How a PA system works, from the mixer to the speaker. Decibels, amplifiers, ohms, series and parallel wiring, and how to set up a small system that sounds right and doesn't blow up. Written for beginners. Read it, work through the tools, then pass the quiz.
Every PA system, from a single speaker on a stick to a stadium rig, is the same five blocks in the same order. If you can draw this chain from memory, you can fault-find any system: start at the source and walk forward until the signal disappears.
| Level | Where you find it | Cable | Rule |
|---|---|---|---|
| Mic level | Microphones, DI boxes | XLR (3-pin), balanced | Needs the mixer's gain (preamp) to bring it up. Never plug a mic into a line input. |
| Line level | Mixer outputs, laptops, DJ decks, keyboards | XLR, TRS jack, RCA | The "normal" level everything talks at. Mixer out to active speaker in is line level. |
| Speaker level | Power amp output to passive speaker | Speakon, heavy 2-core | High current. Only ever amp-to-passive-speaker. Never into a mixer or active speaker. |
A decibel (dB) is not a fixed amount of sound. It is a ratio, a way of comparing two levels. Our ears hear in ratios, so dB matches how loud things feel. Learn four numbers and you can reason about any system.
Twice the amplifier power. You barely notice it.
Twice the voltage, four times the power. Clearly louder. Also what you lose every time you double your distance from a speaker.
Ten times the power. Sounds about twice as loud to a person.
Stand 2 m from a speaker. Walk to 4 m: 6 dB quieter. To 8 m: 12 dB quieter. This is why one speaker cannot cover a big room.
A 500 W speaker turned up 6 dB needs 2 000 W to do the same job. Power gets expensive fast. Moving the speaker closer is free.
| Change | Power | Sounds |
|---|---|---|
| +3 dB | 2× | barely louder |
| +6 dB | 4× | clearly louder |
| +10 dB | 10× | twice as loud |
| +20 dB | 100× | four times as loud |
When someone says "it was 100 dB at the bar", they mean dB SPL: sound pressure measured against the quietest thing a human can hear (0 dB). You measure it with an SPL meter or a phone app, set to A-weighting, which ignores the deep bass the way ears do.
| dB SPL (A) | Sounds like | For crew |
|---|---|---|
| 60 | Normal conversation at 1 m | Background music at a cocktail function |
| 75 | Busy restaurant | A speech system doing its job |
| 85 | Heavy traffic | South African OHS limit for 8 hours a day. Above this, ear protection for crew. |
| 95 | Loud bar, dance floor edge | Typical corporate party peak. About 45 minutes of safe exposure. |
| 105 | Front of stage at a concert | Minutes, not hours. Earplugs for anyone working there. |
| 120 | Jet engine, pain threshold | Never. A limiter should stop the system here. |
A "small PA" is anything you can set up in under an hour with two people: two tops on stands, one or two subs, a mixer. It covers 90% of corporate work: speeches, awards, a DJ for 150 people, a cocktail function. Know the parts and what each one is for.
A 10", 12" or 15" woofer plus a horn. They carry voice and the "music". Aim them at the back third of the audience.
In the B&W kit: RCF Evox 12 columns and the Evox 8s on the music bus.
8", 12", 15" or 18" drivers that only do bass, typically below 100 Hz. One sub per side, or both together in the middle (see Module 3).
In the B&W kit: JBL single 8" and double 8" powered subs.
A sub on the floor with a slim vertical column of small drivers on top. Wide and even coverage, tidy on stage, fast to set up. Covered properly in Module 3.
In the B&W kit: the Evox 8 and Evox 12 are column arrays. The D208A is a true double-8" line-array element.
Where every source meets. Each channel has gain, EQ, aux sends and a fader. Main L/R goes to the speakers.
Turns a laptop, keyboard or DJ output into a balanced mic-level signal that can run 50 m on XLR without hum. Lift the ground switch if it buzzes.
XLR for everything signal. Speakon for passive speakers. Two cable types, two stand types, three adaptors. Count them in and out.
An active (powered) speaker has the amplifier and crossover built in. It needs a line-level XLR in and a power cable. Most small PAs today are active, including every column array. A passive speaker is just drivers in a box; it needs a separate power amp and a Speakon cable. Passive systems are cheaper per box, lighter, and you only run one cable to the stage, but you must match the amp to the speaker (Lesson 5).
An amplifier takes the small line-level signal from the mixer and makes a big copy of it, with enough voltage and current to push a speaker cone back and forth. It does not add sound. It only scales what it is given, including any noise, hum or distortion from upstream.
Every active top is three things in one box: a crossover that splits lows to the woofer and highs to the horn, a limiter that stops you destroying it, and one or two amplifier channels. That is why an active speaker has a gain knob and a few DSP presets on the back: you are setting the amp, not just the speaker.
Impedance, measured in ohms (Ω), is how hard a speaker "pushes back" against the amp. It only matters for passive speakers, but it matters a lot: get it wrong and the amp shuts down, overheats, or dies.
| Boxes in parallel | 8 Ω boxes | 4 Ω boxes |
|---|---|---|
| 1 | 8 Ω | 4 Ω |
| 2 | 4 Ω | 2 Ω |
| 3 | 2.7 Ω | 1.3 Ω |
| 4 | 2 Ω | 1 Ω |
Most amps stop at 4 Ω. Stay at or above the number printed on the amp.
You never think about ohms with an active speaker. The amp inside is already matched to the driver. You just need enough mains power on the cable feeding it, which is Module 5.
There are only two ways to wire more than one speaker to one amp channel. Parallel is what you get when you "link through" from one box to the next. Series is rare in PA but you must recognise it.
Where you put the speakers decides most of what the audience hears. The mixer can only polish it. Three rules cover almost every small job.
If one mic is 10 cm from a mouth, any other open mic must be at least 30 cm away from that mouth. Closer than that and the two mics fight each other, which sounds hollow and feeds back sooner. Fewer open mics is always better: mute what isn't being used.
Gain staging is setting each stage of the chain so the signal is strong but never clipping. Done right, the system is quiet when it should be and loud without distortion. Done wrong, you get hiss (too low early on) or distortion (too high early on), and no amount of turning the speakers up or down fixes it.
Do it in the same order every time. The order protects the gear: speakers come on last and go off first, so no thump ever reaches the drivers.
| Symptom | Check first | Then |
|---|---|---|
| No sound at all | Speaker power and gain, mute buttons, main fader | Swap the XLR from mixer to speaker |
| One side silent | That speaker's cable and gain | Swap L and R cables at the mixer: if the silence moves, it's the mixer side |
| Hum or buzz | Ground lift on the DI, laptop charger | Different power socket for mixer and speakers |
| Feedback | Mic in front of the speaker line, too many open mics | HPF on, narrow EQ cut, turn the monitor down |
| Distorted, "crunchy" | Red clip light anywhere in the chain | Lower the gain where it clips, raise it after |
| Thin, no bass | Subs on and linked, polarity switch | Move subs together or to a wall |
Ten questions. Pick an answer for each, then press Mark my answers. You need 8 out of 10 to pass this module. You can retry as often as you like.
Ten questions. Circle one answer for each. The answer key is on the last page. Pass mark: 8 out of 10.