A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss.
Modern devices are computerized electroacoustic systems that transform environmental sound to make it audible.
Modern devices also utilize sophisticated digital signal processing to improve speech intelligibility and comfort for the user.
Processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction.
Modern hearing aids are configured to match the hearing loss, physical features, and lifestyle of the wearer.
The hearing aid is fitted to the audiogram and is programmed by frequency.
The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting.
Almost all hearing aids in use in the US are digital hearing aids.
Devices similar to hearing aids include the osseointegrated auditory prosthesis and cochlear implant.
Hearing aids are used for sensorineural hearing loss, conductive hearing loss, and single-sided deafness.
Hearing aid benefits depend on the type, severity, and etiology of the hearing loss, the technology and fitting of the device, and on the motivation, personality, lifestyle, and overall health of the user.
Hearing aids are incapable of truly correcting a hearing loss.
HAs aid to make sounds more audible.
The most common form of hearing loss for which hearing aids are sought is sensorineural, resulting from damage to the hair cells and synapses of the cochlea and auditory nerve.
Sensorineural hearing loss reduces the sensitivity to sound. and a hearing aid can partially accommodate by making sound louder.
Other sensorineural hearing loss deficits in spectral and temporal processing that affect speech perception are more difficult to compensate for using digital signal processing and in some cases may be exacerbated by the use of amplification.
Conductive hearing losses do not involve damage to the cochlea.
In conductive hearing losses a hearing aid is able to sufficiently amplify sound to account for the attenuation caused by the conductive component.
With conductive hearing loss sound that is able to reach the cochlea at normal or near-normal levels, can transmit signals to the brain normally.
Difficulties with hearing aids: fitting, occlusion effect, loudness recruitment, understanding speech in noise, and feedback.
Fedback is generally now well-controlled through the use of feedback management.
Types of hearing aids vary in size, power and circuitry.
Among the different sizes and models are:
Vacuum tube hearing aid, transistor body-worn hearing aid, hearing aids with earmolds, receiver-in-the-canal hearing aids, In-the-ear hearing aid, In-the-canal hearing aid, completely in the canal hearing aids, bone anchored hearing aid
Body worn aids consist of a case and an earmold, attached by a wire.
The case contains the electronic amplifier components, controls and battery, while the earmold typically contains a miniature loudspeaker.
Body worn aid designs can provide large amplification and long battery life at a lower cost.
There are two major classes of hearing aids – behind the ear (BTE) and in the ear (ITE).
With BTE hearing aids the case hangs behind the pinna.
The case is attached to an earmold or dome tip by a traditional tube, slim tube, or wire which courses from the superior-ventral portion of the pinna to the concha, where the ear mold or dome tip inserts into the external auditory canal.
The case contains the electronics, controls, battery, and microphone(s).
The loudspeaker, or receiver, may be housed in the case or in the earmold or dome tip.
The receiver in canal style of BTE hearing aid is often smaller than a traditional BTE and more commonly used in more active populations.
BTEs are generally capable of providing more output: indicated for more severe degrees of hearing loss.
BTE HAs can be used for nearly any kind of hearing loss.
BTEs come in a variety of sizes, typically depending on the output level needed, the location of the receiver, and the presence or absence of a telecoil.
BTEs are durable, and readily repairable.
BTEs have controls and battery doors that are easy to operate. easily connected to assistive listening devices, such as FM systems.
BTEs are commonly worn by children because of durability.
In the ear aids (ITE) devices fit in the outer ear bowl.
ITEs are larger, easier to insert and can hold extra features.
ITEs are sometimes visible when standing face to face with someone.
ITE hearing aids are custom made to fit each individual’s ear.
ITE hearing aids can be used in mild to some severe hearing losses.
Feedback, may be a problem for severe hearing losses.
ITEs are 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 has to be replaced frequently as the child grows.
New ITEs made from a silicone type material that mitigates the need for costly replacements.
ITE hearing aids can be connected wirelessly to FM systems.
Mini in canal (MIC) or completely in canal (CIC) aids are generally not visible unless the viewer looks directly into the wearer’s ear.
These aids are intended for mild to moderately severe losses.
Completely in the ear canal hearing aids fit tightly deep in the ear, are small, are barely visible, does not have a directional microphone, and its small batteries will have a short life,.
Completely in the ear canal hearing aids position in the ear prevents wind noise and makes it easier to use phones without feedback.
Larger versions of in the ear canal hearing aids can have directional microphones.
In-the-ear hearing aids are typically more expensive than behind-the-ear counterparts: due to mold fitting.
With the IIC aid the majority of the ear is not blocked by a large plastic shell, so sound can be collected more naturally by the shape of the ear, and can travel down into the ear canal as it would with unassisted hearing.
Depending on their size, some models allow the wearer to use a mobile phone as a remote control to alter memory and volume settings.
IIC types are most suitable for users up to middle age, but are not suitable for more elderly people.
Extended wear hearing aids are hearing devices that are non-surgically placed in the ear canal.
These devices are worn for 1–3 months at a time without removal.
They are made of soft material designed to contour to each user and can be used by people with mild to moderately severe hearing loss.
Their close proximity to the ear drum allows an improved sound directionality and localization, reduced feedback, and improved high frequency gain.
Behind the ear or in the canal hearing aids require daily insertion and removal.
Extended wear hearing aids are worn continuously and then replaced with a new device.
