How Do PA Systems Work?

By Paul Bright


The goal of a PA system is to provide "public address", or a way to transmit audio communication to a group. This transmission can begin with a microphone, which is a device that can assist in magnifying an audio source's volume. A microphone is classified as a device that transforms sound into an electrical signal. Microphones used in PA systems are usually dynamic or condensers. Dynamic microphones are more rugged than condensers and are able to withstand the elements a little better. Condenser microphones utilize their own power source and produce better-quality audio signals, but can sometimes be so sensitive that they also receive background noises.


If a microphone or another audio source is used in a PA system, it is plugged into a mixer. The mixer allows for multiple channels of sound to be broadcast at different levels. This can help prevent feedback if a PA system will involve multiple microphones, instruments, or other audio sources. For example, someone may use a PA system to sing along with a pre-recorded CD. The CD track could be plugged into one channel, while the singer's voice would be broadcast through another.


The amplifier is usually side by side or incorporated with the mixer. The amplifier's job is to magnify the audio signal by manipulating its varying frequency qualities. Gain in an amplifier refers to the decibel level of the sound coming out of the speakers. Another quality, Output Dynamic Range, refers to the loud and soft levels of a specific channel's sound. Too low of an output could result in just broadcasting noise; too high of an output can lead to distortion.


The loudspeaker is the output end of the PA system, transforming the electrical signal back into sound that a group can hear. A good loudspeaker system will separate the differing sound frequencies and broadcast them through different sound channels for better quality output. Parts of a loudspeaker system include a woofer, which broadcasts low frequency sounds; and tweeters, the drivers of high frequency output. Some speakers also contain crossover systems that are responsible for separating these frequencies, reducing the electrical noise that can sometimes accompany a PA system broadcast.

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