1. Amplification Systems For
Individuals with Hearing
Impairement: Individual & Group
Presented by :, Pargat Singh
pargatsingh0007@gmail.com
Lecturer in spl. education

2. We know that there are different types and
degrees of hearing loss. Not all the hearing losses
can be treated with medicines and/ or with
surgery. When the hearing loss is irreversible like
in cases of sensori-neural or mixed loss or in
some chronic cases with conductive hearing loss
then these individuals can have the option of use
of amplification devices. Amplification devices
basically function by amplifying the sound or
increasing the loudness of the sound and
reaching it to the ear of the user. An
amplification device is an electronic device that
helps a person with hearing impairment to hear
better. There are different types of amplification
devices and each has its advantages and
limitations.

3. Definition of Individual and Group hearing aids:
Hearing aid is an amplifier whose function is to increase the
intensity of sound and deliver it to the ear with as little distortion as
possible.
A hearing aid can be defined as an electronic device that amplifies
sounds to a degree and in a manner that will enable a person with
hearing impairment to utilize his remaining hearing in an effective
manner. Amplification devices are now being used for several
centuries and have undergone a lot of changes as development in
technology has occurred. Individual hearing aids have gone from
being bulky, cumbersome table models to tiny, delicate instruments
that can be placed deep inside the ear canal and are invisible.

4. Amplification devices can be classified into
 Individual amplification system
 Group amplification systems

5. Parts of the hearing aids
•Microphone
•Amplifer
•Receiver
•Volume Control
•Battery

6. How does a hearing aid function?
•Microphone captures the acoustic signal from the
air changes in to electrical energy.
•The signal is amplified (increased in intesity) by
the amplifier
•This modified signal is converted back into
acoustic signal by receiver and delivered to the
ear.
•The power source of the hearing aid is a battery

7. Types of hearing aids:
Individual hearing aids are classified on the basis
of several parameters. These include:
A.] The place where they are worn on the user:
Based on the place where the hearing aids are worn on the
user’s body, they can be classified into body level aids and
ear level aids. As the names suggest, the body level hearing
aids are placed on the body at the level of the chest, while the
ear level hearing aids are worn on the ear.

8. 1. Body worn hearing aids:
These are also known as pocket hearing aids. A pocket
hearing aid can be worn in the pocket or with the help of a
harness and is bulky in size. This type of hearing aid consists
of a rectangular box like case, a cord and an external receiver
attached to the cord. The receiver is attached to an ear
mould. These hearing aids can be attached to an external air
or bone conduction receiver. Body-worn hearing aids are
very commonly used in our country.
Body worn hearing aid with single cord

9. Advantages:
•Can provide high gain and has less chances of acoustic
feedback due to more distance between microphone and
receiver.
•Larger controls and larger batteries allow old patients to
handle it easily.
•These are more sturdy and durable.
•Body level hearing aids are less expensive to buy and
maintain.
•They also have lesser problems of feedback squeal if the
ear moulds are not good.

10. Disadvantages:
•Body worn hearing instruments are less appealing
and cumbersome because of their large size and
cords.
•The microphone placement is not very ideal as it is
chest mounted.
•There is a difficulty in eliminating the effects of
cloth rubbing noise.
•The cords are difficult to manage and are prone to
damage easily.

11. 2. Ear level hearing aids:
As the name suggests, ear level hearing aids are worn on the ear.
These can be of different types such as post-aural (behind-the-ear
aids) and intra-aural (in-the-ear aids, in-the-canal aids, and
completely-in-the-canal) aids.
a] The behind-the-ear hearing aids :
The behind-the-ear hearing aids are designed to fit behind
the pinna. The microphone, receiver and amplifier are
mounted in the characteristic banana shaped curved case
that fits neatly behind the pinna and rests against the
mastoid prominence. A thin plastic tube or hook connects
the case of the aid to the ear mould.

12. They can incorporate a wide range of performance characteristics and
circuitry such as programmable and digital. The behind-the-ear
hearing aids are more expensive to buy and maintain than the body
level hearing aids. They are small and thus easy to wear in children.
They offer more flexibility with respect to adjustments in the output
signal. As the microphone is at the level of the ear, these aids provide
all advantages of binaural hearing when worn binaurally. Localization
of sounds is easy compared to two pocket model hearing aids mainly
due to position of the microphone. The figure shows the parts of a
BTE aid.

