Therapeutic equipment I Lecture (2)

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.

Thank you