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CONTROL FEEDBACK

05.07.2016

There is nothing worse than spending an entire event struggling with feedback demons. You may have been taught to fight feedback with a graphic EQ, but there is a better way. Actually, that’s not true: there are six better ways. Use my guide to controlling feedback onstage and mix in fear no more.

“The feedback frequency is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them.” –Wikipedia

Method #1 – Microphone Placement

Close Miking

For loud stages and busy rooms, close miking is generally the way to go. It might not always be the best for sound, but for the maximum gain before feedback, you have to kiss the mic. Remember, with each doubling of distance, sound level is cut in half. Plus, if you’re working mostly with Shure SM58and SM57 microphones, that’s how they are designed to be used anyway.

For corporate audio this usually means teaching your presenter how to handle the mic. For theatre this means adjusting headworn capsule placement. I have seen sound designers successfully mic a play without headworn microphones, but it’s tricky (see How To Mic An 800 Seat Theatre With Floor Mics).

Polar Pattern

sound-design-live-how-to-control-feedback-in-live-sound-polar-pattern

From SoundOnSound

For concert sound you almost never use an omnidirectional mic. Microphones with a cardioid pickup pattern have the most rejection at the rear of the mic capsule, which should be pointed at the stage monitor.

Don’t cup the mic! This will defeat the directional pattern, turning it into an omnidirectional mic.

Corporate and theatre events require specific and stable placement of the microphone capsule. Some sound engineers argue in favor of using omnidirectional capsules on the grounds that they are easier to place and produce more reliable results with the movement of the actor. My experience is that none of that matters when the audience can’t hear the actor because you can’t get enough gain.

I’ve done a lot of musicals and concerts with omnidirectional head-worn microphones in the past, though, and it’s always a struggle. The performers can’t hear themselves, and if the audience starts clapping or singing along, chaos ensues. Why did I do this? Because it was what I had available. These days I try to let directors and event producers know way ahead of time about the limits of working with certain equipment. If possible, I’ll schedule a test so they can hear the difference in the performance space.

Method #2 – Speaker Placement

Stage Monitors

Floor wedges should be placed on-axis and as close to the performer’s head as possible. I’ve heard people suggest moving the monitor away from the performer for better gain before feedback, but don’t do that. That just creates lower sound levels at their ear level, so you’ll have to turn it up louder. Most live stages are loud enough as it is, so anything you can do to lower the stage monitor level will be helpful.

how-to-control-feedback-in-live-sound-hotspotHave you ever seen those little Hotspot monitors? I haven’t seen them in a few years, but I love the idea. Put a small monitor on a stand and you significantly reduce its distance to the performer.

Sometimes, because of sightline issues or stage layout, you can’t get a monitor right in front of a performer where a cardioid microphone’s off-axis point is. This happens often with drummers and keyboard players whose instruments take up so much space and lead vocalists who want clear sightlines. This is when you need a hyper-cardioid or super-cardioid microphone and this is why many live music venues have a collection of Shure SM58 (cardioid) and Beta SM58A(supercardioid) microphones, or similar.

If you find yourself stuck with a drummer or piano player whose stage monitor is at a 90° angle to a cardioid microphone, try cheating the microphone out closer to 45° to get more rejection. If an artist requests a monitor position that is less than ideal for your microphone selection, go ahead and do it, but warn them that you may run into feedback problems and need to reconfigure the speaker and mic.

I’ve seen some pretty creative microphone and monitor placement that allow for very high gain before feedback. If you are working with acoustic instruments, ask the performers if they have any tips for placement. I used to work with a cello player in Portugal who placed the stage monitor a little behind himself so that it wasn’t pointed at his microphone but it was still aimed at his head. It worked great.

Stage monitor placement for theatre deserves its own article, but my number one tip is to start the conversation early. Explain your limitations to the production team and discuss ways to best accommodate the actors. You don’t want to realize in tech rehearsals that the actors can’t hear the musicians and that the director won’t allow downstage speakers. I often lobby for small downstage monitors straight out of the gate. I also try to make friends with the set director and builder as quickly as possible, alerting them to the fact that I’ll probably need help hiding speakers around the stage.

FOH

Make sure your FOH speakers are covering the house and not the stage. This means checking the speakers’ off-axis angles to make sure they are not spilling onto the stage or creating strong wall reflections. (See also: How To Tune A Sound System In 15 Minutes.) I’ve heard people say that all microphones must be at least six feet behind FOH, but I’ve seen it done many different ways. Some situations call for more separation and control, others less.

