FITTING FM SYSTEMS ON
CHILDREN WITH
HEARING LOSS

 

EVALUATION OPTIONS

 

A. Audio-Visual Checks

B. Electroacoustic Measurements
          Verifying Performance
          **Matching FM’s to HA’s**

C. Real Ear Evaluation
          Verifying Performance
          Matching FM’s to HA’s

D. Behavioral Evaluation
          Speech Recognition

 

Basic Principles

 

1. The auditory signal should be as _______________ as possible

This facilitates learning

Ideally this is achieved with minimal changes of _______________

 

2. There are different signal input levels to the _______________mic and to the FM mic in typical use situations

 

 

Typical input to HA mic - _______________ dB SPL

 

Typical _______________to FM mic - 80 dB SPL

 

3. Think in terms of _______________ rather than gain

Goal is to match SPL levels at the _______________ so that signal is consistent (exceptions will be discussed)

Therefore, for same _______________, gains will differ because input levels are different

 

EXAMPLE
using overall signal levels

 

Say that Mary hears best when level at the eardrum is 100 dB SPL

For the HA Fitting

 

65 dB SPL input + _______________ dB gain = 100 dB SPL

For the FM Fitting

_______________ dB SPL input + 20 dB gain = 100 dB SPL

 

4. Use _______________-weighted noise for frequency response and use tone sweep for SSPL90

 

All of the energy in complex signal sums to an overall _______________, there is not 70 dB at every _______________, but 70 dB overall, therefore…..

 

 

The SPL at 1 kHz will be lower for 70 dB speech weighted noise than for 70 dB _______________tones. But….

 

For a pure tone sweep, there IS _______________ dB at every frequency

 

 

5. Use _______________ volume control first, then HA, to match output for HA and HA+FM conditions

 

Ideally want the child to put on HA and _____   _______________settings when using FM

Need to check electroacoustically to determine if this is possible

 

6. Optimize the testing

 

 

Try to do electroacoustic measures before patient arrives

Always perform _______________measures if possible.

When you have options to receive FM only & FM+ENV, start first with the signal arrangement used _______________.

 

 

 

 

Match FM to HA Characteristics

          Two Demonstrations:

                    a)  Billy

                    b)  Charlie

 

Electroacoustic Match can be obtained PRIOR to patient arrival if FM receiver is available

 

In the case of BTE FM systems, child may be wearing the aid

Let’s assume BTE aid has been _______________ and is an appropriate fit

 

 

SIMPLIST CASE – Billy


MILD TO MODERATE HEARING LOSS

 

(…space for notes)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are four basic evaluation steps!

 

1) HA - 65 dB SPL complex signal

2) HA & FM - 80 dB SPL _______________ signal

3) HA – 90 dB _______________signal

4) HA & FM – 90 dB pure tone signal

 

 

Steps to Match HA and FM Outputs
for Mild to Moderate Hearing Loss
Preliminary Setup:

1. Set HA to User Settings

2. Set Test Equip for Complex Signal

3. Set Test Equip to display OUTPUT,

    not gain

4. Go into _______________ Function

 

 

 

Set up for testing HA alone

          -- Place BTE attached to _______________into test box

 

 

Change setting to Curve 1-Put HA in test box

 

Curve 1. Test HA alone with _______________ dB SPL complex input

 

Set up for testing HA & FM

-- place FM transmitter mic in test box, transmitter and BTE outside test box on foam pad

 

Change setting to Curve 2-Put FM Transmitter in test box, Attach FM Receiver Boot to HA

 

Curve 2. Test HA&FM system (set to FM only) with 80 dB SPL _______________ input

 

 

Compare Curves 1 and 2 : EHA65 and EFM80

Adjust volume if necessary to match HA alone output,

If a programmable hearing aid , make and new program and refer to that as “FM Program”

 

Change setting to Curve 3-Put HA in Test Box

Curve 3. Test HA alone with _______________ dB SPL pure-tone sweep input

 

Steps to Match HA and FM Outputs
for Mild to Moderate Hearing Loss
 Setting Gain- Billie, continued

 

Change setting to Curve 4-Put FM Transmitter in test box, HA with FM Receiver Boot and 2cc coupler outside

Curve 4. Test HA&FM system (set to FM only) with 90 dB SPL _______________sweep input

 

Match Max Output- Billie

Compare Curves 3 and 4, EHA90 and EFM90

Adjust max output if necessary in the “FM Program”, to match HA output

 

(Examples of test strips):  SUMMARY

 

These curves are

closely aligned except for the

high frequencies

at the typical Input levels (1&2).

