An Update on Hearing Aid Testing

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An Update on Hearing Aid Testing

• Reading Speech-Maps or SPLograms
• Niki Timar, Audiologist
• Vancouver Island Health Authority South Island

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Background

• Audiologists used to routinely test hearing aids
  in the booth, using aided audiograms

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Background

• Research has shown aided audiograms are not a
  good way to test modern hearing aids
• BC Public Health is switching over to the newer
  way of testing, using Real-Ear or simulated
  Real-Ear measures
• This is why you might not be receiving aided
  audiograms recently

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What is a SpeechMap or SPLogram?

• A graph showing hearing thresholds, maximum safe
  or acceptable levels, and the performance of the
  hearing aid
• Speechmap is the proprietary term Audioscan
  uses for their software
• SPLogram is a term coined by Richard Seewald
  and his group, from the University of Western
  Ontario, for use with the Desired Sensation Level
  (DSL) hearing aid prescription formula

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Audiogram on Speechmap Screen
In dB Hearing Level (HL)
Normal Hearing
Speech Banana
Hearing Thresholds
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Speechmap or SPL-o-gram
In dB Sound Pressure Level (SPL)
Hearing Thresholds
Speech Banana
Normal Hearing
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Difference Between Speechmap and Audiogram
Loud
In dB Sound Pressure Level NOT Hearing Level
Soft
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Too Loud
Aided Speech Banana
Inaudible
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Why Not Aided Audiograms?

• Aided audiograms only show one thing the
  response of the hearing aid to very soft sounds
• Aided audiograms do not tell anything about how
  loud the hearing aid is, and whether it is
  potentially damaging to a childs hearing

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Real-Ear Testing

• Instead of Aided testing in the booth, we now
  rely on Real-Ear Testing as our main hearing aid
  test

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What is Real-Ear Testing?

• Real-Ear testing is objective testing with the
  hearing aid in the ear.
• Basically, we place a microphone in the ear just
  past the hearing aid, and measure what the actual
  output of the hearing aid is, close to the eardrum

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Why the Changes in Methodology?

• A Short Lesson on Hearing Aid Technology

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Hearing Aids

• Hearing aids are now digital
• Hearing Aids are no longer linear, they use
  COMPRESSION

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Dynamic Range

• One important concept for understanding
  compression and hearing aid function is DYNAMIC
  RANGE
• This is the range of usable hearing for a given
  individual between the quietest sounds they can
  hear (hearing thresholds) and the loudest sounds
  they can tolerate (loudness discomfort levels)

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HL
Hearing Thresholds
Dynamic Range
Maximum Output
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SPL
Maximum Output
Dynamic Range
Hearing Thresholds
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Linear Hearing Aids

• Until the 1980s, hearing aids were linear
• They added the same amount of amplification, no
  matter how loud the input sound

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Linear Amplification

• 140
• 120
• 100
• 80
• 60
• 40
• 20

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Peak Clipping

• 140 dB is dangerously loud for most people
• To keep the sound levels safe, hearing aids used
  Peak Clipping they just stopped at a given
  level for example, they wouldnt make anything
  louder than 120 dB
• This caused DISTORTION in the hearing aids

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Peak Clipping

• 140
• 120
• 100
• 80
• 60
• 40
• 20

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Compression

• In the 1980s, as a way to keep sounds comfortable
  but undistorted, manufacturers started using
  compression limiting
• Instead of amplifying the same amount no matter
  what the input, for sounds approaching the limit,
  less amplification would be used

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Compression

• 140
• 120
• 100
• 80
• 60
• 40
• 20

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Even Newer Advances

• As technology advanced, it became possible to
  have different compression levels for different
  frequency ranges, and for different intensities
• This is where digital hearing aids shine, as more
  capability can be added in these functions,
  without adding size or battery drain

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So What Does This Have to Do With Speechmap?

• Testing just quiet sounds in the booth does not
  tell us about what the hearing aid does to speech
• Digital hearing aids often have noise
  suppression, which makes quiet, non-speech-like
  sounds even quieter, to avoid amplifying annoying
  sounds like fridges humming
• Aided audiograms are tested using quiet,
  non-speech-like sounds (tones)

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Limitation of Aided Audiogram

• This slide shows the hearing aids response to
  quiet non-speech tones
• We can infer how much speech the child can hear,
  but it does not show differing performance for
  soft, versus loud, speech
• It does not tell us if the hearing aid is too
  loud, or if there is distortion
• There are no targets, so we dont know if this is
  a good fitting

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• The Speechmap shows soft speech, loud speech and
  very loud sounds, showing, in this case, that
  they all give acceptable responses
• It also shows Speech Intelligibility Index (SII),
  which predicts how much of the speech signal is
  audible for a given input

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• You may also see Speechmap tables, depending how
  your local audiologist likes to look at things

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• The Speechmap shows clearly the limitations of
  what can be achieved with hearing aids for
  difficult fittings
• This keeps us from trying to increase the volume
  where it does not help, and would only cause
  feedback problems

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The End