midterm 1 Flashcards
input
intensity of acoustic signal entering the device
-as dB or loudness descriptor in the software
gain
amount of amplification added to the input signal
-the dB added to each frequency range and the input level
output
intensity of the signal thats delivered to the ear canal
-the signal arriving at the tympanic membrane
equation to describe what is arriving at the tympanic membrane
dB input + dB gain = dB output
dB is always within _______
dB SPL
-remember there are different conversion factors but these are not intended for everyone
acoustic horn principle
as a signal arrives to a large horn and is channeled down to a smaller space, this causes the signal to increase (SPL increases)
-these horns amplify sound when waves are reflected into a narrower area
what are the acoustic benefits with hand cupping
-can add clarity to consonants
-can add 5-10 dB of gain
-can attenuate acoustic signals arriving from the rear
-effective for some with borderline hearing/very mild HL around the 1500 Hz area
explain the carbon microphone process and how it goes from acoustic signal to an electrical signal
the acoustic signal arrives to the microphone and vibrates the diaphragm which gets compressed and when it moves inward, the carbon balls get pushed together (positive voltage flow). the sound waves goes outward and will bring the diaphragm out with the carbon balls (negative signal)
-this back and forth direction results in an electrical wave that matches the input acoustic signal
what is the purpose of the receiver
converting that electrical signal back to an acoustic signal for the ear to hear
-after it becomes an electrical signal it will go through the receiver and will become an acoustic signal again
quick overview of a carbon microphone
sound wave → arrives at microphone → pushes on diaphragm and compresses carbon balls → creates a analog signal as the sound wave continues → creates a analog electric signal → receiver picks up the electric signal and makes it back to an acoustic wave
importance of a vacuum tube amplifier
this was the first HA with an amplifier that added gain to increase the amplitude of the analogous electrical signal
-vacuum tube amplifier was the first one created/used
transistors
electrical component used to increase current flow of the signal
-amplifies the amplitude of a signal
resistors
electrical component used to add or remove resistance to the flow of the current
-modifies the output
-can add more or less of certain frequencies
potentiometer
small resistors that the amount of control used can modify the output signal in the ear analog HA
function of the potentiometer
controls the flow of the signal
-can increase clarity, output and can add in certain frequencies
-can decrease output
-can reduce feedback
3 impression materials
addition cured silicone, condensation cured silicone and methyl-methacrylate
viscosity
how easily it flows before it is cured
-high will provide resistance during flow, will stretch the aperture
-low is runny, no resistance, no stretch to aperture
shore value
if it will remain its shape or will it be altered after its cured
-high or low shore value (will stay or will change)
stress relaxation
the materials ability to return to shape after removal from canal
-high and low stress relaxation (bounces back and does not bounce back)
contraction ratio
looking at the shrinkage over a 7 day period
-will it be the same or does it shrink
addition cured silicone
low viscosity, high shore value, high stress relaxation, will not shrink
condensation cured silicone
high viscosity, high shore value, high stress relaxation, will not shrink
methyl-methacrylate
medium viscosity, low shore value, low stress relaxation, will shrink
what is the ideal depth for an ear mold impression
2 mm beyond the second bend
risk factors within patient Hx
-immunocompromised or diabetic (infection risk)
-therapeutic blood thinner (bleeding risk)
-Hx of ear surgery (potential ear canal malformation)
-any allergies to silicone, lubricant ingredients, etc.
