Download Identify different types of hearing devices

Identify different types of hearing
devices
Contents
Key to resources
2
Introduction
4
Different types and styles of hearing aids (devices)
5
Different types of assistive listening device (ALD)
7
Other hearing devices
9
Hearing device components
10
Analogue and digital hearing aids (devices)
14
Glossary
15
Feedback to activities
17
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Key to resources for activities
Note: Print this Key to resources for activities and refer to it as you work
through the task guide.
Resource
number
Resource title
1
Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney
Chapter 1: Introductory concepts

Section 1.3: Types of hearing aids
Chapter 10: Selecting and adjusting hearing aids

Section 10.1: Selecting hearing aid style
Complete Your Case Studies, Slide 2, to review this topic
2
Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney
Chapter 3: Hearing aid systems
3

Section 3.11: Assistive listening devices. This gives a useful
overview of ALDs’ specific uses.

Sections 3.5–3.10: These sections offer more of an insight into
these ALDs.

Sections 3.2–3.4: Concentrate your reading on Section 3.4,
particularly 3.4.5.
Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney
Chapter 16: CROS, bone-conduction, and implanted hearing aids

Section 16.2: Bone-conduction hearing aids (Introduction)

Section 16.2.1: Applications of bone-conduction hearing aids

Section 16.2.4: Disadvantages of bone-conduction hearing aids

Section 16.3: Implanted and semi-implanted hearing aids

Section 16.3.1: Bone-anchored hearing aids

Section 16.3.2: Middle-ear implants
See also Martin, FN and Clark, JG (2006) Introduction to Audiology (9th
edn), Allyn & Bacon, Boston. Go to Chapter 8: The inner ear, then turn to
the section on ‘Vestibular mechanism’.
The website Hear-it <www.hear-it.org> provides useful summaries of
each of the devices in Dillon’s chapter. Look in the ‘Facts’ section of the
site.
To find out more about BAHAs, see Cochlear (a manufacturer) at
<www.cochlear.com.au>.
To find out more about middle-ear implants, see Vibrant Med-El (a
manufacturer) at <www.vibrant-medel.com>.
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Complete Your Case Studies, Slide 2, to review this topic.
4
Dillon, H (2001) Hearing Aids, Boomerang Press, Sydney
Chapter 2: Hearing aid components

Section 2.1: Block diagrams
Look especially at Figure 2.2, which is a representation of a
three-channel compression hearing aid in block diagrams. The
last paragraph of this section gives you a good summary.

Section 2.2: Microphones

Section 2.3: Amplifiers

Section 2.6: Receivers

Section 2.5: Tone controls and filters

Sections 2.8–2.10

Section 2.12: Batteries

Section 2.4: Digital circuits
Find out about some of the initial advantages of digital
processing over analogue processing.
Complete Your Case Studies, Slide 2, to review this topic.
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Introduction
In this unit we are going to look at what makes up a hearing device. We’ll
start by looking at hearing aids (devices) from a distance, in all their
variations. Then we’ll quickly zoom in, break open the cases of a few
hearing devices and look at the bits that fall out. Then we’ll start to move
back again, putting the pieces together to see how and why different hearing
devices are produced.
But why is it important to have an understanding of how hearing aids
(devices) work?
Imagine for a moment that, sitting in front of you, is your next client, Mrs
Bessie Tulliver. Mrs Tulliver is relying on you to help her select the best
hearing device for her hearing loss and needs. There are two hearing aids
(devices) that seem to best match her hearing loss: the outstandingly named
Concorde Supersound, and the Symphonic Dulcette. But which is best?
Surveying the impressive list of things each hearing aid (device) is supposed
to do, you see that the Supersound uses “six intelli-bands to constantly
adjust the incoming sound to maintain a perfect signal level and removes
interfering noises using the patented beamformer and noise-delete systems,
which together pinpoint the people you want to hear, all housed within an
almost-invisible, stylish, ergonomically designed post-auricular range of
cases”. The Dulcette, on the other hand, is described as “a small, behind-theear aid (device) which compresses the sound within seven digital channels,
suppresses ambient noise and uses adaptive directional microphones”.
Would you know that the Supersound, at almost twice the price of the
Dulcette, appears to be essentially very similar?
As we consider the technology involved in a modern hearing device, we will
be using the first 10 chapters of your textbook Hearing Aids by Harvey
Dillon. We’ll be dipping into it so that, at the end of this unit, you will have
a very good grasp of where to look in the text to find the answer to a
question, as well as what makes up the common, garden-variety hearing aid
(device).
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Different types and styles of hearing
aids (devices)
Sometimes ‘hearing aids’ and ‘hearing devices’ are used to mean the same
thing. However, as we will see, there are many more hearing devices than
just hearing aids. Hearing aids are just one group of hearing device.
Nonetheless, hearing aids are the largest and most common form of hearing
device, so let’s consider them first.
Hearing aids (devices) come in a vast array of shapes, sizes, colours, styles –
and each hearing aid (device) manufacturer has its own variety. The
following links give you a taste of the ranges from most manufacturers
represented in Australia. They are listed alphabetically by manufacturer
name. You don’t need to work your way through them all, but if you do,
you’ll gain a bird’s-eye view of the current hearing aid (device) market.

