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Diagnostic Audiology I > Hearing Aids I Final > Flashcards

Hearing Aids I Final Flashcards

1
Q

occlusion

A

blockage of ear canal

cartilaginous outer 1/3 - vibrates & trapped making own voice louder

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2
Q

microphone

A

converts acoustic to electrical

  1. sound energy enters inlet
  2. creates vibrations on diaphragm
  3. creates movement to & from electrate
  4. generates electronic sinal
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3
Q

low cut

A

inbuilt imperfection of microphone

very low sounds will be dampened due to length of wave

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4
Q

resonance

A

characteristic of cavity
vibrate at max amplitude due to dimentions
4k-5kHz in mic (helmholz)

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5
Q

microphone limitations

A 
low cut
resonance
easily damaged
sensitive to noise
wind noise
internal noise
adds distortions
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6
Q

omni vs directional mic

A

directional - more focus front, cardiod, reduces low freq sounds
omni - 360, sports, kids,

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7
Q

amplifier & parts

A

takes battery power & amplifies signal

diodes, integrated circut (IC), capacitors

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8
Q

peak clipping

A

done primarily by amplifier
sound input above max capacity of HA
adds distortions
(max amp range determined by battery power)

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9
Q

two types of peak clipping

A

symmetrical - odd harmonics clipped

asymmetrical - odd & even harmonics clipped

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10
Q

other distortions

A

complex sound

combination tones

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11
Q

digital hearing aids vs. analog journey

A

digital: M - AMP [analog - digital (numbers) - analog (electric)] R
analog all electrical signal

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12
Q

receiver

A

electric to acoustic transducer
resonance in cavities - all designs prone to resonance
solution - acoustic damper - smoothes peaks dur to resonance
cannot use damper in thin tube - moisture

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13
Q

ALD’s why?

A

hearing aid limits [ noise, distance, reverb ]

benefits everyone

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14
Q

classroom acoustics

A

unoccupied room <35dB SPL

reberb time

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15
Q

RECD

A

real ear coupler difference
use especially for pediatrics
could be dangerous

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16
Q

aural rehab

A
  1. case history
  2. candidacy
  3. HA fitting [verification or functional gain measurements]
  4. Validation
  5. Counseling/Aud training
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17
Q

cavities that simulate ears

A

coupler & ear simulator

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18
Q

limitations of ear simulators

A

delicate
expensive
good with low & high frequencies (better simulate ear)

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19
Q

ANSI Measurements

A

OSPL avg (HFA), OSPL 90, HFA at 50, THD, EIN

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20
Q

why OSPL 90?

A

90 - hearing aid gets saturated

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21
Q

EIN

A

equivalent input noise
only issue if TH in low f good
internal noise

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22
Q

THD

A

Percent not signal

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23
Q

Verification - insertion gain methods

A
  1. Speech mapping

2. Pure tones

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24
Q

dB SPL

A

dB HL+RETSPL+RECD

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25
Q

speech mapping

A

meet 90% of targets

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26
Q

pure tone verification (insertion gain)

A

REUG - measures gain of ear canal w no amp
REAG - with aid
REIG - REAG-REUG

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27
Q

limitations to insertion gain methods

A
  1. patient cooperation
  2. audiologist confidence
  3. cost
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28
Q

Functional Gain Measurements

A

unaided & aided gain through sound field testing

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29
Q

Advantage to FGA

A

patient’s voice heard

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30
Q

resonance of adult canal

A

2600Hz, higher in kids up to 4k

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31
Q

3 types of coupling systems

A
  1. earmold
  2. earshell
  3. domes (modulated)
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32
Q

earmold

A

deep impressions (fit) - beyond second bend & helix lock
severe to profound losses
good for pediatrics
good hold

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33
Q

advantages of deep fit

A 
better retention
closer to TM: better quality
avoids leakage & feedback
avoid occlusion effect
better self perceived voice
34
Q

deep fit limitations

A
  1. helix lock insertion with dexterity issues
  2. requires good impression skills
  3. pain insertion & removal
  4. curvy ear canals
35
Q

modifications of coupling

A
  1. vent
  2. dampers
  3. sound bore
36
Q

vent

A

any opening that allows air to move in & out of canal
smaller = lower frequencies can escape
larger= more higher frequencies can escape

