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An Update on Hearing Aid Testing. Reading Speech-Maps or SPLograms Niki Timar, Audiologist Vancouver Island Health Authority – South Island. Background . Audiologists used to routinely test hearing aids in the booth, using aided audiograms. Background.

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An update on hearing aid testing l.jpg

An Update on Hearing Aid Testing

Reading Speech-Maps or SPLograms

Niki Timar, Audiologist

Vancouver Island Health Authority – South Island


Background l.jpg
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


What is a speechmap or splogram l.jpg
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 child’s 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 1980’s, 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 wouldn’t 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 aid’s 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 don’t know if this is a “good” fitting


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The End achieved with hearing aids for difficult fittings


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