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Transcript
Hearing Aids (HA)
Or technology to the rescue
Upcoming Talk: Isabelle Peretz
Musical & Non-musical Brains
Nov. 22 @ 12 noon + Lunch
Rm 2068B South Building
Finishing up with Tinnitus

One last method of treatment

Tinnitus retraining therapy

Habituation to tinnitus sound to reduce
aversiveness
HA Basics

BTE


ITE


In the ear
ITC


Behind the ear
In the canal
CIC

Completely in canal
HA History

Ear trumpets

Prehistoric


Speaking tubes (17th century)


In-ear, around ear
Limited frequency range


Direct sound from mouth
Aurical Aids


Hollowed ram horns
Effective at less than 1000 Hz
Artificial ear drums (19th century)

Perforated ear drum



Try to insert rubber, cotton or dermal layer
Wire attachment to ossicles
Ineffective
Early Electronic HAs

Carbon-based (early 20th century)

Carbon microphone

Sound  Diaphram: moves carbon globules



Problems



Static, no additional amplification
Bulky, large battery
Benefits


Motion of carbon in electric field creates current
Gain 30 dB SPL
Greater frequency range (500 – 2000 Hz)
Vacuum Tube (circa 1920)

Multiple vacuum tubes response to current in
microphone

Problems


Expensive, Multiple batteries, bulky
Benefits

Powerful (up to 140 dB SPL gain)
Analogue Technology (75%
sold)

HA: no more vacuum tubes by 1953


Transistors introduced 1952
Transistors: Cheaper to produce, much less
energy required, equal power

Head-mounting


Allowed for integrated circuits


Multiple transistors & resistors in same area
Benefits


Eye-glass, Barrettes
Cheaper, less bulky, improved frequency range
Problems

No signal processing

All linear changes in amplification
HAs Design

Microphone  Amplifier  High/Low pass
filters  Attenuators  Adder  Variable
gain amplifier  speaker (output)
Digital HAs (25%)

Convert analogue signal to digital

Advantages

Much greater capacity for signal processing


Less energy consumption



Preprogrammed environments
Lighter
Cheaper to produce
Problems

Programmability?
HA Effectiveness

HOH Population 40% neutral or dissatisfied
with HA (Cochran, 2002)


No difference between Digital & Analogue
Problems

Battery 100 hrs (1 week to 10 days)


Will run out, must be replaced/recharged
Limited benefit in noise

Best if 1 meter or less