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Hearing aid

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A hearing aid is a sophisticated medical device designed to improve hearing. It functions by making environmental sounds audible to individuals experiencing hearing loss. In most countries, these instruments are classified as regulated medical devices. They are distinct from personal sound amplification products (PSAPs). Those are simple amplifiers that do not meet the strict standards of a hearing aid. While they cannot correct a hearing loss, they serve as vital tools for making sound perceptible.

Block diagram of digital hearing aid
Block diagram of digital hearing aid

Modern hearing aids are computerized electroacoustic systems. They transform environmental sounds according to specific audiometrical and cognitive rules. This process involves digital signal processing to improve speech intelligibility. This term refers to how clearly a person can understand spoken words. The system performs several complex tasks simultaneously. It includes feedback management to stop whistling sounds. It uses wide dynamic range compression to balance volume. It also employs noise reduction and directionality to help users focus on specific sounds.

فوناك
فوناك

There are several distinct categories of hearing instruments. Behind-the-ear (BTE) aids are a major class. The electronic case hangs behind the pinna, which is the visible part of the ear. This case connects to an earmold or a dome tip via a tube or wire. A common variation is the receiver-in-the-canal (RIC) style. In RIC models, the loudspeaker or receiver is placed inside the ear canal. These are often smaller and popular with active users. BTE devices are very versatile and can manage severe hearing loss. They are also durable, making them common for children.

Hörapparat - 1 - 2020
Hörapparat - 1 - 2020
Hörapparat - 2 - 2020
Hörapparat - 2 - 2020

Another class includes in-the-ear (ITE) hearing aids. These devices fit directly into the concha, the outer bowl of the ear. Because they are larger, they can often hold more features. Some ITE models are custom-made for the individual. This process involves taking a physical impression of the ear. A specialized CAD system then creates a 3D model of the outer ear. The final shell is often produced using rapid prototyping like stereolithography. Within this group, there are even smaller versions. Mini in canal (MIC) or completely in canal (CIC) aids are designed to be nearly invisible.

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Bonavoxshop

History shows how these devices have evolved significantly. Early amplification was passive rather than electronic. People used ear trumpets or ear horns to gather sound energy. These were simple cones that directed sound into the ear canal. The first portable electronic hearing aids were body-worn devices. Harvey Fletcher invented these while working at Bell Laboratories. These early aids consisted of a large case and an earmold. The case was about the size of a pack of playing cards. It was carried in a pocket or on a belt.

Hearing aid glasses
Hearing aid glasses

Fitting a device is a precise scientific process. It must match the wearer's specific audiogram and lifestyle. An audiogram is a test that measures hearing levels. This is often performed by a Doctor of Audiology (AuD) or a Hearing Instrument Specialist (HIS). The most reliable way to adjust a device is through real ear measurement. This uses a silicone probe tube microphone near the eardrum. This ensures the amplification is correct for the individual's anatomy. The quality of this fitting determines how much benefit the user receives.

Direct Audio Input connector
Direct Audio Input connector

Hearing aids address various types of hearing pathologies. Sensorineural hearing loss is the most common type. This occurs due to damage to the hair cells and synapses in the cochlea. It also affects the auditory nerve. This type of loss reduces sound sensitivity. Conductive hearing loss is another type that does not involve the cochlea. Hearing aids often treat conductive loss very effectively. They amplify sound enough to overcome the attenuation, or weakening, of the signal. Once the sound reaches the cochlea, the nerve can transmit signals to the brain.

Madame de Meuron
Madame de Meuron
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Hearing induction loop hearing aid.jpg
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فوناك.jpg
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Direct Audio Input connector.jpg
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Block diagram of digital hearing aid.svg
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