Final Review Flashcards
What is the difference between custom, modular and semi-modular hearing aids?
Custom hearing aids are customized to the specifics of a patient’s ear. Hearing aid components are manufactured to work and fit within a custom shell based on a patient’s ear impression.
Modular hearing aids consist of standardized components that come in a variety of sizes but are not customized to the patient’s ear. They can be faster to obtain, cheaper, and possibly disposable.
Semi-modular hearing aids may tailor the shell, but the inner components are typically standardized.
What steps can be taken to improve hearing aid reliability?
Covering the mic – water/sweat resistant
Nanocoating, waterproofing, water repellent layers to keep moisture out
Automatic volume controls, swipe controls
Electrical programming
How does a CROS (contralateral routing of the signal) hearing aid function?
There are two devices, one in a profoundly deaf ear and one in a good ear; it
transfers the signal from the better ear to the worse ear. This is good for a unilateral
hearing loss if there is one unaidable ear.
What are the components needed for hearing aid programming?
A computer (and something to connect the hearing aid to the computer)
Hardware to connect HA to computer (e.g. HiPro)
Software to program the connected HA (e.g. NOAH, manufacturer software)
What is reverberation? How do you eliminate the ill-effects of reverberation on speech perception?
Delayed versions of the sound from the original sound; the sound is smeared out in
time and less audible
To prevent reverberation:
Carpeting/Curtains
Don’t use an empty room
Acoustically treated walls
Take sound where it is the strongest (e.g. right by the speaker’s mouth) and
transmit it directly into the listener’s ear. [wireless transmission]
Compare induction loop vs FM vs IR vs sound amplification system.
Induction loop:
Sound is converted to an electric current that travels through wires around a
room. Can be transmitted to a hearing aid/device via electromagnetic waves. Is not ideal for privacy, can be picked up in adjacent rooms. Signal can be affected by where someone sits in a room
Frequency Modulation (FM) System:
Talker wears a microphone and hearing-impaired person wears receiver. More portable system. Signal is not converted into another form of energy but rather modulates.
Infrared (IR) transmission
Audio signals transferred via infrared electromagnetic waves. Similar to radio signals but occurs at very high frequencies. Because at same frequency of light waves, easily blocked by opaque things. Cannot be used in direct sunlight. Used in closed spaces / short distances. Good for places that need privacy (ex. Courtrooms)
Sound amplification
A PA system, contains a microphone and a loudspeaker. Relatively easiest to set up. Gives clear feedback to the speaker when there is an issue. Improves the SNR for all listeners in a room, but not to the same degree of benefit you’d see with the other systems. Can still be prone to reverb.
What is SSPL?
Saturated Sound Pressure Level. Measure of maximum output of a hearing aid.
What are different types of real ear measurements?
Real ear to coupler difference (RECD)
Real ear insertion gain (REIG) - first you do aided gain, with the HA on the ear in
position, then you do a second measurement without the HA.
Real ear unaided gain (REUG) -measures the resonance and natural gain of the
canal without amplification and occlusion
Real ear occluded gain (REOG) -measures the gain in signal level when the canal is
occluded with the coupler but not amplified
What are the differences between electroacoustic measurements and real ear
measurements.
Electroacoustic measures are for quality control – not done on the patient. Use couplers instead of the patient’s ear – gives an approximation but not exact because every ear is different. Some performed at full on gain (don’t do on a patient because you would just blow their hearing and it would be painful). Want to make sure the HA is calibrated according the ANSI and the manufacturer’s standards
Real ear measurements are done on the patient. Provides information about the actual dB levels reaching the patient’s ear to determine whether desired levels are being obtained.
What are the different couplers used in hearing aid measurements? Which hearing aid styles are they compatible with?
HA1 coupler: used for ITE and ITC aids; does not include ear mold simulator
HA2 coupler: used for pocket or body hearing aids; includes an earmold simulator
(which is connected to the BTE hearing aid tubing or the receiver of body aid)
HA4: variation of HA2 coupler used for BTE or spectacle aids and is rarely used
Explain gain frequency response vs. OSPL90
GFR:
Measure output when input is 50 or 60dB. American standard is 50dB, and you test to see the gain at all frequencies. Measured with full on gain setting, trying to match up our results with the manufacturer targets at a semi-loud level and not at an extreme loudness like 90 dB.
OSPL90:
90dB SPL is the max input that a HA can handle. Output you get out of the hearing aid when an input of 90 dB SPL is presented. Measured with full on gain setting.