Extended wear hearing aids protect against moisture and earwax and can be worn while exercising, and showering, and are popular with those who are self-conscious about the aesthetics of BTE or ITC hearing aid models.
Extended wear hearing aids disadvantages include regular removal and reinsertion of the device when the battery dies, inability to go underwater, earplugs when showering, and for some discomfort with the fit since it is inserted deeply in the ear canal, and it is the only part of the body where skin rests directly on top of bone.
CROS hearing aids transmit auditory information from one side of the head to the other side of the head.
Candidates for CROS hearing aids include: poor word understanding on one side, no hearing on one side, or who are not benefiting from a hearing aid on one side.
CROS hearing aids appear similar to behind the ear hearing aids.
The CROS system assists the patient in sound localization and understanding auditory information on their poor side.
A bone anchored hearing aid (BAHA) is a surgically implanted auditory prosthetic based on bone conduction.
The BAHA uses the skull as a pathway for sound to travel to the inner ear.
With conductive hearing loss, the BAHA bypasses the external auditory canal and middle ear, stimulating the functioning cochlea.
BAHA uses the skull to conduct the sound from the deaf side to the side with the functioning cochlea.
Individuals under the age of two-five in typically wear the BAHA device on a Softband.
The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing.
BAHA does not restrict the wearer from any activities such as outdoor life, sporting activities etc.
A BAHA can be connected to an FM system by attaching a miniaturized FM receiver to it.
Spectacle hearing aids are worn by people with a hearing loss who either prefer a more cosmetic appeal of their hearing aids by being attached to their glasses or where sound cannot be passed in the normal way, via a hearing aids, perhaps due to a blockage in the ear canal, or if the client experiences continual infections in the ear.
Spectacle aids come in two forms, bone conduction spectacles and air conduction spectacles.
Bone conduction spectacles transmit sounds via a receiver attached from the arm of the spectacles which are fitted firmly behind the mastoid process, by means of pressure, applied on the arm of the spectacles.
Sound is passed from the receiver on the arm of the spectacles to the cochlea via the bony portion.
Bone conduction aids generally have a poorer high pitch response and are best used for conductive hearing losses or where it is impractical to fit standard hearing aids.
Sound is transmitted via hearing aids which are attached to the arm or arms of the spectacles.
Glasses may incorporate a directional microphone capability, which are able to discern between sound coming from the front and sound coming from the sides or back of the user.
This can allow for amplification of the sound coming from the front, the direction in which the user is looking, and active noise control for sounds coming from the sides or behind.
Recent hearing aids include wireless hearing aids.
FM listening systems are now emerging with wireless receivers integrated with the use of hearing aids.
Bluetooth connectivity is innovation in wireless interfacing for hearing instruments to audio sources such as TV streamers or Bluetooth enabled mobile phones.
Most older hearing aids have only an omnidirectional microphone.
Directional microphones have been found to be the second best method to improve the signal-to-noise ratio.and the best method was an FM system, which locates the microphone near the mouth of the desired talker.
Adaptive directional microphones automatically vary the direction of maximum amplification or rejection to reduce an interfering directional sound source;
The processor attempts to provide maximum amplification in the direction of the desired speech signal source or rejection in the direction of the interfering signal source.
Adaptive directional microphones can provide improved speech recognition in noise.
Every electronic hearing aid has at minimum a microphone, a loudspeaker (receiver), a battery, and electronic circuitry.
Analogue hearing aids make all the sounds picked up by the
microphone louder.
Digital hearing aid (DHA) technology processes the sound using digital technology.
Digital hearing aid transmitting microprocessor processes the digital signal received by the microphone according to an algorithm that allows certain-frequency sounds to be made louder according to the individual user’s settings and adjusts to various environments.
This gives users with limited hearing abilities the opportunity to perceive the whole range of ambient sounds, despite the personal difficulties of perception of certain frequencies.
Moreover, even in this “narrow” range the DHA microprocessor is able to emphasize desired sounds (e.g. speech), lowering unwanted loud, high, etc., sounds at the same time.
According to research DHAs have a number of significant advantages compared to analogue hearing aids:
Adaptive adjustment.
Effective acoustic feedback reduction.
Effective use of directional microphones.
Directional microphones can be adaptively controlled.
Extended frequency range.
A larger range of frequencies can be implemented with frequency shifting.
Flexibility in selective amplification.
Improved connection to other devicessuch as smartphones and televisions is possible.
Noise reduction.
Speech recognition enhancement.
Smartphones have all the necessary hardware to perform the functions of a digital hearing aid: microphone, AD converter, digital processor, DA converter, amplifier, and speakers.
The operational principles of hearing aid applications correspond to general operational principles of digital hearing aids: the microphone perceives an acoustic signal and converts it to digital form.
The whole adjustment process is automated so that the user can perform audiometry on their own.
Personal sound amplification products (PSAP) are designed for people without hearing loss.
Unlike hearing aids devices to compensate for hearing impairment, the use of PSAP does not require a medical prescription.
Some devices simply amplify sound, while others contain directional microphones, equalizers to adjust the audio signal gain and filter noise.
Hearing aids do not provide immediate improvement, as an adjustment period can last from several hours to several months.
In 2022, the FDA issued a final rule to improve access to hearingestablishes a new category of over-the-counter (OTC) hearing aids, enabling consumers with perceived mild to moderate hearing impairment to purchase hearing aids directly from stores or online retailers without the need for a medical exam, prescription or a fitting adjustment by an audiologist.