1890 |
The electric
hearing aid is patented by Alfonzo Miltmore. These devices make use of
a carbon dust microphone, an earphone and a very large battery pack yet
are very unreliable in efficiency due to humidity, dust particles, and
the movements of the wearer. The carbon microphone consists of carbon particles
in between a fixed electron plate and a vibrating electron. The current
flowing between the electrons varies depending on the pressure exerted
on the vibrating electrode by the carbon particles providing amplification. |
1898 |
The first electric
aid, the Akoulathon, reaches production. |
1900 |
The carbon ball
is invented by Hutchison and Kelley, greatly improving the reliability
of carbon microphones. These hearing aids utilize a microphone, an earphone,
an amplifier (the vacuum tube is located here), and two batteries, one
to warm the vacuum tube filament and one to amplify. |
1934 |
The vacuum
tube hearing aid is introduced and produced by multiple English manufacturers. |
1947 |
The transistor
is invented and quickly adapted to the hearing aid. The transistor, along
with advances in battery technology, make the devices much smaller, cheaper
and energy efficient. |
1959 |
Nicholas &
Clark make an in-the-canal (ITC) device. |
1962 |
The Zeta noise
blocker is invented by Linear Technology. This device incorporates circuitry
to remove environmental noise from speech. |
1980-1985 |
Many circuits
are introduced that make use of analog sound processing. |
1987 |
A joint project
between the University of Wisconsin and Nicolet Instrument Cooperation
produces the first digital hearing aid. |