hearing aid hearing aid a hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. small audio amplifiers such as personal sound amplification products (psaps) or other plain sound reinforcing systems cannot be sold as "hearing aids". hearing aidin-the-canal hearing aidother namesdeaf aid early 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 audible, according to audiometrical and cognitive rules. modern devices also utilize sophisticated digital signal processing to try and improve speech intelligibility and comfort for the user. such signal processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction. modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. the hearing aid is fitted to the most recent audiogram and is programmed by frequency. this process is called "fitting" can be performed by the user in simple cases, or is performed by a doctor of audiology, also called an audiologist (aud), or by a hearing instrument specialist (his) or audioprosthologist. 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, as analog aids are phased out. devices similar to hearing aids include the osseointegrated auditory prosthesis (formerly called the bone-anchored hearing aid) and cochlear implant. uses hearing aids are used for a variety of pathologies including sensorineural hearing loss, conductive hearing loss, and single-sided deafness. hearing aid candidacy was traditionally determined by a doctor of audiology, or a certified hearing specialist, who will also fit the device based on the nature and degree of the hearing loss being treated. the amount of benefit experienced by the user of the hearing aid is multi-factorial, depending 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. over-the-counter hearing aids, which address mild- to moderate- hearing loss, are designed to be adjusted by the user. hearing aids are incapable of truly correcting a hearing loss; they are an 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, which a hearing aid can partially accommodate by making sound louder. other decrements in auditory perception caused by sensorineural hearing loss, such as abnormal spectral and temporal processing, and which may negatively 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, which do not involve damage to the cochlea, tend to be better treated by hearing aids; the hearing aid is able to sufficiently amplify sound to account for the attenuation caused by the conductive component. once the sound is able to reach the cochlea at normal or near-normal levels, the cochlea and auditory nerve are able to transmit signals to the brain normally. common issues with hearing aid fitting and use are the occlusion effect, loudness recruitment, and understanding speech in noise. once a common problem, feedback is generally now well-controlled through the use of feedback management algorithms. candidacy and acquisition 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. hearing aid outcome can be represented by three dimensions: hearing aid usage aided speech recognition benefit/satisfaction the most reliable method for assessing the correct adjustment of a hearing aid is through real ear measurement. real ear measurements (or probe microphone measurements) are an assessment of the characteristics of hearing aid amplification near the ear drum using a silicone probe tube microphone. current research is also pointing towards hearing aids and proper amplification as a treatment for tinnitus, a medical condition which manifests itself as a ringing or buzzing in the ears. types there are many types of hearing aids (also known as hearing instruments), which vary in size, power and circuitry. among the different sizes and models are: vacuum tube hearing aid, circa 1944 transistor body-worn hearing aid. pair of bte hearing aids with earmolds. receiver-in-the-canal hearing aids in-the-ear hearing aid in-the-canal hearing aid woman wearing a bone anchored hearing aid hearing aid application body-worn body worn aids were the first portable electronic hearing aids, and were invented by harvey fletcher while working at bell laboratories. body 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. the case is typically about the size of a pack of playing cards and is carried in a pocket or on a belt. without the size constraints of smaller hearing devices, body worn aid designs can provide large amplification and long battery life at a lower cost. body aids are still used in emerging markets because of their relatively low cost. behind the ear a modern behind the ear hearing aid. the audio tube to the speaker is barely visible. a modern behind the ear hearing aid with a minicell battery behind the ear hearing aids are one of two major classes of hearing aids – behind the ear (bte) and in the ear (ite). these two classes are distinguished by where the hearing aid is worn. bte hearing aids consist of a case which hangs behind the pinna. the case is attached to an earmold or dome tip by a traditional tube, slim tube, or wire. the tube or wire 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 (traditional bte) or in the earmold or dome tip (receiver-in-the-canal, or ric). the ric 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 and may therefore be indicated for more severe degrees of hearing loss. however, btes are very versatile and can be used for nearly any kind of hearing loss. btes come in a variety of sizes, ranging from a small, "mini bte", to larger, ultra-power devices. size typically depends on the output level needed, the location of the receiver, and the presence or absence of a telecoil. btes are durable, easy to repair, and often have controls and battery doors that are easier to manipulate. btes are also easily connected to assistive listening devices, such as fm systems and induction loops. btes are commonly worn by children who need a durable type of hearing aid. in the ear in the ear aids (ite) devices fit in the outer ear bowl (called the concha). being larger, these are easier to insert and can hold extra features. they are sometimes visible when standing face to face with someone. ite hearing aids are custom made to fit each individual's ear. they can be used in mild to some severe hearing losses. feedback, a squealing/whistling caused by sound (particularly high frequency sound) leaking and being amplified again, may be a problem for severe hearing losses. some modern circuits are able to provide feedback regulation or cancellation to assist with this. venting may also cause feedback. a vent is a tube primarily placed to offer pressure equalization. however, different vent styles and sizes can be used to influence and prevent feedback. traditionally, ites have 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 had to be replaced frequently as the child grew. however, there are 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, for instance with a body-worn fm receiver with induction neck-loop which transmits the audio signal from the fm transmitter inductively to the telecoil inside the hearing instrument. 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. cics are usually not recommended for people with good low-frequency hearing, as the occlusion effect is much more noticeable. completely-in-the-canal hearing aids fit tightly deep in the ear. it is barely visible. being small, it will not have a directional microphone, and its small batteries will have a short life, and the batteries and controls may be difficult to manage. its position in the ear prevents wind noise and makes it easier to use phones without feedback. in-the-canal hearing aids are placed deep in the ear canal. they are barely visible. larger versions of these can have directional microphones. being in the canal, they are less likely to cause a plugged feeling. these models are easier to manipulate than the smaller completely in-the-canal models but still have the drawbacks of being rather small. in-the-ear hearing aids are typically more expensive than behind-the-ear counterparts of equal functionality, because they are custom fitted to the patient's ear. in fitting, the audiologist takes a physical impression (mold) of the ear. the mold is scanned by a specialized cad system, resulting in a 3d model of the outer ear. during modeling, the venting tube is inserted. the digitally modeled shell is printed using a rapid prototyping technique such as stereolithography. finally, the aid is assembled and shipped to the audiologist after a quality check. invisible-in-canal hearing aids invisible-in-canal hearing aids (iic) style of hearing aids fits inside the ear canal completely, leaving little to no trace of an installed hearing aid visible. this is because it fits deeper in the canal than other types, so that it is out of view even when looking directly into the ear bowl (concha). a comfortable fit is achieved because the shell of the aid is custom-made to the individual ear canal after taking a mold. invisible hearing aid types use venting and their deep placement in the ear canal to give a more natural experience of hearing. unlike other hearing aid types, with the iic aid the majority of the ear is not blocked (occluded) by a large plastic shell. this means that 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, instead of taking the iic out to do this. iic types are most suitable for users up to middle age, but are not suitable for more elderly people. extended wear hearing aids extended wear hearing aids are hearing devices that are non-surgically placed in the ear canal by a hearing professional. the extended wear hearing aid represents the first "invisible" hearing device. 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 results in improved sound directionality and localization, reduced feedback, and improved high frequency gain. while traditional bte or itc hearing aids require daily insertion and removal, extended wear hearing aids are worn continuously and then replaced with a new device. users