Biomedical Engineering Reference
In-Depth Information
FIGURE 6-7
Therapies according
to the degree and
type of hearing loss.
[Adapted from
(Bernhard, Steiger
et al., 2011).]
6.5
HEARING AIDS
6.5.1 History
Until the advent of electronic amplification, hearing aids consisted of horns (ear trumpets)
of various sizes and sophistication, as shown in Figure 6-8, which increased the size of the
sound collection aperture and therefore provided some amplification. The effective gain
of these horns is approximately equal to the ratio of the input to the output cross sectional
area.
FIGURE 6-8
Early
hearing aids.
(a) Advertisements
for ear trumpets and
tubes. (b) Engraving
showing an ear
trumpet in use.
(Ganot 1872), with
permission.
