WILLY T talks PA, FOLDBACK, MULTI-CORE and STAGEBOX, fluently.

A PA, as the name suggests, is a Public Address System. The term public address is simply that, a way in which one person’s voice or music can be heard over many, to address the public. At its simplest a PA is a combination of microphone, amplifier and speaker, e.g. a loudhailer. All PA systems operate using variations of the same basic equipment and operating principles and, in theory, all systems are the same – it’s just a matter of scale.

Generally speaking a PA is a combination of two totally separate sets of speaker and amp systems. The Front Of House system is set up for the audience. It is called FOH as the mixing desk is located among the punters and refers to both the mixer and the main amp/speaker system. The other totally separate Foldback system is for the artist/talent to hear themselves onstage.

All the different sounds to be mixed together – from vocals, acoustic, electric and electronic instruments, samplers, turntables, etcetera – are sent to the FOH mixing desk or console. The sounds onstage are coming from many different sources, at different electrical levels. What comes out of microphones – at Mic Level – is a tiny electrical ‘signal’, measured in mVolts or 1/1000th of a volt. Usually around 2 or 3 millivolts, but a meaty kick-drum can hit +4dBv!

The signal coming from electronic gear like samplers, CD players, MIDI sound modules, DJ decks, etcetera comes out at a much stronger level compared to mics – it’s called Line Level. Line outputs are measured in whole volts! Line level is the common denominator among sound gear, allowing equipment to be easily inter-connected without too much fine-tuning.

At its most basic, a mixing desk is simply a way of electrical level-matching and adjusting volumes, so each component in the chain leading to the loud speakers can ‘talk to each other’ and make the system work. Each mic-input on a mixing desk contains a pre-amp, which boosts the weak microphone signal up to line-level. As mixers become more complex [read: more expensive] they have better quality components and extra facilities on board like tone controls, routing and the auxiliary sends we looked at last week. The mixed and blended sounds emerge from the mixing desk as a stereo pair to feed the left and right FOH speaker stacks.

When large amplification is needed, the problem arises of the performers onstage being unable to hear themselves. This can be caused by crowd noise or most often by the artists being drowned out by the other onstage instruments. (Fuckin’ guitarists!)

To overcome instrument/stage level and time-delay problems, monitors or foldback speakers are put onstage for the performers to hear themselves and other sounds. There are separate sends for each musician or group of musicians enabling each individual muso to hear their own personalised mix of any or all of the instruments and vocals in their foldback ‘wedges’. These individual mixes are all separate from each other, and are totally independent from the FOH stereo mix that goes out into the room. In small PAs foldback is normally done from the FOH desk using the pre-fade auxiliary sends; aka ‘doing foldback from FOH’.

Rather than have a squillion leads flowing offstage down to the mixing desk, all the different signals are sent to FOH by one big lead called a Multi-core or ‘snake’ that runs through the venue from the stage to the desk.

The multi-core is a collection of tiny leads – conductors – bundled into one thick lead each forming a separate balanced audio line. As the multi is the umbilical chord of the whole PA they are often buried in a trench or rigged above the audience (‘flown’) for safety … and to make them ‘punter proof’!

All the leads from the stage signals are patched into the ‘stagebox’ – a big box with a panel of 3-pin female XLR inputs for mic leads – which is attached to the multi-core. All signals in the multi-core are at mic level to allow for longer lengths of cable to be run from the stage to FOH without any electrical voltage drop, which could degrade the sound. (And we can’t have degradation at a rock gig!) Any line-level signals must plugged into a DI unit and converted to mic-level before being sent to the FOH desk by the stagebox/multi.

In larger PAs, or for acts with many instruments or musicians onstage; the foldback system is too complex to be dealt with by one person from FOH so a separate foldback system is used. A ‘split’ stagebox/multi is used to send the signal to both the FOH mixing desk and to a dedicated foldback desk. A split box has duplicate sets of male 3-pin XLR connectors wired electrically ‘in-parallel’ so that they mirror the mic inputs. This allows the one female 3-pin XLR input signal to feed both the multi-core to FOH and the parallel XLR connector into which we patch leads to the foldback desk. On some systems this is done internally with one input and two multi-cores emerging, with one going to the foldback desk and the other to the FOH desk.

All the components, leads and gear that make up ‘the rig’ are working towards the one goal: smoke & mirrors … SHOWBIZ! Make it loud but make it clean and invisible, so punters look to the band not FOH!

WILLY T runs Giraffe Media. Providing Words, Pics and Live-Audio Recording Services to the entertainment industry. Email  for more information.

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