Intercom & Communications Systems
Introduction
Comms is the one system every department touches. Lighting has its own console, audio its own desk, video its own rack -- and all of them share the intercom. It is the first thing plugged in and the last thing struck, and on a bad day it is the only thing standing between a hundred people and chaos.
It is also the system newcomers are handed first, usually with no explanation. Somebody gives you a beltpack, tells you to go to channel two, and the show starts. This book is what nobody told you: what the line actually is, why it hums, what the termination switch on the back of the power supply does, and how to find the dead pack before the director asks why camera three has gone quiet.
It covers wired partyline, matrix, digital and IP systems, wireless, and IFB, because a working crew meets all five, often on the same job.
How to Use This Book
Read it in order the first time. It runs the way the system does: what a conversation is, then the wire that carries it, then the bigger systems, then the day itself -- planning, proving, running and fixing.
Keep a notebook
Write down the channel plan for every show you work: who was on which channel, which packs went to which positions, where the antennas were and which corner of the building dropped out. Comms problems repeat per venue, not per show, and the second time you are in that room the notebook saves you an hour.
A note on the words
The trade uses several words for the same thing. Comms, intercom, cans and talkback all mean the system; a beltpack is a pack or a belt pack; a biscuit is a small single-channel station. Party-line, partyline and conference line are the same topology. This book uses the words most widely understood on a stage and names the alternatives where they matter.
A note on safety
Comms carries DC power on the same conductors as audio -- thirty volts nominal on a standard two-wire line -- so a shorted connector drops the whole line, and plugging a microphone into a comms circuit can damage it. Headsets sit on your ears for a twelve-hour day: a comms headphone is expected to give twenty decibels of acoustic isolation or better, and running one loud enough to beat a noisy stage is how crew lose hearing slowly. Nothing here qualifies you to do electrical work.
Why Comms Matter
A show is a few dozen people doing separate skilled jobs in the dark, to the second, with no chance to confer. Comms is the only reason that works.
Intercom is how a crew becomes one coordinated team — without it, a show falls apart.
The crew's nervous system
Intercom (comms) is the communication system the crew uses to talk to each other during a show — headsets and beltpacks connecting the director, operators, and departments so they can coordinate in real time. It is, in effect, the nervous system of a production: it is how the director calls the cues, how departments coordinate their actions, how problems are reported and solved, and how the whole crew works as one. A show runs on its comms — the director says take camera two and the switcher does it, the stage manager calls standby and everyone prepares. Without comms, a crew cannot coordinate a complex live show.
This makes comms genuinely essential, not just convenient. The coordination that lets dozens of people execute a live show together depends entirely on reliable communication, and that runs over the comms system. Comms failures are serious — if the crew cannot communicate, the show falls apart. Comms is what turns a crew into a coordinated team.
Comms across the production
Comms connects everyone who needs to coordinate during a show: the director and the technical crew (camera, switcher, lighting, audio, etc.), the stage manager and the stage, and the various departments. Different people are on the comms system, often organized so the right people can talk to each other (the director to the camera operators, the stage manager to the crew). This lets the complex web of a live production coordinate — everyone hearing the calls they need and able to communicate. Comms is the connective communication layer across the whole production, tying the departments and roles together.
This connects to crew coordination and show calling: the directing, the cue-calling, the departmental coordination all happen over comms. The comms system is the technical infrastructure that carries all this communication. Understanding that comms connects the whole production — carrying the director's calls, the coordination, and the crew's communication — shows its central role. It is the system that makes coordinated live production possible, and audio professionals often set up and manage it.
Who is on comms, and who is not
The crew on headset are the ones whose timing depends on somebody else: the director, the switcher, camera operators, the stage manager, lighting and video operators, audio, and the floor. The people NOT on headset matter just as much -- talent, most of the band, the audience -- because everything you say is heard by everyone on your channel and nobody else, and forgetting which group you are talking to is the commonest comms mistake there is.
A newcomer is usually handed a pack and a channel number. Ask two questions before the show: who else is on this channel, and who do I call if I need somebody who is not.
On the job
Twenty minutes to doors on a corporate general session. You are the A2 and you are wearing a pack on channel two with the video crew. The stage manager is on channel one with the director and the client. A presenter walks on stage early, in the dark, and starts testing their clicker. You can see it; the director, looking at a programme feed, cannot. You press the talk key you have -- channel two -- and say it, and four video operators hear you and the stage manager does not. Nothing happens. Ten seconds later you reach for the pack, find the channel-one key, and say it again, and the stage manager walks on and quietly takes the presenter back to the wing. The lesson is not that you were slow. It is that you did not know, before the show, which key reached the person who could act -- and that is a thing you set up in the afternoon, not something you work out in the dark.
How to do it
- Find the comms position and ask which channel your department is on.
- Draw a pack, a headset and a battery if the pack takes one.
- Put it on, set the headset so one ear is open to the room if the job needs it.
- Press talk and ask for a check; wait for somebody to answer you by name.
- Ask who else is on this channel and which channel reaches the stage manager.
