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

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

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

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

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

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

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

Photo has been removed to minimize file size. 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

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

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.

Photo has been removed to minimize file size. Acoustic hearing aids Figure 1.11 Three acoustic era instruments: (a) The Auricle, (b) the horn, and (c) the speaking tube. Photo has been removed to minimize file size.

Photo has been removed to minimize file size. Carbon aid Photo has been removed to minimize file size. Figure 1.12 A carbon aid (The Acousticon) without its battery.

Photo has been removed to minimize file size. Vacuum-tube 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