Two requirements get conflated constantly: play the same thing on all the amplifiers and play this thing on only some of them. They need different mechanisms, and buying the wrong one is the usual reason a "zoned" system turns out not to be.
Mirroring sends one audio stream out of several outputs at once. A split site with three amplifier racks needs three sound outputs, all playing the same bell at the same instant. Without it, the second rack's bell lands a fraction of a second after the first and you hear a slap-back echo across the quad.
<PlaybackDevice>3</PlaybackDevice>
<MirrorDevices>4|5</MirrorDevices>All three outputs are driven from the same decoded buffer, so they start together. Press Ctrl+O in the console to list every device with its index rather than guessing which USB adapter is which.
Zoning is the opposite requirement: this announcement goes here and not there. Because the audio has already been distributed to the amplifiers, zoning has to happen physically — by muting the amplifiers that should not hear it. That means a relay board.
The short version: mirroring is software and free; zoning needs a £20 relay board.
A zone relay board sits between the scheduling system and the amplifier mute inputs, or their power, depending on how the rack is wired. To send an announcement to one zone the system opens the mute relay of every other zone in use for the duration, then releases them. A four-channel board covers two zones plus a bell and a lamp; eight channels covers four zones.
ZoneRules tags an announcement with its target zone. When it plays, the mute relay of every other zone currently in use is opened for the duration and always released afterwards — including if the announcement is interrupted, which is the part worth checking in any system you evaluate. A zone that stays muted after a failure is a fire-safety problem, not an inconvenience.
Zone mapping is fixed rather than configurable: channel 1 is the bell, 2 and 3 are the first two zone mutes, 4 is the emergency lamp, and 5 and 6 are zones C and D on an eight-channel board. Fewer settings to get wrong, at the cost of having to wire to the map.
The example below is a secondary school spread across three teaching blocks and a sports hall, with one amplifier rack per building. It shows which outputs are mirrored, which are zoned, how many relay channels that needs, and where the single scheduling machine sits.
| Zone | Covers | Amplifier | Relay channel |
|---|---|---|---|
| A | Main teaching block | Rack 1 | 2 |
| B | Sixth form + library | Rack 2 | 3 |
| C | Sports hall | Rack 3 | 5 |
| D | Dining + outside | Rack 3 | 6 |
Bells go everywhere: no zone tag, no relays operated, all three racks fed by mirroring. "Year 11 to the hall" goes to A and B only, so C and D are muted for the announcement. A fire drill goes everywhere at top priority, and the emergency path deliberately ignores zone targeting entirely — an evacuation is not a zoned message.
Zoning exposes a problem that a single-zone system hides: different spaces need different levels. A sports hall needs considerably more than a library, and the same announcement at one level will be inaudible in one and startling in the other.
Set the physical gain per amplifier rack, not in software. The software's volume — including time-based volume profiles that drop levels after hours — should be the content level, applied across the site, with each rack trimmed once at install so the zones sound equal. Trying to compensate for a badly trimmed rack in software means every other sound is wrong.
Zones add hardware, wiring and failure modes, so they should be earned rather than assumed. A single hall, a building where every announcement is meant for everybody, or a site where nobody will maintain the relay wiring is better served without them. Specifically, skip zones when:
Relay zoning is exactly as granular as your amplifier distribution. It cannot subdivide a rack.
Try the live demo — including the hardware panel that drives the relays.
What is the difference between mirroring and zoning?
Mirroring plays the same audio out of several outputs simultaneously, so a multi-amplifier site stays in sync. Zoning mutes the amplifiers that should not hear a given announcement. Mirroring is software only; zoning requires a relay board.
How many zones can I have?
Up to four. Two zones need a four-channel relay board; three or four need an eight-channel board, which uses channels 5 and 6 for the third and fourth zone mutes.
What happens if an announcement is interrupted mid-way?
The mute relays are always released, including on interruption or failure. A zone is never left muted.
Do emergency announcements respect zones?
No, deliberately. Emergency audio plays everywhere at top priority and suppresses scheduled playback until reset.
Can I zone down to an individual speaker?
Not with relay zoning, which works at amplifier-circuit granularity. Per-speaker control requires addressable IP endpoints, which is a different class of system.
How do I know my relay board is compatible?
Boards speak one of two byte protocols, A0 or FF. Run the built-in bring-up test (Ctrl+G), which pulses each channel and prints the result, and set the protocol accordingly before wiring to anything live.
Part of the Multilarm school bell and factory bell guides.