13. Advantages:
•Cosmetically these are more popular due to the smaller
size.
•Microphone placement in the hearing aids is at the ear
level and hence resembles natural hearing to a great
extent.
•
Disadvantages:
•BTE hearing aids are costlier than the pocket hearing aids.
•As compared to body worn aids, these aids are delicate
and prone to early damage. Servicing and repairing can be
quite costly. Sweat can be the main cause of problem in
these instruments.

14. b] Intra-aural (In the ear) hearing aids:
The intra-aural hearing aids are of three main types - the
in-the-ear, in-the-canal and completely-in-the-canal aids.
These are very small hearing aids that are placed inside
the ear pinna, inside the external auditory canal and
deep inside the external auditory canal respectively.
These in-the-ear type instruments are generally
considered to be acoustically superior to the other types
as the microphone is within the ear and the receiver is
near the tympanic membrane. All the parts of these
hearing aids are housed in a hard plastic casing called as
the shell, which is made by taking the ear impression of
the user.

15. These instruments are also called as custom instruments as they
are housed within a custom made mould specifically for the user.
These instruments are generally suitable for individuals with
mild to severe hearing impairment. The following figures show
the parts of an in-the-ear hearing aid and different types of in-
the-ear aids.

16. Advantages:
•Natural enhancement provided by pinna is utilized due to position of
the microphone at the ear level.
•Cosmetically these are more appealing than the other hearing aids
Disadvantages:
•Due to smaller and fewer user controls, fewer acoustical
modifications are possible.
•These are not useful for average losses (500, 1k, 2k) beyond 70 dB,
due to feedback problems
•They are expensive and not recommended for children because the
entire hearing aid will need to be re-cased if the size and shape of the
ear changes. In BTEs and pocket model aids, only ear moulds need to
be changed.
•These aids are less durable and expensive to purchase and maintain.

17. B.] Mode of Operation:
Based on the mode of operation or presentation of the
signal, hearing aids can be classified as air conduction
aids and bone conduction aids. This refers to whether
the amplified signal is delivered to the ear via the air
conduction route or the bone conduction route.
1.] Air-Conduction hearing aids:
These are designed to convert the amplified electrical
energy back to acoustical energy by an air conduction
receiver and direct it through the ear canal via the ear
mould.

18. These are designed to convert the amplified electrical energy into
mechanical vibrations. The mechanical signal is then delivered to the
ear through a bone vibrator that is placed behind the ear on the
mastoid bone, bypassing the outer and middle ear to a great extent. It
is mainly used in cases of congenital abnormalities of outer ear or in
cases of chronic ear discharge. Bone conduction fitting is possible with
body worn hearing aids and not with ear level hearing aids. In this
case, the external air conduction receiver of a body level hearing aid is
replaced by the bone conduction vibrator. The cord is attached to a
headband and a vibrator. The following figure shows a body worn
hearing aid attached to a bone conduction vibrator.
Bone conduction hearing aid

19. C.] By the type of circuitry:
Hearing aids can also be classified based on the manner in
which the signal processing is carried out by the circuit of the
hearing aid.
1.] Analog hearing aids:
Analog hearing aids have a microphone that picks up
continuously varying sounds in the environment and converts
the sound into electrical signal and amplifies the electrical signal
which is transduced via the receiver back to acoustic sounds to
fit the needs of the hearing aid user.

20. 2.] Programmable hearing aids:
These aids have a circuitry that functions in the same fashion as the
analog circuitry; however the parameters of the signal are
controlled digitally. These aids are more comfortable and
compatible with the person’s hearing loss as they can be
programmed as per the needs of the client.
3.] Digital hearing aids:
Fully digital hearing aids have the most advanced and most
expensive type of circuitry called as Digital Signal Processing (DSP).
These aids are nothing but wearable computers, in which the
analog signal is converted into a digital signal. All functions of this
aid are programmed by software. This can be fitted for all degrees
of hearing losses.