risk factors based on otoscopy
-collapsing canal (may limit depth)
-perforation or PE tubes
-malformations
-thick hair growth
-piercings (need to cover)
what is the purpose of the open jaw impression
they can increase the size of the aperture for a snugger fit
-the condyle of the mandible moves forward and will pull the anterior canal wall with it
how to treat bleeding post impression
apply pressure to the wound for 10 minutes using a large cotton otoblock soaked in a vasoconstrictor
-recheck a week later
what frequencies contribute the most to speech intelligibility
95% of the information we need to understand a word comes between 500-5000 Hz
-within this, 2000 Hz has the most contribution
linear amplification
adds equal amount of gain to soft, moderate and loud input levels
-does not take the dynamic range into account
nonlinear amplification
uses compression to increase the intensity of soft signals while decreasing the intensity of loud signals
-output signal is shaped into a reduced dynamic range by adding more gain to soft sounds and less gain to loud sounds
describe the abnormal loudness growth function
individuals with HL can have troubles with hearing soft sounds, but loud sounds are equally as loud as normal hearing
-this the is premise behind the abnormal loudness growth
-they have limited/no hearing in low frequencies than perceive louder sounds at that level, results in a reduced dynamic range
how can HL result in an abnormal loudness growth
with sensory loss and OHC damage, this can result in the loss of amplification of those soft signals
how do HAs manage frequency specific variations in a persons dynamic range
they can alter soft sounds to add gain and can remove gain from loud sounds
-can be done through compression ratios (CR) that can shape the output signal into a reduced dynamic range
frequency resolution
refers to the auditory system ability to detect discrete frequencies in the cochlea
how does frequency resolution change with SNHL
when OHCs can no longer amplify soft inputs, the basilar membrane can no longer produce the sharp tuning curve, which creates a difficulty hearing in noise
-the primary signal is no longer enhanced and get tangled in with background noise
-these sharp peaks supplies the frequency resolution we need for speech intelligibility
temporal resolution
the auditory systems ability to detect small time related changes in the acoustic stimuli over time
-the ability to rapidly pick up and identify different timing elements and processes in order for speech to be intelligible
what processes support temporal resolution
-gap detection (spoon vs. soon)
-phonemic duration (the length of words/statements/sounds)
-temporal ordering (boots vs. boost)
-suprasegmentals (patterns of stress, intonation and rhythm)
temporal envelope
slow overall change in intensity over time
-the outline, low detail
-supplies speech intelligibility in quiet
temporal fine structure
rapid oscillations within the temporal envelope
-detail, more information
-supports detection of signals in noise
what are some benefits of spatial hearing
-makes sound localization possible
-able to focus on one conversation
-can unmask sounds that are otherwise obscured by noise
interauarl level differences (ILD)
differences in loudness arriving to one ear and the other based on where it is coming from
-relies on higher frequencies
interauarl timing differences (ITD)
differences in timing delays of the signal arriving to one ear and the other ear
-relies on lower frequencies
head related transfer function (HRTF)
pinna and head affects
-explaining how sound can arrive and be altered in various ways
-measurements within the canal shows patterns of amplitude peaks and notches within high frequency amplitudes as they arrive from different angles
explain why two ears are better than one ear
-allows ILD, ITD and HRTF signals to be audible
-binaural loudness summation
-improved localization
-binaural squelch
-minimized risk of the unaided ear effect
-suppresses bilateral tinnitus
binaural loudness summation
action potentials in the brainstem increase loudness when two ears receive auditory input signals
-the patient will perceive greater loudness with bilateral devices
-lower output levels reduce the risk of loudness discomfort or feedback
how much gain is seen from binaural loudness summation
-in normal thresholds, there is 2-3 dB of gain
-in suprathresholds, there is 5-8 dB of gain
binaural squelch
the brainstem will manipulate the signal to enhance it
-comparing two signals and the decision is being made for what it should detect and what to ignore
benefits of binaural squelch
improved intelligibility in noise and the ability to focus on one signal while ignoring others by taking advantage of these different SNRs
describe the unaided ear effect
it has been found that 25-33% of people with symmetrical loss has suffered from reduced WRS following 1 year of monaural HA usage
-pure tones did not change, but speech intelligibility declined within the unaided ear due to a central mismatch
explanation of the binaural process benefits
sound localization, sound amplification is more comfortable, better understanding of speech in a noisy environment, better sound quality and can help prevent sensory deprivation
bianural interference
binaural signals interfere with the ability to understand
-occurs due to age related atrophy of the corpus callosum
-reduced intelligibility in noise occurs
what causes HA feedback
occurs due to not a snug fit within the canal causing the output to slip outside and can reamplify creating a feedback loop
-sounds like a squawking noise
what causes patient complaints of occlusion?
the sound of a hollow voice
-occurs due to cartilage vibrating
what happens when a microphone gets closer to a receiver?
