can change volume and settings without the aid of a hearing professional. the devices are very useful for active individuals because their design protects against moisture and earwax and can be worn while exercising, showering, etc. because the device's placement within the ear canal makes them invisible to observers, extended wear hearing aids are popular with those who are self-conscious about the aesthetics of bte or itc hearing aid models. as with other hearing devices, compatibility is based on an individual's hearing loss, ear size and shape, medical conditions, and lifestyle. the 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, the only part of the body where skin rests directly on top of bone. cros hearing aid a cros hearing aid is a hearing aid that transmits auditory information from one side of the head to the other side of the head. candidates include people who have 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 can appear very similar to behind the ear hearing aids. the cros system can assist the patient in sound localization and understanding auditory information on their poor side. while cros hearing aids can be quite effective, the long-term solution for those with hearing issues on one side is to use a bicros system. this creates more of a balance for wearers. bone-anchored main article: bone anchored hearing aid a bone anchored hearing aid (baha) is a surgically implanted auditory prosthetic based on bone conduction. it is an option for patients without external ear canals, when conventional hearing aids with a mold in the ear cannot be used. the baha uses the skull as a pathway for sound to travel to the inner ear. for people with conductive hearing loss, the baha bypasses the external auditory canal and middle ear, stimulating the functioning cochlea. for people with unilateral hearing loss, the 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 the usa) typically wear the baha device on a softband. this can be worn from the age of one month as babies tend to tolerate this arrangement very well. when the child's skull bone is sufficiently thick, a titanium "post" can be surgically embedded into the skull with a small abutment exposed outside the skin. the baha sound processor sits on this abutment and transmits sound vibrations to the external abutment of the titanium implant. the implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing. the surgical procedure is simple both for the surgeon, involving very few risks for the experienced ear surgeon. for the patient, minimal discomfort and pain is reported. patients may experience numbness of the area around the implant as small superficial nerves in the skin are sectioned during the procedure. this often disappears after some time. there is no risk of further hearing loss due to the surgery. one important feature of the baha is that, if a patient for whatever reason does not want to continue with the arrangement, it takes the surgeon less than a minute to remove it. the 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. two main brands manufacture bahas today – the original inventors cochlear, and the hearing aid company oticon. eyeglass aids during the late 1950s through 1970s, before in-the-ear aids became common (and in an era when thick-rimmed eyeglasses were popular), people who wore both glasses and hearing aids frequently chose a type of hearing aid that was built into the temple pieces of the spectacles. however, the combination of glasses and hearing aids was inflexible: the range of frame styles was limited, and the user had to wear both hearing aids and glasses at once or wear neither. today, people who use both glasses and hearing aids can use in-the-ear types, or rest a bte neatly alongside the arm of the glasses. there are still some specialized situations where hearing aids built into the frame of eyeglasses can be useful, such as when a person has hearing loss mainly in one ear: sound from a microphone on the "bad" side can be sent through the frame to the side with better hearing. this can also be achieved by using cros or bi-cros style hearing aids, which are now wireless in sending sound to the better side. spectacle hearing aids these are generally 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. pathway 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 sounds are transmitted via a receiver attached from the arm of the spectacles which are fitted firmly behind the boney portion of the skull at the back of the ear, (mastoid process) by means of pressure, applied on the arm of the spectacles. the sound is passed from the receiver on the arm of the spectacles to the inner ear (cochlea), via the bony portion. the process of transmitting the sound through the bone requires a great amount of power. bone conduction aids generally have a poorer high pitch response and are therefore best used for conductive hearing losses or where it is impractical to fit standard hearing aids. air conduction spectacles unlike the bone conduction spectacles the sound is transmitted via hearing aids which are attached to the arm or arms of the spectacles. when removing your glasses for cleaning, the hearing aids are detached at the same time. whilst there are genuine instances where spectacle aids are a preferred choice, they may not always be the most practical option. directional spectacles these 'hearing glasses' incorporate a directional microphone capability: four microphones on each side of the frame effectively work as two directional microphones, which are able to discern between sound coming from the front and sound coming from the sides or back of the user. this improves the signal-to-noise ratio by allowing 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. only very recently has the technology required