Hearing Aids 1 Flashcards
(23 cards)
What are the 5 digital hearing aid components?
- Microphone
- Analogue to digital converter
- Digital processor (computer)
- Digital to analogue converter
- Receiver/loudspeaker
What are the 3 key characteristics of hearing aids?
- Maximum output (Sound Saturation Pressure Level)
- Gain
- Frequency Response
What is the maximum output or SSPL?
This measures how loud a hearing aid can go.
The SSPL for a low powered hearing aid (mild-moderate) is typically 120dB.
The SSPL for a high powered hearing aid (severe-profound) is typically 135dB.
What is hearing aid gain?
Gain refers to the difference between the output and input of the hearing aid.
The gain is the amount the hearing aid amplifies by e.g. if we put in 50dB and the output is 110dB, then we have a gain of 60dB.
What is the frequency response?
The frequency response for a hearing aid is the range of frequencies it is able to amplify e.g. most hearing aids amplify over a range of about 200Hz - 4000+Hz.
What are the two general hearing aid styles?
- In the ear hearing aids.
- Behind the ear hearing aids.
What are the three types of in the ear hearing aids?
- Invisible in canal (IIC)
- Completely in canal (CIC)
- In the canal (ITC)
What are the four types of behind the ear hearing aids?
- Receiver in canal (RIC)
- Open fit (open ear)
- Behind the ear (BTE)
- Power (high powered)
What’s the difference between BTE, open and high powered hearing aids compared to RIC?
The Open ear, behind the ear and high powered hearing aids all have the receiver/loudspeaker housed in the hearing aid.
The receiver in canal hearing aid is when the receiver/loudspeaker is at the end of the wire that goes down into the ear canal.
What are the two levels of output for BTE hearing aids?
- Output can be through a tube via a conventional ear mould.
OR - Output can be an open fitting which sends the signal via a narrow tube attached to a dome.
What are the advantages of BTE with conventional ear mould?
- BTEs can be used for all types of hearing losses from mild to profound.
- Conventional BTEs use a fitted ear mould which completely fills the outer ear and ear canal. This seals the ear canal and helps prevent the hearing aid whistling because the filled ear canal separates the sound output from the microphone.
- They are larger so are easier to handle and most likely to be recommended to children so they don’t get broken or fall out.
What are the advantages of BTE Open Fit hearing aids?
- Cosmetic benefits because they are smaller and less able to be seen.
- More comfortable.
- Reduction of occlusion effect (sensation of hearing your voice in your head when you talk out loud).
- Normal ear/concha resonance because your ear canals are open so the resonance can boost your hearing by 2-5kHz.
What are the advantages of RIC hearing aids?
- They are smaller than receiver in the hearing aid aids so have the cosmetic appeal.
- Can be used for mild to severe hearing losses because the receiver is closer to the ear drum compared to BTEs.
- More gain for higher frequencies because you’re not having to drive the sounds through the tube like in the open fittings.
- Smoother frequency response in the mid-high frequencies for same reason as point 3.
- There is less whistling because the receiver is further away from the microphone.
- Reduction of occlusion effect.
- Normal ear/concha resonance.
- Offer comfort.
What are the advantages of in the ear hearing aids?
- All digital components are housed in a case which is custom made to the individual’s ear.
- Suitable for mild to severe hearing losses because the hearing aid is so close to the tympanic membrane (ear drum).
What are the 7 types of signal processing techniques used in hearing aids?
- Compression
- Frequency Compression
- Multi-channel flexibility
- Multi-programme aids
- Noise suppression
- Directional microphones
- Feedback suppression
What is compression?
The gain of the hearing aid must vary depending on the input signal. A compression aid turns down its gain as the input to the aid increases.
Typically seen in a sensory hearing loss with recruitment e.g. requires high gain for low intensity sounds and low gain for high intensity sounds.
What is frequency compression?
People with moderate-profound hearing losses may have no usable hearing in the higher frequencies.
There’s no point in amplifying these sounds because the person will not be able to hear them.
So hearing aids can be programmed to take higher frequency sounds and squash them down into lower frequencies and deliver them into the ear at a lower frequency where the hearing is better.
What is multi-channel flexibility?
Multi-channel hearing aids is when you can divide their amplification across different frequencies (low, mid and high) so different levels of gain and compressions can be applied across each of the different frequencies.
What are multi-programme aids?
Depending on the person’s environment, they can switch their hearing aid to a different programme that is more suited for noisy situations e.g. out shopping or in the streets with a lot of background noise compared to their programme when they are sat at home in a quiet environment.
To switch programmes, they can use a remote control device or their phone.
How do hearing aids attempt to supress unnecessary noise?
Hearing aids try to reduce amplification of unnecessary sounds by recognising what is a noise signal and what is a speech signal.
It will do this channel by channel and it will try to detect the presence of speech and turn down the gain if no speech/minimal speech is present.
If there is speech detected, it will turn its gain up and amplify the speech signals.
What do directional microphones do to minimise the problem of background noise and the main target sound both being speech?
They point forwards to amplify the person you’re facing. Therefore, it doesn’t amplify sounds that are coming from behind you. They work based on time of arrival of sound. So sounds that reach the front microphone first are amplified and sounds that reach the back microphones first are not.
However, the microphones can be adapted so if the person talking to you is walking round and round, the microphone and its amplification can follow that person walking around you and continue its amplification.
What is acoustic feedback?
This is when amplified sounds leak from the ear canal back to the microphone and causes uncomfortable whistling.
What is feedback suppression?
If the hearing aid detects a whistling sound, the hearing aid will replicate an equal sound but it’s opposite in phase e.g. when the soundwave has a rarefaction, the new sound will produce a compression etc.
The combination of these two sounds cancel each other out and so it makes silence. This is called a feedback cancellation loop and it aims to supress unnecessary acoustic feedback that is uncomfortable for the user.
