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HA Technology Flashcards

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1
Q

What are the component parts of a HA?

A

Microphone
Amplifier
Receiver
Battery
Other stuff ie volume, converters

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2
Q

What is a HA?

A

An electronic device enabling a hearing impaired person to make best use of their residual hearing

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3
Q

Describe the function of a microphone

A

Collect and funnels sounds transducing it from acoustical/mechanical energy to electrical signals

Has backplate (bottom) and diaphragm (top). SPL makes diaphragm vibrate which converts sound wave into electrical energy and sends off further into HA

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4
Q

What is an amplifier?

A

Increases or limits sound coming in to the HA

Amplifies a quiet sound to make more audible OR
Limits a louder sound to make it more comfortable

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5
Q

What is GAIN?

A

The additional volume/power added by the amplifier:

Output + input = gain

Outgoing from amplifier added to the original incoming sound wave

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6
Q

Describe function of a receiver

A

Transducers electrical signal back to acoustical/mechanical energy by converting back to sound vibrations

Air and bone conduction receivers

Digital HA requires analogue signal to e digitalised hence ADC and DAC converters

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7
Q

Characteristics of a HA battery?

A

Chemically stored energy - converts to electrical energy when activated (remove tab)

Zinc air battery (Za) most common

Size 10. Yellow smallest
312 Brown
13. Orange
675 blue. Largest

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8
Q

Equation to work out battery life?

A

C
—
T I T x I = C

CAPACITY total hours it can provide, measured in Milliamps (mAhrs) of charge in hours.

TIME In hours
I = CURRENT current measured in milliamps (mA)

Ie C 260mAhrs divided by I 2mA = 130 hrs (Time)

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9
Q

Step by step journey of a sound wave through a HA?

A

Microphone
ADC converter
Amplifier
Volume control - optional
Battery - powers everything
DAC converter
Receiver

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10
Q

Name 2 types of microphone

A

DIRECTIONAL - better in noise
ie cartoid - forward facing

OMNI DIRECTIONAL better in a quiet environment.

Directional can be implemented as one dedicated MC (with 2 ports and a delay) or 2 identical MC’s combining signal processing.
Makes sound clearer but BGN still there

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11
Q

3 scenarios of noise management?

A

Speech in quiet At home
Noise only. Wembley
Speech in noise. Restaurant

SIQ high/low freq start/stop gain only amplifies
NO steady freq continuous gain only amplifies
SIN combination - reduces noise

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12
Q

What factors determine which HA type/style?

A

Type of loss
Degree of loss
Dexterity
Lifestyle
Personal preference

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13
Q

What are the advantages of a BTE?

A

For all hearing loss
Lowest chance of feedback
More powerful (up to 130dB)
Electronics not in the ear
Best for ear infections
Interchangeable attachments
Moulds - different materials for allergies/grips

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14
Q

What are the disadvantages of a BTE?

A

Not discreet
Large, heavy & bulky
Impacted by wind more so
Sounds travels further to the TM
NHS provide for free

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15
Q

What is a trimmer/trimpot?

A

Trimmer are manual tools which take frequency up or down but now it is done automatically

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16
Q

What are the benefits of ear moulds?

A

Anchor to keep HA in place
Provides sound channel to TM
Acoustically shapes the signal
Must be easy to fit and comfortable to wear

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17
Q

Ear mould style will depend on?

A

Type and degree of loss
Shape and size of pinna and EAM
Dexterity
Cosmetics

Custom made so will require impressions

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18
Q

What are the 2 main styles of BTE ear moulds? What are they for? Describe an open fitting.

A

BTE FULL SHELL - suitable for all HL
covers full area of pinna/concha
Vent can be drilled in to prevent/reduce occlusion
BTE SKELETON - mild to moderate loss
Sounds can escape so good for those who suffer occlusion. Mild HL generally low frequency and therefore occlusion May occur.
BTE OPEN FITTING simply a smaller or mini version of the BTE with no mould rather the sound is transmitted straight to the ear canal through a thin plastic tube that is attached to a tip that comfortably sits within the ear. For mild to moderate loss that can help with occlusion as sounds escape.

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19
Q

What are the 3 materials used for BTE ear moulds and their pros and cons?

A

HARD ACRYLIC - durable, easy to insert, clean and modify. Limited power. For mild HL
SOFT ACRYLIC - softens with body heat, better acoustic seal than hard. More difficult to clean, porous soo absorbs , discolours. For moderate to severe HL.
SILICONE - increased gain available and less feedback due to it being the best seal. Comfortable.
Have to replace often, difficult to fit/clean, modifications harder. For profound hearing loss.