become small enough to be fitted in the frame of the glasses. as a recent addition to the market, this new hearing aid is currently available only in the netherlands and belgium. stethoscope these hearing aids are designed for medical practitioners with hearing loss who use stethoscopes. the hearing aid is built into the speaker of the stethoscope, which amplifies the sound. hearing aid applications hearing aid applications (haa) are software which, when installed on mobile computational platforms, transforms them into hearing aids. the principle of haa operation corresponds to the basic principles of operation of traditional hearing aids: the microphone receives an acoustic signal and converts it into a digital form. sound amplification is achieved by the means of a mobile computational platform, in accordance with the degree and type of the user's hearing loss. the processed audio signal is transformed into an audio signal and output to the user into the headphones/headset. signal processing is implemented in real time. constructional features of mobile computational platforms imply preferred use of stereo headsets with two speakers, which allows carrying out binaural hearing correction for the left and right ear separately. haas can work with both wired and wireless headsets and headphones. as a rule, haas have two operation modes: setup mode and hearing aid mode. setup mode involves the user passing an in situ-audiometry procedure, which determines the user's hearing characteristics. hearing aid mode is a hearing correction system that corrects the user's hearing in accordance with the user's hearing thresholds. haas also incorporate background noise suppression and acoustic feedback suppression. the user can independently choose a formula to enhance the sound, as well as adjust the level of the desired amplification to their wishes. haas have several advantages (compared to traditional hearing aids): haas do not cause any psychological inconvenience; it is possible to achieve the highest sound pressure level and get high sound quality (due to large speakers and a long battery life); it is possible to use more complex audio signal processing algorithms and a higher sampling rate (because of capacious battery); the possibility to implement more convenient application control functions for people with poor motor skills; resistance to ingress of earwax and moisture; software flexibility; the large distance between the microphone and the speaker prevents the occurrence of acoustic feedback; the set up of haas in simple cases does not require special equipment and qualifications; the user does not need to purchase and carry any separate device; various types of headphones and headsets can be used. haas also have some disadvantages (compared to traditional hearing aids): because the microphone is not located in the ear, it does not use the functional advantages of the auricle and the natural acoustics of the outer ear. they are more noticeable and less comfortable to wear. technology the first electrical hearing aid used the carbon microphone of the telephone and was introduced in 1896. the vacuum tube made electronic amplification possible, but early versions of amplified hearing aids were too heavy to carry around. miniaturization of vacuum tubes lead to portable models, and after world war ii, wearable models using miniature tubes. the transistor invented in 1948 was well suited to the hearing aid application due to low power and small size; hearing aids were an early adopter of transistors. the development of integrated circuits allowed further improvement of the capabilities of wearable aids, including implementation of digital signal processing techniques and programmability for the individual user's needs. compatibility with telephones a sign in a train station explains that the public announcement system uses a "hearing induction loop" (audio induction loop). hearing aid users can use a telecoil (t) switch to hear announcements directly through their hearing aid receiver. a hearing aid and a telephone are "compatible" when they can connect to each other in a way that produces clear, easily understood sound. the term "compatibility" is applied to all three types of telephones (wired, cordless, and mobile). there are two ways telephones and hearing aids can connect with each other: acoustically: the sound from the phone's speaker is picked up by the hearing aid's microphone. electromagnetically: the signal inside the phone's speaker is picked up by the hearing aid's "telecoil" or "t-coil", a special loop of wire inside the hearing aid. note that telecoil coupling has nothing to do with the radio signal in a cellular or cordless phone: the audio signal picked up by the telecoil is the weak electromagnetic field that is generated by the voice coil in the phone's speaker as it pushes the speaker cone back and forth. the electromagnetic (telecoil) mode is usually more effective than the acoustic method. this is mainly because the microphone is often automatically switched off when the hearing aid is operating in telecoil mode, so background noise is not amplified. since there is an electronic connection to the phone, the sound is clearer and distortion is less likely. but in order for this to work, the phone has to be hearing-aid compatible. more technically, the phone's speaker has to have a voice coil that generates a relatively strong electromagnetic field. speakers with strong voice coils are more expensive and require more energy than the tiny ones used in many modern telephones; phones with the small low-power speakers cannot couple electromagnetically with the telecoil in the hearing aid, so the hearing aid must then switch to acoustic mode. also, many mobile phones emit high levels of electromagnetic