- Set your pack volume with the show running, not in a quiet room.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| You speak and nobody answers | Wrong channel, or talk key not latched | Check the channel, press and hold rather than tapping, and ask again by name |
| You can hear but nobody can hear you | Headset microphone muted at the pack, or mic boom swung up | Check the pack's mic mute and that the boom is down near the mouth |
| Everyone winces when you talk | Mic too close, or you are shouting over a noisy stage | Boom two fingers from the corner of the mouth, speak at a normal level |
Practice it
On your next call, before the show.
- You know your channel and who else is on it.
- You know which key reaches the stage manager.
- Somebody has answered your check by name.
- Your level is set with the room noisy, not quiet.
- You know where the spare pack and batteries are.
How Comms Systems Work
Every comms system is one of two conversations wearing different hardware: a room everybody can speak into, or a line between two people. Learn which one you are on and the rest follows.
A hub, beltpacks, and headsets — and a few kinds of comms for different needs.
The parts of a comms system
A comms system has a few core parts. A base station or matrix is the hub that ties the system together and routes the communication. Beltpacks are the units crew members wear, connecting them to the system and letting them control their channels. Headsets (worn with the beltpacks) let crew hear the comms and talk (a headphone and a microphone). The crew wear beltpacks and headsets, connected back to the base or matrix, forming the communication network. Wireless comms (wireless beltpacks) free crew to move, like other wireless systems. Understanding these parts — hub, beltpacks, headsets — is the basis for setting up and using comms.
Comms systems can be wired (beltpacks connected by cable back to the base) or wireless (wireless beltpacks, with the same RF considerations as radio microphones), and modern systems are often networked or digital. Whatever the technology, the structure is the same: a central hub connecting the crew's beltpacks and headsets into a communication network. Knowing the parts and how they connect lets you set up a comms system and understand how the crew's communication flows through it. The comms system is the infrastructure that carries the crew's coordination.
Kinds of comms: party line, matrix, IFB
There are a few kinds of comms for different needs. Party line is the simplest: everyone on a channel hears everyone else on it, like a group conversation — simple and common for smaller crews, where everyone shares one or a few channels. Matrix comms is more flexible and powerful: it can route communication between specific people and groups, so different people can have different channels and talk to whoever they need — used on larger, complex productions where the coordination is more elaborate. IFB (interruptible foldback) is a special kind: a one-way feed (usually of program audio and cues) to on-air talent's earpieces, which can be interrupted by a director to give them instructions — used in broadcast to talk to presenters.
Understanding these kinds tells you how comms is organized for different shows: party line for simple shared communication, matrix for flexible routing on complex shows, and IFB for cueing talent. A production may use several — a matrix system for the crew, party-line channels within it, and IFB to the presenters. Knowing the kinds of comms and what each is for lets you understand and set up the right communication structure for a show. The kind of comms is matched to the production's coordination needs.
Party-line and point-to-point
A party-line is a shared conference. Everybody keyed to that channel hears everybody else, as though they were standing in a circle. It is cheap, instant, and gets noisy as soon as more than about eight people are busy on it.
Point-to-point is a line between two parties, dialled or assigned. Nobody else hears it. A matrix is a machine for making a great many point-to-point lines at once, and for building party-lines inside itself.
Most real shows run both: party-lines for the departments that work as teams, point-to-point for the people who need a private word.
The four systems you will meet
Analogue two-wire partyline is the stage standard: beltpacks on microphone cable, power and audio on the same conductors. Digital partyline runs the same idea over network cable with more channels. Matrix is the big installed system, with keypanels and assignable keys. Wireless is a base station and roaming packs, and on a modern show it is most of the crew.
They interconnect, and the joins are where the trouble lives. A four-wire interface is almost always what sits between two of them.
How to do it
- Look at the connector. Three-pin XLR is analogue two-wire; RJ45 is digital or matrix.
- Count the channels on the pack. One or two is analogue; more is digital or matrix.
- Find the power supply or main station and read what it says it terminates.
- Ask whether the wireless base is on the same system or a separate island.
- Trace one cable end to end before the show so you know the shape of it.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Two halves of the crew cannot hear each other | Two separate systems with no interface between them | Find the four-wire interface, or accept it and agree a relay person |
| Adding a pack makes everyone quieter | Too many stations bridging the line, or termination now wrong | Check that exactly one termination is switched in, and count the stations |
| Wireless users hear the wired crew but not each other | Base station assigned to the wrong channel, or antenna placement | Check the base's channel assignment before suspecting the radio |
Practice it
On any system you can get your hands on.
- You know whether it is party-line, point-to-point or both.
- You have found the power supply and the termination.
- You know how many stations are on each channel.
- You know what is joined to it and by what.
The Wire Itself — Two-Wire Partyline in Detail
Two-wire partyline is the system that looks simplest and bites hardest, because one pair of conductors carries the power, the audio and everybody's crosstalk at the same time.
What is actually on the cable
A standard analogue partyline runs on microphone cable. The screen is ground, one conductor carries the DC power and the audio together, and on two-channel systems the third conductor carries the second channel. That is why a comms cable looks exactly like a microphone cable and must never be used as one: there are thirty volts sitting on the pin a microphone expects to be quiet.