Bernafon International: <www.bernafon.com.au>

Interton: <http://interton.com>

Oticon: <www.oticon.com.au>

Phonak: <www.phonak.com>

ReSound: <www.gnresound.com>

Siemens: <www.siemens-hearing.com.au>

Sonic Innovations: <www.sonici.com>

Starkey: <www.starkey.com>

Unitron Hearing: <www.unitronhearing.com.au>

Widex: <http://sc.widex.com>
Note that some of these links are to Australian websites, and others are to
international websites. At time of writing, some manufacturers’ Australian
websites were not up to date! This is worth noting, as some of the hearing
aids (devices) you read about might not be available in Australia. One of the
reasons the Australian websites might not be current is that hearing aid
(device) manufacturers are continually producing new ranges, so keeping
the website up to date is a full-time job. The best way to find out which
hearing aids (devices) are available in Australia is to contact the companies
directly by phone and ask.
If you’ve looked at only a few of the above links, you may be feeling a bit
overwhelmed.
There are, however, only five basic types of hearing aid (device):

Body Aid

Behind-The-Ear (BTE) aid

In-The-Ear (ITE) aid
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
In-The-Canal (ITC) aid

Completely-In-the-Canal (CIC) aid.
There are also several uncommon hearing aids (devices), such as the
Spectacle Aid and the Bone Conductor Aid, which have special
applications. Of the five basic types, by far the most commonly fitted are the
BTE and ITC.
Activity 1
Go to Resource 1
1. Which style of hearing aid (device) is least visible to others?
2. Which style/s of hearing aid (device) is/are most reliable?
3. Which type/s of hearing aid (device) is/are easiest to clean?
4. Which type of hearing aid (device) is least sensitive to wind noise?
Feedback is provided at the end of this document.
Sometimes a conventional hearing aid (device) is not appropriate. For
example, your client may really only have difficulty hearing on the phone,
but in all other situations they manage without significant difficulty. Fitting
a hearing aid (device) might help them with the phone, but it’s rather like
providing someone who has difficulty reaching down to pick up things from
the floor with a miniature crane. A pair of tongs might do just as well, and
be less trouble to use.
In instances such as this, an assistive listening device (ALD) might be more
appropriate.
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Different types of assistive listening
device (ALD)
ALDs can be fitted instead of hearing aids (devices), and they can also be
fitted to work in conjunction with hearing aids (devices). ALDs usually
perform more specialised functions than hearing aids (devices), and are thus
chosen according to specific need/s.
In this section it may seem as if we’re jumping around the textbook
randomly, however all you need to grasp is a taste of the variety and range
of options available.
Activity 2
Go to Resource 2
Now that you’ve read this, name three ALDs which could be used for
someone (with or without a hearing aid (device)) who has difficulty hearing
on the phone:



