How to avoid acoustic feedback when having heavy vocal effects during a live performance?

Question

I recently had to perform a live an EP of electronic (experimental/neo-classic) I released. Vocals are being radically altered through an FX chain.

Despite that I did some tests in my home studio without feedback, once at the rehearsal in the club, I encountered a massive feedback problem (+ that night the usual PA was replaced by a sound engineering student) and I had to cancel all the tracks featuring vocals.

I am very new at performing vocals and I would like to know what I am doing wrong and how to find a way around or compromise to still be as near as possible to the EP vocal's vocal processing while avoiding any feedback issues.

My setup is the following:

IN: Mic → Scarlett 2i2 (soundcard) connected to MacBookPro/Ableton
OUT: MacBookPro/Ableton -> Scarlett 2i2 (soundcard)

FX on vocals

List of effects on the vocal insert:

1.utility (raise volume up)
2.vocal control multiband compressor
3.Auto-tune
4.Compressor
5.Reverb (25% wet)
6.Tube amp simulator
7.Compressor

Basically I then simply layer my live vocals on top of the instrumentals and chorus background:

The map of the sound system in the club I performed

The subwoofer was on the floor and the rest of the speakers were suspended 1m50cm above the floor. I had two behind me (my setup was put on the table in the picture), and two others cornered in the space.

Answer 1

The trouble with using compressors live is that they magically transform themselves from devices which reduce the peaks of the performance into ones that turn up the quiet bits.

Your three compressors [& probably a contribution from your amp sim, which will also compress] is that your are turning UP your quiet bits a whole lot more than you thought you were turning down your loud bits.

For live work, you're going to have to sound check at full volume with this structure & see what additional [bad] influence each of those comps has; perhaps think about putting a noise gate early in the chain to help combat it, or invest in feedback suppression for the front of house [tough when it's not your front of house.]

Depending on whether you use hand-held or mic stand may affect the frequencies at which you get feedback. Hand-held is likely to squeal first, on a stand may boom, if there's enough resonance in the stage.

There's also what mic you're using & how you use it.
A standard SM58-style cardioid is going to be your best bet unless you can afford a good headset mic [& I mean a pro one, not something you can plug in a computer] & which only suits certain performance styles, visually.
The other thing about a standard SM58 is you have to avoid what all the 'cool kids' do, wrap your hand round the ball end, rapper-stylie. That is just the worst technique & actually will cause feedback on an otherwise well-behaved system. Don't choke the mic, let it breathe. It's got a fairly obvious bit to use as a handle. Use it.

Don't do this -

Do this

^{Images ©Getty Images.}

See also Sweetwater: 5 Ways Your Mic Technique Is Ruining Your Vocals

& just because I liked this one…

…and depending on which way those speakers are pointing, you may actually have to stand way over here…