group.pptx

Group amplification
Submitted by –zareen ahad
Submitted to – Mr Bhowmick kandpal

Introduction
◦ 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
individual with hearing impairment.

Sound enhancement Technology
1. HARDWIRE SYSTEM:
◦ Hardwire system provides a direct connection
between the sound source and the individual.
◦ In hardwire systems, a wire connects the
microphone to the amplifier, which is connected
directly to the receiver (headphones, ear buds).
◦ The teacher’s (speaker’s) microphone is connected
to an amplifier and the resulting amplifier signal is then delivered to a
series of headsets located in fixed positions.

1. wireless microphone may be used to give the speaker
more mobility. The microphone has to be placed close to the
lip of the teacher. The individual headset has the volume
control (gain control). This control allows adjusting the
individual gain independently to each ear according to the
degree of hearing loss of the child (listener).
2. An additional microphone wired to the amplifier may also
help to hear other children and to hear themselves, which
helps in self-monitoring and in child to child communication
(Bess, 1981).
3.The number of headphones to be connected to the system is
depends on the capacity (power) of the amplifier. 10, 12 or
16 students can be connected with the hardwire system.

Advantages:
◦ 1. These systems generally provide a wide frequency
range, low distortion and high sound pressure output
under the headsets (Clavert, 1964).
◦ 2. They offer high fidelity sound.
◦ 3. They may be adapted to the child’s hearing loss and
are fairly reliable and simple to operate (Bess, 1981).
◦ 4. The cost of hardware is very less.
◦ 5. Not susceptible to electromagnetic interference.

Limitations:
◦ Unfavorable SNR may occur due to the presence of monitoring
microphone (Bess, 1981).
◦ Lack of mobility for student and teachers.They lack flexibility, in that
they seldom allow for individual adjustment of frequency (Bess 1981).
◦ Repair service is not readily available (Clavert, 1964).
◦ They are not specified as devices by Food and Drug Administration
(FDA), therefore there are no standards for the EAC (gain, frequency
response). So to see its function real ear measurement should
beperformed periodically.

2. INDUCTION (Audio) LOOPS SYSTEM:
◦ The components of a "loop" induction system are a microphone, an
amplifier, and a length of copper wire that loops the seating area. The
microphone picks-up the acoustic voices and generates a magnetic
field that couples with the telecoil in the hearing aids (Vaughn and
Lightfoot, 1987).
◦ Some loops are connected to standard public address systems.
◦ The electric current flowing through the loop creates a magnetic field
that can be picked up by a hearing aid set on the T-Switch. Portable
receivers are available for hard of hearing individuals without a hearing
aid T-switch. To pick up the signals, listeners must sit within or near the
loop.
◦ The acoustic gain of loop induction system varies between 3dB-5dB.
The amount of amplification is directly related to The distance of the
hearing aid from the loop.

Advantages:
◦ Gives better SNR.
◦ Mobility of children is not affected in the classroom.
◦ Frequency range is large.
◦ Constant and equal distribution of teacher’s SPL in
◦ classroom.
◦ Same hearing aid can be used inside and outside the class. So the kind of
output the individual gets inside the class and outside, is the same.
◦ It is relatively inexpensive and easy to install.

Disadvantages:
◦ Requires hearing aid or some device with Telecoil.
◦ The output of hearing aid is different when using it with M- position and T-position. The output is
more for (M) microphone position than T-position.
◦ There might be a time delay in the signal received through M-position and T-position. This can affect
intelligibility of speech by the child.
◦ When on ‘T’ position, child will hear only what the teacher says but not what other children say in the
class. ‘MT’ position helps to overcome this problem, but may result in poorer SNR as ambient noise is
also picked up by the microphone.
◦ Loop induction system generates high level of internal noise.
◦ There is a “spill over” of the signals in all direction.
◦ There is also interference by other devices producing electromagnetic field in the same or near by
room.

FREQUENCY MODULATION SYSTEMS
◦ FM systems, originally designed for and restricted to
classroom use, are now benefiting hard of hearing users in
general society. They work in this way: Sound is picked up at
the source by a microphone, the speech is frequency
modulated into a radio frequency carrier wave and
transmitted through air by an FM transmitter.
◦ The FM receiver worn by the HI person receives the signal
and demodulates the speech, amplifies it and delivers it to
the ear via earphone or listener’s hearing aid.

◦ Frequency bands that are dedicated for low power FM
transmission for individuals with hearing impairment include
72-76 MHz and 216-217 MHz. These frequencies tend to
have least interference.
◦ 216 MHz band is used for longer range requirements i.e. up
to 300 feet, where interference is a problem, or where good
sound quality is a must.

Advantages
◦ Provides benefit to all normal hearing listeners as well as children
with HL in the room.
◦ Often the most inexpensive procedure of improving classroom
acoustics.
◦ Speakers/teachers report lessened stress and less vocal strain
during teaching activities.
◦ It can be connected with other instructional equipments (like TV,
cassette tape/CD player, etc.) to improve the auditory signals.
◦ High mobility for speaker and listener.
◦ Not susceptible to electromagnetic interference.

Disadvantage
◦ May not provide adequate benefit in excessive noisy or
reverberant listening environments.
◦ Primarily used only for normal hearers and listeners with milder
degrees of HL
◦ May not be feasible in smaller rooms due to feedback problems
associated with the interactive effects of reflective surfaces and
speaker closeness.
◦ May not benefit children with sever recruitment or hypersensitive
hearing.

Infrared (IR)
◦ Infra-red transmission means that the transmission of signals by
infra-red light.
◦ In Infrared Systems the sound picked up by the microphone (FM
microphone), is converted into infrared light waves, which are then
dispersed throughout the listening environment through an IR
transmitter.
◦ A special IR receiver is worn by the listener, which converts these
light waves back to sound.
◦ Like FM systems, infrared systems are useful in group situations
and may be adapted for individual use as well.

Advantages:
◦ It offers a high fidelity signal of broad frequency range.
◦ The frequency range extends from 100 Hz to 8000Hz. (Mark & Ross, 1982)
◦ Gives high output, about 120 dB.
◦ SPL can be controlled by individual listener.
◦ Reliable and durable.
◦ The IR receiver are universal and can be used with any IR transmitter (Bess,
1981).
◦ Mobility is not affected.
◦ IR can be commonly used in courtrooms, movie theaters and live performance
theaters, conventions and with TVs.

Disadvantages:
◦ It can not be used outdoors or in a room without an emitter.
◦ 2. Susceptible to interference from bright sunlight or
fluorescent lights.
◦ 3. Typically requires line-of-sight between the IR transmitter
and the receiver i.e. any obstruction in front of receiver affects
the signal.

group.pptx

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