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For clarity, monitors are usually rung out with no signal. Pink noise is typically used in conjunction with a RTA mic in order to tune a system (to its environment, etc.).
You can test to see if this is a contributing factor by using the bypass button. Bypass it and listen, does the problem go away? Push the bypass button again (so that it is not bypassed), does the problem return?
ringing out your system
thats a very dangerous thing to be doing
especially if you dont know what your doing
the soundcraft comes with a frequency analyzer
so you can see problem frequencies before they feedback
there feedback suppression looks very good in vids ive seen
you would lock down the obvious frequencies manually
and let the 'active mode' run during the show
you should have +12db of boost avaliable on the vocal mic through the mains
ie the mains need to be far enough away from the vocal mic that it there is 12 db of headroom before feedback starts
so you had the drummers vocal mic turned up too loud
but it was also picking up the drums live and delayed through the pa
it also sounded like there was a bass wave wrapping down one wall
amazing how so many technical issues can arise in the simplest set up
if you had moved the stage plot around it could have helped
but it was also picking up the drums live and delayed through the pa
it also sounded like there was a bass wave wrapping down one wall
amazing how so many technical issues can arise in the simplest set up
if you had moved the stage plot around it could have helped
I insert ear plugs and clear the room before I ring the system, so no ones' hearing is threatened.
The other danger is you can easily pop compression drivers if you get too ham fisted. Most of the time, the feedback comes on fairly gradually. So if you slowly increase the gain of a few sliders on a 31-band graphic, you can find most of the problems before they break over into really strong feedback; this is actually the goal.
Unfortunately, you occasionally find a problem that comes on fast and hard. I keep one hand on the frequency sliders, and one on the global volume/gain, and if a really strong feedback spike occurs I quickly turn the volume/gain off. If you don't catch the spike fast enough, you may pop a tweeter diaphragm.
Another issues is sometimes the feedback frequency is too high to hear. I remember a job where the front line monitor woofers were pressing of the cabs out like they had DC applied. When this occurred you could also hear power supply hum.
I believe the issue is the HF horns were feeding back at a super sonic frequency and the HF amp was being driven into hard clipping. Although we could not hear a tone, we got sort of a sense that the air was being pressurized; essentially you can't hear it, but you can feel it. Hard to describe, but if you experience once, it's a lot easier to recognize the second time.
On this system, the LF and HF were sent to the left and right channels of a power amp. So when the HF amp was pushed into clipping it sucked the power supply dry; causing hum in the woofers. Apparently this produced some DC offset in the woofer amp as well.
The audio techs running the system that day did not know what was going on. They were too far away to feel the effect and wound up blowing a horn driver. The horn made sort of a clack when it finally gave out, and then no more highs.
Since I had seen this problem before, I asked the lead tech to come up on stage to discuss. They replaced the monitor and were able to resolve the problem after I explained what was going on. I don't remember if they found/dipped the problematic frequency, or simply applied an LPF.
Ringing the system is pretty much essential if you don't have better tools that can eliminate the problem. Ringing out a system allows it to play louder without feedback, and it typically makes the system sound considerably better as well. An RTA does not take place of this task, although it can make it easier to identify problem frequencies.
Feedback suppressors do essentially the same thing, and are automatic (for the most part). Unfortunately they may color the sound a bit or, over correct; which degrades the sound. I spec'ed a rack full of Sabine FBX-SOLO feedback suppressors for a system I designed in the mid 90s. I thought they did a good job most of the time, but had sort sort of a digital sound to them. Also I think there may be some advantage to using global system EQ instead of just tuning the individual channels. If there are room resonances, you want to dial them out of the entire system, and not just the mics.
I do agree there is some risk to ringing a system, but IMHO it's worth it, although you absolutely should wear ear plugs and clear the room to mitigate the risk to everyone's hearing. You should also be as gentle with the system as you can. You don't want to push the system into strong feedback, and if it breaks over you want to to stop it as soon as possible.
My final though: If you don't have the aptitude to learn how to ring a system, perhaps you should not be running sound in the first place. It's not that hard.
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I once had terrible feedback in my lead vocalists mic. He was a couple feet behind the mains, but was dead center between them. The summing of the subs was causing the feedback. I had a digital crossover at the time, so I delayed one side of the PA slightly, thus moving the summing over a couple of feet. Feedback vanished.
