Some of it has already been explained somewhat, but I'll try to give some info as well.
A great answer, but I can't imagine the OP is still watching this post for details 15 years after making itSome of it has already been explained somewhat, but I'll try to give some info as well.
A DMX universe is 512 channels of 256 levels. A DMX channel is not the same as a console channel/fixture.
If you patch a dimmer to DMX address 1, that dimmer has 256 levels of control between 0 and 255 (out to full brightness). If you patch a 3-channel RGB LED fixture to DMX address 11, you will have 256 levels of red control on channel 11, 256 levels of green control on channel 12, and 256 levels of blue control on channel 13.
Now, where do the universes come in? With the DMX universe being 512 channels, you can fit up to 170 3-channel RGB fixtures onto it (taking up 510 of those channels). So, what if your show has 250 RGB fixtures? A single DMX universe will not be able to control them all, because 250 RGB fixtures require 750 DMX channels. So, you need to add a second universe. If you have a bunch of 30-channel moving lights, you can put a max of only 17 fixtures on a universe. So again, if you have 30 of those fixtures, you will need more than one universe to control them.
Beyond just the technical reasons for additional universes, they are often used in an organizational fashion. For instance, on my current TV show, my universes are allotted as follows:
1 - Set Dimmers
2 - Overhead Dimmer West
3 - Overhead Dimmers East
4 - Not Used
5 - LEDs 2nd Floor South (added when 7 filled up)
6 - LEDs 1st Floor
7 - LEDs 2nd Floor
8 - First Unit Fixtures
In pretty much every situation, the receiving fixture has absolutely no idea what universe it is on. You address the fixture to address 25, and it listens to address 25. It does not matter if it's in universe 1 or 100. It just sees a stream of 512 channels, and listens to the 25th (plus whatever range of channels the fixture uses). For instance, if I address my RGB fixture at 25, plug it into universe 2 on my console, and want to control it on channel 100 on the console, I patch fixture 100 at 2.25 in the console. If I move it to universe 4, I patch fixture 100 at 4.25. The fixture itself still just sees the 25.
As to your question about the forerunner box being in the second universe, that's solely a matter of how it is patched into the console (unless there's something very strange going on). It could be plugged into universe 1 or 3 or 7, and you would just need to reassign the patch in the console to the correct universe.
Hopefully, that helps some.
@samiwas Welcome to the "those" club along with the rest of us.What the heck? I didn’t go searching for a thread...it was on the general thread list! Why on earth was it displayed if it was from 2003?? Weird. I guess that’s what I get for forum-ing at 3:30am after 13 hours at work!
Now I’m I one of those people.
OH, I'm certainly in that club. My high school had a large, 12-dimmer system with slider patch...dimmer sliders were about 15" of travel as I recall. Wish I could remember the details. We upgraded to a 0-10v control system using, I believe, a 25-pin serial cable. Didn't have DMX until I was in college in the 90s.
Perhaps this https://www.controlbooth.com/threads/ariel-davis-lightboard.6069/#post-67006 will excite some memory cells.
Those are definitely the same manufacturer, and a search led me to this thread. This is almost the same board I started on in the late 80s as a high-schooler. Ours had 12 dimmers, 40 patchable circuits, and two large levers that swapped the dimmers from house light to stage lighting control.Perhaps this https://www.controlbooth.com/threads/ariel-davis-lightboard.6069/#post-67006 will excite some memory cells.