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AUDE 5450 AMP 1 > Exam 2: Microphones > Flashcards

Exam 2: Microphones Flashcards

1
Q

how does a carbon mic work

A

sound wave comes in and hits diaphragm
compression of diaphragm pushes carbon balls together creating a positive voltage flow
decompression causes diaphragm to push back out making a negative voltage flow and carbon balls released
the compression and decompression of carbon balls creates a + and - analog electrical signal

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2
Q

what is viscosity

A

how easy material flows
thickness

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3
Q

high viscosity

A

stretches aperature of canal
want this for a tight fitting mold

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4
Q

low viscosity

A

runny
doesn’t change aperature of ear canal
good for earplugs or making deep impressions

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5
Q

what is stress relaxation

A

ability for ear impression to go back to shape after removal from ear canal

silicone is high stress

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6
Q

what is compression ratio

A

shrinkage over a 7 day period

low shrinkage is silicone

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7
Q

what is shore value

A

after cure hardness, stability in the impression box

low shore value is methyl
high is silicone

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8
Q

Describe the importance of stretching the aperture

A

stretching this area for a well fit earmold
if we do not do this we get an uncomfortable earmold because the skin rubs against the plastic

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9
Q

Define temporal resolution and the auditory processes which support it.

A

AS ability to detect small time related changes in acoustic stimuli over time
Good auditory temporal resolution processing is needed to understand speech in noise
temporal resolution

gap detection: spoon vs soon, identifies syllables, start or end of words & sentences

phonemic duration: can vs can’t, similar words are differentiated by differences in duration & order

temporal ordering: keep order sounds enter as (boots vs boost)

suprasegmentals: provide us with meaning, patterns of stress, intonation and rhythm

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10
Q

Explain binaural loudness summation. Its suprathreshold benefits and how this benefit supports hearing aid fitting strategies.

A

improvement in hearing threshold when compared to monaural hearing
+3 at threshold, +6 at 50dB HL, & +9 at 90 dB HL

Results in PT perceiving greater loudness with bilateral devices
Less gain is needed to reach comfortable listening levels
Can fit a PT with less loudness in order for them to hear the words

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11
Q

What does an IP rating indicate? What does a 6/8 IP rating suggest?

A

what we look at to decide is the device dust and moisture resistance

IP68
Dust light
Protects against long periods of liquid immersion

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12
Q

Describe the cause of the occlusion effect (OE) and associated patient complaints. Describe the degree of LF threshold loss associated with OE concerns

A

Common complaint is when LF threshold is better than 50dB HL
Voice sounds boomy, hollow, or in a barrel
This is caused by insufficient venting and/or insufficient canal length
Most noticeable w/ vocalizations of ee and oo
Baby jeanie is teeny tiny
Skull transduces LF energy generated by the voice. The bc signal becomes trapped in the canal

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13
Q

Describe two management techniques used to reduce OE

A

vent size: venting allows LF environmental sounds to travel directly to eardrum without amp

stabalize devie in bony canal: extend end of canal into bony portion to reduce OE vibrations

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14
Q

Describe the impact vent size has on high frequency output

A

Larger vent = less HF output you get from the HA

When HF output energy increases it can overcome the vent’s inertia and escape the canal through the vent. This creates a feedback loop limiting the gain added to HF signals

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15
Q

Describe the piezoelectric effect and the limits of piezoelectric microphones

A

what was attached to backplate was a salt crystal and if you create flow of current threw this and twisted it, the twist and bend would create a + and - electrical current flow
*same mic, have salt crystal to replace carbon balls
problem
high temp & humidity would stop the current flow - HA died quickly (>110 deg)
didn’t last long

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16
Q

Be prepared to explain how a microphone transduces an acoustic signal to an analog electric signal

A
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17
Q

Compare & contrast Electret microphones and MEMS Microphones how do they function? memes vs electric
know differences? why is one better than the other? explain

A

MEMS: more stable, doesn’t absorb moisture, doesn’t drain bettery due to smaller space bw backplate and diaphragm, stability remains even with harsh environment donditions (-40 to 185 deg)

ECM: less stable due to susceptibility of humidity, moisture, dirt, debri degrading the sensitivity of mic over years, diaphragm can absorb moisture, backplate loses charge at high temps (110), glue breaks down on the diaphragm due to environmental conditions

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18
Q

Define microphone sensitivity

A

Mic sensitivity (contemporary): ability of the mic to pick up sounds

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19
Q

What input frequency range can a microphone collect?

