This set of Audio Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Audio Devices – Public Address Systems”.
1. What is the full form of PA system in audio devices?
a) Public address
b) Phase action
c) Power action
d) Public action
View Answer
Explanation: The full form of PA system is public address system. As the name suggests it is a system that is used to address public. It is used in sports meets, public meetings, concert etc. It is also used to convey information to isolated locations such as railway station, airports, hospitals etc.
2. The intensity of sound increases with the distance in PA system.
a) True
b) False
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Explanation: The above statement is false. The intensity of sound decreases with the distance. Hence when a large gathering is to be addressed, sound needs to be amplified so that people at a distance from the stage may obtain good intensity of sound for comfortable listening. The system which fulfills this function is called ‘Public Address System’.
3. Which type of system is the PA system in audio devices?
a) Electroacoustic
b) Electro dynamic
c) Electromagnetic
d) Piezo-electric
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Explanation: PA (Public Address) system is an electroacoustic system, in which sound is first converted into electrical signals by a microphone. The electrical audio signals are amplified, processed and applied to another transducer the loudspeaker, which converts the audio signals into sound waves.
4. To which stage is the output of microphone fed in PA system?
a) Voltage amplifier
b) Loudspeaker
c) Power amplifier
d) Mixer
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Explanation: The output of a microphone is fed to a mixer stage in PA system. The function of the mixer stage is to effectively isolate different channels from each other before feeding to the main amplifier. It can be either a built-in unit or a separate unit.
5. How many types of mixers are there in a PA system in audio devices?
a) 1
b) 2
c) 3
d) 4
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Explanation: There are two types of mixers. The simplest one does not use pre-amplifiers, but uses only gain control and isolating series resistor. A little more sophisticated one uses common pre-amplifier for separate channels and an emitter follower.
6. Which gain control is used in processing circuit in PA system in audio devices?
a) Master
b) Slave
c) Key
d) Optical
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Explanation: Processing circuit has the master gain control which changes the gain of the system for high frequencies up to 15-20 KHz and low frequencies up to 500-1000 Hz. It also has the tone control i.e. Bass and Treble control. The bass control is a low pass filter while the treble control is a high pass filter.
7. Which amplifier uses push-pull type amplifier circuit in PA system?
a) Power amplifier
b) Voltage amplifier
c) Driver amplifier
d) Frequency amplifier
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Explanation: Power amplifier gives power amplification to the signal. It uses push-pull type of amplifier circuit in general. The output of the power amplifier is connected to the loudspeaker through a matching transformer to match the low impedance of the loudspeaker for maximum transfer of power.
8. Which of the following convert electrical signals into pressure variations resulting in sound waves in PA system?
a) Mixer
b) Microphone
c) Loudspeaker
d) Driver
View Answer
Explanation: The final stage in a PA system is loudspeaker. The electrical audio signals are amplified, processed and applied to another transducer the loudspeaker, which converts the audio signals into sound waves. Loudspeaker is a transducer that converts electrical signal into pressure variations which results in sound waves.
9. How is the sound power distributed amongst the audience to achieve uniformity in PA system?
a) More loud speakers in listener’s area
b) 1 or 2 loudspeaker near a stage
c) 3 or 4 loudspeaker near a stage
d) More loud speakers in listener’s area
View Answer
Explanation: Loudness of sound is contained in the low notes and the intelligibility in high notes. So in PA system, it is required to have sound which is uniformly distributed amongst the audience. This means that instead of one or two loudspeakers near a stage, the sound power should be distributed uniformly with more loudspeakers in listener’s area.
10. Which type of microphone does not pick up reflected sound as well as the sound waves from the loudspeakers in PA system?
a) Electret
b) Moving coil
c) Ribbon
d) Cardioid
View Answer
Explanation: Microphone should not pick up the reflected sound as well as the sound waves from the loudspeakers. This can be made possible by the use of cardioid microphone. As the name suggests the directivity pattern is roughly shaped like a heart.
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