Microphone for Feed to Control Room Theatre

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

Contents

• Method #0 – Psychology
• Method #1 – Microphone Placement
  • Close Miking
  • Polar Pattern
• Method #2 – Speaker Placement
  • Stage Monitors
  • FOH
• Method #3 – Instrument/Source Placement
  • Drums
  • Electric Guitars
• Method #4 – Mix
  • Stage Monitor
  • FOH
  • Compression
• Method #5 – The Holy Grail
• Method #6 – Don't Give A Fuck
• #ObligatoryBonus – EQ
  • • Ambient Changes
• Other Tricks To Try
  • Feedback Eliminator
  • Frequency Training
  • Microphone Splitter
  • Polarity and Delay
  • Separate Speakers
    • Turn Down
• Conclusion

Method #0 – Psychology

I had to include this step 0 because the more I thought about it and the more I talked to other sound engineers, the more this came up. When it comes to improving your GBF (gain before feedback), start with the beginning of your signal chain and work forwards.

Example 1: Jason works as an AV tech on city council meetings. He was having lots of feedback problems and asked for my help. After we went through everything in the signal chain and made improvements where we could, the most important change we made was simply explaining to the council members the importance of proper microphone positioning. Nothing else we did made more of an impact than getting that first step right.

Example 2: When Brian Adler works as a monitor engineer in situations where he expects the GBF to be an issue, he will purposely start with vocal mikes way too loud in the mix. This will give the performer a little shock and start the sound check off by asking their mix level to be turned down, instead of what normally happens.

Probably the biggest tip I can give in this area is to be proactive and be a pack leader. You don't want to wait until the stage is all set up and you are halfway through the sound check before you approach the guitarist about potentially moving his amp for a less face-melting experience. Instead, while you're giving them a hand loading in, mention that "What we normally do here is put the guitar amp on this stand so that you can hear it well and I can get a better mix out front."

Or for vocalists: "We've found that the ideal position for the monitor is with this microphone in this position. If you want it to be somewhere else, I'm totally fine with that, but it might not be able to get as loud, so we'll have to work around that."

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 SM58 and 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

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.

Have 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

If 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 duct insulation or vinyl that screws right into the wall. It made a big difference.

For more on this topic, see 5 Pro Drummers Explain How to Make a Drum Kit Quieter on Stage.

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.

I 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! 😉

Method #6 – Don't Give A Fuck

"These setups that we're working on, there's EQs everywhere. If there's still feedback, it's too loud. So lower it or let it ring all night. I don't give a fuck." —Dimitris Sotiropoulos

I laugh every time I read this quote, but there is plenty of truth to it. Half of what I write on Sound Design Live is about psychology. People don't trust sound because they can't see it. That also means they don't trust you because they can't see what you're doing. Letting the monitor feedback for a second before you bring it down communicates to the artist that it has reached it's maximum level and that you are turning it down.

Q: But you do use EQ, right?

A: Um, yeah, most of time. At least to attenuate some low end.

#ObligatoryBonus – EQ

This is your last tool in the war on feedback. Use high-pass filters to remove the rumble from guitars and the proximity effect from vocals. Use narrow-band filters on a parametric EQ to surgically remove problem frequencies. Although it's your last step, it's also necessary. Temperature, humidity, and performance changes throughout the night will require compensation.

I recently worked with a sound engineer who would cut the low end from all of his vocals up to 200Hz in the stage mix. That's a lot! But it worked. A few years ago I worked on an outdoor event where everything would be balanced during the afternoon sound check, then explode into feedback at night because of environmental changes.

So I think we can agree that some amount of EQ is necessary, but watch out for assuming too much. There is a process that we sound engineers call "ringing out the monitors" that often takes place before any artists have arrived. We use this process to lessen the amount of time we will need to chase feedback during sound check. I gotta tell you that over years of working on live events I do this less and less. Why? Because if you do it before sound check then you are making a lot of assumptions about the sound that can all be ruined by changing a mic or its placement. You're also making changes to the speakers' performance and sound quality without due cause. A better technique is to test for feedback, make note of those frequencies, but hold out on makes changes until you need more gain.

I sort of hate the fact that "ringing out" is supposed to be a normal part of our job. Under normal circumstances, with high-quality equipment and a properly optimized system, you shouldn't have to do this. The fact that it is a normal part of our job makes me realize that there are a lot of sound systems out there that need your TLC.

Pulling half the bands down on a graphic EQ is like removing a tumor with a wiffle ball bat.

If this is the first article you've ever read from me, you may wonder what I have against graphic EQs. For system EQ, their fixed frequency, bandwidth, and logarithmic spacing make them unhelpful. They maintain popularity until today because they seem to give you a visual (graphical) representation of the changes you are making. Unfortunately, the visual is misleading. While you appear to be making surgical incisions, you are really making ⅓ octave tonal changes. You can prove this to yourself by measuring one. Here's a step-by-step guide.