A

Sensitive collection from <100 Hz to as high as 15000 Hz

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20
Q

a mic can collect wide range of frequencies than what appears on HA’s final frequency response

A

true

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21
Q

Differentiate the causes of acoustic noise from the causes of electrical noise.

A

Anything that causes diaphragm to move will transduce into an electrical signal

Acoustic - gasses & air flowing around us goes into sound port and moves the diaphragm
Electrical - comes from circuits in HA that are after the mic in ha

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22
Q

What is an acceptable intensity of a mics internal noise floor?

A

Noise floor of best HA mic is ~ 25 dB SPL
Higher noise floor = more noise to PT

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23
Q

what is internal noise floor

A

This is a measurement of both acoustic and electrical noise

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24
Q

wind noise output is greatest where

A

in LF (>/= 80dB SPL depending on direction)

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25
Q

reduces wind using acoustic resistance

A

wind screen over a mic

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26
Q

What is the dynamic range of an analog hearing aid microphone? Of a digital hearing aid microphone?

A

Analog mic = 115 dB SPL (can collect input signals up to this before input distortion

Digital mic = ONLY 96 dB SPL (anything > results in input distortion)

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27
Q

what is mic dynamic range

A

loudest & quietist acoustic input a mic can collect & convert to a usable electric signal

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28
Q

what is front end distortion

A

Front end distortion occurs when sounds picked up by the mic exceeds its dynamic range
A mic can only take so much intensity before distortion occurs
Complaints are due to loud music or the user’s own voice

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29
Q

Why do musicians prefer analog HA’s?

A

better replicate original signal
they like things loud and as long as it is below 115 it is picked up and nice and clearly replicated

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30
Q

Distortion in analog happens with input

A

> /= 115 dB SPL (0-115, anything louder sounds distorted)

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31
Q

Distortion in digital mic happens with input

A

> /= 96 dB SPL (0-96, anything louder sounds distorted)

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32
Q

why do digital hearing aids have a lower microphone dynamic range

A

range difference b/w analog & digital HA’s
This is due to analog to digital converter (ADC)
Used to transduce an analog electric signal to a digital signal
16 bit ADC supplies a 0-96 dB dynamic range and louder sounds are peak clipped
\

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33
Q

how is front end distortion managed in digital hearing aids

A

Mic has dynamic range
Analog could be 0-115
Digital to 96 - starts distorting above it
If we shift the range of mic in loud situations you can collect loud sounds without peak clipping but can’t collect soft
If we shift range in soft situations you can collect soft sounds but not loud ones anymore

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34
Q

Move form 16 bit to 19 bit HA in other digital devices allowing_____ dB dynamic range

A

108

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35
Q

what is the ideal distance for sound collection

A

w/in 6 ft

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36
Q

what does +10 dB SNR mean

A

desired signal is 10 dB louder than the undesired signal

ideal listening

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37
Q

what is 0 dB SNR

A

desired and undesired signals are equally as loud

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38
Q

what is -10 dB SNR

A

desired speech is -10dB SOFTER than the undesired signal

undesired is 10 louder than undesired

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39
Q

what is ideal signal to noise ratio is for people with normal hearing

A

+2 SNR

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40
Q

Describe the impact of microphone distance on SNR

A

SNR becomes poorer as distance bw mic and desired signal increases
Closer to the mic the louder it is over the noise
Improved SNR
Further it is from the mic harder it is to hear over the noise because noise becomes louder
Reduced SNR

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41
Q

what is PT complaint we encounter in regards to mic distance on SNR

A

cannot hear spouse talking from another room
mic cannot pick up sound ideally
6 ft is furthest is can reach - shaking hands is the closest you should be with ideal amplification

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42
Q

What is the ideal distance for sound collection?

A

Ideal mic sensitivity w/in 6 ft

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43
Q

what is SNR

A

difference in volume bw desired and undesired signal

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44
Q

Which frequency range is associated with undesired background noise?