21. D.] By the amount of maximum gain:
Gain refers to the amount of amplification provided by the
hearing aid. Some hearing aids provide less amount of gain while
some amplify sounds to a greater extent. There are international
and national standards that classify hearing aids based on the
amount of gain provided by the aid. Generally, the classification
is as follows:
•Strong class – full on gain 65 dB
•Moderate class - full on gain 55 dB
•Mild class - full on gain 45 dB

22. E.] Number of ears amplified:
Based on the number of ears provided the hearing aid and the manner in
which this amplification is provided hearing aids can be classified in three
different ways.
1.] Monaural Fitting: When a hearing aid is used only in one ear the fitting
is called as monaural fitting. This aid thus has one microphone, one amplifier,
and one receiver.
2.] Binaural fitting: When amplification is provided to the two ears by way
of two different hearing aids, it is referred to as a binaural fitting. This
hearing aid thus has two different microphones, two amplifiers and two
receivers. Binaural fitting helps a person to locate the sound and improves
speech intelligibility in noisy environment.
3.] Pseudo binaural fitting: One body worn hearing aid fitted with V or Y
cord gives amplification simultaneously to both the ears then this type of
fitting is called pseudobinaural fitting. This type of fitting is still preferred in
Indian scenario as it is economical compared to binaural fitting.

23. Tactile Aids
Tactile aids help those individuals with hearing
impairment who get limited benefit from hearing aids.
In this these devices, the signal are transmitted
through the tactile mode to help those individuals who
do not benefit from the auditory mode.
Tactile aids are of two types :
1. Vibro-tactile
2. Electro-tactile

24. •A vibro tactile aid convert sounds (acoustical energy) to
vibrations.
•Electro-tactile devices convert acoustical signals in to
mild electrical signals that cause a tingling sensation on
the skin.
•Both types of tactile devices have of a microphone that
picks-up sounds and a processor that codes the signals
picked up.
•Vibro-tactile devices have one or more vibrators which
transmit the coded signal to the skin through vibrations.
•Electro-tactile devices have electrodes that transmit the
signal to the skin through electrodes.
• The vibrators/electrodes can be placed on various
places on the body such as the wrist, fingers, arm, chest,
abdomen, waist or thighs.

25. Stages in hearing aid selection for children:
1. First step is to quantify the child’s residual hearing and to
determine candidacy for hearing aid fitting.
2. Before hearing aid trial, child should have custom earmoulds.
Clinician can make parents aware about the various options
available with respect to types of earmould, allow them to choose
the appropriate one for their child.
3. During pre-selection of hearing aids, issues like type and style of
aid, ears to be fitted and specific electroacoustic characteristics to
be chosen are considered before further assessment.

26. Cleaning, Care and Maintains of Hearing Aid
1. Hearing Aid should be cleaned every day
2. To clean hearing aids, use dry cloth/tissue or brush.
3. Store hearing aids overnight in a clean, dry and safe place.
4. Keep the hearing aid in the box.
5. If possible place the hearing aid with the silicon bag to
remove moisture from the hearing aid.
6. Try to avoid hearing aid from getting wet in rain, or during
washing face.
7. Avoid keeping near electronic & hot places or magnetic
fields. E.g. On electronic equipments like Fridge, TV music
system, Computers etc.
8. Try to avoid breakage or falling of hearing aid.

27. Classroom Strategies
General Strategies
If the student lip-reads :
oHave students sit closer to the teacher.
oSpeak slowly, naturally, & clearly.
oDo not exaggerate your lip movements
or shout.

28. Group amplification devices:
Imagine a typical classroom situation, where it is not possible
for the teacher to be very close to each and every child at the
same time or the classroom environment could have lot of
reverberation. In such cases, in spite of using a hearing aid, the
student with hearing impairment may face lot of difficulties in
listening. Group amplification devices could be of great help to
the listener in this situation as it enhances signal to noise ratio
Group amplification systems generally consist of a mic, an
amplifier and several receivers for delivering signals to
individuals with hearing impairment. There are different types
of group amplification devices commercially available such as
hardwire system, induction loop system, FM system, and
infrared system.