Because power and audio share a conductor, anything that loads the power loads the audio. A shorted connector does not quieten one pack; it drops the channel.
Termination, and why there is exactly one
The line is terminated at one point, and only one. Termination sets the impedance the stations work into; two terminations halve it and the system goes quiet and strange, while none leaves the line ringing and hot. The switch is usually on the power supply or the main station, and on a long day somebody will have flipped it.
Sidetone, and why you hear your own voice
Sidetone is your own voice fed back into your own earpiece. It sounds like a fault and is the opposite: without it, a headset feels dead, you cannot tell whether your microphone is live, and everybody shouts. Telephones have done it deliberately since the 1920s for the same reason.
Every pack has a sidetone level, and it is the first thing to set for a new user. Too little and they shout; too much and they whisper and nobody on the channel can hear them. Set it with the room at show noise, not in a quiet shop.
The numbers a two-wire line runs on
Figures from RTS's Handbook of Intercom Systems Engineering. Where this varies, it varies by manufacturer and by how long the cable run is -- so check the manual for the system in front of you before you treat any of these as a limit.
| Quantity | Figure | Why it matters |
|---|---|---|
| System termination | 200 ohms for RTS and Clear-Com | One termination only; two makes the line quiet and strange |
| DC power on the line | 30 volts nominal | Shared with the audio on the same conductor |
| Station bridging impedance | 10000 ohms or greater | Lets many stations sit across the line without loading it |
| Stations before a 6 dB drop | up to 50 | The level falls slowly rather than suddenly |
| Stations for a 3 dB change | about 20 across the line | Useful rule when a channel starts sounding thin |
| Peak signal the line tolerates | 5 volts peak-to-peak | Sets the ceiling on how many people can talk at once |
| One station talking | maximum 2 volts peak-to-peak | Two talkers make 4 volts and leave 1 volt of headroom |
| Standard cable | 22 AWG shielded microphone cable | 24 AWG shortens the maximum distance |
| Cable resistance (22 AWG) | about 3.2 ohms per 100 feet of cable round trip | Each conductor is about 16 ohms per 1000 feet; the current goes out and back so both count — 32 ohms per 1000 feet round trip |
| Where response starts to suffer | around 10000 feet of cable | Capacitance rolls off the top end before DC fails |
| Mains input | 120 or 240 volts AC | Most supplies take either |
The headroom line is the one worth memorising. A station can put two volts peak-to-peak on a line that tolerates five, so two people talking together use four and leave one. That is the arithmetic behind the oldest rule on comms: one person talks at a time.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Whole channel goes dead when one pack is plugged in | Shorted connector or damaged cable on that drop | Unplug packs one at a time until the line returns, then replace that cable |
| Everything is quiet and sounds odd | Two terminations switched in | Find both and switch one out; there is exactly one termination per channel |
| The line hums and the hum changes as you walk | Comms cable run alongside mains, or a ground loop through a shared circuit | Reroute away from power, and do not defeat an earth to cure it |
| Top end dull on a very long run | Cable capacitance on a run approaching several thousand feet | Shorten the run, use a heavier gauge, or split with a powered interface |
Practice it
With a two-wire system and a multimeter, powered but with no audio running.
- Exactly one termination is switched in per channel.
- The line measures near thirty volts with the system idle.
- No comms cable is being used as a microphone cable.
- Runs are routed away from mains cable.
- You know the station count on each channel.
Matrix and Four-Wire Systems
A matrix is a machine whose whole job is deciding who hears whom. Once a show is big enough that one shared line will not do, this is what replaces it.
What a matrix actually does
A matrix is a central frame with ports. Every panel, pack, camera, phone line and partyline hangs off a port, and the matrix connects any port to any other in either direction. A key on a panel is an instruction to the matrix: when I press this, join me to that.
Because the joins are software, the same hardware becomes a different system between two shows. That is its strength and the reason it goes wrong: the rack is fine and the configuration is not.
Four-wire, and why interfaces are four-wire
Four-wire means separate send and return paths -- two pairs, audio one way on each. Two-wire mixes both directions on one pair, which is why it needs a hybrid to join the two. Almost every interface between a matrix and anything else is four-wire, and almost every interfacing problem is a level or a mode mismatch at that join.
Keypanels and assigning keys
A keypanel is a row of keys, each assigned to a destination -- a person, a party-line, a group, an IFB. Talk and listen can be separate. The assignment is the show's comms design made concrete, and it is worth photographing the panel before anybody changes it.
How to do it
- Confirm the frame is powered and the system is online, not in a fault state.
- Walk the panels and press each key, confirming you reach the labelled destination.
- Check the partyline ports against the wired packs on the floor.
- Test every interface — telco, radio, camera — in both directions.
- Save and back up the configuration before anybody edits it.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| A key reaches the wrong person | Assignment changed, or a panel moved to a different port | Check the port the panel is on before re-assigning anything |
| One direction works and the other does not | Four-wire send and return swapped, or level set on one side only | Check the interface's send and return independently |
| Howling or echo on an interface | Two-wire to four-wire hybrid not nulled | Null the hybrid with the far end quiet, per the interface's procedure |
Practice it
On a matrix system you can access.