Explain Input Output Functions
Examine the gains / outputs at each frequency across a range of SPLs
that are inputted (go from softer to louder sounds)
You want to show a non-linear graph for a non linear hearing aid»_space;
showcases compression to avoid peak clipping and distortion
Compression threshold = level where the curve / graph changes from
linear to compression
Explain Distortion
Artifacts or extraneous signals that interfere with the main signal
If >10%, not good for speech perception
A common type of distortion is harmonic distortion, where harmonics
in a complex sound interfere with the listener hearing that sound
Is measured to ensure that:
▪ Hearing aids meet their required specifications
▪ Compare the sound quality of two hearing aids
▪ Determine the maximum output of hearing aid before a signal
is clipped/distorted
Explain a Magnetic Response
See the strength of the telecoil (on RTG position)
Measured with HA in test box
Compare against manufacturer’s standards
Explain the real ear to coupler difference
Acoustics in a 2cc coupler are different than the acoustics in the ear, and each ear is
different. There will always be a gap between electroacoustic and real ear measurements because the coupler will never mimic a real person’s ear canal + middle ear. A negative RECD = inadequate seal of the transducer to the ear (e.g., foam ear tip), a larger than average ear, or a poorly placed probe tip. Useful in HA fitting and audiometry, esp. with babies or people with small ECs
The RECD is dependent on…
▪ Ear canal volume: Individual differences affect RECD, age affects RECD
▪ Leakage, vents and open fittings
▪ Diameter of tubing
▪ Transducer type»_space; inserts vs headphones
▪ Probe microphone location
What is the real ear to dial difference
The difference between the measurement in the canal and the dB
measurement showing up on the audiometer dial. Can help convert between dB HL (audiometer dial) to dB SPL (real ear measure) rather than using conversion equations
Explain real ear aided gain
Gain of the HA in the person’s ear
HA is IN THE EAR and TURNED ON
SPL near the eardrum, A, minus the SPL picked up by the control
microphone, C
Explain real ear unaided gain
How much extra sound (or lack thereof) is presented to the eardrum when
there’s no hearing aid in the ear
The mic pics up how much sound is right outside of the pinna vs in the ear
canal»_space; could be different due to resonant frequencies in the ear canal and
the acoustics in there
Explain real ear insertion gain
How much extra sound is presented to the TM solely because the HA is IN
THE EAR
Do 2 calculations
▪ REAG and REUG
▪ Once you have those, subtract them and you get REIG
Explain real ear occluded gain
The difference in dB, across frequencies, between the signal level measured
in the ear canal and the input signal, with the hearing aid on the ear and
turned off
Hearing aid is IN THE EAR but TURNED OFF
Tells us the properties of the ear mold, if it has a vent, if it’s doing what it
needs to do or not
Acoustics of earmold: HA in ear and off – REUG
Factors that affect real real ear testing are…
Positioning of probe
* Loudspeaker orientation, location and angle
* Background noise
* Cerumen blockage
* Diameter of tubing
* Leakage, vents and open fittings
Vents vs. Dampers vs. Horns
Vents– – filters out low frequencies
Dampers - dampen mid & high frequencies; smooths out frequency response, less spikey signal (bumps/peaks in mid frequencies – not good for speech perception)
Horns – enhancing high frequencies – grows or shrinks; either attenuates low frequencies or enhances high frequencies – narrow at one end and broader at the other
Steps in Making Earmold Impressions
a. Otoscopy, check that the ear canal is clear
b. Take a cotton block and tie the strings together so that it’s not falling out/the
string doesn’t fall apart
c. Using the otolight to push the cotton block in past the second bend in the ear
d. Perform otoscopy again and make sure there are no gaps
e. Mix the molding material for a few seconds/until it is blended well
f. Put the molding material into a syringe
g. Insert and put the molding material in until it comes out well.
h. Wait for it to harden; it’ll be good when you test it with your nail
i. Turn counter clockwise to take out
j. Perform otoscopy again and make sure no material’s left behind
What is compression?
Changing the rate of growth across a sound’s perceived intensity or pitch
Bring sounds into a person’s dynamic range – allowing them to have distinctions between soft medium and loud sounds
Why is compression needed?
so the listener can get benefit from soft sounds; so loud sounds are not so loud as to be painful
Types of compression - (remember 2 –3 types for exam)
i. High level compression – occurs at high intensity sounds
ii. Wide dynamic range – compressing throughout wide range of input
values
iii. Low level compression – compress low intensity sounds
iv. Fast acting – acts fast – attack and release times are faster to
compress
v. Slow acting
vi. Multichannel
Characteristics of a compressor
Attack time (time it takes for compressor to react to increase in input level) vs release time (time it takes for compressor to react
to decrease in input level)
Potential uses of compression
a. Increase dynamic range of people with SNHL to be able to benefit from loud,
moderate, and soft sounds
b. Prevent loud sounds from becoming uncomfortably loud
c. Avoid peak clipping / distortion
Advantages and disadvantages of bilateral hearing aid fittings
a. Advantages: directionality/localization, redundancy/binaural summation –
improves SNR, you have a backup, delay onset of auditory deprivation, can
help to suppress tinnitus
b. Disadvantages: cost, occlusion, easier to handle one HA, binaural
interference (if loss is asymmetrical – poorer ear can interfere with speech
perception); hemisphere asymmetries; wind noise
Explain Sampling
a. Taking measurements of the signal at regular intervals while ignoring the
other time points.
b. The time intervals at which the sampling occurs determine the sampling
rate.
c. Sampling rate: greater than twice the highest frequency in the signal (Nyquist
criteria)
What are the difficulties faced by individuals with SNHL?
a. Decreased audibility
b. A smaller dynamic range
c. Decreased frequency resolution
d. Decreased temporal resolution (temporal masking, gap detection)
What are the basic components of a hearing aid? Describe them in one or two
sentences.
Microphone (converts acoustic energy to electrical), preamplifier
(amplifies minute electrical signal), Analog to digital converter (converts electrical
to electronic), digital signal processor (digital calculations), digital to analog
converter (converts electronic to electrical signal), final amplifier (amplifies
electrical signal further), receiver (converts electrical to acoustic).
What is peak clipping? How do you prevent it?
Signal is amplified too much/goes above the max output of the hearing aid; when the signal is cut so it doesn’t exceed the max output
(causes distortion – certain parts of the signal are “cut off)
What is directivity index? How does the DI relate to speech perception?
The DI is a calculation of a ratio of sensitivity / frontal sound relative to all
other sounds coming from all other directions based on the assumption that
usually when you are talking to someone, they are in front of you
i. Directional – will be a higher ratio – and higher is better for better
speech perception – more sound is coming from the front and less
from the sides / background
ii. Omni – whatever you get from all directions – the number will be lowe