Feedback is provided at the end of this document.
ALDs can be used with or instead of hearing aids (devices), in situations
where a conventional hearing aid (device) either does not help, or cannot be
successfully managed. For example, a readily available ALD is the Binaural
Listener, in which a microphone, amplifier and battery are housed in a box
which is similar in shape and size to a personal stereo. Lightweight
headphones are connected to the box.
For people who have severely reduced sensitivity and manipulation ability
in their hands and fingers, the Binaural Listener is a good alternative to a
conventional hearing aid (device). The headphones are larger and more
easily placed on the head by the client or carer. The controls on the box are
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large and can be held in front, so are much easier to use than the little
controls on a conventional hearing aid (device). There are many examples of
this type of ALD on the market.
Most hearing aid (device) companies supply a few options. Several
companies, such as Printacall <www.printacall.com.au> and Word of
Mouth Technology <www.wom.com.au> specialise in ALDs and carry a
large range. There are also a number of ALDs available through electronic
stores such as Dick Smith, Tandy or JB Hi-Fi, and from manufacturers of
other sound equipment, such as Sennheiser (available from Syntec at
www.syntec.com.au). The company Phoenix Hearing Instruments carries a
very large range of ALDs and many hearing aid (device) options. Examples
can be found on their website <www.phoenixhearing.com.au>.
Many ALDs are used in conjunction with hearing aids (devices). Hearing
aids (devices) perform well at close range and in quiet environments. They
perform less well at greater distances and in noisy conditions. ALDs can be
used to help improve the performance of a hearing aid (device) in the face of
these difficulties.
Activity 3
Go to Resource 2
1. Lady Catherine de Bourgh has a moderate sensorineural hearing loss
but is no longer able to manage to insert a conventional hearing aid
(device). Her audiometrist has tried ITEs and BTEs. What could she
use instead?
2. Mrs Profound has been finding it increasingly difficult to talk on the
phone, and lately has been avoiding picking it up, because she can’t
understand anyone any more. Her hearing aid (device) is functioning
appropriately, and it is apparent that she relies on lip-reading to
communicate.
What options could you suggest to Mrs Profound to help her with the
phone? Tick all that apply.
(a) Suggest a different kind of hearing aid (device).
(b) Give her information about the National Relay Service.
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(c) Give her training in using the telecoil on her hearing aid
(device).
(d) Give her information about Telephone Typewriters (TTY).
(e) Suggest that she may consider a cochlear implant.
(f) Suggest a volume-control phone.
Other hearing devices
Hearing aids (devices) and ALDs go a long way in helping people with
hearing loss and other associated difficulties. However, sometimes a person
may have specific physical conditions which make a conventional hearing
aid (device) and/or ALD inappropriate. In these cases, alternatives must be
considered.
Go to Resource 3
Sometimes a person has such significant difficulty hearing that none of the
above hearing devices and/or ALDs are able to significantly improve their
communication abilities. In these cases, one of several alternative devices
may be appropriate.
The most common of these is the cochlear implant. Invented by Professor
Graeme Clark (Melbourne), the cochlear implant has significantly improved
options for people with very significant hearing losses. Go to
<www.audiology.asn.au> to read a short description of how the cochlear
implant works.
Brainstem implants are another type of device which provide a sensation of
sound for people who are unable to benefit from a hearing device, ALD or
cochlear implant. Read more about brainstem implants at <www.hearit.org>.
There are other implantable and semi-implantable devices about, however
these are the main ones. It’s vital that, as hearing professionals, we’re aware
of the array of hearing aid (device) options available, including the less
common ones, as you never know when you may meet someone who needs
one. You may be the first point of contact for someone who needs a BAHA
implant. Although you may not be the person to fit the BAHA, your client
will depend on you to refer them to the person who will.
Now let’s focus on the components that make up the most common hearing
aids (devices), which we looked at in Resource 1.0
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Hearing device components
The BTE, ITE, CIC, Body Aid and Spectacle Aid all have in common the
key components which form the building blocks of any conventional
hearing aid (device).
The key building blocks of a hearing aid (device) are:

microphone

amplifier

filters and processors

receiver (the little loudspeaker).
Sound signals are converted to electrical signals by the microphone. These
electrical signals are then modified by the amplifier/s, filters and/or
processors. The resultant electrical signals are then converted back into
sound signals by the receiver.
Activity 4
Go to Resource 4
Use Resource 4 for the remainder of this task guide.
Having read these sections of your textbook, draw the block diagrams for
the following components next to their name.

Microphone:

Amplifier:

Receiver:
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Feedback is provided at the end of this document.
Microphones, amplifiers, receivers and filters
Let’s now look more closely at each of these components.
Go to Resource 4
The earliest form of electronic hearing aid (device) consisted of a
microphone, battery and receiver, with the receiver providing its own
amplification. Amplifiers were soon added, allowing greater amplification
of the signal.
As you know, hearing loss for most people is not equal at all frequencies.
For most people there is a greater degree of loss at some frequency regions
than at others. For such people, equal amplification at all frequencies does
not provide the best possible result.
It is for this reason that filters are used in hearing aids (devices), allowing
some sound frequencies to be amplified more, and other sound frequency
regions to be amplified less.
Telecoils and DAI
There are two other common electrical hearing aid (device) components: the
telecoil and direct audio input (DAI). These both allow the hearing aid
(device) to receive a signal from another device. In the case of the telecoil,
the signal is received magnetically, and in the case of the DAI the signal is
received electronically (through a plug).
Go to Resource 4
Using the telecoil, a hearing aid (device) can pick up signals from induction
loop systems. A loop system is a loop of wire usually connected to a public
address system of some kind. A common use is in a church, where the loop
system is placed around the seating area. Another common use of a loop
system is in a cinema, where the person can use their telecoil to listen to the
movie soundtrack. Because the telecoil is picking up the soundtrack, the
microphone on the hearing aid (device) can be switched off, so the loud
crunching and munching of potato chips from the row behind is not
amplified by the hearing aid (device).
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Fast-forward your textbook for a moment to Chapter 3, and reread Section
3.6 (‘Induction loops’) to revise your understanding of how this works.
Another use for the telecoil is with the phone, where it can again provide a
clear signal with less interference.
Using DAI, a hearing aid (device) can pick up signals from a range of audio
devices and hearing aid (device) assistive listening devices. For example, a
client’s iPod can be plugged directly into the hearing aid (device); likewise,
the sound output from a computer can also be plugged directly into the
hearing aid (device). A Bluetooth device can be plugged into the hearing aid
(device), enabling the hearing aid (device) to receive signals from Bluetooth
devices such as mobile phones.
Remote controls
One accessory for use with hearing aids (devices) is a remote control. The
remote control allows the hearing aid (device) to be adjusted remotely, and
so reduces the need for controls on the hearing aid (device) itself.
Go to Resource 4
Batteries
Finally, no electronic hearing aid (device) will function without a source of
electricity. In early-model hearing aids (devices), the battery was similar in
size to a moderate car battery, however they are now quite a bit smaller.
Activity 5
Go to Resource 4
1. Which is correct? Tick the correct answer.
Modern hearing aid (device) microphones:
(a) create no noise of their own
(b) are sensitive to vibrations
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(c) have a magnet and diaphragm
(d) have a completely flat frequency response
2. The most efficient type of hearing aid (device) amplifier is the Class
B. True or false?
3. Hearing aid (device) receivers operate using:
(a) electrical forces
(b) pressure forces
(c) astral forces
(d) magnetic forces
4. Name the following filters:
a. a filter that provides more gain to frequencies in a certain band:
b. a filter that allows more gain to high frequencies than low
frequencies:
c. a filter that allows more gain to low frequencies than high
frequencies:
5. Hearing aid (device) telecoils pick up magnetic signals. True or
false?
6. Hearing aid (device) batteries last all year, just like watch batteries.
True or false?
Feedback is provided at the end of this document.
All the components listed above are connected together in similar ways to
form a functional hearing aid (device). However the finished product
doesn’t always look the same.
Now it’s time to go back inside the hearing aid (device), and consider in
more detail how the heart of the hearing aid (device) modifies the sound
signal to produce a better result for the person wearing the aid (device).
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Analogue and digital hearing aids
(devices)
First, let’s discuss the difference between analogue and digital signal
processing.
Go to Resource 4
Initially all hearing aids (devices) were analogue (analog) hearing aids
(devices). In an analogue hearing aid (device), when you follow the sound
signal as it is converted into an electrical signal and then back into a sound
signal, you will find that the electrical signal is analagous to the sound
signal. That is, if you were to draw each signal on paper, they would look
like each other.
In the early 1990s, digital hearing aids (devices) started to appear. The key
difference between analogue and digital hearing aids (devices) is in the
amplifier and filter section of the hearing aid (device). Whereas in an
analogue hearing aid (device) all the signals retain the original shape of the
sound signal, in a digital hearing aid (device), all the signals are converted
into a digital signal – a combination of 0s and 1s.
Activity 6
Go to Resource 2
1. Write three key advantages of digital over analogue for hearing aids
(devices).