- Every key has been pressed and reached the labelled destination.
- Every interface has been tested in both directions.
- Hybrids are nulled.
- The configuration is saved and backed up.
Digital Partyline, IP and Virtual Clients
The middle ground: the simplicity of a partyline with the channel count of a matrix, running on network cable instead of microphone cable.
Digital partyline over network cable
A digital partyline puts several channels down one network cable and powers the packs over it. The pack gains a display and a menu, so a user can change channel without a screwdriver, and the system can carry far more than the one or two channels an analogue line manages.
What it does not change is the discipline. More channels means more places to be on the wrong one.
Intercom over IP, and people who are not in the building
An IP interface puts a comms channel onto a network, and a virtual client -- an app on a laptop or phone -- joins it from anywhere. A remote director, a client at home, a second venue: all become a key on somebody's panel.
The cost is latency and dependence on a network you may not control. Treat a remote participant as a guest on the system, not a core path, and never put a show-critical cue on a link you cannot test.
How to do it
- Agree which channel they join and what they must not hear.
- Test the link end to end at least a day before, not on the show day.
- Check the delay by asking for a count-back and listening for the lag.
- Agree a fallback — a phone number — and write it on the comms plan.
- Tell the crew there is a remote on the channel, because behaviour changes.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Remote participant hears the show late | Network latency through the IP path | Accept it for listening, never for cueing; keep cues on local comms |
| Remote drops out repeatedly | Network congestion or a consumer connection at the far end | Fall back to the phone path and carry on; do not debug mid-show |
| Digital pack shows the right channel but hears nothing | Channel assigned at the pack but not enabled at the main station | Check the assignment at the station, not at the pack |
Practice it
On a digital or IP system.
- It has been tested end to end on a different day.
- The delay has been heard and judged acceptable for its use.
- No show-critical cue depends on it.
- A fallback exists and is written down.
Wireless Comms
On most modern shows the majority of the crew are on wireless packs. The system is only as good as where you put the antennas, and that decision is made before the crew arrives.
The base, the transceivers and the packs
A wireless comms system is a base station, one or more remote antennas or transceivers placed around the space, and roaming beltpacks. The packs talk to whichever transceiver has them, and hand over as people walk, the way a phone moves between masts.
Coverage is therefore a question about the building, not the product. A venue with a steel grid, a concrete core and a basement dressing room needs transceivers in each, and finding that out at rehearsal is too late.
Sharing the air
Wireless comms sits in the same crowded spectrum as the microphones and the in-ears. Who coordinates it varies: on a big show the RF engineer owns everything that radiates, and your packs are on their plan. Say what you are bringing before you switch it on.
Antenna cable, and why the run matters
From RTS's Handbook of Intercom Systems Engineering. Loss in antenna cable is the quiet killer of wireless coverage, because it costs you range at both ends. Where this varies, it varies with cable type and frequency -- a higher band loses more per metre than a lower one.
| Rule | Figure | Why |
|---|---|---|
| Antenna cable in a wireless system | should rarely exceed 100 feet | Loss reduces both transmit reach and receive sensitivity |
| VHF runs | 100 feet is usually achievable | Lower frequencies lose less per unit length |
| Coaxial runs between system parts | up to about 1000 feet | Beyond this the loss stops being worth it |
| Fiber between system parts | over about 3300 feet (1000 metres) | The answer when the distance is genuinely long |
| Cable routed near mains over long distances | precautions above about 1000 feet (300 metres) | Induced hum and interference grow with run length |
The practical reading: put the transceiver near the people and run network or fiber to it, rather than putting it near the rack and running a long coax to an antenna. Distance in the data path is cheap; distance in the aerial path is not.
How to do it
- Walk the building before you rig, including basements, stairwells and dressing rooms.
- Put transceivers where the crew will actually stand, not where the rack is.
- Keep antenna cable runs short, and run data to the transceiver instead.
- Declare your frequencies to whoever coordinates RF on the job.
- Walk-test every area with a pack on your ear before the crew call.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| A pack drops out in one part of the building | No transceiver covering that area, or a structural blocker | Add or move a transceiver; walk-test again |
| Range is poor everywhere | Long or lossy antenna cable | Shorten the aerial run and move the transceiver closer to the people |
| Interference that comes and goes | Another radio system sharing the band, often arriving later in the day | Coordinate with whoever owns RF; do not simply change channel and hope |
| Packs fine at rehearsal, failing at show | A full room of bodies absorbing signal | Walk-test with the room full where you can, and plan margin |
Practice it
In a venue you can walk.
- Every working position has been walk-tested with a pack.
- Aerial cable runs are short.
- Frequencies are declared to whoever coordinates RF.
- Spare packs and charged batteries are at the comms position.
IFB, Program and ISO
Three things that are not conversations: feeding somebody the show, cutting in over it, and taking one person aside. Each has a precise meaning and crews use the words loosely.
IFB — interruptible foldback
IFB sends a person a feed -- usually programme audio -- which the director can interrupt to speak to them. A presenter hears the show in their ear until the director says "wrap it up", at which point the show audio ducks or disappears and the director's voice replaces it.
