A basic public address (PA) system is made up of three essential components. The first is a source of sound which could be a microphone, a musical instrument or another device which can produce audio, such as a CD player. The next item is an amplifier. This augments the velocity of the sound so that it can be heard in a location where lots of people are gathering, such as a hall or school. The third of the three components is a speaker system. Although a PA can work with just one speaker, pairs are usually used in a stereo set up, each conveying the signal of the left and right channels of the amplifier equally to produce a binaural effect.
What sort of speakers are there to choose from? You may need to know the difference if you require speaker hire as part of a temporary PA set up for a social event or concert.
This sort of speaker is increasingly common in smaller venues and pubs in Australia. They are usually fairly small for the amount of sound that they can produce. When a pair of active speakers are used, they don't need a dedicated amplifier. So long as the signal from the audio source is sufficiently strong they do the amplification themselves. With built-in amps, active speakers just need a pre-amplified signal from a mixer unit. In a stereo configuration, active speakers can be adjusted independently of one another, which makes them easy to fine tune.
Unlike active speakers, passive ones don't have amps built into them. This means that they do not need to be plugged into a dedicated power source meaning they have an advantage over active ones in places with few power outlets. They need to be connected to a power amplifier, however, from which they receive their audio signal and their power. Passive speakers often have multiple drivers in them which split the sound according to the frequency it is pumping out.
With a PA that is being used by musicians, a certain amount of sound should be played back to them. If speakers are placed behind musicians using pick-ups or microphones, then undesirable feedback is likely to occur. Instead, hire foldback, or wedge, speaker cabinets which can be placed on the floor in the opposite direction to the way the band will face. This means they can hear what they are playing accurately without messing up the sound the PA creates.