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20
Q

What Ear piece retention options are there?

A

Retention grip for micro moulds
Custom aids/moulds can have canal locks out if anti Tragus partially raised then helix lock, skeleton in full concha or half skeleton.
Lacquering May also help:
Hard - hypoallergenic ITE/custom
Soft - less slide better grip
Nano - extra smooth very hygienic protects against moisture
No lacquering - rough least slide good hold no allergy protection

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21
Q

How does tubing effect sound?

A

The internal diameter affects passage of sound.
Narrow tube - loss of high frequency as amplification hits tube and bounces back eventually losing energy

Longer tubing will increase SPL at TM as close so less gain required therefore less chance of feedback but reduces high frequency so will reduce clarity

Shorter tubing allows low frequency to dissipate soo reduces occlusion effect and enhances high frequency

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22
Q

What are acoustic horns and how do they affect sound?

A

Particular tube which is used if venting impossible due to feedback or size of ear.
Size of diameter will affect performance however generally increased air dissipates occlusion but also enhances frequency

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23
Q

What is the purpose of AC ear hook damper?

A

It is a fused mesh or plastic filter used to remove unwanted peaks soothing out the frequency curve.

Modern HA’s have an automatic frequency equaliser

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24
Q

What are the advantages of an RITE/RIC?

A

Own voice more natural
Natural amplification occurs as more ear available
Less conspicuous
No impression required
Wide variety of choices
Easy receiver replacement

