Transcript Figures for chapter 3.

Figures for Chapter 3
Hearing aid systems
Dillon (2001)
Hearing Aids
Custom ITE construction
Photo removed to minimize
file space
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
Analog and
digitally-programmable
block diagrams
Analog hearing aid
microphone
receiver
Signal path
Programmable hearing aid
Signal
path
Digital
controller and
memory
Source: Dillon (2001):
Hearing Aids
programmer
interface
programmer
unit
Figure 3.2 Block diagram of an analog
hearing aid (top) and a digitally
programmable hearing aid (bottom).
Induction loop signal path
Current
Magnetic field
Sound
wave
Voltage
Voltage
Sound
wave
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
Current and magnetism
Magnetic
Flux
Current
Source: Dillon (2001):
Hearing Aids
Figure 3.4 Lines of magnetic flux flowing around a
conductor carrying a current.
Addition of magnetic flux inside loop
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
A two-turn magnetic loop
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
Audio
amplitude
Frequency modulation
(a)
Unmodulated
carrier
amplitude
Time
Modulated
carrier
amplitude
(b)
(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
Speech-operated switching
Rx
Control signal
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.
Source: Dillon (2001): Hearing Aids
Sound field amplification system
Rx
Tx
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.
Source: Dillon (2001): Hearing Aids