1. Figures for Chapter 1 Introductory concepts
Dillon (2001)
Hearing Aids

2. Audibility of formants
First formant
Second formant oo
Sound level ee
250
500
1000
2000
4000
Frequency (Hz)
Figure 1.1 Similarity of the two vowels oo and ee when the second formant is inaudible because of hearing loss (grey area).
Source: Dillon (2001): Hearing Aids

3. Reduced dynamic range (a) (b) (c) Norm Sam Too loud Intense Moderate
Weak
Too
soft
(a)
Norm
Intense
Moderate
Weak
Too
loud
soft
(b)
Intense
Moderate
Weak
Too
loud
soft
(c)
Sam
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.
Source: Dillon (2001): Hearing Aids

4. Reduced spectral resolution
1000
250
4000
Sound level
(a)
1000
250
4000
Frequency (Hz)
Excitation
(b)
Figure 1.3 (a) Sound spectrum, and (b) representation in the auditory system for normal hearing (dotted line) and sensorineural hearing impairment (solid line).
Source: Dillon (2001): Hearing Aids

5. 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

6. Gain-frequency response
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

7. SSPL or OSPL90
Figure 1.6 Saturated sound pressure level frequency response of an in-the-ear hearing aid.
Source: Dillon (2001): Hearing Aids

8. Photo has been removed to minimize file size.
Figure 1.7 A BTE hearing aid.
Source: Dillon (2001): Hearing Aids

9. 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

10. Component location Microphone Volume control Receiver Battery
Vent
Microphone
Fitter control
Volume control
Battery
Component location
Microphone
Ear-hook
Volume control
Switch
Battery
Receiver
Amplifier
Fitter controls
Figure 1.9 The typical location of components in an ITC and a BTE hearing aid.
Source: Dillon (2001): Hearing Aids

11. Photo has been removed to minimize file size.
Spectacle aids
Photo has been removed to minimize file size.
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.

12. Photo has been removed to minimize file size.
Acoustic hearing aids
Figure Three acoustic era instruments: (a) The Auricle, (b) the horn, and (c) the speaking tube.
Photo has been removed to minimize file size.

13. Photo has been removed to minimize file size.
Carbon aid
Photo has been removed to minimize file size.
Figure A carbon aid (The Acousticon) without its battery.

14. Photo has been removed to minimize file size.
Vacuum-tube aid
Photo has been removed to minimize file size.
Figure A relatively late vacuum tube hearing aid, with its two separate batteries.
Source: Dillon (2001): Hearing Aids