Hearing Aids Flashcards
What is the goal of a hearing aid?
amplify sounds thereby increasing the signal to the wearer: provide audibility
What a hearing aid not?
A cure for hearing loss
What is the hearing aid made up of?
mic+amplifier and complex signal processors
How many people in the UK are affected by hearing loss?
1 in 6
How many people in the UK would benefit from hearing aids?
1 in 10
What are the 2 types of HA?
Behind the ear (post-aural)
In the ear
Describe the BTE
• Worn behind pinna
• Coupled to concha via plastic tube and earmold
• Delivers sound to external auditory meatus (ear canal)
Describe the ITE
• More restricted acoustics • Aesthetics
What ate the types of ITE?
Full concha
Half concha
In the canal
Completely in the canal
How do bone conduction hearing aids work?
• Sound transmitted through mechanical vibration of cranial bones, to cochlea rather than through outer/middle ear (air conduction)
• Bypasses the outer/middle ear: for conductive losses
What are the issues of BC HA?
- Cosmesis of headband
• Headband discomfort (headaches, pressure) - Low gain, poor sound quality
What is the difference between Bone anchored and bone conduction?
Bone anchored the bone vibrator implanted directly into patient
How is a bone anchor fitted?
• Titanium screw inserted into skull
• Aidattachedtoscrew
• For patients with chronic conductive hearing loss/outer/ middle ear pathology
What are the components of hearing aids?
air conduction receiver (speaker)
Microphones- two or more to reduce background noise
Mechanical potentiometer for volume controls
Mechanical switch for program switching
Battery
Telecoil- converts electromagnetic fields to electrical energy (phones)
What is the change in a microphone
Converts sound into electrical
What is the change in a receiver?
Converts electrical back into sound
What is the process in a digital amplifier?
Sound- Voltage- Digital signal- digital processing- digital signal- Voltage- Sound
What is gain in terms of amplification?
measure of amplification applied to signal (at particular frequencies): difference between input level and output level
What is amplification set according to?
Hearing loss
What are the two types of amplification?
Linear
Non-linear
Describe Linear amplification
• Gain constant for all levels of input
• 1:1 ip/op slope
• 70 dB sound amplified same level as 40 dB sound
Describe non-linear amplification
Gain varies according to input level • <1:1 ip/op slop
When in non linear amplification commonly used?
Modern hearing aids
What does non linear amplification do?
Makes sound comfortable
Allows us to avoid overamplifying louder sounds
What happens in non linear amplification?
We compress (squeeze down) larger input signals to make
the output more comfortable
What are directional and omni directional microphones good for?
Directional microphones useful for different acoustical environments
What is modulation detection/ amplitude modulation noise reduction?
Noise more stationary than speech, less gain for stationary inputs
What is synchrony detection?
Identifies presence of speech (harmonics) and rejects other (noise)
What are the two types of noise reduction algorithms?
Modulation detection and synchrony detection
What do Noise reduction algorithms do?
Asses input
Reduce gain in frequencies dominated by noise
What is telecoil pickup more commonly known as?
The loop system
Describe the loop system
• Inductive pickup in HA housing picks up
signal from induction loop around room/area
• Removes background noise by cutting out HA mic
What do assisted listening devices improve?
signal to noise ratio by transmitting amplified sound directly to HI listener
What do assisted listening devices target?
Typically target a single problem: TV, phone, signalling/alerting/lecturing
What does the physical fit of an earmould provide?
Interface between HA and user
What does the physical fit of a hearing aid facilitate?
efficient transfer of sounds from receiver to the
external auditory meatus
What can the poor fit of an earmould affect?
The Benefit of the hearing aid
List 5 things that the earmould should be.
• Comfortable
• Easy to fit and remove
• Cosmetically acceptable
• Easy to clean
• Good contact for acoustic fit
List 6 benefits of the slim tube and dome
• Low visibility
• Improved ear ventilation
• Natural low freq sounds can enter ear
• Reduce occlusion effect (head in a barrel)
• Comfortable
• Same day fitting
What are slim tube and dome not suitable for and why?
not suitable for more severe losses. High gain=leakage and feedback
How does an electro acoustic fit happen?
Programming the hearing aid parameters via hearing aid fitting software
What is gain?
Level of amplification
Describe setting gain.
- Most important parameter (gain=level of amplification)
- Fit gain in range between hearing thresholds and
uncomfortable loudness levels
• This area is known as the dynamic range - Area reduced with hearing impairment
What is NAL formula fitting gain?
- One example of prescription formula
• Mathematical formula for generating gain values - Average based on 1000s of data
• Thresholds+ULLs+formula=GAIN CURVES
For real ear measurements what must we measure?
The levels of gain reaching the tympanic membrane
What is the purpose of real-ear measurements?
to acoustically verify that the correct, prescribed amount of gain is reaching the ear drum
Why do we do real-ear measurements?
Everyone’s ears are different shapes and sizes
• Is the software accurate in its gain measures?
• Could be under- or over-fitting gain
What are REMs a crucial part of?
hearing aid fittings and its benefits is widely proven scientifically
What is the method of real-ear measurements?
- Place small probe microphones in ear (6 mm from TM)
- Measure level differences with and without hearing aid
- Match up measured gain curve to prescribed target
What must a patient do after the HA is fitted?
Build up use
Why must patient build up use of HA?
• HA requires acclimatisation. Patient hears sounds not heard
in years, this can feel odd, sound internalized. But good!
• Eg, fridge noise. Great that patient hearing such low sounds, but not nice! Brain acclimatises and filters out
What happens at follow up appointments after HA is fitted?
- Fine-tuning and troubleshooting
* Outcome measures
What are common problems of HA?
Poor fitting - pain HA whistling Blocked mould-wax Blocked tubing- condensation Sweaty ear canal Aid too loud Aid too noisy Aid to tinny Background noise
What happens if the HA is poorly fitted/ hurting the patient?
- Check patient is inserting earmould correctly
* Make new earmould
• Shave off parts of earmould
What must we do is the HA is whistling?
- Check mould to see how fits and contacts with ear
- Make new softer mould with greater contact
• Increase feedback suppression parameter - Turn down gain slightly
How does whistling in the HA occur?
Feedback caused by amplified sound escaping from the ear and is re-amplified by the HA
What do you do if the mould is blocked by wax?
Wash or remove wax
What do you do if there is condensation in the tube?
- Insert small vent into air mould to improve air circulation
- Replace tubing
What do you do if there is a sweaty ear canal?
Narrow bore vent into mould to allow better air circulation
What do you do if the aid is too loud?
- Reduce overall gain below recommended levels
* Once patient has acclimatised then increase
What do you do if the aid is too noisy?
- Reduce low frequency gain
* Add vent to mould
What do you do if the aid is too tinny?
Reduce high frequency gain
What do you do if there is a problem with background noise in the HA?
Program hearing aid to allow for directional microphone and
increase noise reduction algorithm strength
How does the counselling process occur with HA problems?
- Discuss problematic situations
• Recommend ALDs
• Explain acclimatisation to patient - Manage expectations