37
Q

adv to vents

A
  1. occlusion affect - allows sounds out (315Hz)
  2. helps high frequency HL - taking out low frequencies will prevent upward spread of masking
  3. moisture control
38
Q

Disadvantages to vents

A
  1. feedback
  2. low frequency hearing loss not rec (low cut)
  3. less directionality
  4. lower OSPL 90
  5. direct sound
39
Q

dampers

A

800-2500Hz removed for BTE

1500-3500 Customs

40
Q

Sound bore

A

horn & reverse horn

41
Q

horn effect

A

wider opening at canal - changes resonance, +6-+12 in high frequencies

42
Q

reverse horn

A

narrower at canal
reduces amp in high frequency
avoid downward spread of masking (high masking low)

43
Q

compression threshold

A

where compression begins (gain changes)

44
Q

knee point

A

any point compression ratio changes

45
Q

compression ratio

A

change in input : change in output

46
Q

limiting

A

CR = 8:1 or more slowly increasing gain before saturation

47
Q

peak clipping vs. limiting

A

peak clipping is linear at saturation

limiting is nonlinear lower distortion

48
Q

expansion

A

less gain to soft sounds

CR: 1:1.1 or more

49
Q

attack time

A

time required to apply compression

50
Q

release time

A

time required to release compression

51
Q

overshoot

A

slow attack time: beyond required output

52
Q

TILL

A

Treble increase in low levels

more compression in high intensity high frequencies

53
Q

BILL

A

Bass increase in low levels

more compression in low frequency high intensity sounds

54
Q

types of compression

A
  1. low level - more compression in soft sounds, loud linear
  2. wide dynamic range - compression at all levels
  3. high level - more compression in loud sounds, soft sounds more linear
55
Q

compression benefits

A
  1. safe, comfort
  2. SNR improvement
  3. reduces intesity difference bt sp sounds
  4. normalizes loudness
  5. may improve intelligibility
56
Q

compression limitations

A
  1. distortion
  2. benefits not as high older users - linear - power
  3. AT/RT variation
57
Q

bands

A

gain for specific frequencies

58
Q

channels

A

compression ratio for specific frequency regions

59
Q

open fitting issues for directionality

A
  1. low frequency leakage
  2. direct sound
  3. creates third source of sound
60
Q

directional benefit factors

A
  1. directivity of hearing aid (internal & external delay)
  2. reverberation
  3. distance of noise & speaker
61
Q

listening situations

A
  1. speech close, noise far
  2. speech far, noise close
  3. noise close, speech close
  4. speech far, noise far (same direction) - directivity not helpful
62
Q

SNR benefit from directionality

A

2-3dB

63
Q

directional processing happens when

A

first - affected by compression

64
Q

compression affect on directionality

A

reduces front-back difference: reduces SNR benefit from front, helps back

65
Q

localization & compression

A

cues are reduced by compression - reduces interaural time difference

66
Q

directivity disadvantages

A 
low cut responses
target sounds from back or side
greater internal noise
reduced localization
wind noise
requires closed fitting
67
Q

noise reduction

A

winer filter

spectral subtraction

68
Q

noise characteristics

A 
low f
random
low intensity
less variation
narrow modulation depth
69
Q

winer filter

A

reduce gain in poor SNR channel

70
Q

spectral subtraction

A

mic analyzes signal & estimates noise & eliminates

71
Q

feedback reduction

A

closed fitting

  1. gain reduction
  2. phase cancellation
  3. path cancellation
72
Q

gain reduction

A

reduce overall gain or in specific region

73
Q

phase cancellation

A

detects where feedback happens, alternate wave generated to cancel

74
Q

path cancellation

A

feedback detector cancels signal before getting to the mic

75
Q

frequency lowering

A
  1. compression

2. transposition

76
Q

frequency compression

A

reduces frequency separation

77
Q

frequency transposition

A

uses existing frequencies

78
Q

free field

A

no reverb

79
Q

diffuse field

A

exert substantial effects on waves, equally distributed

80
Q

quasi - free

A

minimal reverb moderate affect

81
Q

signals in sound field

A

pure tones - standing waves
warbles (FM)
narrow band noise

Diagnostic Audiology I (2 decks)

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