It is one-way. The talent does not talk back on it. That is the whole design: the person on air must be able to listen without being able to broadcast into the crew's ears.
Programme feed and mix-minus
Anyone who is both heard in the show and listening to the show must be fed a mix that does not contain themselves. A presenter hearing their own voice delayed by a fraction of a second cannot speak. That subtraction is a mix-minus, and it is the audio department's job, but comms is where it is consumed.
ISO, and the private word
ISO isolates one party from the channel so the director can speak to them alone. The rest of the line carries on without hearing it. It is the polite alternative to clearing a whole channel.
Tally, and what the red light is really saying
Tally is a signal, not a camera feature. The switcher tells the system which source is on air, and the system lights a lamp on that camera, in that operator's viewfinder, and often on the presenter's monitor. It is comms in the sense that matters: information travelling so people can act on it without anybody speaking.
An operator whose tally is on holds the shot and does not move. An operator whose tally goes out is free to reframe. Tally failing is therefore a show problem rather than a nuisance, because the whole convention collapses and everyone has to be told verbally instead.
Stage announce and dressing-room paging
Not everybody who needs to hear something is wearing a headset. Stage announce puts a comms position onto loudspeakers in the room, and paging reaches dressing rooms, corridors and the green room. It is how a stage manager calls the half, calls beginners, and gets a performer to the stage without sending a runner.
It is also the one comms path the audience might hear, so it is worth knowing which key opens it before you lean on it by accident.
How to do it
- Agree who can interrupt — usually the director, sometimes a producer too.
- Confirm the feed is a mix-minus of that presenter.
- Fit the earpiece and dress the cable so it is hidden and will not pull out.
- Set the level with the presenter speaking and the show audio running.
- Test the interrupt with the presenter talking, so they feel what it does.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Presenter stumbles and cannot speak fluently | Hearing themselves delayed — the feed is not a mix-minus | Get audio to remove them from their own feed; do not just lower the level |
| Presenter does not react to the director | Interrupt not reaching them, or level too low under the programme | Test the interrupt with programme running, not in silence |
| Crew hear the presenter talking to themselves | A talkback path left open on what should be a one-way IFB | Confirm the IFB is one-way at the panel |
Practice it
With a presenter and an IFB, before a rehearsal.
- The feed contains everything except that person.
- The interrupt has been tested against live programme.
- The earpiece is fitted, hidden and strain-relieved.
- The presenter has heard it and agreed the level.
- It is one-way, with no talkback path open.
Interfacing to Everything Else
No comms system stands alone. It is joined to telephones, two-way radios, cameras and other people's systems, and every join is a place where levels, directions and expectations disagree.
Why interfacing is where the trouble lives
Each system was designed on its own terms. One expects four-wire at line level, another two-wire with power on it, a third a dry contact for its call light. An interface is a translator, and a translator can be wrong in three ways at once: wrong level, wrong direction, wrong signalling.
Test an interface in both directions separately. Most interface faults work one way and fail the other, and a single round-trip test hides that.
Cameras, the standing problem
Camera intercom is its own recurring difficulty on every broadcast job. The camera carries comms down its cable to the CCU, where it reappears as something the matrix has to be told about, and the arrangement differs by camera manufacturer. Expect to spend time on it and ask the vision engineer how this particular fleet does it.
Telephone and two-way radio
A telco interface puts a phone line on a key, which is how a remote contributor joins without any network at all. A radio interface bridges the site's walkie channel onto comms, which is how the comms crew hears security and the loading dock. Both are four-wire joins with a level set at each end.
How to do it
- Establish what each side expects — level, two-wire or four-wire, and signalling.
- Connect and test one direction with a known talker and a known listener.
- Test the other direction separately.
- Null any hybrid with the far end silent.
- Label both ends and write the interface on the comms plan.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| One direction clear, the other unusable | Level set on one side only, or send and return swapped | Test and set each direction independently |
| Echo building on a joined system | Hybrid not nulled where two-wire meets four-wire | Null it with the far end quiet |
| Call light works one way only | Signalling not translated, only audio | Check the interface supports the call signalling, not just audio |
Practice it
On a system with at least one interface.
- Each direction has been tested separately.
- Hybrids are nulled.
- Signalling as well as audio has been checked.
- Both ends are labelled and on the comms plan.
Cable, Headsets and the Physical Layer
Comms fails physically far more often than it fails electronically. The connector, the cable and the thing on somebody's head are where the faults are.
The headset is the part that touches a person
A headset is worn for twelve hours. Single-muff leaves one ear open to the room, which is what most floor crew need; double-muff isolates, which is what a director in a loud position needs. The microphone sits near the corner of the mouth, not in front of it, and a boom swung up is the commonest reason somebody cannot be heard.
Headsets are also the commonest consumable. A crew of twenty will kill cables, and a spare headset at the comms position saves a show.