Method #3 – Instrument/Source Placement

sound-design-live-how-to-control-feedback-in-live-sound-drum-shieldIf you are working with a loud rock band and you place the lead vocalist right in front of the drummer, guess what happens? Your vocal mic will be full of drums and your vocalist won’t be able to hear. This happens all the time, and explains why you see the bands on Saturday Night Live using a drum shield on that very small stage.

Your goal is to balance every source input for the performers and audience. Now let’s talk about the most frequent offenders.

Drums

Drums are loud. Some drummers are interested in harmony and balance, and will change their technique, use brushes, and dampen their instruments. Those drummers are in the minority. Why? Well, have you ever played drums? It’s fun as hell to play loud, and boring as shit to play soft, or so goes my personal experience.

If you’re on tour, you’ll need a rug and a drum shield. If you’re full-time at a venue, put absorption everywhere. Two of the noisiest venues I’ve worked at have pulled the same trick and covered their ceiling and walls with black semi-rigid insulation or vinyl that screws right into the wall. Big help.

Electric Guitars

I’m a guitarist, and as such I’m fully aware of how hard it is to hear myself without the amplifier blaring. The only way I was able to handle this in my band was to learn to play without hearing. In the real world, getting a guitarist’s amp as close to their head as possible will help. Put it on a chair or milk crate. Most are open-back, so put a bunch of absorption back there.

In my interview with Larry Crane he mentions a guitarist who built a Plexiglass shield for his amp that redirected the sound upward at an angle so that he could play with feedback and do fancy things with his amp without blasting the stage. Pretty smart.

sound-design-live-how-to-control-feedback-in-live-sound-guitar-amp-doghouseI worked on a show last year where the guitarist made a shield for his amp from case lids and jackets. This helped it not bleed into other microphones as much.

Buford Jones is famous for doing whole tours mixing from inside a truck outside of the venue. (He’s even more famous for mixing some band called Pink Floyd.) These were large venues where they had little acoustic sound coming from the stage. The guitar amps where all in dog houses off-stage and all of the performers were on IEMs (in ear monitors). Most of us won’t experience that, but it gives you an idea of how far people will go to control sound levels on stage. If you are worried about approaching a guitarist to discuss changing their setup, just remember that asking them to turn down their amp and put it on a stand is nothing compared to removing it from the stage entirely.

Method #4 – Mix

Stage Monitor

Most performers these days are wise to the challenges of microphone feedback on stage and will make specific requests for their monitor mix. I’ve made it a practice to not add anything to a stage monitor mix until expressly asked to, except for vocalists who almost always need reinforcement. When musicians walk in the door saying, “Just give me a mix of everything,” they likely don’t know what they need. Smile and nod.

I’ve made it through entire shows without adding anything to some performers’ stage monitors because the stage layout allowed them to hear everyone. I’ve also worked on shows where the band has skipped sound check then walked on stage expecting a complete mix. I try not to work off of assumptions and I give people only what they need, because the lower your stage volume, the better your FOH mix will be, and everyone will be happier.

FOH

In small to medium venues, you aren’t “mixing” in the classical sense, you are doing sound reinforcement. You are balancing the acoustic energy in the room for a more pleasant musical experience. From my interview with Howie Gordon:

The other thing I hear a lot about [is] guys setting the whole mix base from the drums, and in my opinion that’s the last thing you should do because the thing that immediately suffers is vocals. It’s the one instrument that can’t control its own stage volume. -Howie Gordon

And from my interview with Larry Crane:

How many times have you been blown out of the water by the mains because you’re trying to keep up with the stage? It’s like, “No, no, no! That’s not necessary.” You’re not building the mix up from the kick drum at that point. You’re building the mix down from what’s happening on the stage, and you’re filling in what’s missing, just a little bit. -Larry Crane

If you need definition on the bass guitar, roll off the low end and mix it in. If you are missing the melody from the keyboard, bring up the right hand. If the guitarist is too loud then invert the polarity and lower his volume in the house with deconstructive interference. That’s how noise cancelling headphones work.

(Just kidding! You know I’m kidding, right? If you actually try that and it works, keep it to yourself.)

Compression

Normally, I love compressors, but they raise the noise floor and reduce dynamic range, and therefore reduce gain before feedback. I would really like to use compression on lapel mics during corporate presentations, for example, but I’m often on the verge of feedback and can’t spare the gain.

Method #5 – The Holy Grail

IEMs, e-drums, synths. Done! 

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