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CSD 5400 REHABILITATION PROCEDURES FOR THE HARD OF HEARING. Amplification Hearing Aids. Preliminary Remarks. One of the most critical elements of any rehabilitation plan (child or adult) is the fitting of appropriate amplification

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preliminary remarks
Preliminary Remarks

One of the most critical elements of any rehabilitation plan (child or adult) is the fitting of appropriate amplification

This is the only recognizable way, at this time, to maximize residual hearing

The primary objective of modern amplification theory is to make speech audible without introducing distortion and to restore a more “normal” range of loudness experience

preliminary remarks1
Preliminary Remarks

Fitting of appropriate amplification should only be done by a trained professional


Licensed hearing aid dispenser

Hearing aids are the most common form of amplification, but not the only one

selecting the hearing aid candidate
Selecting theHearing Aid Candidate

What factors do we consider, after a hearing assessment, in making decisions about recommending amplification?

1 degree of hearing loss
1. Degree of Hearing Loss

Right or wrong, this continues to be a major parameter in deciding whether or not to recommend amplification

Many studies demonstrate poor correlation between hearing sensitivity and self-perceived handicap (activity limitation)

In general, as the degree of HL increases, the need for amplification increases, but overall HA benefit decreases

problem fittings
“Problem Fittings”

Unilateral hearing loss

Lots of residual hearing

Mild hearing loss

Normal hearing throughout a broad area of the audiometric range

Profound degrees of HL/very little residual hearing

Unusual/atypical configurations

2 motivation
2. Motivation

Very common for people to believe they have HL, but only a small percentage will ever utilize HAs or even try them


Poor advice from MDs

Lack of understanding of HL and HAs

Financial concerns

Here are some common factors that cause people to try amplification

acceptance of hearing loss
Acceptance of Hearing Loss

How realistic is the client regarding the amount or type of communication problems the hearing loss is causing?

Is the client still angry about the hearing loss?

4 cosmetic concerns
4. Cosmetic Concerns

“Hearing aid effect”

It is real


How concerned is the client over hearing aid size and style?

hearing aids
Hearing Aids

First hearing aids were manufactured by Siemens Electronics in 1912

The two major trends that drive current hearing aid design include

  • Miniaturization
      • Overall size, components, batteries
  • Enhanced signal processing
hearing aid development
Hearing Aid Development


recent advances in signal processing
Recent Advances in Signal Processing

Multiple memories

Provides access to different amplification characteristics

Increases flexibility

Noise reduction circuits

Sophisticated ways to improve the signal-to-noise ratio

Major complaint of most listeners

Feedback control

Feedback is the audible signal related to an interaction between certain components of a hearing aid

As hearing aids became smaller, feedback was a major limitation and complaint

recent advances in signal processing1
Recent Advancesin Signal Processing


Allows the dispenser to set and control a number of different properties of the HA

Increases “precision” of the fitting

Increases hearing aid flexibility

Digital processing

Major tech advance of the 1990’s

Talk more about this later

Tremendous improvement in HA fidelity and flexibility

Multiple channels

Allows separate frequency bands to be established and processed (manipulated) separately and independently

basic components of a hearing aid
Basic Componentsof a Hearing Aid


Converts sound waves to an electrical signal


Increases the amplitude of the electrical signal from the microphone


Converts the amplified electrical signal back to sound


Provides power to drive the amplifier

basic hearing aid components
Basic Hearing Aid Components

Putting everything together

Let’s look at each of these components in a little more detail…


Drive the amplifier

Come in about 6 sizes denoted by a number

675, 312, 13, 230, 10A, 5A

Sizes are not interchangeable

Come in different materials

Mercury (banned), silver oxide, zinc-air

Materials can be used interchangeable, but battery life might vary


Two types are used


Designed to respond primarily to sounds originating from in front of the wearer, not behind

Helps to improve S/N

Non-directional or omnidirectional

Equally sensitive in all directions


The amplifier determines the “gain” of the hearing aid

Hearing aid gain is the difference, in dB, between the input level of an acoustic signal and the output level

Generally matched to the degree of hearing loss and the dynamic range of the listener

Also determines the method of output limitation and how the hearing aid increases intensity throughout it’s functional range

If the HA has a volume control, it is tied to the amplifier


Most modern hearing aids use an internal air conduction receiver


You can’t see them

Other receiver options exist

Bone conduction HAs


Implantable (later)

Vibrotactile HAs


other common hearing aid features
Other CommonHearing Aid Features

On-off switch

Allows the hearing aid to be shut off completely

Battery saving device

Levers, switches, feature of the VCW

other common hearing aid features1
Other CommonHearing Aid Features


Special circuit that enhances telephone communication or allows compatability with loop systems (later)