Headsets and cable, by the numbers
From RTS's Handbook of Intercom Systems Engineering. These are the figures a comms system is specified around. Where this varies, it varies by manufacturer: a dynamic headset microphone and an electret want very different impedances, and plugging the wrong one in gives a thin or dead signal rather than an obvious fault.
| Part | Figure | What it means on the job |
|---|---|---|
| Headset microphone impedance | about 150 to 500 ohms | The range a standard dynamic comms headset works in |
| Electret microphone impedance | 1000 to 2000 ohms and needs powering | A different beast; it will not simply swap in |
| Push-to-talk microphones | around 500 ohms | Sits in the same range as a headset mic |
| Headphone impedance expected | 50 to 1000 ohms | Low-impedance phones need a suitable amplifier to get level |
| Acoustic isolation wanted | 20 dB or more | Protects hearing and keeps the stage out of the ear |
| Low-impedance wiring to cut crosstalk | 470 ohms | Lower impedance carries less crosstalk between pairs |
| Crosstalk — single cable, two shielded pairs | about 10 feet | Two channels in one cable interfere soonest |
| Crosstalk — dual ribbed cable | about 30 feet | Better: the pairs are further apart |
| Crosstalk — separate cables | 50 feet and more | Separate cables are the fix when crosstalk bites |
| Balanced microphone input run | up to about 100 feet depending on cable | The practical limit for a mic-level tie |
| Total line capacitance at length | about 100 nF on a long run | What rolls the top end off before DC fails |
Two practical readings. First, if two channels in one cable are bleeding into each other, the answer is separate cables, not more gain. Second, a headset that sounds thin is usually the wrong microphone type for the system, not a faulty one — check whether the pack expects dynamic or electret before you bin it.
How to do it
- Count out packs, headsets and batteries against the channel plan plus spares.
- Test every headset on a working pack before it leaves the shop.
- Coil and label comms cable separately from microphone cable.
- Check the boom and the earpiece on each headset for cable damage at the strain relief.
- Bring more headsets than packs, because headsets fail first.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Intermittent audio that comes and goes as somebody moves | Headset cable broken at the strain relief near the connector | Swap the headset; flex the cable at the connector to confirm |
| Thin or quiet microphone on one headset | Wrong microphone type for the system, dynamic against electret | Check what the pack expects before condemning the headset |
| Two channels bleeding into each other | Both channels sharing one cable over a long run | Split onto separate cables rather than adding gain |
Practice it
With a box of headsets and a working pack.
- Every headset has been tested on a working pack.
- Comms cable is labelled and stored apart from microphone cable.
- Spare headsets and batteries are at the comms position.
- Channels that bleed are on separate cables, not turned down.
Setting Up & Running Comms
Comms is designed in the afternoon and judged in the dark. Everything that makes it work on the night was decided while the room was still lit.
Plan the channels, test it thoroughly, and keep the crew talking through the show.
Setting up and testing comms
Setting up comms for a show means planning the communication structure (who needs to talk to whom — what channels and groups), configuring the system (the base/matrix, the beltpacks, the channels), distributing and fitting the crew with beltpacks and headsets, and testing thoroughly that everyone can communicate as needed before the show. The planning is key: thinking through the production's coordination needs (the director to these people, the stage manager to those, IFB to the presenters) and setting up the channels to match. A well-planned, well-tested comms setup means the crew can coordinate smoothly; a poorly-planned one causes confusion and failures.
Testing is essential because comms is show-critical: before the show, you confirm every crew member can hear and be heard on the right channels, that the director's calls reach the right people, and that the whole communication structure works. This is the same prep-and-test discipline as every other system, applied to comms. Audio professionals often set up and manage comms (it is audio-adjacent), so knowing how to plan, configure, and test a comms system is valuable. A thoroughly set-up and tested comms system is the foundation of a coordinated show.
Comms etiquette
Using comms well requires etiquette, because many people share the system and clear communication is critical. Good comms etiquette: keep it brief and clear (comms channels are shared, so say what is needed concisely and no more — chatter clogs the channel), identify who you are talking to when needed, acknowledge and confirm (a copy or got it so people know you heard), and stay off the channel when you do not need it (especially keeping non-essential talk off during critical moments). This is ordinary crew etiquette, applied to a shared channel. Good etiquette keeps the shared comms clear and useful for everyone.
Poor comms etiquette — chatter, unclear messages, talking over others, clogging the channel — degrades the communication everyone depends on and can cause real problems during a show. The professional uses comms with discipline: brief, clear, confirmed, and off the channel when not needed. This keeps the shared communication system working as the reliable coordination layer it needs to be. Good comms etiquette is essential to professional crew work, and it is how the comms system stays clear and effective through a busy show. Everyone on comms shares the responsibility to use it well.
The channel plan
Before any cable is run, somebody decides who hears whom. That is the channel plan: a list of channels, who is on each, and which key reaches the people who are not. On a small show it is four lines on a notepad; on a large one it is a drawing. Either way it exists before the packs are handed out, or it gets invented badly during the show.
The test of a plan is a question: if the one person who can stop the show needs to be reached, who can reach them and on which key? If the answer takes more than a second, the plan is wrong.
Proving the system
A comms system is proven by using it, not by looking at it. Every position, every pack, every interface, with a person at each end saying their name. The time to find the dead drop is while the lights are on.
Comms discipline
A shared channel only works if everyone keeps it short. Say who you want, say what you need, get off. Do not hold the key while you think. Do not have a conversation that belongs to two people on a line of twelve. And never say anything on comms you would not say with the client standing behind you, because on most shows they are.
