Reply To: Ringing Out The Room – Channel or Overall PEQ?

[Andreas]

Yep, George, that’s what I’m thinking as well. Placing a Mic in the middle of the room (=in front of the PA) you’re likely to be able creating feedback at any frequency, depending on the distance between the PA and the mic (you’re not adressing room resonances with such a setup at all!). If you’re driving left and right PA from that mic, observed feedback frequencies are pretty much random and will vary with slightly moving the mic (phase effects from left and right side of PA).
You may place a measurement mic (connected to a RTA) somewhere in the room, preferably a boundary layer mic if there are reflecting walls to measure your room. But you may also encounter a venue with highly reflecting walls on every side, no chance to EQ the room that way at all, since there were peaks and notches at different frequencies everywhere.
A rectangular room should have fundamental resonances at two frequencies only (left-right and front-rear) and maybe the first harmonic.
The louder you try to run your PA, the more problems you’ll get. And when the room is filled with audience, things will change as well.
So I repeat what already was said a lot: With IEMs you really should not have serious issues with feedback from vocal mics, except you’re a) running too loud or/and b) allow your mics to catch audio from the PA (either direct or by reflection).