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Therapeutic equipment I Lecture (1) What’s A Hearing Aid? • Hearing aids are miniature electronic devices that sit in or on the ear, and selectively amplify and process sounds. • All hearing aids contain one or more microphones to pick up sound, an amplifier that amplifies and processes sound, a receiver or speaker that sends the signal from the amplifier into your ear, and a battery, or power source. • All of these components are packaged into various styles to fit people’s cosmetic needs and power requirements. Human ear Hearing Loss • There are three kinds of hearing loss: –Sensor neural –Conductive –Mixed hearing loss Sensor neural Hearing Loss • Also known as nerve deafness, the inner ear or actual hearing nerve itself is damaged. • About 90% of all people with hearing impairments suffer from sensor neural hearing loss. • Most common. Conductive Hearing Loss • Outer and/or middle part of the ear fail to work properly. • Sounds become "blocked" and are not carried all the way to the inner ear (where hearing is still normal) • Not permanent; temporary hearing loss Mixed Hearing Loss • A combination of a conductive and sensor neural hearing loss. • Both the middle and inner ear are involved. Causes of Conductive Hearing Loss • a buildup of fluid in the middle ear. • wax in the ear canal • puncturing of the eardrum • problems or injury to the bones or membrane which carry sound from the external ear through the middle ear to the inner ear. Sensor neural Hearing Loss • Usually permanent. • not medically or surgically treatable. • In most cases, the cillia or the nerves from the inner ear to the brain are damaged. • wearing hearing aids may be of significant benefit. Causes of Sensor neural Hearing Loss • The natural aging process. • Exposure to loud noises. • Infection or other disease. • A genetic disorder Treatment • Sensor neural hearing loss is usually permanent, no medically or surgically treatable. • In most cases, the nerves from the inner ear to the brain are damaged. • However, most people with this hearing loss find wearing hearing aids to be of significant benefit. Identifying Hearing Loss • Ranges have been established to help people identify how much difficulty they should expect from their hearing loss. The typical ranges for an adult are: • -10dB to 25dB = Normal range • 26dB to 40 dB = Mild hearing loss • 41 dB to 55 dB = Moderate hearing loss • 56 dB to 70 dB = Moderately Severe hearing loss • 71 dB to 90 dB = Severe hearing loss • over 90 dB = Profound hearing loss Types of hearing aids (1) Behind‐the‐ear (BTE) aids: –A plastic case containing most parts; resting behind the ear connected to an ear mold – Easy to be cleaned and handled. (2) In‐the‐ear (ITE) aids: – All parts contained in a shell, which fills in the ear canal – Relatively easier to handle than smaller aids such as ITC & CIC (3) In‐the‐canal (ITC) aids & (4) completely‐in‐the‐cana l (CIC) aids: – All parts contained in tiny cases, which fits partly or completely in the ear canal – Smallest in size, which makes it difficult to handle and adjust for some users Hearing Aids: Basic Components Electronic components: • Microphone • Amplifier circuitry • Miniature loudspeaker/receiver • Battery Microphones • Microphones are transducers that convert acoustical energy into electrical energy. • The three main types of microphones (according to their principles of operation) are: • Dynamic (moving-coil) • Ribbon • Condenser Condenser microphones • A capacitor is an electrical device able to store electrical charge between two closely-spaced conductors (plates). • Capacitance (C) measures how much charge (Q) is stored for a given voltage (V), such that C = Q/V • Capacitance is inversely proportional to the distance (d) between plates • Condenser microphones generally have flatter frequency responses than dynamic, and therefore mean that a condenser microphone is more desirable in the hearing aid. • There are two types of condenser microphones; standard condenser and electret condenser. • A standard condenser microphone consists of a small diaphragm that vibrates in response to acoustic pressure. Standard condenser microphones have very high output impedance, so they are not suitable for transferring signals over even a very small distance. Electret condenser microphone • An electret condenser microphone combines a condenser microphone with a Field Effect Transistor (FET), which amplifies the signal and transforms the impedance to a more useful level. • This characteristic of electret condenser microphones makes them very sensitive to small sounds. • The electret condenser microphone operating voltage is 3v, operating frequency ranged from 20Hz to 20 KHz, and operating temperature from -20c to 70c Limitations • Some problems in background noise. • Can amplify loud sounds to the point where they can be uncomfortable. • Problems with manipulation. This is a big problem for ITC and CIC aids.