How to do it
- Walk the channel plan with the production manager and agree it.
- Set up every position, including the ones nobody thinks will be used.
- Have a person at each position check in by name on each channel they hold.
- Test every interface in both directions.
- Walk-test the wireless coverage in every area the crew will occupy.
- Leave a spare pack, spare headset and batteries at the comms position.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| A position is dead and nobody noticed until the show | It was never checked because nobody was standing there in the afternoon | Check every position, including unstaffed ones, during setup |
| Channel unusable because everyone is talking | Too many people on one channel, or no discipline | Split the channel by department, and brief the discipline explicitly |
| Nobody can reach the stage manager quickly | Channel plan never answered that question | Put the stage manager on a key everybody holds |
Practice it
On your next show, during setup.
- The channel plan is written and agreed.
- Every position has checked in by name.
- Every interface is tested both ways.
- Wireless coverage is walk-tested where people will stand.
- Spare pack, headset and batteries are at the comms position.
Troubleshooting & Reliability
Comms faults repeat. The same half-dozen things go wrong on every system ever built, and each has a first thing to check that takes ten seconds.
Comms is show-critical — keep it working and fix problems fast.
Troubleshooting comms
Because comms is show-critical, troubleshooting it fast matters. Comms problems are diagnosed with the systematic method: a crew member who cannot hear or be heard might have a beltpack, headset, channel, or connection problem; a whole channel down points to the base/matrix or its configuration; wireless comms issues point to RF, batteries, or range. Tracing the problem — is it the headset, the beltpack, the channel, the connection, the system — isolates it, and the audio professional managing comms fixes it fast so the crew stays coordinated. Quick comms troubleshooting keeps a show running.
Comms failures during a show are serious because the crew loses coordination, so fixing them fast (or having backups) is important. The same calm, methodical troubleshooting as for any other system applies, with the comms-specific knowledge of the system's parts and structure. Knowing the comms system well (because you set it up) lets you isolate and fix problems quickly. Keeping comms working through the show — fixing problems fast and keeping the crew talking — is a key responsibility, because the coordination of the whole show depends on it.
Reliability and the coordinated show
Comms reliability is essential because the whole show's coordination depends on it, so it is set up carefully, tested thoroughly, and often backed up for critical productions. A reliable comms system, used with good etiquette, keeps the crew coordinated through the show — the director's calls reaching the operators, the departments coordinating, problems being communicated and solved. This reliable communication is what lets a complex live production run as one coordinated effort. The audio professional who sets up and maintains reliable comms enables the coordination that makes the show possible.
Pulling it together, comms is the communication infrastructure that turns a crew into a coordinated team, and keeping it reliable — well-planned, well-tested, well-used, and quickly fixed when needed — is what keeps a show coordinated. Combined with good etiquette from everyone on the system, reliable comms is the backbone of live production coordination. Understanding comms — its importance, its parts and kinds, setting it up, the etiquette, and keeping it reliable — equips you to manage the nervous system of a show. Reliable comms is what makes the coordinated show possible.
Work from the line, not from the pack
A user reports a dead pack. The pack is the least likely cause. Ask first whether anyone else on that channel is affected: if the whole channel is down it is power, termination or a shorted drop, and if it is one person check their headset first, then their pack, then their cable — in that order, because the headset fails most.
The faults that look like something else
Hum that changes as you walk is a routing problem, not a faulty pack. A channel that goes quiet when one more person plugs in is termination or loading. Audio that works one way is an interface. Dropouts in one corner are coverage. None of these is fixed by swapping the thing in the user's hand, which is what everybody tries first.
Redundancy, and what you do when it all goes
Comms fails and the show does not stop. That means a second way to talk has to exist and be known before it is needed: a radio channel, a phone number, a runner, or simply an agreed place to meet. Decide it in the afternoon and tell people, because inventing it mid-show does not work.
How to do it
- Ask whether anyone else on that channel has it; that halves the problem immediately.
- If it is one person, swap the headset first, then the pack, then the cable.
- If it is the channel, check termination and power at the supply.
- If it is wireless, ask where they were standing, not what they were doing.
- Fix it quietly, and tell the person it is fixed.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| One user dead, everyone else fine | Headset, then pack, then cable | Swap the headset first — it is the most likely and the quickest |
| Whole channel dead | Power, termination, or a shorted drop on that channel | Check the supply, then unplug drops one at a time |
| Hum that changes as you move about | Cable routed beside mains, or a ground loop | Reroute; never defeat an earth to cure a hum |
| Wireless dropouts in one area only | Coverage, not the pack | Move or add a transceiver; walk-test again |
| Comms fine, but one department is not responding | They are on a different channel, or their key is not assigned | Check the channel plan before assuming a fault |
Practice it
Think through a show you have worked.
- You ask whether anyone else is affected before touching anything.
- You swap the headset before the pack.
- You know where the termination and power supply are.
- A fallback way to communicate exists and the crew knows it.
- You fix faults without making them an event.
Comms in the Coordinated Show
Comms is not a department. It is the thing that makes the departments into a show, which is why the person who runs it well is trusted far beyond their job title.
