An electronic system used in the broadcasting of information (predefined) or spot announcements of movements in particular locations of the commercial building, public places, high rise buildings, and other places and it is called public address system.
The public address system is an electronic system used for amplification and distribution of human sound signal (20Hz to 20kHz) with help of input transducer (microphone), output transducer (loudspeaker), medium, and signals conditing circuit (amplifier, modulation, demodulation, filter and other).
The block diagram for public address system with wire and wireless medium is shown in fig. 1 and fig. 2, respectively.
The microphone is used to convert the sound signal or audio signal into an electrical signal.
The modulation technique is used to transmit electrical signals or information signal or modulating signal to a long distance with the help of a carrier signal. The modulation technique is classified into two categories like analog modulation (Amplitude Modulation, Frequency Modulation, Phase Modulation), and digital modulation (Amplitude Shift Keying, Phase Shift Keying, Frequency Shift Keying and other).
The amplification circuit is used to amplify the signal. The filter circuit is used to remove unwanted frequency or noise.
Wire (coaxial cables, fiber cables, and other) or wireless communication is used as a medium to transmit data from microphone to loudspeaker.
The demodulation circuit is used to remove the carrier signal from the modulated signal and send an electrical signal to the loudspeaker through the filter or/and amplifier. The filters and amplifiers have used both sides for performing the good quality operation.
The loudspeaker convert the electrical information signal to sound signal.
Nowadays, the public address system is integrated with a fire alarm system for notification of unhealthy conditions or provides a clear view of the problem at a particular location. They also provide information to peoples for performing the different tasks as safety from fire without panic.
The Public Address System is used in various places like schools, sports stadiums, colleges, airports, public transportation vehicles and facilities, and live or recorded music venues and events.
The Public Address System is available with more numbers of microphones, mixing units to mixed and modifies various sources information, amplifiers, and filters, and loudspeakers for wider volume distribution.
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