Without being there it's nearly impossible to diagnose your feedback problem. There are so many things it might have been.
- Your amp in the kickback position could have been resonating the upper atmosphere and bleeding into another mic. Were you using overhead mics on the drums?
- It could have been the low freqs from the subs bouncing back into any of the mics. Even acoustic coupling if the stage was resonant.
- It could have been a combination on stage and FOH exiciting a mode in the room. Did you run a RTA before sound check?
Now, even though it could have been many things, a good tech should have found the cause within a minute, two at the most. Completely correcting it might take a few minutes, but finding the culprit should be simple.
So why didn't your sound tech just mute each mic one at a time until it disappeared?
One at a time:
- Yes the drums were mic'd. kick, snare, hat, 3 tom mics (spread across 5 toms), and yes, two overhead condensers. The drummer was positioned at about 4:00 to me and raised up a foot or so, with probably 8 feet max separating my kickback amp and the drum riser. So yes, considering where my amp was, it was pretty much a straight shot to the drum riser and firing upwards from 8 feet way, could easily have been firing into the same vertical plane as the drum overheads, as well. I n which case, assuming I had thought of this at the time, a quick attempted fix would have been to reverse the positioning of my amp so that it was at my right foot, firing away from the drums instead of at my left foot firing towards them.
- The subs were located on the floor, in front of (not on) the stage.
- Don't think they ran an RTA but I'm not sure. The FOH guy is a friend and a pro, but set-up was a real clusterflock due to circumstances beyond our control so we didn't really have the time we could/should have and he was doing a lot of stuff on the fly.
There was another bassist in the house during our first set and he told the FOH guy he thought the bass tone was too muddy and boomy, so the FOH guy and I spent about 10 minutes on our first break trying to square that away. It made a difference in the house (or so my wife said), but the stage sound didn't improve and actually got a bit worse as the night went on.

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