Master comms, and you keep the whole production talking as one.
The complete comms picture
Pulling it together, comms is the essential nervous system of a production: it connects the crew, carries the director's calls and the departmental coordination, and lets a complex live show run as one. Managing it well means understanding the parts (hub, beltpacks, headsets) and kinds (party line, matrix, IFB), planning and setting up the right structure, testing it thoroughly, using and promoting good etiquette, and keeping it reliable through fast troubleshooting. The professional who manages comms well keeps the whole production coordinated, which is foundational to any live show. Comms mastered is the crew's reliable communication backbone.
This connects all the communication and coordination on a show — the calling, the crew work, the production coordination — to the technical comms infrastructure that carries them. Comms is where the communication craft meets the technical system, and audio professionals often own it. Understanding comms fully — why it matters, how it works, how to set it up and run it well — equips you to manage the communication that holds a show together. Mastering comms is mastering the production's nervous system.
The audio professional and comms
Comms is often the audio professional's responsibility (it is audio-adjacent — headsets, mics, audio routing), so understanding and managing it is a valuable part of the audio skill set. The audio professional who can set up, run, and troubleshoot a show's comms — alongside stage and mixing skills — is more capable and valuable, because they can handle the communication infrastructure the whole show depends on. Comms competence rounds out the live-audio professional, adding the show's coordination layer to their craft.
Growing in comms means gaining experience setting up and running comms on shows, learning specific comms systems, and handling the comms for larger, more complex productions. It is a practical, essential, often-overlooked part of live production that audio people frequently own. Combined with the rest of live audio — the basics, live sound, stage, wireless, mixing, monitors — comms competence makes you a complete live-audio professional who can handle not just the show's sound but the communication that coordinates it. Mastering comms makes you the person who keeps the whole crew talking, which is essential to every show.
Glossary
| Base station / matrix | The hub routing the comms communication |
| Beltpack | The unit crew wear to connect to comms |
| Comms / intercom | The crew's real-time communication system |
| Headset | Headphone-and-mic worn to hear and talk on comms |
| IFB | Interruptible foldback — cues to on-air talent |
| Matrix | Flexible comms routing for complex shows |
| Party line | A channel where everyone hears everyone |
| Comms etiquette | Brief, clear, confirmed use of the shared channel |
Practical sign-off
Comms is learned setting up real systems. The learner plans a comms structure, sets up and tests a system, applies good etiquette, and troubleshoots a comms problem. A mentor signs off when the learner can set up and run comms for a show.
- Explained the parts and kinds of comms (party line, matrix, IFB)
- Planned, set up, and tested a comms system for a show
- Applied and promoted good comms etiquette
- Troubleshot a comms problem and kept the crew coordinated
What the comms operator is really doing
Running comms is not maintaining a radio system. It is noticing that the lighting operator has gone quiet, that the director is about to ask for something the floor cannot hear, that two departments are talking past each other on the same channel. The system is the easy part.
This is also the fastest way for a newcomer to become known. Everybody hears you work. A calm, short, accurate voice on a busy channel is noticed by every department head in the building within an hour.
Writing it down for the next person
The comms plan outlives the show. Channel assignments, pack numbers, transceiver positions, which interface goes where, and what failed. The next technician inherits that room, often at short notice, and a page of notes is the difference between an hour of discovery and ten minutes of setup.
How to do it
- Collect every pack and headset against the count you issued.
- Note which headsets failed and tag them rather than putting them back in the case.
- Record the channel plan as it ended up, not as it was drawn.
- Note the transceiver positions that worked and the areas that dropped out.
- Charge or remove batteries before the case goes back on the truck.
What goes wrong
| Symptom | Likely cause | What to do |
|---|---|---|
| Packs missing at the end of the night | Issued without a record of who took them | Count out and count in; a list on the case is enough |
| The same dead headset keeps coming back into service | Returned to the case untagged | Tag it when it fails, not when you get back to the shop |
| Next crew in the same venue repeats all the coverage work | Nothing written down about what worked | Keep the venue notes; comms problems repeat per venue |
Practice it
At the end of your next show.
- Every pack and headset is accounted for.
- Failed gear is tagged, not returned to service.
- The comms plan as it ran is written down.
- Venue notes are kept for the next time.
Where to Go Next
Comms touches every department, so it opens more doors than most specialisms. The two obvious next steps are deeper into networks, because modern comms runs on them, and sideways into the show-calling roles that live on the other end of the headset.
The first ninety days
Work every comms call you can get, on as many different systems as possible. Write the channel plan for each one, even when nobody asks you to. Learn one matrix properly rather than three badly. And listen to how the best person on the channel talks — short, named, unhurried — because that is the skill, and it is learnable by imitation.
Where this leads
Comms engineer on larger shows, or into AV networking, where the same systems arrive as traffic on a switch. Stage management and show calling are the other direction: the people who use comms hardest tend to come from the crew who kept it working.
What the gear actually looks like
Every device named in this book, in one place. Recognition is the whole point of Chapter 4 — use this page to attach a picture to each name before you meet it on a dock at six in the morning.
Find the destination.
Work along the path between them.