Where the 44-frame ceiling of DMX512 comes from, how unicast Art-Net differs from multicast sACN, why your switch needs IGMP snooping and why Wi-Fi at a venue is a bad idea.
Start with the arithmetic everything else grows from.
DMX512 runs on RS-485 at 250 kbit/s. Every byte travels with one start bit and two stop bits — 11 bits, exactly 44 microseconds. A frame holds 512 channels plus the start code, so 513 bytes: 22.6 milliseconds. Add the BREAK that opens each frame and you get a ceiling of roughly 44 frames per second. Not "about 44 on cheap interfaces" — a physical limit of a standard written in 1986.
Two consequences follow, and they shape the whole rig.
First: one DMX line carries exactly 512 channels. Not "as many as it can manage" — those 512 already consume the entire time budget. Want more? You need a second line, a third, a tenth.
Second: a dimmer rack on the far side of the hall means a separate cable across the hall. Twenty universes on a large venue means twenty cables, and the crew will look at you unkindly.
Network protocols solve the second problem only. The first one they don't touch at all — 512 channels per line stay 512 channels.
Laptop ──Ethernet──► switch ──► node at the truss ──DMX──► fixtures
└─► node at the portal ──DMX──► fixtures
A node is a box that listens to the network and turns packets back into DMX. One universe per output: a four-output node feeds four lines. The long cable is now a single network run, and the DMX tails are short — from the node to the nearest fixtures.
This isn't only about convenience. Ethernet fails noticeably less often than a twenty-metre DMX cable dragged across the floor, stepped on and snagged by a road case.
Both protocols wrap the same 512 bytes into UDP. The difference is delivery, and it matters more than it looks.
Art-Net (port 6454) is sent to an address: the console knows the node's IP and sends the packet there. The scheme is transparent — you can see who talks to whom — and a cheap unmanaged switch will do. Universe addressing is 15-bit: seven bits of Net plus eight of SubUni, i.e. 32768 universes. You will never need that many.
sACN (also known as E1.31, port 5568) broadcasts to a multicast
group: the address is derived from the universe number —
239.255.<high byte>.<low byte>. The console doesn't know who is
listening; nodes subscribe to the groups they need. For large rigs this is
the right model: a packet goes out once instead of being copied per
recipient.
And this is exactly where things break.
Without switch support, multicast behaves like broadcast: the switch doesn't know who wants the group, so it floods every port just in case. Thirty sACN universes at 40 frames is roughly 30 × 638 bytes × 40 per second ≈ 6 Mbit. Multiply by the number of ports, add video and control on the same wire, and you get a switch that starts dropping frames.
The cure is a checkbox called IGMP snooping on a managed switch: it listens to who subscribed to what and delivers each universe only to ports that asked for it. A twenty-euro unmanaged switch has no such checkbox.
Hence the practical rule: simple rig — Art-Net on an unmanaged switch; many universes — sACN, but with a switch that speaks IGMP. The middle option, "sACN on a cheap switch", works right up to the evening when you added another ten universes.
Tab Settings → Network output; settings apply on the fly: protocol (both at once is fine), node address for Art-Net, base universe number.
The network runs in parallel with USB — the same frame goes out 40 times a second to both. Only universes that actually contain fixtures are sent; empty ones don't take airtime.
We send sACN with a fixed priority of 100, the standard default. Worth knowing if you were planning two sources on one universe arbitrated by priority: Flux Lights won't sort that out, and our redundancy works differently — the backup simply stays silent while the main console lives.
Addresses. Computer and nodes on the same subnet. Art-Net historically
lived in 2.x.x.x and 10.x.x.x; many nodes ship with something like
2.0.0.1. The easiest approach is static addressing, written on tape stuck
to the node itself.
Turn Wi-Fi off. Not "don't use it" — switch the adapter off. Otherwise, the moment someone kicks the cable, the system will cheerfully route traffic through the venue's wireless — and your light will run through an access point that the whole audience joins at the interval.
A separate network. A shared switch with video and guest internet works fine until content upload to the media server starts. If there is only one network, at least ask for a separate VLAN.
Gigabit once you pass a couple of dozen universes. 100 Mbit is formally enough, but headroom for peaks and stray broadcast traffic is worth having.
Check the fixture, not the node's LED. The LED says "packets are arriving", not "the fixture understood them": the address may be off by one universe, and that is the single most common mistake on a get-in.