphone connection (technical matters)) (http://www.gfern.com/btha/btha.html).
- Bluetooth adapter for behind the ear hearing instruments. (http://www.elihearing.com/)
"Hearing Aid" is the title of a track from They Might Be Giants' 1990 album, Flood.es:Audífono de:Hörgerät ja:補聴器 nl:Hoortoestel