Telecoil

A hearing aid or deaf aid is a device designed to improve hearing. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers such as PSAPs or other plain sound reinforcing systems cannot be sold as "hearing aids".

Earlier devices, such as ear trumpets or ear horns, were passive amplification cones designed to gather sound energy and direct it into the ear canal. Modern devices are computerised electroacoustic systems that transform environmental sound to make it more intelligible or comfortable, according to audiometrical and cognitive rules. Such sound processing can be considerable, such as highlighting a spatial region, shifting frequencies, cancelling noise and wind, or highlighting voice.

Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. This process is called "fitting" and is performed by audiologists. The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting. Devices similar to hearing aids include the bone anchored hearing aid, and cochlear implant.

Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible. Two primary issues minimize the effectiveness of hearing aids:

Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible. Three primary issues minimize the effectiveness of hearing aids:

There are several ways of evaluating how well a hearing aid compensates for hearing loss. One approach is audiometry which measures a subject's hearing levels in laboratory conditions. The threshold of audibility for various sounds and intensities is measured in a variety of conditions. Although audiometric tests may attempt to mimic real-world conditions, the patient's own every day experiences may differ. An alternative approach is self-report assessment, where the patient reports their experience with the hearing aid.

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