Transcript public address system

PUBLIC ADDRESS SYSTEM
As apart of Active Learning Assignment (ALE) in the
subject of Audio & Video System [AVS]
Code:2151101
Student Name :SAGAR BHUMI K.
Enroll no. : 141083111002
Branch : Electronics & Comm.
Sem. : V
 TOPICS IN-SIDE:Sr. No.:
Topic
Page
No.:
1
INRODUCTION
3
2
BLOCK DIAGRAM
5
3
REQUIRMENT OF PA SYSTEM
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4
TYPICAL PA INSTALLING
PLANNING
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5
PA SYSTEM FOR A DEBATING
HALL
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6
PA SYSTEM FOR COLLEGE
SPORTS
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7
APPLICATION
16
Introduction:A public address system (PA system) is an
electronic sound amplification and distribution
system with a microphone, amplifier and
loudspeaker.
 The intensity of sound decrease with the distance
to receive good intensity of sound for comfortable
listening.
 The system fulfils this function is called public
address system.
 Or simply PA system.
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First electronics public address system from
about1920 ,used to amplify a speaker’s voice
when addressing crowd.
It consisted of a microphone attached vacuum tube
amplifier increase the power gain which drove
loudspeaker.
 BLOCK DIAGRAM :
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It is an electronics system in which converts into electrical
signal by microphone.
The electrical audio signals are amplified and fed into another
transducer the loudspeaker which converts the audio signals
into the sound wave.
The block diagram consist :Microphone
Mixer
Voltage amplifier
Processing circuit
Driver amplifier
Power amplifier
Loud speaker
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Microphone:It is a electrical transducer it pick up sound wave and
converts into the electrical variations called audio signal.
Mixer :The output of the microphone is fed into the mixer stage.
the mixer stage is to effectively isolate different channels
from each other before feeding into the main amplifier.
Voltage amplifier :It further amplifies the output of the mixer.
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Processing Circuit :These circuit have master gain control and the tone controls.
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Driver amplifier :It is gives voltage amplification to the signal to such an extent
that when fed to the next stage the internal resistance of that
stage is reduced .
Power amplifier :it is gives desired power amplification to the signal. it is pushpull type of circuit in general. the power amplifier connected
to the loudspeaker.
Loudspeaker:It converts electrical audio signal into pressure variation
resulting in sound.
 Requirements of a public address system:
The following precautions should be taken while installing a
PA system:-
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Acoustic Feedback:Sounds from the loudspeaker should not reach the
microphone, as a acoustic feedback will result in a loud
howling sound.
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Distribution of sound intensity :Loudness of the sound is contained in low notes and the
intelligibility in high notes. As high notes suffer grater
attenuation with distance than the low note intelligibility
suffers at further distance.
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Reverberation :In a reverberation medium the intelligibility is poor. The Pa
system should throw additional power in those areas where
the direct gets submerged in the echoes.
Dynamic Range Limitation:The amplifier of a good PA system is equipped with a level
limiter which keeps the output level constant when the input
level exceeds a certain predetermined value.
Matching :Matching of the loudspeaker impedance with the output
impedance of the amplifier is necessary for maximum transfer
of energy from amplifier to loudspeaker.
Grounding :Chassis and shields of equipments and coaxial cables should
be properly earthed through water pipes.
Typical PA Installation Planning:
Installation of a PA system need carefully thought and logical
planning.
Planning for the following typical situation :I.
Public meeting
II.
Auditorium having large capacity
III. Debating chamber
IV. Football stadium
V.
College sports
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system for a Debating Hall :-
In this system microphone are to be fitted for each speaker on
his/her desk.
The audience may be present in the public gallery and they
should be able to hear the debate.
Loudspeakers shall mainly be concentrated on the audience
to avoid acoustic feedback.
Some sound reinforcement is disable in the debating
chamber and this has to be done without causing feedback.
Auto-voice control is essentially required to keep the
channels dead until a microphone is actually used.
In some low-cast system a switch is used to make the
microphone on when the speaker wants to use it.
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A typical system show in fig.
For 24 persons participating in the debate about 150 persons
listening to the deliberation.
 PA system for college sports:
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The annual event of college sports requires coverage to the
teachers and guests on the entrance side to the spectator
students on the opposite side of the field and to the
participants In the field.
The field and students enclosure can be covered by four
columns, two on each side.
Enclosure for teachers and guests can be covered by two
columns .one columns is adequate for the marquee.
A 60W amplifier will be adequate to give 10W each column
for field and students enclosure and 5W to each column for
teachers and guests and one 5W column in the marquee.
 Application
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of PA system :-
Used in
Sports meets
Public meeting
Auditoriums
Concerts & functions
Railway station
Airports
Hospitals
Factories etc..
THANK YOU…. 