2. Write down the point Harvey Dillon makes regarding what digital
aids (devices) can’t do:
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Feedback is provided at the end of this document.
The heart of an analogue hearing aid (device) is the amplifiers and filters. In
the digital hearing aid (device) the heart is the digital signal processor. As
almost all new hearing aids (devices) are now digital, this will be our focus
of our discussion, however the discussion can be applied to any method of
sound processing.
Glossary
Acoustic hearing
aid (device)
effects
Anything non-electrical that affects the sound reaching the
eardrum (pinna, microphone tubing, ear hook, ear mould tubing,
ear mould/ear shell, sound bore, venting, ear canal)
ALD
Assistive listening device
BTE
Behind-The-Ear hearing aid (device)
CIC
Completely-In-the-Canal hearing aid (device)
Digitally
programmable
The settings of a digitally programmable hearing aid (device) are
adjusted by a computer or programming device. This allows for
much greater flexibility in adjustment than is possible using
trimpots. Note that a digitally programmable hearing aid (device)
is an analogue aid (device)
Electro-acoustic
hearing aid
(device) effects
Anything that pertains to the hearing aid (device) transducers
(microphone, receiver and everything between them)
ITC
In-The-Canal hearing aid (device)
ITE
In-The-Ear hearing aid (device)
MC
Mini-Canal hearing aid (device)
MPO
Maximum power output : this is usually used to mean OSPL90
NRS
National Relay Service: an Australian government service which
allows a person using a TTY to communicate with someone who
does not have a TTY (see <www.relayservice.com.au> for more
information)
OSPL90
The (output) SPL (sound pressure level) produced by a hearing
aid (device) when it receives a 90dB input
Peak clipping
A method of maximum output limiting in which the peaks of the
signal that would otherwise be greater than the maximum level
are ‘clipped’. As a result there is no reduction in gain, but there is
significant distortion
REIR
Real Ear Insertion Response. REIG stands for Real Ear Insertion
Gain, while IG stands for Insertion Gain. Note that REIR, REIG
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and IG are generally used interchangeably
REUG
Real Ear Unaided Gain; note that REUR and REUG are generally
used interchangeably
REUR
Real Ear Unaided Response
Signal-to-noise
ratio (S/N or SNR)
A measure of the level of the desired signal, relative to the level
of undesired signal (background noise). The larger the SNR, the
less the undesired signal masks the desired signal
Trimpot
A tiny potentiometer on a hearing aid (device) which allows the
settings of the hearing aid (device) to be adjusted (using a
screwdriver)
TTY
Telephone typewriter: a device which allows a hearing-impaired
person to send text via an ordinary phone. The text can only be
read by someone else with a TTY
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Feedback to activities
Activity 1 feedback
1. Which style of hearing aid (device) is least visible to others?
CIC
2. Which style/s of hearing aid (device) is/are most reliable?
BTE, Spectacle Aid, Body Aid
3. Which type/s of hearing aid (device) is/are easiest to clean?
BTE, Spectacle Aid
4. Which type of hearing aid (device) is least sensitive to wind noise?
CIC
Activity 2 feedback
Resource 2: Now that you’ve read this, name three ALDs which could be
used for someone (with or without a hearing aid (device)) who has difficulty
hearing on the phone:

an amplified telephone

a telephone coupler

a sound-absorbing pad (eg foam rubber)
Activity 3 feedback
1. Lady Catherine de Bourgh has a moderate sensorineural hearing loss
but is no longer able to manage to insert a conventional hearing aid
(device). Her audiometrist has tried ITEs and BTEs. What could she
use instead?
She could use a headphone ALD such as a binaural listener.
2. What options could you suggest to Mrs Profound to help her with the
phone? Tick all that apply.
(a) Suggest a different kind of hearing aid (device).
 (b) Give her information about the National Relay Service.
(c) Give her training in using the telecoil on her hearing aid
(device).
 (d) Give her information about Telephone Typewriters (TTY).
 (e) Suggest that she may consider a cochlear implant.
(f) Suggest a volume-control phone.
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Activity 4 feedback
Resource 4: Having read this section of your textbook, draw the block
diagrams for the following components next to their name.

Microphone:

Amplifier:

Receiver:
Activity 5 feedback
1. Which is correct? Tick the correct answer.
Modern hearing aid (device) microphones:
(a) create no noise of their own
 (b) are sensitive to vibrations
(c) have a magnet and diaphragm
(d) have a completely flat frequency response
2. The most efficient type of hearing aid (device) amplifier is the Class
B. True or false?
False. The Class D is the most efficient.
3. Hearing aid (device) receivers operate using:
(a) electrical forces
(b) pressure forces
(c) astral forces
 (d) magnetic forces
4. Name the following filters:
a. a filter that provides more gain to frequencies in a certain band:
Band-pass filter
b. a filter that allows more gain to high frequencies than low
frequencies:
High-pass filter (also known as a low-cut filter)
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c. a filter that allows more gain to low frequencies than high
frequencies:
Low-pass filter (also known as a high-cut filter)
5. Hearing aid (device) telecoils pick up magnetic signals. True or
false?
True
6. Hearing aid (device) batteries last all year, just like watch batteries.
True or false?
False. Most batteries only last a week or two of consistent use. A
hearing aid (device) draws current like a transistor radio, not like a
watch.
Activity 6 feedback
1. Write three key advantages of digital over analogue for hearing aids
(devices).

Digital aids (devices) can perform more complex processing.

Digital aids (devices) can make decisions about how to
process the sound.

Digital aids (devices) are more efficient (in terms of size and
power consumption) than analogue.
2. Write down the point Harvey Dillon makes regarding what digital
aids (devices) can’t do:
Digital aids (devices) do not provide ‘CD sound quality’.
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