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.
||The first electric
aid, the Akoulathon, reaches production.
||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.
|| The vacuum
tube hearing aid is introduced and produced by multiple English manufacturers.
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.
Clark make an in-the-canal (ITC) device.
||The Zeta noise
blocker is invented by Linear Technology. This device incorporates circuitry
to remove environmental noise from speech.
are introduced that make use of analog sound processing.
||A joint project
between the University of Wisconsin and Nicolet Instrument Cooperation
produces the first digital hearing aid.