View
216
Download
2
Embed Size (px)
Citation preview
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
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
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
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
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
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
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
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
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