I hate graphic EQs. I don't use them unless I don't have a better choice. You're talking about ⅓ of an octave. That's like a C to an F on a piano.

Michael Lawrence – Fighting Microphone Feedback WITHOUT a Graphic EQ While Mixing Monitors from FOH in a Reverberant Room

Basically, the only things that graphic EQs are good for are ear training and maybe use in the battlefield that is Monitorland. For more, see my interview with Dave Swallow, my interview with Bob McCarthy, and my review of McCarthy's book.

Another consideration is where you will insert these EQ filters. Your first idea might be to insert them on the master output buss of the mixing console. Consider that this has global repercussions on the entire mix. You are affecting the system response and mix balance. If possible, scale your changes back to the smallest local change possible. Is the feedback originating from a single microphone to all outputs? Insert your EQ on that microphone's input channel first. Is the feedback frequency present to varying degrees in all vocal microphones? Insert the EQ on the vocal buss.

In the world of my dreams, I would be able to insert filters on a per-send basis from each input channel for maximum transparency. Unfortunately, the only way I know to accomplish that on modern mixing consoles is to create a duplicate input channel for each send, which is overly complicated.

Ambient Changes

Humidity and temperature changes throughout the night will require compensation, especially if you are outside. My first big lesson in this came will working for the band O'QueStrada in Portugal at an outdoor concert at the Centro Cultural de Belém. I had all of my monitor mixes set just on the edge of feedback, which seemed fine during soundcheck. We came back that night to start the show and as soon as I unmuted the band I also unleashed a storm of microphone feedback.

At the time I didn't understand that a rise in relative humidity at that location would result in less high-frequency air absorption. I could have compensated for the change in humidity with a high-shelf filter.

The lesson: Don't mix your stage monitors to the edge of feedback if you expect a rise in relative humidity and be prepared to compensate with a high shelf filter.

Temperature changes are less obvious. It would take a a 20ºF change in temperature to produce a 2% change in the speed of sound, which may be only enough to shift your acoustic crossover point by one seat. Unless you are working outside with some very large changes in temperature, I wouldn't worry about its affect on microphone feedback.

Other Tricks To Try

Feedback Eliminator

If you look up reviews for feedback eliminators they are almost equally bad and good. You never see them on professional productions. Part of the issue is that sound engineers don't like things to be out of their control, but the main problem is that these units just don't work that well. Everyone who has used them has horror stories.

That being said, sometimes pro audio feels like a war zone, and I will never judge you for using one. Especially for corporate events where you have several lapel mics walking around a stage and you only need to stop one frequency from feeding back on one microphone for three seconds at a time. Or small setups where you are very limited in the way of EQ.

Frequency Training

Imagine the show-stopping seconds you could save if you could identify feedback frequencies immediately without using an analyzer. There are some nice apps out there that will train you to identify frequencies. This is not the same skill as having perfect pitch. It's pitch memory and anyone can learn it. Most of them train you using the 32 bands of a standard graphic EQ, which isn't ideal, but is a great place to start, helping you avoid a frequency-wide sweep. I've used Audio Frequency Trainer and Quiztones. Read more about my experience here: My Results from 30 Days of Ear Training.

Microphone Splitter

Don't have a digital mixer or a separate mix console for the stage? Try splitting a few channels for more control. Let's use the lead vocal microphone as an example. Right before it comes into the mixing board, connect a splitter or use a Y cable for the most basic passive version. This will give you two copies of the lead vocal coming into the mixing board. Mix one for the house, mix one for the stage. This will allow you to roll off way more low end then you normally would and make other adjustments to the stage mix without significantly affecting the house.

Polarity and Delay

It has been suggested to me that you can invert polarity or add small amounts of channel delay to get more gain before feedback. I've never had success with this. It just moves the feedback to a different frequency, makes it attack slower, or makes no change at all.

Separate Speakers

From the Meyer Sound Design Reference by Bob McCarthy ©1998:

One solution is to double the number of stage monitors and separate them into music and vocal systems. This has the advantage allowing for separate EQ and, in additon, the musicians find it easier to localize their voice and their instruments since they come from different positions.

Thanks to ra byn for tipping me off to that one.

Turn Down

While on tour with Ringling Bros., I found that in some arenas I had GBF for days and in others I could barely get the main vocal up above the band. Our system and performers being the same, I had to accept the fact that my headroom changed from week to week. The audience didn't know it was different, so as long as the balance was good I could adjust the overall level as necessary.

Conclusion

Your best tool for controlling feedback in live sound is stage layout. That means microphone placement, speaker placement, and instrument/source placement. Then you can work on the mix and if you still can't get enough gain before feedback, use EQ. If you're lucky, you'll work with a synth-pop band (call me, Active Child!). If you're unlucky, challenges abound, everyone's a dick, and you just let it ring all night, cause fuck it.

What are your best tips for fighting feedback on stage? Comment below!

daltonmonertafte.blogspot.com

Source: https://www.sounddesignlive.com/how-to-control-feedback-in-live-sound/

Share this post