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‐canal (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.