PS: Also don't forget microphones installed in instruments.
Our biggest feedback problems are not usually our 3 vocal + 1 conga microphones but the microphones installed in our 2 acoustic guitars!
We play one enclosed, smaller space once a week where since I'm closest to the Bose L1S, I have to be very careful about where my guitar is pointing.
I think the AKG c 535 EB may have been the problem. After better setting of gain, we can get up to about 8 without feedback (and this is in a smaller apartment).
However, there is however a ferocious Buzz when turned up. Maybe a cable? Or maybe the fact that we've got two mics each into their own vocal processor, keyboard, and drum machine going into the Mackie mixer, into L1?
Thanks for coming back to tell us how you've managed to improve the feedback problem.
The AKG C535 EB is a beautiful microphone. It's one of my favourites. However, the polar pattern is cardioid and it can be difficult to manage on a live stage. I replaced it with the Neumann KMS 105 (another great microphone), that is much easier to manage in a live setting because it has a tighter supercardioid polar pattern. I kept the AKG for lower volume applications and other singers.
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It's not just the polar pattern. The SM58 is a supercardioid microphone but has an unfortunate frequency response curve that is more prone to feedback than other microphones we can use.
I also use a KMS105 and it's much less likely to feedback than an SM58. In fact, my issue is more with the omnidirectional microphone mounted in my guitar than my vocal mic.