Openfit Hearing Aids: Some practical considerations

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Open-fit Hearing Aids Some practical
considerations

• Ruth BentlerUniversity of Iowa

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Cant ignore the market!
One company noted they expect that 80 of their
market will be OC by the end of the
year! Better Hearing Institute indicates that
slim-tube open-fit devices have increased
first-time hearing aid users by 29 (as per
Sergei Kochkin survey)
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The basic goals of an open fitting

• Eliminate (or at least reduce) plugged sensation
  and occlusion effect
• Allow low-frequencies to leak out
• Allow natural sounds to pass through
• Take advantage of residual canal resonance (?)
• Not sacrifice high frequency amplification
• Avoid feedback
• Be cosmetically acceptable

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A little history . . .

• Open products first popular in late 1960s IROS
• Used with Libby Horns (with a little more
  success) in the 1980s
• Used (without much success) with ITEs in 1980s
  and 1990s

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Open Fitting (or Open Fitting?)

• Starkey Aspect XtraTM ,Destiny
• Sonic Innovations ionTM
• GN Resound (were sending our competitors back
  to the drawing board) AirTM, PulseTM
• MicroTech SenecaTM
• Oticons Delta and Corda tubing option for
• Syncro
• Tego, Tego Pro
• Bernafon SwissEarTM
• Unitron ModaTM
• Widex Inteo elan TM
• Plus Magnatone, Vivatone, Hansaton, Audina, GHI,
  UHS, SeboTek?

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What to call these things??What choices do we
have?
RITE/C
MBTE
"O"
OF
OE
"OC"
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In fact, we can think of many combinations
Kuk, 2008
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1. In this fitting, does it matter if the
receiver is in the aid (RITE) or in the ear canal
(RITA)?
Mini-BTE-OC-RITE
Mini-BTE-OC-RITA
Receiver Housing in open tip
Thin-Tubing in open tip
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A few issues to consider first

• Feedback is not an issue.
• Acoustics of narrow tubing
• Roll off in the highs?
• And a resultant narrower frequency response?
• Peakier response?
• Smaller receiver/lower output handling

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Same Brand and Processing(with RITE versus RITA)
Smaller Receiver (Better Fit in The Ear)
Mueller, 2006
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Another Current Product (with RITE versus RITA)
Mueller, 2006
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Peakier Frequency Response?
Mueller, 2006
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1 cont. In this fitting, does it matter if the
receiver is in the aid (RITE) or in the ear canal
(RITA)?

• Depends on you reason for asking, but in general,
  NO
• No less feedback
• No wider frequency range
• No more/less peaky response

No!!
Receiver Housing in open tip
Thin-Tubing in open tip
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Practical consideration?

• Effect on bandwidth/gain, and peakiness is not
  consistent across manufacturersfind out for
  yourself (verify).

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2. Is the wearer really free from occlusion?
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How much occlusion?

• AudioScan Verifit System
• Insertion Gain test
• KEMAR with standard left ear
• REUR REOR measured with 55 dB pure-tone sweep

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2 cont. Is the wearer really free from occlusion?

• Chart shows comparison with earlier study using
  different vent sizes.
• Testing conducted with 20 subjects (10m, 10f).
• Open tips compared from three different
  manufacturers. No difference. Average values
  shown on chart. Largest effect at any frequency
  for any single ear was 6 dB.
• Behavioral judgments agree with objective finding.

Receiver Housing in open tip
Thin-Tubing in open tip
MacKensie, 2006
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2 cont. Is the wearer really free from occlusion?
Yes!

• Chart shows comparison with earlier study using
  different vent sizes.
• Testing conducted with 20 subjects (10m, 10f).
• Open tips compared from three different
  manufacturers. No difference. Average values
  shown on chart. Largest effect at any frequency
  for any single ear was 6 dB.
• Behavioral judgments agree with objective finding.

Receiver Housing in open tip
Thin-Tubing in open tip
MacKensie, 2006
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Practical consideration?

• Amount of occlusion depends on the choice you
  make in coupling hearing aid to the earfind out
  for yourself (verify).

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3. Should the traditional prescriptive formulae
be used for fitting these open things?

• Is insertion loss a component used to derive
  ear canal targets for either the NAL or DSL?
• Remember there is none, or almost none
• Skip the gain.
• (Gus Mueller) Does the ear canal care how the SPL
  got therebody aid, oxen horn or OC fitting?