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25
What are the disadvantages of RITE/RIC?
Limited fitting range (albeit now up to 105dB) Wind noise (REALs - wind suppression) Electronics in the ear - no good for ears that react to moisture/technology Dexterity Domes required
26
What power receivers are available for RITE?
60dBHL mild to moderate HL 85dBHL moderate to severe HL God’s sound quality, little disruption, feedback reduced 100dBHL Severe loss, encased mould selection wires attached separately power/flex or micro mould, can be used with domes 105dBHL severe to profound power/flex mould only
27
What are the types of domes and their purpose?
OPEN domes - least occluding & good for those with near normal hearing. Threshold below 1kHz. Be ware feedback. SINGLE/DOUBLE dome dependent on whether occlusion or feedback most likely to be issue. POWER/DOUBLE dome significantly occlude ear.
28
What are the ITE options and their power?
ITE covers anything which goes in the ear: ITC in the canal up to 100dB (will require half or full concha shell) CIC completely in the canal 85-90dB IIC invisible in the canal 80dB Vents essential to prevent occlusion in IIC/CIC but low quality of sound as only 1 microphone
29
Advantages of CIC/IIC?
virtually invisible Microphone located in more natural sound gathering position Allows outer ear to provide high frequency emphasis and enhanced Localisation Requires less power as close to TM No occlusion
30
Disadvantages of CIC/IIC?
Short battery life Dexterity Wax can plug receiver No telecoil Directional only mic
31
What modifications are there for ITE’s?
DEXTERITY- extraction cord length, finger nail notches, raised volume control ACOUSTIC - ‘belled’ canals goes in narrow then opens up. EXTENDED RECEIVER TUBE close to TM increases SPL helps those with infections but can lose high frequency LOCKS - canal and helix
32
What is occlusion? How do we prevent it?
Low frequency sounds enter ear canal and are trapped between mould/dome and the TM. Patients with a low frequency loss (250/500) worse than 60dBHL unlikely to notice. Prevention: stop sound entering space (impractical) or allow sounds to dissipate to some extent (vents)
33
What is a vent and what are the benefits?
A vent is a column or air between air in the canal and air outside which allows: Reduction in occlusion (through dissipation) Pressure equalisation More natural speech in quiet Improved clarity in BGN Loud low frequency less intrusive However vents can increase risk of feedback
34
3 types of vents and their variations?
Parallel vent Y vent Trench/groove vent Each designed to reduce amplified low frequency by allowing sound/air to leak out. Mild low freq HL - large vent Severe low freq HL - short vent Tube, cast or collection vents. Varieties: COLLECTIONvent - good for occlusion, large entrance, small exit CAST vent - superseded by collection in custom made. Used for BTE OVAL vent - IIC FREE vent - for small ears
35
What are the physics of venting?
Length and diameter of vent affect its effect. They are inversely (opposite) related. Short vent more sound than long Wide vent more sound than narrow Short vent with large diameter optimal as acoustic resistance is minimal but can result in feedback
36
Vent sizes according to dBHL?
Less than 20 - open fitting/ 3/4mm vent 20-40. Medium vent 2mm 40-60. Small vent 1mm 60-70. Small/pressure vent CIC/ITC only 70+. No vent
37
What is feedback?
High frequency amplified sound that leaks out of ear canal and is picked up be microphone. (Replays round in a loop) Signal adds ‘in phasez’ with incoming signal and May be amplified over and over (loop) again resulting in oscillation
38
What are the causes of feedback?
Poor seal Poor fitting ear mould Wax pushes HA/dome away from and sound reflects off wall into vent Receiver/microphone too close Receiver tube detached Vent too large, vent insert fallen out Vent too close to microphone Port
39
What gain reduction strategy can we do to mitigate feedback?
Maximum gain that can be achieved in different frequency regions is limited Need to know max amplified gain for each frequency before feedback will occur then set a safety valve Can be done by clinician at the time, fitting software can do at the time or by the HA itself when worn.
40
What are the standard feedback solutions?
Plug ear tightly to get a better seal Decrease high frequency amplifier Turn volume down Consider more impressions to ensure accurate and achieving best possible seal Longer tube length - closer to TM less gain required Decrease vent size - trade off with occlusion Feedback trimmers Electrical solutions: Phase inversion Frequency shifting DFC Dynamo feedback cancellation
41
What are the 2 types of feedback trimmers?
BASE and TOP CUT BASE- reduces occlusion, improves clarity, tinny. Increased chance of feedback TOP CUT - reduces feedback and tinny sounds. Can reduce clarity.
42
What is phase inversion and frequency shifting?
Electrical solutions to mitigate feedback. Phase inversion inverts the sound soo it is out of phase therefore reduces sound. Frequency shifting shifts the input signal slightly soo does not match soo less amplification. Called decorrelation
43
What is the purpose of GAIN?
Optimise speech audibility Optimise speech intelligibility Match preferred loudness levels Avoid loudness discomfort Provide good sound quality Based on: Hearing aid experience Age and gender Tonal quality of patients language
44
What is linear gain?
Gain is different at each frequency however HA circuit applies a fixed amount of gain for all input levels until saturation. Input/output graph
45
What is Lybargers Half gain rule?
Half AC threshold + Half the air-bone gap + 10dB reserve
46
What are the limitations of the half gain rule?
If, for example, using 25dB Soft sounds at 5dB will exit aid at 30dB still very quiet Loud sounds of 75dB would exit aid at 100dB - too loud!
47
What are the corrections to the half gain rule?
Conductive or severe loss More Than half gain. Canal aids, binaural fittings, open fittings and asymmetrical loss all require LESS than half gain rule.
48
Explain reduced gain for canal aids, binaural fittings, open fittings and asymmetrical loss.
CANAL AID: only third gain required as receiver closer to TM plus gain provided by pinna and concha. BINAURAL FITTINGS: gain reduced by 3-6dB due to summation of two aids working together OPEN fittings: less gain required due to natural resonance of pinna and concha ASYMMETRY (big difference better right and left ear) gain required by worse ear maybe less due to poor speech discrimination in that ear.
49
What are the 5 benefits of a binaural fitting?
