Setting Up a Processor

01What a processor does

A loudspeaker processor — also called a DSP, a speaker management system or a crossover — sits between the mixer and the amplifiers. The desk hands it a finished stereo mix. It splits that mix into the bands each speaker is built for, lines them up in time, protects the drivers, and sends every band to its own amplifier channel.

It does four jobs, and you will set them up in this order:

1 · Crossover

Splits the mix by frequency. Bass to the bins, everything above to the tops. A 3-way rig adds a mid band.

2 · EQ

Tames the room and the boxes. For crew: leave it flat unless the engineer has saved a preset.

3 · Delay

Lines speakers up in time so the subs and tops hit together, and so fills down the room do not echo the mains.

4 · Limiter

A ceiling on each output. Stops a big amp cooking a speaker when someone pushes the mixer too hard.

Blue is line level on XLR. Yellow is speaker level on Speakon. The processor only ever sees and sends line level: it never touches a Speakon lead.

When you need one, and when you don't

Passive rig (bins and tops on rack amps): always. Without it the amps send full-range to every box and the tops get bass they cannot handle.
Powered boxes (Evox, powered subs): the DSP is inside the box. You usually do not need a processor, but one is still useful to delay fills and align subs.
Mixed rig (passive mains, powered fills): one processor runs it all. Fills get a full-range output with a high-pass and a delay.

Crew rule
You do not design the preset. The engineer does that once, in daylight, with a measurement mic. Your job is to load the right preset, route the outputs correctly, prove every box, and never unmute a limiter-less output into a passive speaker.

Typical hire kit: a 2-in / 6-out loudspeaker processor in the amp rack, driving passive double-18 bins and 12" or 15" passive tops.

02Ins and outs

FBT DLM 260 front: screen, encoder, 6 output mutes — A 2-in / 6-out processor. Front: input meters, the screen, and one mute button per output. Rear: inputs A and B from the mixer, outputs 1 to 6 to the amps, labelled on tape before the first cable goes in. Product photo: FBT.

Rear: 2 XLR in, 6 XLR out, tape labels — A 2-in / 6-out processor. Front: input meters, the screen, and one mute button per output. Rear: inputs A and B from the mixer, outputs 1 to 6 to the amps, labelled on tape before the first cable goes in. Product photo: FBT.

Most processors you will meet are 2-in / 6-out or 4-in / 8-out. The inputs take the mixer's main left and right on XLR. The outputs are also XLR, line level, one per amp channel or powered box. Everything is balanced, so cable runs can be long.

A typical 2-in / 6-out rear panel. Inputs are XLR female, outputs XLR male, so you cannot plug a lead in the wrong direction. The labels under the outputs are tape, written by you, before the first cable goes in.

The front panel

Input meters: show signal arriving from the mixer. No meter, no signal: the fault is before the processor.
Output mute buttons: one per output. On site you unmute these one at a time, never all at once.
Output meters and limit lights: a limit light flashing means that output has hit its ceiling. Occasional flicker is fine. Solid is too loud.
Preset recall: the saved setups. Load the one named for tonight's rig. Most units can lock the panel so a knee does not change it mid-show.

Label first, cable second
Put a strip of tape under the six outputs and write what each one feeds. Then write the same on the amp inputs. A rig wired against its labels is a rig that will be fault-found in the dark.

03Routing: which output feeds what

Routing is the map from inputs to outputs. Left-side speakers take input A. Right-side speakers take input B. Subs usually take A+B summed, because bass is not directional and one mono sub feed keeps every bin working together. Choose a rig and set the outputs. The tool checks your map.

Routing matrix

Rig

Set every output.

Standard map for mono subs + stereo tops: 1 Sub (A+B) · 2 Sub (A+B) · 3 Top L (A) · 4 Top R (B) · 5 Fill L (A, delayed) · 6 Fill R (B, delayed).

Three maps you will use

Rig	Out 1	Out 2	Out 3	Out 4	Out 5	Out 6
2-way, mono subs	Sub A+B	Sub A+B	Top L (A)	Top R (B)	spare	spare
2-way + delay fills	Sub A+B	Sub A+B	Top L (A)	Top R (B)	Fill L (A) +delay	Fill R (B) +delay
3-way stereo	Sub A+B	Sub A+B	Mid L (A)	Mid R (B)	High L (A)	High R (B)

The classic mistake
Output 3 is labelled "Top L" but inside the processor it is still set to full range, or still routed from the preset before. The box plays, so nobody checks, and the tops get bass all night. The label is not the routing. The screen is the routing. Check both.

04Crossover points and slopes

Each output has a high-pass filter (cuts below) and a low-pass filter (cuts above). A sub output is high-passed around 30 to 35 Hz to protect the driver and low-passed around 100 Hz. A top output is high-passed at the same 100 Hz. Where the two meet is the crossover point. The slope says how steep the cut is: 24 dB per octave Linkwitz-Riley (LR24) is the safe default, because the two sides add back to flat.

Crossover tool

Rig

Sub box

Top box

Sub / top crossover: 100 Hz Sub protection high-pass: 35 Hz

Defaults: sub HPF 35 Hz · sub/top crossover 100 Hz · mid/high 1.6 kHz · all filters LR24.

