PA System

Features any Well-Designed System Should Have

The sound from a good public address system should be:

• Clean
• Clear
• Intelligible
• Natural
• Balanced
• Evenly dispersed
• Adequate

Some of these terms overlap or are interdependent, but our aim in specifying and setting up a PA system - whether it is a permanent installation or a touring one - is that it can meet all these criteria. Other artefacts - intentional effects, or dynamic control - may be added later (and may be requirements for some specific applications), but the design of the core system needs to address its core function, which is to make things louder without changing them in any other way.

Clean Sound

Clean sound is free from distortion and noise.

Distortion is what happens when the output signal differs in form from the input signal. Ideally the relationship between the sound source and what the audience hears should be linear: the PA system's output at the listening position should vary in direct proportion to the sound source (the only permissible difference is in amplitude). Any non-linearity in that relationship is distortion.

Clarity

Another word for clarity is transparency: we want the sound system to have the same effect on sound as a high quality optical lens has on light; it can make what we are looking at appear larger or smaller, but in every other respect it should behave as if it wasn't there.

What this means, in practice, is that its reproduction should be detailed and accurate, and a key component in this is the high-frequency delivery of the loudspeaker system: in general, better high-frequency performance (greater high-frequency range and lower distortion) will result in a more transparent-sounding system. However (see ‘Naturalness’, below), a system that over-emphasises high frequencies will tend to sound ‘thin’ or ‘harsh’, while a system that over-emphasises lower frequencies will sound less-transparent, no matter how good the HF drivers are.