 

Additional _______________ frequency info. Is

often desirable.

 

 

SUMMARY--MATCHING FM TO HA

 

Curve 1. Test HA alone with 65 dB SPL complex input-EHA65

Curve 2. Test FM&HA System (set to FM only) with 80 dB SPL complex input-EFM80

Curve 3. Test HA alone with 90 dB SPL pure-tone sweep input-EHA_______________

Curve 4. Test FM &HA System (set to FM only) with 90 dB SPL pure-tone sweep input-EFM90

 

 

 

SECOND CASE

More Difficult Case-Charlie

 

 

Severe to Profound Hearing Loss (thresholds greater than 80 dB HL)

If the typical use mode is FM+ENV

 

-- unamplified speech at the location of the HA mic is below the auditory area of the person with hearing loss

 

 

 

SEVERE TO PROFOUND HEARING LOSS

           (…space for notes)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So in this case, we want to amplify the FM signal to a HIGHER intensity than that achieved with the _______________

 

          -- environmental signal (with more gain) is now audible

 

 

Steps to Match HA and FM Outputs
for Severe to Profound Hearing Loss
Preliminary Setup-Same as Before

1. Set HA to _______________ Settings

2. Set Test Equip for Pure-tone Signal

3. Set Test Equip to display _______________, not gain

 

 

 

Steps to Match HA and FM Outputs
for Severe to Profound Hearing Loss
Setting Gain- Charlie

 

Put HA in test box, Set system to pure tone

 

Step 1. Test HA alone with 65 dB SPL, _______________-Hz input-OHA65

 

Put FM mic in test box, HA with FM Receiver boot/2 cc coupler outside box, Set Unit to receive FM only signal

 

Step 2. Test FM&HA with the same 65 dB SPL, 1000-Hz input-OFM65

 

Compare Outputs from Steps 1 and 2

Adjust volume of HA with FM Receiver Boot to match HA alone output

 

Make new Program if necessary

Now they are matched in output AND gain for _______________ dB SPL inputs

 

Step 3. Test HA&FM system with 80 dB SPL, 1000-Hz input-OFM80

If the output increases by at least 10 dB then you are done!

 

Step 4. If the increase was:

15 dB- Then reduce FM output by 5 dB

  5 dB- Then increase the FM volume by 5 dB

  0 dB-This suggests that the FM transmitter has   

                     a very low compression threshold, so

                     _______________ the FM output by 5 dB

 

Run HA alone (65 dB SPL) complex noise-EHA65

Run HA&FM system (80 dB SPL) complex noise-EFM80

 

Verify that EFM80 is greater than EHA65 across the frequency range

 

 

SETTING MAXIMUM OUTPUT

 

Same Procedure as for Mild to Moderate Hearing Loss

Match output to 90 dB SPL Sweep Pure Tone Signal, ie. compare EHA90 and EFM90

 

In Systems with FM Precedence Effect
Must Consider _______________Mode

If FM only is the typical mode, testing is done

 

If FM+ENV is the typical mode, more testing is required to ensure adequate output across modes

 

When Matching to HA output
consider two FM conditions
(room must be quiet)

 

FM + ENV Mode On but FM mic receiving _______________ input-EEF65

Put HA attached to 2 cc coupler in test box and FM transmitter and mic outside

 

FM+ ENV Mode On but _______________ mic receiving no input-EFE80

Put FM mic in test box and HA attached to 2cc coupler _______________ box