A

energy of noise is in lfs and a lot of noise that is louder than speech at 250 up to 1500 Hz
speech signal
all energy for intelligibility is in the highs
Complaint of noise comes from amp signals around 1200-1500 Hz and above this not a lot of noise masks speech above this

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45
Q

what is a null

A

refers to point of max attenuation

where mic stops collecting sound

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46
Q

0 deg azimuth

A

right in front
center

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47
Q

90 deg azimuth

A

to the right if ha is on the right

48
Q

180 deg azimuth

A

directly behind

49
Q

270 deg azimuth

A

to the left if ha is on the right

50
Q

what is an omni directional mic

A

mic that collects sounds equally from all directions

51
Q

what is a directional mic

A

mic focuses sound collection towards one azimuth and attenuates sensitivity from others

52
Q

what is a polar plot

A

How the mic responds to sound from different directions

shows sensitivity and attenuation (null) at different angles

shows where mic collects sounds and stops collecting sounds at different points

53
Q

does a null only attenuate horizontally

A

NO

does so up and down and around

54
Q

describe cartiod polar plot

A

mic collects sound from the front but attenuates all sound at the rear
Looks like a heart
Collects max at 0 deg but at 270 and 90 starts to attenuate and at 180 there is a null

55
Q

describe hyper-cartiod polar plot

A

a lot of signal collection at the front
Nulls are on the side with come collection at the rear
Max sensitivity at 0 deg, some from behind with nulls at 120 deg and 240 deg

56
Q

describe super-cartiod polar plot

A

similar sound collection at front, back is broadened allowing more signal from back
Max sensitivity at 0, more from behind than hyper, still null at the sides
Better reduction of noise

57
Q

describe bi-directional polar plot

A

attenuation is happening at 90 and 270 deg with sensitivity at front and back equally
Use this when driving a car to hear what is in front and behind you but not the window noise beside you

58
Q

Polar pattern is a sphere on paper

A

omnidirectional

59
Q

Has equal output regardless of orientation to sound source

A

omnidirectional

60
Q

Can pick up a group

A

omnidirectional

61
Q

Cannot be aimed at one source to favor one source over another

A

omnidirectional

62
Q

Most sensitive to sound sources in the front of mic and least sensitive to sound sources directly behind

A

cartiod unidirectional mics

63
Q

a lot of signal collection at the front
Nulls are on the side with some collection at the rear

A

hyper cartiod

64
Q

more sensitive to sound sources that are directly behind the mic than hyper
signal collection at the front

A

super-cartiod

65
Q

Equally sensitive to sounds from the front and back and least sensitive to the sides

A

bi directional

66
Q

no null angle
di = 0dB

A

omnidirectional
looks like a circle

67
Q

+/- 90 deg null angle
DI = 4.8dB

A

bidirectional
dipole
looks like a snowman

68
Q

180 deg null angle
DI = 4.8 dB

A

cardioid
looks like a heart

69
Q

+/- 120 deg null angle
DI = 5.8dB

A

supercardioid

looks like a mushroom

70
Q

+/-110 deg null angle
DI = 6.0dB

A

hypercardioid
looks like our face scrubber

71
Q

How does a directional mic use in-phase and out-of-phase signals to create a polar plot null

A

in phase = analog electric signal
out of phase = stops diaphragm movement & doesn’t create an analog electric signal

72
Q

in phase signals

A

they move the diaphragm creating an analog electric signal

73
Q

out of phase signals

A

they STOP diaphragm movement not creating an analog electric signal

74
Q

Define directional mic roll-off

A

Happens when directional mics are turned on
Directional roll off = low frequency output is reduced

75
Q

why is LF output reduced with directional mic roll off

A

when directional is on, attenuation occurs naturally including LF output and because they are wide and broad, LF are more likely to arrive out of phase to the mic making a loss of LF output

76
Q

What causes roll off and how is it managed?

A

LF output is reduced causing a6dB/octave LF roll-off of intensity perceived by PT as reduced volume

fixed with equalization filters that add LF energy to replace the attenuated output signal

77
Q

what is PT complaint of roll off we encounter

A

When PT goes into noise, background noise is attenuated but volume also drops too
This is because LF output gives us volume/loudness and when taken away voices get softer

78
Q

gives us clarity & understanding

A

HF

79
Q

gives us volume/loudness and when taken away voices get softer

A

LF

80
Q

what is an equilzation filter used to fix roll off

A

add LF energy to replaced the attenuated output signal
Bass boost in softwares to counteract this natural issue with mics
If PT has normal/near normal LF hearing, do not need to add bass boost but if they have HL in LF >/= 50 then add it

