Audiology 6- Hearing aids Flashcards
1
Q
what are the components of a hearing aid?
A
- sound is picked up by the microphone and converted to a wave form which is converted into a numerical representation before processing it (in an Analogue to Digital converter)
- the numbers are then manipulated in the digital processing, tailoring it to the individuals hearing loss
- it is then sent to a digital to analogue converter, transforms it from numbers back to an varying electrical analogue waveform
- the waveform is then sent into via the receiver into the individuals ear
2
Q
what is gain in a hearing aid?
A
- how much will it amplify by
- the difference between the output and input of the hearing aid
- typical maximum gain for low powered hearing aid is 50dB
- for high powered aids the maximum gain is approx. 75dB
3
Q
what is maximum output of a heairing aid?
A
- as loud as the amplifier will go
- also known as saturation sound pressure level (SSPL)
- typically the SSPL for low powered hearing aids (mild/moderate loss) is 120 dBSPL or less
- for high powered aid (severe/ prodound loss) the SSPL is 135dBSPL
- does not exceed the uncomfortable loudness level of the wearer
4
Q
what is frequency response of a hearing aid?
A
- range of frequencies over which the amplifier amplifies
- most aids amplify over a range of about 200Hz to 4000Hz +
- Difficult to push anything above 4000 Hz through the tube of a behind the ear hearing aid
5
Q
what is distortion of a hearing aid?
A
- how much does it distort the output signal as compared to the input signal
6
Q
What is a behind the ear/ power aid (receiver- in- the- aid) ?
A
- has a microphone, battery, processor, receiver all housed within hearing aid case, shaped to fit behind the pinna
- output through tube via conventional earmold or open fitting
7
Q
what are the two types of hearing aid styles
A
- in the ear
- behind the ear
8
Q
What is a behind the ear with convention earmold hearing aid?
A
- have a fitted earmold which almost completely fills the outer ear and ear canal
- separates sound output from the microphone and so reduces feedback
- may be easier to handle as they’re bigger
9
Q
What is a behind the ear open fit hearing aid?
A
- open fitting has a number of benefits:
comfort
reduction of occlusion effect
uses normal ear resonance
cosmetic benefits (smaller and can’t been seen) - but cannot be used for severe or profound loss as they aren’t powerful enough
10
Q
What is a receiver- in - the canal hearing aid?
A
- similar to open fit aids but receiver is at the end of a wire and situated in the ear canal
benefits over a receiver in the aid fitting
- receiver in the can means it is smaller
- can be used for mild to severe loss
- offers more gain in high frequencies
- smoother frequency response in the mid-high frequencies
- reduction of occlusion effect
11
Q
what are in the canal, completely in the canal and invisible in the canal hearing aids?
A
- components all housed in a case which is custom made to the individuals’ ear
- suitable for mild to moderate/ severe losses
12
Q
what is a compression hearing aid?
A
- amplitude compression
- high gain for low intensity sounds
- low gain for high intensity sounds
- gain must vary depending on the input signal
- a compression aid turns down its gain as the input to the aid increases
13
Q
what is signal processing
A
- number of different strategies to:
- makes the hearing aid more comfortable for the users
- offers more benefit in terms of speech perception for the user
14
Q
what is a frequency compression hearing aid?
A
- circuit that compresses the higher frequencies down to the lower frequencies where the user’s hearing is better
- improves speech perception in adults and children but alters the pitch of sound
15
Q
what is a multi-channel hearing aid?
A
- you can divide the amplification strategy across different frequency bands so different amounts of gain and different compression strategies can be applied across these bands
- some hearing aids have 20 channels or more
- means a hearing aid can be tuned to match an individuals audiogram configuration
- beneficial for people with moderately or steeply sloping hearing loss
- can lead to improved speech perception and sound quality
16
Q
what is a multi-programme aid?
A
- two or more different processing set-ups which can be saved to an individual aid and allows the patient to switch between them depending on the listening situation
- e.g. second program may be implemented for noisy situations or music
17
Q
what is a noise reduction/ cancellation aid?
A
- attempts to sperate speech signals from noise signals and process the two types of signals differently
- attempts to detect the presence of speech and turn down the gain if no speech or minimal speech is present
- a speech non-speech detector analyses fluctuation in signal amplitude
- if the speech/ noise signal envelope is characteristic of speech, the hearing aid is programmed to amplify that channel
- if the speech/ noise envelope is characteristic of noise, the signal is assumed to be noise and amplification in the channel reduced
- works better for speech in background noise that is not speech noise e.g. traffic
18
Q
what is a directional/ multi- microphone hearing aid?
A
- most effective method of improving the signal- noise ratio
- directional microphones that enhance the hearing aids sensitivity to sounds from a desired direction, over other directions
- only technology that can effectively pick out desired speech signal in undesired background speech
- can be fixed or adaptive
- uses dual/ multi-microphones the hearing aid can be set to amplify sounds from one direction
- works on time of arrival of sound. sounds that reach the front mic first are amplified, those that reach the rear mic are not
19
Q
what is acoustic feedback?
A
- caused by amplified sound leaking from the ear canal back to the microphone
- occurs when earmould is poor acoustic fit
- occurs when an ear canal is occluded or partially occluded by wax
20
Q
A
