Hearin Aids

8/8/2019 Hearin Aids

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Not being able to see

isolates you from objects.

Not being able to hear

isolates you from people

Immanuel Kant


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H

E

A

R

I

N

G

AI

D

S


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RESIDUALHEARING


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Overview

HISTORY

TYPES

TECHNOLOGY PROGRAMMERS

SELECTION CRITERIA


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HISTORICAL PROSPECTIVE OF

HEARING AIDS .


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Hearing Aid Types

Body Aids

Behind-the-ear (BTE)

In-the-ear(ITE) In-the-canal(ITC)

Completely-in-canal(CIC)


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Body level BTE

IN THE EAR

HEAR

ING AIDS

INDIVIDUAL HEARING AIDS


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Technology

Analog

Digital


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Linear amplification

Oldest type of hearing aid amplification

Amplifies all inputs same amount

Does not address nonlinear nature of loudnessgrowth in SNHL

Uses peak clipping to prevent reaching LDL

Causes substantial distortion at high inputlevels


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Non-linear techonology:

Compression Threshold (CT)

Compression Ratio (CR)

CR= 2:1

For every 10 dB increase in input level, outputincreases by 5 dB


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Figure 3.2 Block diagram of an analog

hearing aid (top) and a digitally

programmable hearing aid (bottom).

Analog hearing aid

microphone receiverSignal path

Programmable hearing aid

Signal

path

Digital

controller and

memory

programmer

unit

programmer

interface

Source: Dillon (2001):

Hearing Aids

Analog and

digitally-programmable

block diagrams


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Compression limiting versus peak clipping

Peak clipping: chops the tops off

sounds

Compression limiting: rapidly turns

the volume down

To prevent excessive loudness:


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Compression

Control of hearing aid output to within

dynamic range

Weak intensity inputs are amplified more thanhigh intensity

Nonlinear relationship

Cuts down on distortion and uncomfortableoutput levels


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Peak clipping versus compression limiting

Original Clipped Compressed


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Compression

0

20

40

60

80

100

quiet loud

Amount of Noise

Amplific

ation

ReducesAmplificaton

when its Noisy.

Helps you hear more

when its Quieter.Keeps it from being

Painful when its Noisy

Adjustable (manual and

automatic).Different settings in

multiple frequency bands.


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Channel versus Band

In a channel, can change gain, CR, CT, etc.

Band typically refers to ability to change gain only

Can have multiple bands in one channel

Example:In a particular hearing aid, channel onegoes from 250 to 1500 Hz. There are three bandswithin the channel centered at 500, 750, and 1000 Hz.


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Changing the CRorCRin channel one will

affect all frequencies from 250 to 1500 Hz.

Also would have the flexibility to adjust the

gain independently using the three bands (at500, 750, and 1000 Hz) within channel 1


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Microphones

Directional versus omnidirectional

Using Directional can be helpful in noisy

situations. The best hearing aids can switch between the

two.


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Telecoil

Converts magnetic energy to electrical signal

Telecoil option only available on certain styles

Telecoil automatically activated or manual

Push button .


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Advantages

FeedbackManagement

Noise Management

Automatic adjustment between programs


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Programming Hardware and Software

Hi-Pro Box Hearing Instrument Programmer

Interface between computer/fitting software and the

hearing aid Can be a standalone unit or built within the probe mic.

system

NOAH Software platform that facilitates data storage and

transfer Information such as audiometric data can be used with

any manufacturer that has adopted this standard


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NATIONALACOUSTICLABORATORIES NON LINEAR

PROCEDURE (AUSTRALIA)

NAL NL


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Hi pro


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NOAHlinks wireless Bluetooth connection

allows for

easy fittings up to 16 feet away from yourcomputer

without the hassle of programming cables


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Noah link


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Dynamic Range

Range in dB between threshold and loudness

discomfort level

With normal hearing, speech sounds fallwithin the dynamic range


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Wide dynamic range compression

Moderate

Weak

Intense

NormalImpaired


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Conductive Hearing Loss

Loss of sensitivity for all sounds

No reduction in dynamic range

Need gain, once sounds are audible should do well


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Sensorineural Hearing Loss

Loss of sensitivity for low-mid intensity sounds

Complete or partial recruitment

Reduction in dynamic range

Deficits in Frequency and temporal resolution

Need increased audibility and improved SNR to

function at normal levels


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Sensorineural Hearing Loss

Normal Hearing

Uncomfortably Loud 100 dB 100 dB

5 dB

Loud, But OK 0 dB

7 dB

Comfortably, but 0 dB

Slightly Loud 7 dB

Comfortable 5 dB 57 dB

Comfortably, 0 dB dB

But slightly soft

0 dB

Soft 25 dB

ery Soft 10 dB

Dynamic Range = 100-10 = 0 dB 100- 0 = 70 dB

Indicates need for Non-linear processing


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WHAT IS SPEECH BANANA?

It has been found that when speech is presentedfrom about 1mt distance at a conversational

level, each speech sound has a different

intensity and frequency pattern though the

overall intensity of speech is 0- 5dBSPL.

The speech sounds lie in a sort of cluster. If the

border of this cluster are defined, a shape not

unlike a banana emerges. This is called as

speech banana.


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USES OF SPEECH BANANA

speech banana is very useful for hearing aid

fitting.

Speech banana is useful for the selection of

hearing aid.

It is very important in interpreting aidedaudiogram.

Speech banana shows acoustic

characteristics of different sounds that isconsonants and vowels in the language.

It is useful for parental counseling.


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Single versus Multichannel

With sloping hearing loss, single channelcompression may lead to inappropriate degreeof compression in certain frequency regions.

Most advanced circuits are multichannel.

Most individuals will benefit from multiple

channels because different compression valuesare needed in different frequency regions


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Button, switch, or Remote

Hearing aid need the capability to automaticallyswitch between memories depending onenvironment.

Depending on number of options, may have oneswitch, one memory button, or both.

Need to consider dexterity and cognitive functioning

of patient.


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Main contributors to earmold acoustics:

Venting

Dampers

Soundbore/horn effect


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Styles

Standard: Shell Half Shell

Skeleton Semi Skeleton

Semi Canal

Canal Tip


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BinauralAdvantage I

Improved signal clarity in many

contexts due to combination of

Binaural summation

Binaural interaction (squelch)

Minimize the Head shadow effect


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