Starting points

Output	High-pass	Low-pass	Slope	Why
Double-18 bins	35 Hz	100 Hz	LR24	Below 35 Hz the cone just flaps. Above 100 Hz you start to hear voices from the bins.
12" or 15" tops	100 Hz	off (20 kHz)	LR24	Matches the bins. Lower only if the tops are big 15s and there are no bins.
Mids (3-way)	100 Hz	1.6 kHz	LR24	The horn takes over around 1.2 to 2 kHz; the box's spec sheet gives the exact number.
Highs (3-way)	1.6 kHz	off	LR24	Never below the spec-sheet minimum. A horn fed too low dies quietly, then suddenly.
Delay fills (powered)	80 Hz	off	BW12	The box's own DSP does the rest. High-pass only keeps the bass with the bins.

Where the numbers come from
The speaker's spec sheet. Every passive box lists a recommended crossover and a minimum high-pass. The processor does not know what is plugged into it. If you set a horn output to 500 Hz because it "sounded fuller", you have bought a diaphragm.

Typical starting points: double-18 bins 35 Hz to 100 Hz; 12" or 15" tops high-passed at 100 Hz; powered column fills high-passed at 80 Hz with their own DSP left flat.

05Delay and polarity

Sound travels about 343 metres per second: roughly 2.9 milliseconds for every metre. If the subs sit two metres in front of the tops, their sound arrives early. If a fill speaker stands 20 m down the room, it arrives 58 ms before the mains do, and the audience near it hears an echo. Delay fixes both: you hold the nearer speaker back until the sound lines up.

Delay calculator

Fill speaker: distance from the mains (m)

Subs: how far in front of the tops (m)

—

Fill delay (ms)

—

Top delay to match subs (ms)

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Rule used

Fill delay = distance ÷ 0.343 + 5 ms. Example: 20 m fill = 58 + 5 = 63 ms. Subs 1.5 m ahead of tops: delay the tops by 4.4 ms.

The fill rule

Delay the fill by its distance from the mains, plus about 5 ms. The extra few milliseconds make the mains arrive a touch first, so the ear locates the sound at the stage and the fill just adds level. Put the delay on the fill's output, not on the mains.

Polarity: the two-second check

Subs and tops can be out of polarity: one pushing while the other pulls, at the crossover frequency. The bass goes thin exactly where the two overlap. The test: play a track with a steady kick drum, stand in front of the stack, and flip the polarity button on the sub output. One setting has clearly more punch. Keep that one. If you cannot hear a difference, the delay is wrong, fix that first.

Field rule
Delay the fill, not the mains. Delay the tops to the subs, not the subs to the tops. Then flip polarity on the subs and keep whichever is louder.

Powered columns or small tops on the spare outputs make good delay fills down a long room. One output each, delayed to the mains.

06Limiters and gain structure

Technician pressing an output mute on a rack processor, laptop with a frequency graph beside the amps — Unmute one output at a time with the limiter already on. The laptop is the engineer's measurement rig; crew only need the mute buttons and the meters.

A limiter is a ceiling. Signal below the threshold passes untouched; signal above it gets squashed so the amp never delivers more than the speaker can take. Every passive-speaker output needs one, set before the output is unmuted. It is the only thing between a 2 000 W amp and a 600 W driver when the DJ pushes the master into the red at 1 a.m.

Limiter headroom

Amp power into this load (W per channel)

Speaker continuous (RMS) rating (W)

—

Amp is louder than the box by

—

Limiter below amp clip

—

Match

Headroom = 10 × log10(amp W ÷ speaker RMS W). Set the limiter at least that many dB below the amp's clip point, then 2 dB more for safety.

Gain structure: everything at zero

Mixer: main fader at 0, meters peaking around 0 dB on a loud track.
Processor: input gain 0 dB, output gains 0 dB. Volume is not set here.
Amps: attenuators fully up, or at the engineer's marked position. Not "a bit down to be safe": that only moves the clip point and breaks the limiter maths.
Limiters: set from the amp-to-speaker ratio above, then 2 dB more conservative. Red limit lights should flicker on peaks, never stay lit.

Never
Never unmute a passive-speaker output with the limiter switched off "just to test it". Test with the limiter on. If the limiter is wrong, the test will tell you. If it is off, the speaker will.

07The setup process

Amp rack with the lid open and a laminated checklist taped inside — The checklist lives inside the rack lid. Tick it every show. Nobody remembers step 7 at 1 a.m.

This is the order. Print it, tape it inside the amp rack lid, and tick it every time. It takes ten minutes on a rig you know and saves the first half hour of every show you don't.

0 of 10 done.

If it is wrong

You hear	Most likely	Check
Voices coming out of the bins	Sub output set full range or low-pass too high	Sub output low-pass: should be about 100 Hz
Tops sound thin, no weight	Tops high-passed too high, or subs muted	Top HPF about 100 Hz; sub output unmuted; cable to the sub amp
Bass gets weaker when tops come on	Polarity or delay between subs and tops	Flip sub polarity; set top delay to the sub distance
Echo near the back of the room	Fill not delayed	Fill delay = distance ÷ 0.343 + 5 ms
One side silent, input meters fine	Output muted, or wrong routing on that output	Mute button; output screen; XLR to the amp
Limit light solid red on one output	Threshold too low, or that output's gain too high	Output gain back to 0; recheck limiter maths
Nothing on the input meters	Fault before the processor	Mixer master, mixer meters, the two XLRs into A and B

The whole module in one line
Label, route, cross over, limit, prove each box, align, save. In that order, every time.

08Check what you learnt

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.