81
Q

would you add equalization filters if PT has normal/near normal LF hearing

A

no do not need to add bass boost

82
Q

would you add qualization filters if PT has HL in LF >/= 50dB

A

yes add bass boost

83
Q

what is the amount of roll off based on

A

spacing of the mic ports

84
Q

closer mic ports =

A

more LF attenuation

85
Q

smaller devices roll off _____ frequencies

A

MORE

86
Q

further the mics are =

A

less LF attenuation

87
Q

what are directional mic limitations

A

real world benefit DI of ~2-3 dB
Larger vent size = lower DI
directional mic is less effective with moving sound or brief and sudden sounds
visual cues help understanding
can the PT use it correctly and understand how it works

88
Q

what is the importance of electret mic matching and calibration

A

they stop working if they fall out of calibration
sound traveling horizontally shortens time delay and directionality no longer functions

89
Q

what is the importance of tubing for calibration of electret mic calibration

A

if the tubing or receiver length is too short or long the HA mic will not sit parallel to the floor anymore losing the external time delay

90
Q

sensitivity difference > _____ dB decreases mic’s DI

A

1

91
Q

front/bac mics have to be level within _____ deg otherwise DI decreases significantly

A

20

92
Q

what happens in microphone drift

A

When something plug the port, the sound coming in from the back doesn’t reach the diaphragm which doesn’t cause an out of phase signal which means no directionality occurs

93
Q

how does mic drift occur

A

High temps reducing mic sensitivity

Moisture causes damage to diaphragm tension ring

cerumen/debris clog mic port
Need cleaned/checked every 6 months
Electroacoustic measures are done to verify directional mic performance

94
Q

why would we choose telecoil over BT

A

BT is expensive, drains battery life, costly

telecoil costs around $50, cheaper, already in most BTE’s just have to teach PT’s how touse it

95
Q

benefits of telecoil

A

inexpensive
no external power source needed because magnetic field generates its own
no telephone feedback because mic is off
improved SNR on phone or in loop room

96
Q

in a looped environment, what telecoil position is needed

A

verticle

97
Q

if using telecoil for phones, what position is needed

A

horizontal

98
Q

pick-up room loop signals

A

vertical telecoil position

99
Q

pick-up telephone signals

A

horizontal telecoil position

100
Q

Describe the principle of induction

A

Induction principle: takes electromagnetic signals and transduces it into an electrical sine wave
Electromagnetic signals move a magnet with a copper coil
This movement bw copper coil & magnet turns electromagnetic signals to a +/-analog electrical signal without adding an additional power source

MIC is turned off

101
Q

how does a telecoil work

A

tight copper wire coil stores energy in form of magnetic field
induction coilds pick up electromagnetic sine waves that come from telephones or telecoil loops
electromagnetic signal pushes & pulls magnet in copper
signal is then transduced to an analog electrical signal

101
Q

What produces electromagnetic signals?

A

cell phones
hardwired phones (best signals)
microwaves
flip phones
computers

102
Q

moving-coil microphones — work via electromagnetic induction

A

dynamic mic

103
Q

capacitor microphones — contain a thin, stretched conductive diaphragm positioned close and parallel to a metal back plate

A

condensor mic

104
Q

full intensity for verticle coil

A

verticle
silenced horizontally

105
Q

full intensity for horizontal coil

A

horizontal
silenced vertically

106
Q

what is the purpose of a listening check

A

it is a subjective eval of a hearing instrument
will only pick up significant device malfunction

107
Q

what are the LING 6 sounds and why are they used

A

ah, ee, oo, ss, sh, mm
used to test across a frequency range

108
Q

how is a HA linear

A

If there is no change in amplitude from soft to loud ling sounds

109
Q

how is a ha nonlinear

A

mplitude is louder for soft and softer for loud ling sounds

110
Q

how do you determine a directional mic

A

If you turn HA 360 deg and sound attenuates behind HA
If it doesn’t attenuate from behind = omnidirectional

111
Q

dual directional mics consist of

A

2 omnidirectional mics

112
Q

what are the components of dual directional mics

A

External delay is the same
Internal delay is replaced with a calibrated electronic delay in an algorithm of the back mic that is subtracted from the front mic output

113
Q

2 mic sensitivities HAVE TO MATCH (calibrated) at ALL frequencies for effective phase cancellation

A

true

114
Q

How do time delays result in a directional mic?
Why do we have internal and external delays?

A
115
Q

mild HL

A

AGC-i

116
Q

severe HL

A

AGC-o

AUDE 5450 AMP 1 (7 decks)

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