A sound system's job is not to be loud. It is to deliver intelligible sound, evenly, to every person in the room — and almost every bad live sound experience is a failure of one of those three words rather than a shortage of power.
A live sound system is a chain that takes sound happening on a stage, converts it to electricity, makes it much larger, and converts it back to sound in a way an audience can hear properly. That description is uncontroversial and it hides the entire difficulty, because it says nothing about what properly means.
It is worth being precise about the goal before any equipment is discussed, because almost every bad live sound experience comes from optimising the wrong one.
Three requirements, in this order of priority.
Intelligibility. The audience must be able to understand what is being sung and said, and distinguish the instruments from one another. This is the first job. A system that delivers a loud, undifferentiated wall of sound has failed even if every meter is reading correctly, and no amount of additional level improves it — beyond a point, more level makes intelligibility worse, because a room's reverberant field grows with it while the direct sound does not gain any advantage.
Coverage. Everyone in the audience should hear approximately the same show. Not identically — that is physically impossible — but without a third of the room getting a bright, harsh version, another third getting a muddy one, and someone at the side hearing mostly the wall. Coverage is a geometry problem and it is solved by where boxes are aimed, not by how much power feeds them.
Level. Loud enough to be exciting and to sit above the audience's own noise, and not so loud that it hurts, distorts or drives people out. Level is genuinely third. It is the requirement most systems meet easily and the one most people adjust when the real problem is one of the other two.
The order matters because the three interact and the interactions are not symmetrical. Improving coverage usually improves intelligibility. Increasing level usually damages both.
Every live system, from a single powered speaker to a stadium rig, is the same sequence of stages. Learning it as a sequence is what makes faults findable, because a fault is always at a stage and the stages are in a fixed order.
Two things about that list are worth stating explicitly. The room is the last stage and it is the one you did not choose, cannot replace, and usually cannot modify — so it is a constraint the rest of the design has to work around. And the preamp is early: everything downstream amplifies whatever happened there, including the noise, which is the entire subject of the gain-structure lesson later in this course.
Systems get categorised by what they are for, and the categories imply genuinely different priorities.
Band and club reinforcement. Reinforcing live musicians in a room where the audience can also hear the stage directly. The defining characteristic is that the PA is not the only sound source — a drum kit is loud on its own, guitar amps are pointed at the audience, and the system is adding to that rather than replacing it. This is where stage volume becomes the deciding constraint, covered in the monitors lesson.
Installed versus touring. An installed system is designed for one specific room, permanently mounted, aimed once and carefully. It can be optimised in ways a touring system never can, because the room is known. A touring system meets a new room every day, so it is built for adaptability and rapid setup, and it accepts compromises an installed system would not — which is why a good touring engineer's real skill is adapting a known system to an unknown room quickly.
Show relay and distributed systems. Sound distributed to places the main system does not reach: delay speakers further back in a large venue, foyer and dressing-room feeds, overflow areas. The technical requirement here is timing — a distant speaker must be delayed so its sound arrives with the main system's rather than ahead of it, or the result is an echo and a collapsed sense of where the sound is coming from.
Everything in Specialization 5 about how rooms behave applies to live sound, with two aggravating factors.
The first is that the room is usually large and usually reflective — hard floors, hard walls, a high ceiling. Reverberation time is long, and a long reverberation time is directly hostile to intelligibility, because each syllable is still ringing when the next one arrives. This is the physical reason a system in a sports hall sounds bad regardless of its quality.
The second is that the room changes when the audience arrives. People are effective absorbers, particularly at mid and high frequencies. A room tuned empty in the afternoon will sound noticeably duller and shorter once it is full, and the difference is large enough that engineers who tune to a flat response in an empty room routinely find themselves adding brightness during the first song.
This is why a live system is never simply set up and left. The design is done in advance, the tuning is done on site, and the last adjustments are made once there are people in the room.
The stages above describe the signal. The day has its own sequence, and it is worth knowing because almost every problem is cheapest to fix at one specific point in it.
