Figures for Chapter 1

Introductory concepts

Dillon (2001)

Hearing Aids

Figure 1.1 Similarity of the two vowels oo and ee when the second formant is inaudible because of hearing loss (grey area).

So

und

leve

l

ee

250 1000 4000

Frequency (Hz)

500 2000

oo

First formant

Second formant

Source: Dillon (2001): Hearing Aids

Audibility of formants

Sam

Intense

Moderate

Weak

Tooloud

Toosoft

Norm

Figure 1.2 The relationship between the dynamic range of sounds in the environment and the dynamic range of hearing for: (a) normal hearing, (b) sensorineural hearing loss without amplification, and (c) sensorineural hearing loss with a constant amount of amplification for all input levels.

(a)

Intense

Moderate

Weak

Tooloud

Toosoft

(b)

IntenseModerate

Weak

Tooloud

Toosoft

(c)

Source: Dillon (2001): Hearing Aids

Reduced dynamic

range

Figure 1.3 (a) Sound spectrum, and (b) representation in the auditory system for normal hearing (dotted line) and sensorineural hearing impairment (solid line).

1000250 4000Sou

nd le

vel

(a)

1000250 4000

Frequency (Hz)

Exc

itatio

n

(b)

Source: Dillon (2001): Hearing Aids

Reduced spectral

resolution

50

60

70

80

90

100

110

40 50 60 70 80 90 100Input level (dB SPL)

Out

put l

evel

(dB

SP

L)

Figure 1.4 Input-output diagram for a hearing aid with 20 dB gain, showing how the output SPL depends on the input SPL, for a particular signal or frequency.

Source: Dillon (2001): Hearing Aids

I-O diagram

-100

10203040

Frequency (Hz)

Gai

n (d

B)

8 k4 k2 k1 k500250125

Figure 1.5 Gain-frequency response of an in-the-ear hearing aid at maximum volume control position (solid line) and reduced volume control position (broken line).

Source: Dillon (2001): Hearing Aids

Gain-frequency response

8090

100110

Frequency (Hz)

Out

put

(dB

SP

L)

8 k4 k2 k1 k500250125

Figure 1.6 Saturated sound pressure level frequency response of an in-the-ear hearing aid.

Source: Dillon (2001): Hearing Aids

SSPL or OSPL90

Figure 1.7 A BTE hearing aid.

Source: Dillon (2001): Hearing Aids

Photo has been removed to minimize file size.

Figure 1.8 An ITE, an ITC and a CIC hearing aid.

Source: Dillon (2001): Hearing Aids

Photo has been removed to minimize file size.

Figure 1.9 The typical location of components in an ITC and a BTE hearing aid.

Microphone

Ear-hook

Volume control

Switch

Battery

Receiver

Amplifier

Fitter controls

Receiver

Vent

Microphone

Fitter control

Volume control

Battery

Source: Dillon (2001): Hearing Aids

Component location

Figure1.10 Spectacle adapter system showing two different adapters and BTE hearing aids, an earmold, and a spectacle bow. The bow would be cut at the white line and the left half inserted in the adapter.

Spectacle aids

Photo has been removed to minimize file size.

Figure 1.11 Three acoustic era instruments: (a) The Auricle, (b) the horn, and (c) the speaking tube.

Acoustic hearing aids

Photo has been removed to minimize file size.

Figure 1.12 A carbon aid (The Acousticon) without its battery.

Carbon aid

Photo has been removed to minimize file size.

Figure 1.13 A relatively late vacuum tube hearing aid, with its two separate batteries.

Source: Dillon (2001): Hearing Aids

Vacuum-tube aid

Photo has been removed to minimize file size.