PUBLIC ADDRESS SYSTEM As apart of Active Learning Assignment (ALE) in the subject of Audio & Video System [AVS] Code: Student Name :SAGAR BHUMI K. Enroll no. : Branch : Electronics & Comm. Sem. : V

 TOPICS IN-SIDE:- Sr. No.:TopicPage No.: 1INRODUCTION3 2BLOCK DIAGRAM5 3REQUIRMENT OF PA SYSTEM9 4TYPICAL PA INSTALLING PLANNING 11 5PA SYSTEM FOR A DEBATING HALL 12 6PA SYSTEM FOR COLLEGE SPORTS 14 7APPLICATION16

 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.

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 :- 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

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.

Processing Circuit :-  These circuit have master gain control and the tone controls.

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 push- pull 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:- Acoustic Feedback:-  Sounds from the loudspeaker should not reach the microphone, as a acoustic feedback will result in a loud howling sound. 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.

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

 PA 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.

 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:-  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 of PA system :- Used in  Sports meets  Public meeting  Auditoriums  Concerts & functions  Railway station  Airports  Hospitals  Factories etc..

THANK YOU….