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Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

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Page 1: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figures for Chapter 3

Hearing aid systems

Dillon (2001)

Hearing Aids

Page 2: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.1 (a) A faceplate with components mounted, next to a shell far an ITC hearing aid. After gluing the two parts together, all material outside the cutting mark is removed. (b) A close-up of the components mounted on the faceplate.

Source: Dillon (2001): Hearing Aids

Custom ITE construction

Photo removed to minimize file space

Page 3: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.2 Block diagram of an analog hearing aid (top) and a digitally programmable hearing aid (bottom).

Analog hearing aid

microphone receiverSignal path

Programmable hearing aid

Signal path

Digital controller and

memory

programmer unit

programmer unit

programmer interface

programmer interface

Source: Dillon (2001): Hearing Aids

Analog and digitally-programmable

block diagrams

Page 4: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

VoltageVoltage

Magnetic field

Soundwave

Soundwave

Current

Figure 3.3 The complete chain, from sound wave in to sound wave out, for a magnetic loop induction system.

Source: Dillon (2001): Hearing Aids

Induction loop signal path

Page 5: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.4 Lines of magnetic flux flowing around a conductor carrying a current.

Current

Magnetic Flux

Source: Dillon (2001): Hearing Aids

Current and magnetism

Page 6: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.5 A complete induction loop system, showing how lines of magnetism from all parts of the loop add constructively within the region enclosed by the loop.

Source: Dillon (2001): Hearing Aids

Addition of magnetic flux inside loop

Page 7: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Resistor

Figure 3.6 The connections needed to make a loop of two turns using a single run of cable that has two separate wires. The location of an optional series resistor is also shown.

Source: Dillon (2001): Hearing Aids

A two-turn magnetic loop

Page 8: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Unm

odul

ated

carr

ier

am

plitu

de

Aud

ioam

plitu

deTime

(a)

(b)

Mod

ulat

edca

rrie

ram

plitu

de (c)

Figure 3.7 The waveform of a carrier before (b), and after (c), it has been frequency modulated by a sinusoidal audio signal (a).

Source: Dillon (2001): Hearing Aids

Frequency modulation

Page 9: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.8 An FM system with Speech Operated Switching (SOX) in the receiver to select either the local microphone signal or the FM signal (from the aerial) for amplification by the hearing aid.

Control signal

Rx

Source: Dillon (2001): Hearing Aids

Speech-operated switching

Page 10: Figures for Chapter 3 Hearing aid systems Dillon (2001) Hearing Aids

Figure 3.9 Block diagram of a sound-field amplification system comprising a transmitter worn by the teacher, a receiver and amplifier mounted somewhere convenient in the room, and four loudspeakers distributed around the room.

Tx

Rx

Source: Dillon (2001): Hearing Aids

Sound field amplification system