- 1901: At this stage microphones
are being made of carbon dust, but this does not perform well.
Then comes a new development - the carbon ball - which increases
the quality and reliability of electrical hearing aids.
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- 1902: At this stage, the efficiency
of the electrical carbon hearing aid is governed by the relationship
between the size of the microphone and the earphone. The bigger
the microphone compared to the earphone, the more amplification
is achieved. Carbon instruments are produced with a "small-sized"
microphone for mild hearing losses, a double-sized microphone
for moderate hearing losses, and a quadruple-size microphone
for severe hearing losses.
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- 1921: The first vacuum tube hearing aid is
patented and manufactured.
-
- 1933: The Bone Conductor is
invented and used in hearing aids. It is used for all types of
hearing losses, but is most effective in assisting people with
middle ear diseases.
-
- 1934: The first vacuum tube
hearing aid is designed by two manufacturing companies. This
kind of device needs two batteries in order to operate, and is
limited by the lifetime of the batteries, which is often only
one day!! It consists of four elements: a microphone, earphone/receiver,
amplifier and two batteries.
-
- 1945: The development of smaller
batteries, and advances in vacuum tube technology result in the
introduction of the first one piece vacuum tube hearing aid.
This rapidly becomes the standard for the design of new hearing
instruments.
-
- 1947: Up until now, hearing
instruments are only worn on the body. They are heavy and expensive
to use due to high battery consumption. But all this changes,
when the transistor is invented. This proves to be a fantastic
invention, even for hearing instruments. It is small, cheap and
effective, and has a very low battery consumption compared to
vacuum tube instruments.
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