BASIC HEARING INSTRUMENT COMPONENTS

Electret condenser microphone/input transducer

Collects sound waves and becomes the impedance for sound transmission into the amplifier.

Requires an impedance converter (field effect transistor).

BASIC HEARING INSTRUMENT COMPONENTS

Electret Microphones/transducers

Are capable of a frequency response range of 100Hz to 15,000Hz

Frequencies beyond 10,000Hz can have interference from ultrasonic sources

Most hearing instrument microphones do not go beyond the 4,000Hz frequency response (certainly enough to capture most of the fundamental frequencies created in speech production.

BASIC HEARING INSTRUMENT COMPONENTS

The key elements to an amplifier are:

The transistor (transistors stabilize and control electrical current)

The Diode (only allow current to flow in one direction)

The Capacitor (filter the current)

BASIC HEARING INSTRUMENT COMPONENTS

The Integrated Chip (IC) is composed of all the elements of the amplifier and are mounted to circuit boards

BASIC HEARING INSTRUMENT COMPONENTS

“User controls”

Volume control (variable resistor)

Tone control (switched capacitor usually either high pass or low pass filtering)

Telecoil (turns off the microphone and activates an integrated induction coil)

BASIC HEARING INSTRUMENT COMPONENTS

The electromagnetic receiver

Has an armature which must be able to produce high sound pressure levels efficiently. Some are also “impedance matched” to the microphone impedance for an even greater fidelity of sound.

BASIC HEARING INSTRUMENT COMPONENTS

The armature of a receiver is:

a thin, magnetically permeable metal reed with a coil of fine wire around it.

BASIC HEARING INSTRUMENT COMPONENTS

There are three basic receiver responses

1. Class A

2. Class B

3. Class D

Note: Each have some unique frequency response and

output characteristics.

BASIC HEARING INSTRUMENT COMPONENTS

Button Cell Batteries

The power source for all hearing instruments—usually 1.4 volts.

The size determines the capacity. Capacity is rated by a milliamp hour number.

BASIC HEARING INSTRUMENT COMPONENTS

Button Cell Battery sizes are:

1. 675 (blue tape—largest cell

2. 41 (green tape—no longer available

3. 13 (orange tape—very commonly used)

4. 312(brown tape—also common)

5. 10 (yellow tape—for very small aids)

6. 5 (red tape—very small—rarely used)