Five phases of hearing instrument development

• Acoustic resonators

Include cupped hands behind the Pinna, various ear trumpets/horns.

This modification to sound reception resulted in

increased gain of about 10db in the mid-frequency range

and no high freqency amplification.

Five phases of hearing instrument development

• Carbon microphones (developed around 1900)

When coupled with early electronic amplifiers would

produce more gain; however, they also produced significant amounts of distortion

Five phases of hearing instrument development

• Vacuum tubes (developed around 1920)

Were more compact and reliable than the carbon era. Also, created more amplification and less distortion.

Five phases of hearing instrument development

• Transistor (developed in the mid-1940s)

Now, not only could hearing instruments be worn on the body, they could now be worn on the head i.e. ear level. More amplification with even less distortion became a reality.

Five phases of hearing instrument development

• Integrated Circuits (IC) (developed 1970s)

Would utilize thousands of transistors in the design of the amplifier chipset.

Was the beginning of tremendous miniaturization of hearing instruments i.e. from ear level to in-the-ear transducer/amplifier location.

Five phases of hearing instrument development

• Digital age (mid 1990s)

The integrated circuits were miniaturized further to include millions of transistors.

They became “digitized” through the development of analog to digital (A/D) converters.

Hearing Instrument Types

• Body hearing aids

Were found in the carbon, vacuum tube, and transistor phases of hearing instrument development

Hearing Instrument Types

• Eyeglass hearing aids (used transistors & ICs )

Were introduced to “hide” the hearing aid.

Also to “hide” the wiring required for a CROS fitting.

Hearing Instrument Types

• Behind-the-ear hearing aids (use transistors and IC)

Early versions were ear level however, bigger than some ears!

Today’s versions are very small and discreet.

Hearing Instrument Types

• In-the-ear hearing aids

May be either custom or modular in design.

Have an additional acoustic advantage with microphone placement inside of the ear.

Hearing Instrument Types

• Completely-in-the-canal hearing aids

Very discreet—translates into consumer appeal.

Its deep insertion can create added acoustic amplification.