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3 cont. Should the traditional prescriptive
formulae be used for fitting these open things?

• Yet, the original prescriptions were based on
  closed cavity measures

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Here is what you can expect from major
manufacturers (from Bentler et al, 2006)
NAL TARGET
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Practical consideration?

• Whether the prescription provided audibility or
  not is the real issuefind out for yourself
  (verify).

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4. Speaking of gain, how do we measure these
things for quality control (i.e., coupler
measures)?

• Remember, 2-cc measures are only used to verify
  that the hearing aid is working as intended by
  the manufacturer (i.e., quality control)
• NEVER intended to predict human perfor- mance,
  and this is a good example of why not!

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Lets review couplers
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Lets review couplers
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One manufacturers option
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Practical consideration?

• Couplers are only to be used for quality control
  (ie, does the hearing aid work the way the
  manufacturer designed it to work in a
  coupler)find out for yourself (verify in the
  coupler and compare to the manufacturers
  strip).

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5. Should we do anything differently when we set
the MPO of this style of hearing aid?
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For starters . . . How do we select the MPO for a
standard fitting?

• Match it to the previous aids output?
• Add RETSPL to the patients frequency-specific
  LDLs (to take you to 2-cc specs for setting e.g.,
  the AGCo kneepoint)?
• Predict MPO based on the patients hearing loss
  using Pascoe, Dillon, or Bentler data?
• Use whatever shows up in the fitting software
• All of this assumes OC MPO should be (or is) the
  same as closed canal MPO.

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• if the RIC hearing aid uses a small receiver
  (MPO less than 110 dB SPL) in order to provide an
  open-ear fitting option, its fitting range will
  be more limited than a traditional BTE hearing
  aid that uses a larger receiver. (Kuk
  Baekgaard, 2008)

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Open versus closed RESR
PINKClosed GreenOpen
(Mueller, 2007)
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5 cont. Should we do anything differently when we
set the MPO of this style of hearing aid?

• Consider the loss, and the fact that if RITE, the
  MPO may be less due to smaller receiver
• Since the ear canal is open and therefore may
  resonate, it is possible the output will be
  higher.
• Outcome?
• Less
• More
• Maybe cancel each other out?

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5 cont. Should we do anything differently when we
set the MPO of this style of hearing aid?

• Consider the loss, and the fact that if RITE, the
  MPO may be less due to smaller receiver
• Since the ear canal is open and therefore may
  resonate, it is possible the output will be
  higher.
• Outcome?
• Less
• More
• Maybe cancel each other out?

Maybe
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Practical consideration?

• Since the smaller receiver used might limit the
  available output (in a coupler) but the open
  fitting might increase the output (in the real
  ear), the effect of the up-front effort is really
  not knownfind out for yourself (verify).

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6. Which segues to the next issue, CAN we use
probe mic measures to verify these open fits?
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6. Which segues to the next issue, CAN we use
probe mic measures to verify these open fits?
Yes!
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A quick review Methods of probe-mic
equalization

• Modified pressure (reference mic at ear) with
  concurrent equalization (most common method)
• Modified pressure with stored equalization (field
  equalized with reference mic at ear, but
  reference mic turned off during testing)
• Substitution method field equalized for point in
  space with patient absent (rarely used clinically)

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Potential equalization problemswith OC
fittings

• Sound leaking out of ear is picked up by
  reference mic
• Sound leaking out of ear may be greater than the
  input to reference mic from loudspeaker
• Reference mic thinks it is output from loud
  speaker, and so loudspeaker output to ear is then
  turned down
• The result will be less measured hearing aid
  output (and gain)

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Magnitude of problem probably related to

• Gain/output of hearing aid
• Feedback reduction algorithm
• Location of reference mic
• Proximity of reference mic to hearing aid mic
• Openness of the fit
• Residual ear canal resonance of the patient

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Example of concurrent (reference mic on) versus
stored equalization (reference mic off)
RM off
Mueller, 2006
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Different hearing aid and different probe-mic
equipment (REIG using pink noise at 65 dB SPL
input)
RM off
RM on
Mueller, 2006
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Same hearing aid using real speech input for REAR
(65 dB SPL)
Mueller, 2006
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If you happen to have equipment that doesnt
allow you to turn off the regulating mic

• You could simply assume that youre making 5 dB
  error around the peak of the REAR
• Or, you could try lowering the reference mic
  (recall that distance away from the point of
  leakage was one of the factors).