output will decrease when the microphone is closer to the receiver
how does microphone placement impact the intensity of the output signal
the deeper the microphone is, the more pinna affect will occur so it will increase the signal
how does the necessary output relate to recevier and canal size
more output calls for a larger receiver which might not fit within small canals
ingress protection (IP) rating
describes how a device is protected from various materials or contaminants
-various degrees for protection against solids and liquids
-can look at different rates for what the patients is and what they need
soft materials are recommended for ___________, harder materials are recommended for _____________
hard pinna (pediatrics) ; soft pinna (older adults)
vinyl
soft but not grippy, can bend
-greatest for infants (up to 4)
-easily modified
-snug fit required fro high gain devices
-shrinks and discolors quickly
why is vinyl recommended for infants
due to the quick shrinkage and discoloring, there needs replacements often and within the under 4 age group they get replacements around every 3 months. so you can “beat” the pace of shrinkage and discoloration that can occur
silicone
soft and grippy, can bend and be altered in some ways
-pediatrics are preferred
-tight seal to hold high gain
-durable, does not shrink
-can cause blisters, difficulty to modify, and can get expensive
-platinum and heat cure
platinum vs. heat cure
most popular type vs. good for high precision needs
lucite/acrylic
hard material
-best for adults
-easy insertion/removal
-mild to severe loss
-durable, no shrinkage over time
-discrete
-increased risk for feedback
earmold retention
can occur within various parts of the mold like the cymba, antitragus, tragus, or canal
importance of the acoustic seal
the output will depend on the acoustic seal
-movement of the ear canal impact this seal
-so choosing the correct material is needed for the proper seal
full shell with snap o-ring
connects body aid receiver mold
-severe to profound losses
full shell mold
higher output for severe/profound losses
-easy insertion
-maximized retention and acoustic seal
skeleton mold
mild to severe HL
-maximized retention and acoustic seal
-like a full shell but hallowed
semi skeleton variations
portions of the outer rim may be removed allowing easier insertion while maintaining retention
canal mold
lowest degree of acoustic seal
-good for cosmetics
canal lock
adds projection into concha for improved retention by antitragus
-good for cosmetics with the retention lock
half shell
fills half of the concha to improve retention and ease insert
-ease of insertion and retention
3 non-custom couplers
open, closed/tulip, and power
open dome
high frequency loss with normal hearing to 1500 Hz
closed or tulip dome
hearing thresholds better than 40 dB HL below 1000 HL
-provides some mid frequency amplification
power (double) dome
requires hearing thresholds better than 40 dB HL below 1000 Hz
-provides some amplification to mid and low frequencies
what are the primary frequencies affected by the vent effect
20-1300 Hz
-lower frequencies
purposes of venting
-releases low frequencies from the ear canal
-reduces the occlusion effect
-allows unamplified signals to travel directly to the eardrum
-allows aeration of the canal and pressure release
vent effect
anything that allows for the exchange of air between the EAC and outside air is referred to as a vent effect
what can cause the vent effect
earmolds with drilled vent bore, open dome, loosely fit closed domes/power domes, and custom earmolds with slit leaks
explain the relationship between frequency and the acoustic mass of the vent
within the vent, the air has an acoustic mass so in order to cross there needs to be enough inertia to get through
-high frequencies have less energy
-low frequencies have more energy
what frequency can travel through the vent
low frequencies
occlusion effect
occurs when lower frequencies of the voice are vibrating within the cartilage portion of the canal
-a common complaint when low frequency threshold loss is better than 50 dB HL
-voices can sound boomy, hollow or like they are in a barrel
what can cause the occlusion effect
insufficient venting and/or insufficient canal length
how do low frequencies correlate with occlusion effect complaints
the skull is able to transduce low frequencies generated by the voice and when this bone conduction signal gets trapped in the canal it can release the vibration
two techniques to reduce the occlusion effect
venting and extending canal length
how can venting help reduce the occlusion effect
it can release lows out of the canal
-vocalized sounds that cause the OE are within the low frequencies so with venting (and what we know about the inertia needed to get through the vent) it can release these frequencies
how can extending canal length help reduce the occlusion effect
by extending the canal length (canal portion of the mold) into the bony portion, the waves bouncing around are not able to make it to the cartilage therefore they cannot vibrate within the canal and the OE will not occur
-the waves will be bouncing around within the bony portion so this blocks off the cartilage portion and can reduce the OE
as the canal length gets longer, the OE ________
decreases
direct signal
the sound that travels through the vent and hits the TM
-allows patient to hear low frequency signals and environmental sounds naturally when these low frequencies are better than 40 dB
amplified signal
the sound that goes through the HA and gets to the TM at a higher level
-what has gain
3 relationships between the direct and amplified signal
- the direct signal can be masked by the amplified signal
-amplified signal is louder than direct signal (20 dB louder) - correct balance occurs
-equal intensity levels, a good thing - the amplified signal can be masked by the direct signal
-direct signal is louder than the amplified signal, will complain they cannot hear in noise
impact of standing waves in the canal
can cause distortion
-can sound fuzzy or distorted
increasing vent sizes causes _____ high frequency output
less
occluding molds allow for around _____ dB of gain
40
-supports audibility for 60 dB HL
3 mm vent allows for around _____ dB of gain
30
-supports audibility to 60 dB HL
open domes allow for around _____ dB of gain
25
-supports audibility to 50 dB HL
parallel vent
sound bore and vent travel through the earpiece side by side and do not intersect
-best vent for a custom style
angel vent
vent intersects the sound bore as close as possible to the tip of the canal
-decreases high frequency output
-increases potential for feedback
-use as a last resort
half external vent and trench vent
channel from the canal tip, halfway down the canal length that transitions to an internal vent
-behaves like a parallel vent
bigger vents are good for _______ thresholds
better