29. A.] Hard wire system:
These systems couple the sound source via a microphone, amplifier, and
external receiver through the use of hard wire. The microphone is worn by
the teacher in the neck loop. The system is fixed on the desk of the
students in the classroom. Each child’s desk has a control box with volume
control for both ears separately. It functions exactly like a hearing aid; the
signal is picked up by the microphone worn by the teacher. It is amplified
by the amplifier and delivered to the receiver or headphones worn by
students which convert it back to acoustic stimuli. Student can adjust the
intensity of the signal with volume control. The child cannot wear his
individual hearing aid while using this system.
Hard wire system

30. Advantages:
•It improves the signal to noise ratio as the microphone
placement is nearer to the source.
•It is cheaper compared to the other classroom amplification
devices.
•Student can adjust the gain of the signal as per his/her
requirement.
Disadvantages:
•In the older version a microphone was worn only by
teachers so conversation among students was difficult.
•Head phones are bulky so students find it uncomfortable to
wear it for a longer time.
•Students’ mobility is severely restricted due to connected
wires.

31. B.] Induction loop system:
This is one of the oldest and comparatively cheaper forms of assistive
listening technology still popular in educational set ups. Main parts of
this system are microphone, amplifier, a loop of wire and receiver. The
input signal is picked up by a microphone and transmitted through
the loop wire. This wire generates magnetic field, the strength of
which is proportional to the input signal. This energy is picked by the
individual hearing aids with an activated T coil. The received signal is
further amplified by the amplifier of the hearing aid and then
converted into sound signal.
Induction loop system

32. Advantages:
•This system can cover a large area, providing amplification for large
groups of individuals with hearing impairment.
•It can have an individual use too, with an induction loop worn
around the neck by an individual listener.
•Irrespective of the distance the user gets similar kind of input
constantly.
•Use of induction loop improves signal to noise ratio.
•The child is not physically restrained and can move freely.
•The system is used with the child’s own hearing aids, so the electro-
acoustic characteristics selected for a particular child are
maintained in the signal received in the input that the child receives.
•The child can use the hearing aid on the MT setting, whereby the
child can receive the teacher’s voice through the tele-coil and the
other students’ voice through the microphone. This promotes
interaction between the students.
•It does not involve high cost for purchase as well as maintenance.

33. Disadvantages:
•Spill over: If there is more than one room looped in the
same premises, magnetic field generated in one room could
be picked up by a tele-coil in an adjacent room.
•Fluorescent lights, transformers, electric power wires in the
area may cause interference in the induction system, may
sound like a hum or distortion in the output.
•There could be dead spots in the room which means areas
in the room where electromagnetic field does not reach.
•To get the optimum benefit of the induction loop, the tele-
coil of the hearing aid of the user has to be efficient.

34. C.] Frequency modulated system:
This is a wireless system. FM amplification systems usually consist of a mic,
a transmitter, and a receiver.
In this sound is picked up by a microphone and transmitted in the form of
radio frequency modulated carrier waves to a personal receiver worn by the
listener with hearing impairment. The personal FM receiver worn by the
listener must be set to the same channel and radiofrequency as the
microphone and transmitter worn by the person speaking. The frequency of
the FM signals has to be within a bandwidth specified by the National
norms.
Frequency modulated system

35. Advantages:
•These can be used outdoors as well as indoors. Distance as much as 30 TO
200 sq feet can be easily covered by FM systems.
•Clarity of signal is very good.
•These systems being cordless do not restrict mobility of the speaker or the
receiver.
Disadvantages:
•It can pick up the interference from signals passed along the same FM
carrier waves.
•FM systems are very expensive so though they are very effective hardly any
schools for children with hearing impairment have installed it till date.
•A personal FM system is coupled with a person’s own hearing aids. Sounds
are channeled from hearing aid through the FM system making this system
dependent on the integrity of hearing instrument function. Coupling options
for personal FM amplification system include neck loop, silhouette and DAI.
Unlike individual FM system sound field FM system allows everyone within
the area such as a classroom setting to benefit from amplification.

36. D.] Infrared system:
These are wireless type of assistive technologies used to transmit
signals by invisible light waves to the listener. The sound that is
picked up by the microphone is converted into infrared light waves
with the help of diodes which are spread across the room. The
receiver worn by the user converts this signal back to the sound. The
receiver also acts like an amplifier and can be adjusted by the listener
as per his need. Any number of receivers can be used with the emitter
(Crandell et al 1995).
Infrared System

37. Advantages:
•Infrared systems can cover large areas or also can be used as
personal amplification systems.
•It can be used in theaters, auditoriums.
Disadvantages:
•A factor that can inhibit the performance of an infra red system is the
amount of interference caused by lighting within the room as well as
natural sunlight
•This can be used only in enclosed rooms.