Csd 5400 rehabilitation procedures for the hard of hearing
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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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Csd 5400 rehabilitation procedures for the hard of hearing



Hearing Aids

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

    Csd 5400 rehabilitation procedures for the hard of hearing



    Good choice for kids

    Compatibility with direct audio input

    Few problems with feedback

    Microphone placement

    True binaural fitting possible

    Very durable/good repair record

    Csd 5400 rehabilitation procedures for the hard of hearing


    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
    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

    Csd 5400 rehabilitation procedures for the hard of hearing


    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