The principle running through it is the same one the whole course keeps arriving at: the earlier a decision is made, the more it constrains, and the cheaper it is to make well. A box aimed correctly at load-in solves a problem that no amount of mixing later will.
The roles are worth naming, because on small shows one person does all of them and on large ones the divisions are strict — and knowing which job you are doing at any moment prevents a lot of confusion.
Front of house mixes what the audience hears, and owns the main system's tuning and level.
Monitors mixes what the performers hear, and owns everything on stage. On a small show this is the same person as front of house, working from the same console, which is why monitor changes during a performance tend not to happen.
Systems designs, deploys, aligns and tunes the loudspeaker system itself — coverage, crossovers, delays, limiting — and hands a working system to the front-of-house engineer. On a touring rig this is a distinct specialism and the person doing it may not mix at all.
Stage technicians place microphones and DI boxes, run cable, fix what breaks, and deal with instrument changes. They are the people who determine whether a line check finds problems or the first song does.
The pattern to notice is that the further down that list, the earlier the work happens and the less visible it is. A show that runs well is usually one where the systems and stage work was thorough, and a show that runs badly usually reveals that somebody was mixing around a problem that should have been fixed hours earlier.
Systems divide into two arrangements, and the choice affects far more than convenience.
A passive system separates the loudspeakers from the amplifiers: the amps live in a rack, and speaker cable carries amplified signal out to the boxes. The amplifier and speaker are matched by the person specifying the system, which means both freedom and responsibility — Course 10.2 covers what happens when the matching is wrong. Long speaker cable runs lose power and damping, so cable gauge becomes a real design consideration.
An active or powered system puts the amplifier inside the enclosure, usually with the crossover and a protective limiter alongside it. The manufacturer has matched the amplifier to the drivers, tuned the crossover for those specific drivers, and set the limiter to protect them — so a great deal of the specification work is already done, and done better than most people would do it. What arrives at the box is line level down an ordinary cable, and mains power has to arrive there too.
The practical trade: active systems are simpler to deploy, harder to get badly wrong, and put a mains requirement at every speaker position. Passive systems concentrate the power in one place, allow the amplifier choice to be changed independently of the boxes, and demand that whoever specifies them understands impedance, power and cable. For most small and medium work, active has won for good reasons.
The mix position is part of the system design, not an afterthought, because an engineer can only mix what they can hear.
The requirement is to be somewhere representative of what the audience is getting. Two positions are actively bad and both are common. Against the back wall, where low frequencies build up substantially — an engineer there hears too much bass and mixes it out, leaving the rest of the room thin. And under a balcony, where the high frequencies are shadowed and the reverberant field is different from the main floor — an engineer there hears a dull, boxy version and compensates by adding brightness the rest of the room did not need.
A good position is roughly two-thirds of the way back, out of the exact centre line of the room, clear of walls, and within the main system's coverage rather than at its edge. Where the venue makes that impossible, the correction is to walk the room during the show — repeatedly, not once — and adjust for what the audience actually hears rather than what the desk position reports.
Three things, none of which appear on a specification sheet.
Boxes aimed at people. Sound that hits a wall, a ceiling or an empty floor arrives back as reverberation, which reduces intelligibility for everyone. Sound that hits an audience is absorbed by them after they have heard it. Aiming is free and it is the single largest determinant of how a system sounds in a room.
Gain taken in the right place. A system with its gain structure right is quiet between songs and clean at full level. One with it wrong hisses, or clips early, or both, and no amount of good equipment compensates.
Headroom left unused. A system running at its limit sounds worse than the same system running comfortably, because limiters engage, amplifiers approach clipping and drivers approach their excursion limits. A rig that is comfortably larger than the job is not wasteful; it is what allows the job to be done cleanly.
The rest of this course takes those three in turn: how to design coverage for a room, how to set gain across the whole system in a defined order, how to buy back the level a room is stealing from you, and what has to happen on stage for any of it to work.
Intelligibility first, coverage second, level third. A system that is loud everywhere and clear nowhere has failed at its actual job, and turning it up will not fix it.
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