Circuit emits an electromagnetic signal which is picked up by the t-coil

The t-coil signal is amplified and sent to the receiver


other common hearing aid features2
Other CommonHearing Aid Features


Typically the user manually activates the circuit

“T switch”



Advantages to the telecoil

Reduces the occurance of feedback when using the telephone

Improves the signal-to-noise ratio

other common hearing aid features3
Other CommonHearing Aid Features

Volume Control

Directly tied to the amplifier

Some HA styles don’t offer a VCW


Some DSP circuits don’t offer VC

These hearing aids continuously adjust the gain

other common hearing aid features4
Other CommonHearing Aid Features


Some hearing aid styles require a separate earmold

Body HA, BTE, eyeglass HA

Serve three purposes

Deliver the amplified sound from the HA to the ear

Couples the HA to the wearer

Modifies the acoustics of the amplified sound delivered to the ear

Here’s a diagram illustrating some common earmold styles

CD-ROM Ch07.06 and Ch07.07

hearing aid fitting considerations
Hearing Aid Fitting Considerations

There are three major considerations that that need to be addressed when making a recommendation of hearing aids:

What hearing aid style will work best?

What level of technology will work best?

Monaural or binaural?

hearing aid style
Hearing Aid Style

Currently, six styles are available from most manufactureres

Body, eyeglass, behind-the-ear, in-the-ear, in-the-canal, completely-in-the-canal

Nearly every level of technology is available in any style

Every degree of hearing loss can be fit appropriately with every style

body hearing aid
Body Hearing Aid


High gain with no feedback

Large controls



Monaural fitting only


Microphone placement

Body baffle, clothing noise

Newer DSP circuits not available in this style

eyeglass hearing aid
Eyeglass Hearing Aid

Very popular in the 1960’s-1980’s

Needs an earmold


Used to be more cosmetically appealing, especially for people with unilateral HL


Fitting issues

Breakdown and repair

True binaural fitting is not possible

DSP circuits not available in this style

behind the ear bte
Behind-the-Ear (BTE)

Needs an earmold

CD-ROM CH07.04




Good choice for kids

Compatibility with direct audio input

Few problems with feedback

Microphone placement

True binaural fitting possible

Very durable/good repair record



Stigma compared to custom styles

Microphone placement compared to custom styles

Fit with glasses, etc..

Harder to manipulate, compared to custom styles

custom hearing aid styles
Custom Hearing Aid Styles


All components of the HA fit completely in the pinna and/or EAM

Completely changed the approach audiologists take regarding the HA fitting

CD-ROM CH07.05

ite and itc


Cosmetic appeal

Ease of insertion/secure fit

Microphone placement is very realistic

Reduction in wind noise (especially ITC)


Feedback can be a problem

Battery size

Expense (especially as size decreases)

Some desired options might not be available in ITC

Telecoil, directional microphones, VCW

completely in the canal cic
Completely-in-the-Canal (CIC)

These hearing aids sit very close to the TM so the acoustic advantages are different than the other styles

The major drawback is that the listener needs a large enough earcanal to accommodate the minimum size the HA has to be



Easy to use and insert

Reduction/elimination of occlusion effect

Less HA gain/reduction of feedback/phone

Improved localization ability

Elimination of wind noise

Elimination of cerumen problem


Greater high frequency emphasis is possible


Expense, size, gain/output problems, custom features not available

level of technology
Level of Technology

There are currently three major levels of hearing aid technology people are able to access:

Analog hearing aids

Digitally controlled analog hearing aids

Sometimes referred to as “programmable”

Digital hearing aids

analog hearing aid
Analog Hearing Aid

Oldest signal processing strategy

Signal is processed in a manner that’s continuously varying over time

Here’s a schematic of an analog circuit

Hearing aid controls are analog, too

digitally controlled analog hearing aids
Digitally ControlledAnalog Hearing Aids

Uses analog signal processing with digital control over the electroacoustic parameters

Gain, compression, frequency response, etc

Here’s a schematic of such a circuit

Major advantages include flexibility, programmability, greater range of outputs

digital hearing aids
Digital Hearing Aids

Analog signal is converted to a digital representation

Once digitized, the signals are manipulated by processing algorithms (programs) and converted back to analog form

Biggest advantage is complete flexibility and programmability

Here’s a schematic of a digital HA

fitting one ear or two
Fitting One Ear or Two??

Benefits of binaural amplification

  • Localization
  • Binaural summation
  • Elimination of head shadow
  • Improved S/N through binaural squelch
  • Auditory deprivation
a word about hearing aid maintenance
A Word AboutHearing Aid Maintenance..

This is mentioned specifically in the ASHA Scope of Practice for SLPs

Any client of yours wearing hearing aids needs to have their HAs checked daily


Invest in a battery tester

Earmold and receiver checked for wax

Recommended daily HA check procedures

HA troubleshooting guide