One thing I would like to add. In transmission lines, if the
impedance is not the same from the beginning of the
line, through each of the "splits" (Each light), and at the end (
terminator or last light),
power loss (signal loss in dB) can occur. This was an issue in RF lines (cable TV and such) however it can apply here as well. The mismatched
impedance will cause reflections which can cause errors (usually this is what a
terminator is for, however having the
line terminated at 110 ohms, when using a different
impedance cable can cause even more loss)
That being said, my only thought on using a short mic cable with a long cable is that you will have a mismatched
impedance on the beginning
line reducing the signal
power. HOWEVER, I do no think this cause an issue, as long as the rest of the rig is the same.
A horror story of mine that I have using mic vs.
DMX, one that I hope will hit home with everyone. This was my first big show I had ever booked. I did not own
DMX cable, the shop I rented the majority of the lights from did not own
DMX cable (why?), but because I originally wanted to be a live sound engineer, I had miles of mic cable that the shop said was fine to use. Here is the story:
I was to set up a new years show, (20
LED PARS for
stage wash for a band, 4 moving heads with 8 Scanners around the dance area hung on upright
truss sticks uplit with
LED's, and 60
LED uplights around the room). We put up the
stage wash powered and wired for
DMX, I tested it beforehand, everything was ok so we cranked it up so the sound guys could start working. We erected the other
truss uprights with the heads and scanner, tested fine, so we left them. Then the large quantity of uplights we used got placed throughout the room to dress the walls of the space. Everything tested fine individually with my
console driving each
line separately to test. (We had 2 1x4 Opto-Splitters which ran the splits for each
leg of 20 or so lights). After we had connected and tested each branch individually, it was time to do the whole
system. Plugged my
console into the splitter, and went to go see some of my programs work! what the &%#$..............
I had no control over either branch of uplights, Half the
stage lights would respond to my programs, and the other would do something completely different (as if I had them addressed incorrectly however they were fine as I had tested them individually). Good news though...my movers and scanners were working..... After I had suspected a bad cable from the front end of either chain of
LED's I had my crew replace that cable with a known working one...nothing. I started to unplug the last fixtures in the chain, hoping it was a bad
fixture or cable causing some weird issue....nothing. I did the same for the other branch of uplights...nothing. As I knew the branches worked individually I removed a branch of uplights from the splitter and hooked it up directly to the
console. VOILA!! now what is the problem? After plugging it back into the splitter....nothing. I thought my splitter was fried. That was not the case. I called up a good friend of mine who I knew wasn't busy on new years eve. I told him my problem and he was clueless as well. He came through to the event and started to help me diagnose what could be wrong. We went through every thought and still couldn't figure out what was up. He then asked me, "You're using
DMX cable right?" I said, "no mic cable works fine". He was stumped, but he brought out his trunk of
DMX he had in his van. We replaced the first cable in the
line from the splitter. BAM! I had control. We later replaced as much of the mic cable as we could with
DMX before people started to file in. After about multiple hours of headaches and confusion, we had everything in the room working as it should.
Later we tested the mic cable out at the shop, and we found that using the splitter, only some of the mic cable would pass signal, and some wouldn't (hence why the movers and scanners worked but nothing else did). It was impossible to tell which cable was going to work, and which wouldn't. He had never seen anything like this, and neither have I, nor do I ever want to go through that series of problems again, I was drenched in sweat from running around, the client thought I was on drugs because my answers when he asked, "Is everything good?" I replied,"Well I think maybe I don't know, refund, no show maybe I think hold on let me check....". ALL BECAUSE OF MIC CABLE.
So I decided to get the right cable for next time. Since then I have had 0! yes 0! issues with lights not acting as they should because of cabling. In my most humble opinion, using only
DMX cable has proved to save me time, effort, and clients because I have one less thing to go wrong (unless you count each cable as 1 thing, then I have about 80 less things that could go wrong).
If a rental company gives me mic cable, I ask for
DMX. If they do not have any, I usually try and source it elsewhere or buy it myself if I have to. If those are not an option...pray to the gods of theater and hope things go as they should?