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• Testing conducted with the reference mic at the
  normal position and then with it lowered as far
  as possibleabout an inch difference (increasing
  the distance from ear)

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Measured REIG for Low versus High placement
of reference mic
GreenLow
PinkHigh
Mueller, 2006
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REAR for real speech using Low placement
Reference mic on versus off
To determine if low placement was providing
accurate measurements, we tested using the low
placement for reference mic on versus off.
Note that earcanal SPL didnt change.
Mueller, 2006
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Practical consideration?

• Either
• shut the reference mic off,
• lower the reference mic an inch or two or
• add 3-4 dB the measured gain/output
• Do not skip the verification stage!

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7. Can we get as much gain from the open fit
style?

• REMEMBER, you have the maximum vent effect
  working against you.
• Cant get as much LOW FREQUENCY gain, for sure
• but then you probably werent thinking of
  putting this on a low freq, flat, or severe loss
  anyway (right??)

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Practical consideration?

• How much gain do you want?
• Enough to make speech audible
• Enough to make the use content with loudness
• find out for yourself (verify)!

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8. But wait, I heard one manufacturer tell me I
get double gain because the direct paths and the
amplified paths add up (at least 6 dB)!

• (Think back to your acoustics classes)
• Power sum
• Pressure sum
• Requires matched phase and amplitude

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65 input
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85 input
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85 input
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55 input
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65 input
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75 input
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85 input
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Practical consideration?

• There is no free lunch

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9. Does the open feature interact with other
features?

• Feedback Manager Yes (good interaction!)
• DNR Not really if you consider that you cant
  reduce gain if there is none (and there typically
  isnt gain in the lows with open fittings)
• Directional Microphones Not really...at least
  where there is gain! Lets look at that feature
  in more depth.

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Two things we know affect directional advantage
Ricketts, 2000
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Two things we know affect directional advantage
Venting Effect
Ricketts, 2000
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Two things we know affect directional advantage
Ricketts, 2000
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Two things know to affect directional advantage
Port Alignment
Ricketts, 2000
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Summary Do we lose directivity?

• The most commonly asked question
• The bluntest answer
• Directivity is in the mic
• Functional directionality is in the gain
• No gain/No gain to reduce
• Each manufacturer may have different outcome

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10. Any human data on effectiveness?

• Doug MacKensie, Hearing Journal 5950-56 (2006)
• 20 normal hearing adults
• Looked at three premiere products
• Measured occlusion across the three products
• Rated sound quality of own voices (1very hollow
  10very natural across the three products
• Males and females presented separately
• No control (or closed) condition for comparison

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10. Any human data on effectiveness?

• Earl Johnson, Hearing Journal 5980-64 (2006)
• 504 dispensers responded to survey
• 13 questions
• Only two discussed here

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How do dispensers rate overall patient
satisfaction?
Johnson, 2006
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Reasons for dispenser choice of open fit
Very strong influence
No influence
Johnson, 2006
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10. Any human data on effectiveness?

• David Gnewikow and Meredith Moss, Hearing Journal
  5980-64 (2006)
• 338 adult hearing aid users at Bill Wilkerson
• 96 wore GNResound Air
• 54 ITEs
• 41 ITCs
• 40 CICs
• SADL, IOI-HA self-report outcomes

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SADL Negative Features significantly different
Gnewikow Moss, 2006
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IOI-HA Significantly different for Q1 and
Q3
Gnewikow Moss, 2006
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10. Any human data on effectiveness?

• Brian Taylor, Hearing Journal 5974-82 (2006)
• Study A Are experienced users wearing OC hearing
  aids more successful than experienced users of
  other hearing aids?
• Study B Are new users wearing OC hearing aids
  more successful than new users of other hearing
  aids?
• Self-report inventory

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Amplifon Satisfaction
Survey
Taylor, 2006
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Satisfaction
Taylor, 2006
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So what is the bottom line on open fitting?

• Appropriate for sloping or precipitous loss
• Appropriate for mild to even moderate losses
• Manufacturers working on algorithms to avoid
  nulls
• May not be as consequential as it looks
• Is the spectral or temporal disruption?
• No waiting on molds/shells
• Maintains high frequency directionality
• Eliminates occlusion sensation (for the most
  part)
• Sign me up!

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Questions?