Verifying Open-Ear Fittings With Speech-Mapping

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Verifying Open-Ear Fittings With Speech-Mapping
AAA CEU Theater Program
David J. Smriga, M.A. Audiologist Hearing
Industry Consultant
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Strom, Karl, Rapid Product Changes Mark The New
Mature Digital Market Hearing Review Vol. 13,
No. 5, 2006 p.p.70-75
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BTE Growth Spurt

• After 20 or less of the market in the 80s and
  90s, look at BTEs now
• 26.4 in 2004
• 32.6 in 2005
• 42.00 in first half of 2006

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Fueling That Growth

• Directional microphones
• Open fit hearing aids
• 27 of all BTEs sold in first half of 2006

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Why the Renaissance in Open Fit Popularity?

• Minimal occlusion via a narrow tube fitting (or
  large vented earmold)
• Digital feedback cancellation
• Precise frequency response setting
• Mini (or micro) BTE designs
• Open-fit ITE design now available
• Directional microphones with open fit aids?

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Minimal Occlusion
Lybarger S. Earmolds. In Katz J, ed. Handbook of
Clinical Audiology, 3rd edition. Baltimore
Williams and Wilkins 1985 885-910.
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Digital Feedback Reduction Properties
Passive
Active
Phase Canceller
Notch Filter
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Precise Frequency Response/Compression Setting

• Digital hearing instruments offer the most
  precise hearing instrument performance setting
• Multiple bands
• Variable compression settings by band
• Low and multiple knee points
• Variable compression ratios
• This makes digital hearing aids dynamically
  interactive

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• Objective Verification of Open Fittings

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Real Ear Basics
Real-ear loudspeakers
Probe Microphone Assemblies
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Key Issues

• Input stimulus
• Traditional options
• Sweep frequency pure tone
• Noise stimulus
• Speech stimuli
• Activates adaptive features

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The output of a compression aid depends on the
nature of its input signal
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The output of a compression aid depends on the
nature of its input signal
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The output of a compression aid depends on the
nature of its input signal
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Key Issues

• Insertion gain vs. audibility
• Traditional method
• REUR REAR REIG
• Does this verify audibility has been delivered?
• Does this demonstrate improvement with
  open-fittings?
• Audibility method
• REAR compared to audibility threshold

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For this compression hearing aid...Gain for
speech _at_ Gain for tones
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Output for speech is much less than output for
pure tones.
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Speech Is An Excellent WDRC Measurement Stimulus

• It IS the most important input signal that the
  patient will want to hear well and comfortably
• It interacts with multi-band compressors in a
  more realistic way than tones
• band interactions across frequency
• changing intensity

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Understanding an SPLogramThe Unaided SPLogram
Maximum output targets
dB SPL Eardrum reference
Threshold (dB SPL TM)
Normal hearing
1) Recruitment Accommodation
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Example of Open-Fit REAR Result
Aids contribution
Pink banana REAR with aid OFF Green banana
REAR with aid ON
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The SII Score
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An Open-Fit Verification Protocol

• Measure REAR with instrument on ear but turned
  off
• Measure REAR with instrument on ear and turned on
• Adjust gain to maximize SII without invoking
  feedback
• Use the fitting screen as a counseling tool

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• Can Directional Microphones Work In An Open Fit
  Environment?

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The Aided Frequency Response That Reaches The Ear
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Two Omni-directional Mics With Digital Processor
DSP
H. Dillon NAL, CRC for CI and HAI
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Measuring Directional Microphones Using Polar
Plots
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Laboratory Specification of Directionality
Polar Plots
2) Directional Verification
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Conventional Directional Microphone Test (Polar
Plot Measurement)
Sound Field Speaker
Pure Tone Frequency
Anechoic Chamber
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Issues Associated with Conventional Polar Plot
Testing

• Polar plots are obtained in the presence of a
  single pure tone frequency
• Polar plots do not measure in the presence of
  multiple input sources
• Polar plots can not be obtained in the presence
  of non-linear (compression) amplification

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A New Way of Measuring Directional Microphone
Performance

• Obtaining a Directional Microphone Frequency
  Response in the Presence of Multiple Input Source
  Locations

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Verifit Testing System Hardware
Coupler Chamber
Secondary Signal Source
Main Signal Source
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Directional Frequency Response Input Stimulus
Main input signal (512 pure tones 7.8Hz apart)
Frequency (KHz)
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Concept Behind Directional Box Test
Main Speaker
Secondary Speaker
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Clinical Verification of Directional Performance
B) Verifit REM Directional Verification
Test selection
Hearing Instrument Test Linear AGC Directional Dis
tortion Input/Gain Multicurve Telecoil Manual
control Calibration
Real-Ear Measurement Speechmap Insertion
gain Directional Manual control Calibration
2) Directional Verification
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Directionality Test (REM)
Verifit System In REM Directional Mode
Rear Facing Auxiliary Speaker
Subject
Aided Ear With Probe Tube Positioned
2) Directional Verification
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On-Ear Directional Test Result
REAR to Front Signal
REAR to Back Signal
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Viewport Screen View Facilitates Results
Comparison
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Example of Complete Box-test Viewport Result
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SRT-in-Noise Improvement With Open Fit
Directional Mic
Fabry, D., Facts vs. Myths The Skinny On
Slim-Tube Open Fittings Hearing Review, May, 2006
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Conclusions

• Modern open-fits facilitated by
• Digital control of feedback
• Digital control of non-linearity
• Digital improvement in directional performance
• Objective on-ear measurements of open-fit
  products are possible
• Key elements to accomplish this
• Speech input stimuli
• Measure eardrum SPL instead of gain
• Objective measures of directional performance are
  possible
• Can confirm directional function in aided area