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AUDE 5450 AMP 1 > Exam 2: Microphones > Flashcards

Exam 2: Microphones Flashcards

(117 cards)

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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
reduces wind using acoustic resistance
wind screen over a mic
26
What is the dynamic range of an analog hearing aid microphone? Of a digital hearing aid microphone?
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)
27
what is mic dynamic range
loudest & quietist acoustic input a mic can collect & convert to a usable electric signal
28
what is front end distortion
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
29
Why do musicians prefer analog HA’s?
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
30
Distortion in analog happens with input
>/= 115 dB SPL (0-115, anything louder sounds distorted)
31
Distortion in digital mic happens with input
>/= 96 dB SPL (0-96, anything louder sounds distorted)
32
why do digital hearing aids have a lower microphone dynamic range
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 \
33
how is front end distortion managed in digital hearing aids
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
34
Move form 16 bit to 19 bit HA in other digital devices allowing_____ dB dynamic range
108
35
what is the ideal distance for sound collection
w/in 6 ft
36
what does +10 dB SNR mean
desired signal is 10 dB louder than the undesired signal ideal listening
37
what is 0 dB SNR
desired and undesired signals are equally as loud
38
what is -10 dB SNR
desired speech is -10dB SOFTER than the undesired signal undesired is 10 louder than undesired
39
what is ideal signal to noise ratio is for people with normal hearing
+2 SNR
40
Describe the impact of microphone distance on SNR
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
41
what is PT complaint we encounter in regards to mic distance on SNR
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
42
What is the ideal distance for sound collection?
Ideal mic sensitivity w/in 6 ft
43
what is SNR
difference in volume bw desired and undesired signal
44
Which frequency range is associated with undesired background noise?
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
45
what is a null
refers to point of max attenuation where mic stops collecting sound
46
0 deg azimuth
right in front center
47
90 deg azimuth
to the right if ha is on the right
48
180 deg azimuth
directly behind
49
270 deg azimuth
to the left if ha is on the right
50
what is an omni directional mic
mic that collects sounds equally from all directions
51
what is a directional mic
mic focuses sound collection towards one azimuth and attenuates sensitivity from others
52
what is a polar plot
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
does a null only attenuate horizontally
NO does so up and down and around
54
describe cartiod polar plot
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
describe hyper-cartiod polar plot
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
describe super-cartiod polar plot
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
describe bi-directional polar plot
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
Polar pattern is a sphere on paper
omnidirectional
59
Has equal output regardless of orientation to sound source
omnidirectional
60
Can pick up a group
omnidirectional
61
Cannot be aimed at one source to favor one source over another
omnidirectional
62
Most sensitive to sound sources in the front of mic and least sensitive to sound sources directly behind
cartiod unidirectional mics
63
a lot of signal collection at the front Nulls are on the side with some collection at the rear
hyper cartiod
64
more sensitive to sound sources that are directly behind the mic than hyper signal collection at the front
super-cartiod
65
Equally sensitive to sounds from the front and back and least sensitive to the sides
bi directional
66
no null angle di = 0dB
omnidirectional looks like a circle
67
+/- 90 deg null angle DI = 4.8dB
bidirectional dipole looks like a snowman
68
180 deg null angle DI = 4.8 dB
cardioid looks like a heart
69
+/- 120 deg null angle DI = 5.8dB
supercardioid looks like a mushroom
70
+/-110 deg null angle DI = 6.0dB
hypercardioid looks like our face scrubber
71
How does a directional mic use in-phase and out-of-phase signals to create a polar plot null
in phase = analog electric signal out of phase = stops diaphragm movement & doesn't create an analog electric signal
72
in phase signals
they move the diaphragm creating an analog electric signal
73
out of phase signals
they STOP diaphragm movement not creating an analog electric signal
74
Define directional mic roll-off
Happens when directional mics are turned on Directional roll off = low frequency output is reduced
75
why is LF output reduced with directional mic roll off
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
What causes roll off and how is it managed?
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
what is PT complaint of roll off we encounter
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
gives us clarity & understanding
HF
79
gives us volume/loudness and when taken away voices get softer
LF
80
what is an equilzation filter used to fix roll off
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
would you add equalization filters if PT has normal/near normal LF hearing
no do not need to add bass boost
82
would you add qualization filters if PT has HL in LF >/= 50dB
yes add bass boost
83
what is the amount of roll off based on
spacing of the mic ports
84
closer mic ports =
more LF attenuation
85
smaller devices roll off _____ frequencies
MORE
86
further the mics are =
less LF attenuation
87
what are directional mic limitations
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
what is the importance of electret mic matching and calibration
they stop working if they fall out of calibration sound traveling horizontally shortens time delay and directionality no longer functions
89
what is the importance of tubing for calibration of electret mic calibration
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
sensitivity difference > _____ dB decreases mic's DI
1
91
front/bac mics have to be level within _____ deg otherwise DI decreases significantly
20
92
what happens in microphone drift
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
how does mic drift occur
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
why would we choose telecoil over BT
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
benefits of telecoil
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
in a looped environment, what telecoil position is needed
verticle
97
if using telecoil for phones, what position is needed
horizontal
98
pick-up room loop signals
vertical telecoil position
99
pick-up telephone signals
horizontal telecoil position
100
Describe the principle of induction
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
how does a telecoil work
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
What produces electromagnetic signals?
cell phones hardwired phones (best signals) microwaves flip phones computers
102
moving-coil microphones — work via electromagnetic induction
dynamic mic
103
capacitor microphones — contain a thin, stretched conductive diaphragm positioned close and parallel to a metal back plate
condensor mic
104
full intensity for verticle coil
verticle silenced horizontally
105
full intensity for horizontal coil
horizontal silenced vertically
106
what is the purpose of a listening check
it is a subjective eval of a hearing instrument will only pick up significant device malfunction
107
what are the LING 6 sounds and why are they used
ah, ee, oo, ss, sh, mm used to test across a frequency range
108
how is a HA linear
If there is no change in amplitude from soft to loud ling sounds
109
how is a ha nonlinear
mplitude is louder for soft and softer for loud ling sounds
110
how do you determine a directional mic
If you turn HA 360 deg and sound attenuates behind HA If it doesn’t attenuate from behind = omnidirectional
111
dual directional mics consist of
2 omnidirectional mics
112
what are the components of dual directional mics
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
2 mic sensitivities HAVE TO MATCH (calibrated) at ALL frequencies for effective phase cancellation
true
114
How do time delays result in a directional mic? Why do we have internal and external delays?
115
mild HL
AGC-i
116
severe HL
AGC-o

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