Balanced hearing Localisation Speech intelligibility Loudness summation Preservation of hearing
50
What is the benefit of balanced hearing?
2 ears collect and deliver more information than just 1 ear. Soo it becomes easier, more sound and therefore more quality. Also reduces effects of tinnitus as more sound means tinnitus more masked.
51
What is the binaural benefit of Localisation?
One ear can only work out sound from one side. Combined Localisation of the 2 ears means can pinpoint sound, direction and distance including moving sound. Think ITD, IID and IPD
52
How does binaural fitting improve such intelligibility?
Improved speech in noise therefore signal to noise ratio is increased by 2-3dB Binaural squelch gives ability to focus on signal and ignore BGN - does by adding gain to all frequencies meaning we perceive the noise we’re want to hear to be louder than BGN
53
How does loudness summation improve with a binaural fit?
Quiet sounds missed by 1 ear will note be picked up. Due to this gain, volume can be reduced by 3-6dB This reduced gain means less risk of feedback, distortion and not exceeding ULL.
54
How does a binaural fit support preservation of hearing?
Auditory depravation is the gradual deterioration of the brain through lack of stimulation, so it loses the ability to process. Having 2 aids doubles amount of stimulation so minimises this risk.
55
What are the limitations of a binaural fitting?
ASYMMETRICAL LOSS: the greater the degree of loss the more difficult the fit. RETRO COCHLEA LOSS: means processing problems soo more amplification required which can cause distortion. PHYSICAL: dexterity, unaidable ear, abnormalities, size, shape, cognitive ability NEGATIVITY: attitude, stigma, motivation DIPLACUSIS: same sound is perceived to be a very different pitch between the 2 ears. Could be exacerbated by 2 aids.
56
When would a bilateral loss require a monaural fitting?
MEDICAL: size shape deformity PHYSICAL: dexterity disability AUDIOMETERY: asymmetry, different cochlea ability, different prescription TINNITUS: fit to ear with greatest relief PERSONAL: right or left handed, driver or passenger, home life - tv etc rule of thumb nearest ear to 50dBHL at 1kHz
57
How do we test hearing aid performance?
Perturbed in a test box - a computer containing a soundproof box and simulates HA performance. Gives a standard reference to compare all hearing aids on a like for like basis.
58
What are the 2 devices a test box can be connected to in order to test performance?
2cc coupler which mimics ear canal with an aid in it. Or Occluded ear simulator (OES)
59
What are the 3 international standards for a test box simulation?
ANSI American national standards institute IEC 118-7 for the 2 cc test IEC 187-0 for the OES IEC - international electrotechnical commission
60
What is FOG and it’s procedure?
Tests an hearing aids FULL ON GAIN Aids switched on Volume control on full Trimmers switched off Test box produces full frequency sweep at 60 dBSPL (speech level) and measures OUTPUT of the aid,
61
What is the peak gain and high frequency average when testing HA performance?
PEAK GAIN: relates to maximum amount of gain from the HA at any frequency. HIGH FREQUENCY AVERAGE: is the average gain when we combine the results of 1kHz, 1.6 and 2.5kHz ((and divide it by 3)
62
What is OSPL90 test for HA performance?
This measures the maximum power output/saturation (SPL) of the HA. We compare this the ULL’s to prevent loud noises being too uncomfortable. Rule of thumb: ULL + 10dB = ideal OSPL90 figure. Aids on VC on Trimmers off Full frequency sweep 90dBSPL
63
What is the RTG in relation to HA performance?
the REFERENCE THRESHOLD GAIN RTG Establishes a level test free from SATURATION and/or DISTORTION based on the REFERENCE TEST FREQUENCY of 1.6kHz VC manually adjusted until OUTPUT 15dB lower than OSPL90 Full frequency setup and OUTPUT recorded Input intensity 60 dBSPL an RTG graph can show a curve showing the effect of trimmers (which reduces maximum performance)
64
What is distortion?
An unwanted noise caused by components in the aids adding something to the original signal.
65
What are the 3 different types of distortion?
INTERMODULATION distortion HARMONIC distortion EQUIVALENT NOISE INPUT LEVEL - frequency and transient distortion
66
Describe intermodulation distortion
Where 2 input signals consisting of at least 2 frequencies are present - the distortion occurs at the sum add difference of the two original frequencies. Ie 1kHz and 250Hz will produce intermodulation distortion at 750Hz (difference) and 1250Hz (sum)
67
Describe harmonic distortion
It is the measurement of extra frequencies being produced. Harmonic frequencies will be the whole number multiples of the original input signal. Ie 1kHz distortion would happen at 2,3, 4kHz etc Total harmonic distortion is the sum of odd and even harmonics expressed as a % of total output. High powered aids produce more distortion
68
Explain equivalent input noise level and the associated frequency and transient distortions.
EINL is a measurement of noise created by the components/circuits of the HA. OUTPUT is measured with no input signal then has the reference threshold gain deducted. This leaves the level of noise being generated by component parts. This should always be below 30dB More severe HL can cope with higher levels of noise as the patient will not hear it. FREQUENCY distortion - caused by high peaks in frequency response often due to receiver RESONANCE TRANSIENT distortion - ‘ringing’ sound due to rapid charges in signal which amplifier cannot deal with.
69
What does real ear measurement do?
Evaluates HA performance by measuring dBSPL arriving at TM
70
What are the different REM probe lengths for males, females and children?
Males 30 mm Females. 28 mm Child. 25 mm
71
REM process?
Reference microphone on outside (entrance to canal) Probe microphone near TM Loudspeaker emits 65dBSPL at 1metre Compare two readings from each mic: How much sound at TM How much gain added
72
What is REUR?
Real ear unaided response No HA so measures natural resonance of pinna and canal
73
What is REOR?
Real ear occluded response HA in but switched off Assesses effectiveness of vents or changes in meatal length
74
What is REAR?
Real ear aided response HA on and in. Measures total frequency response PLUS any effects from patients ear.
75
What is REIR & REIG?
Real ear insertion response and real ear insertion gain REIR is difference between the unaided and aided frequency responses across entire range. REIG is same but at a specific frequency.

Audiology (15 decks)

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