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Old January 26th, 2008, 10:28 PM   #1
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Live audio - avoiding feedback

This week I ran the audio for a live event with limited success. I'm looking for ways to improve the results.

The event was a corporate meeting in a cafeteria. The room is VERY live (all hard surfaces, no dampening). The facilities people put the self-powered speakers at the back of the room - and the human speakers stood just ten feet in front of them. We're using 12" Mackie's on tall stands.

We had two mics: a Countryman B6 for our company president. (He has a gravelly voice and is notorious for not being heard well over any PA. We also had a handheld dynamic cardiod. Both went through a Sennheiser Evolution G2 Wireless setup, which worked flawlessly.

We have a Mackie 1402 mixer and a Behringer Feedback Destroyer Pro as well as a compressor.

I did the sound check, and the people in the room thought the system was too loud. I calibrated the feedback system standing where I "thought" people would stand. During calibration, the unit puts out a series of clicks and opens up all the frequencies. The feedback grows. When calibration is over, the feedback is eliminated.

The company president came into the room only minutes before he was to speak. I put the B6 on him and by the time I walked away, he bent it about three inches from his mouth. Then he stood in front of one of the speakers.

The audience of about 200 people filed in and were talking loudly - especially in the live room. When the president was ready to speak, I gave him some volume - and got feedback. The crowd noise excited the room frequencies - and the frequencies had changed now that the room was full. Just below the level of feedback, the company president could hardly be heard. Finally people got quiet and we got on with the show.

I rode the faders the whole time. I also messed with the 3ch EQ to get the highest levels without feedback or ringing. Finally, I panned the two mics (partially) across the room, and that really helped.

Another thing that didn't help is that the mixing board was off to the side.

Fortunately, most people I asked said that they heard everything clearly, and that they didn't really think about the audio system. Our company president could have been happier though. He noticed when he couldn't get enough volume and when we were on the verge of ringing and feedback.

Of course, the first improvements will be to move the speakers to the Front of House, and to have the mixing board positioned properly. We will also explain the proper placement of the B6 mic to our pres.

But what about the processing? Setting the Feedback Destroyer before the people entered wasn't effective. Setting it with the audience in the room would have been obnoxious. Maybe I could ride the levels to keep the output low. Essentially, the talking audience served as a white noise generator!

Regarding our talent - we had three people on the dynamic mic. The first has a gravelly voice, and it was hard to get enough volume from him. He held the mic about 4 inches from his mouth. After him a woman spoke with the mic at about 1 foot - and her voice was more effective. The last speaker had a full voice and held the mic at about six inches. I had no problem getting his levels high enough.

Any tips that you can share would be appreciated!
Jon Fairhurst
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Old January 26th, 2008, 11:36 PM   #2
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You had one of those rough audio days, but it sounds like you did really well for the most part. Panning the way you did is an often forgotten technique that was the only thing you could do when the guy stood in front of the speaker. You named most all of the solutions to the issues you had so there isn't much more to add. You didn't have control over the crucial speaker and mixer placement but you know what it should have been. Access to the president was limited and he chose to stand in front of the speaker, a feedback disaster with any mic, and worse with an omni B6. On top of that he tried to eat the thing. You also can't do anything about people who don't use proper mic technique. Even some pros are guilty of that and you can only try to educate them as best you can before they get on the mic.
Your B6 must have been been picking up a lot of room noise to affect the settings on the feedback destroyer. You can set the filters to automatically deal with feedback, or you can do a more traditional notching type of setting that doesn't necessarily change. You can use a combination of the two across the 12 filters per channel to maximize the protection. That device works well but can be tricky to set up right.
Generally an omni lav is very hard to get enough volume into a PA system unless everything is set up just perfectly. One of the big ugly directional lavs is an option if you need a body mic. I've seen them used in many a corporate meeting that was put through a PA.
The correct speaker placement will help with the Pres standing in front of them too, since ideally they should be placed well forward of the stage.

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Old January 27th, 2008, 12:16 AM   #3
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Next time you rig a lav on the Pres, explain to him that you're placing it for optimum pickup and he's not under any circumstances to move it on his own initiative or even touch it. Tell him he may be the boss of the company but he hired you to be the boss of the sound and he needs to let you do your job <grin>.
Good news, Cousins! This week's chocolate ration is 15 grams!
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Old January 27th, 2008, 12:57 PM   #4
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Thats good advice Steve. I just realized that Jon may have been referring to an E6 head mounted mic and not the B6 lav. If you have the directional version that actually is a decent choice for PA work. That being said if it isn't placed correctly you can't get enough volume and it won't sound the greatest. I've used those on a few shows and it can be really fussy to get that boom to stay where it belongs unless you have time to really work on it, and you didn't. The pres bending on it certainly wasn't helping you either. Unless you have the E6 shaped to that person ahead of time, its not fun to get it on in a rush.
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Old January 27th, 2008, 01:37 PM   #5
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Everybody has mentioned speaker placement. I just want to emphasize that 95% of the issues described are most likely due to room layout.

Everything else described is working to overcome issues of speaker placement and room layout. Solve the placement and room layout and everything becomes much easier.

Pres does need some education regarding not standing in front of speakers and not messing with mic placement. If he really wants to wander and not worry about standing in front of a speaker a dynamic hand-held mic (wireless or wired) tends to have much more gain before feedback than any lav.
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Old January 27th, 2008, 02:09 PM   #6
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Hi Jon,

I have run into a simular situation. My solution was two use two Anchor 50 watt powered speakers, each one driving a external speaker, all on stands. That way, a PA speaker is in each corner of the room. They were fed by a Shure Distribution amp.

Or, at least, add one powered speaker to the back of the room for fill. I recently used this technique at a large conference room at a hotel in Monterey and was approached by one of the board members and told that it was the 'best sound he ever heard at a conference'.

This will give you even sound throughout the room keeping the volume low, avoiding feedback.
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Old January 28th, 2008, 03:16 AM   #7
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Thanks for the input everybody!

Yeah, improving the speaker and mixer placement will be huge. I knew the mixer placement was poor, but had no idea that the speaker placement would be that much of a problem. The system sounded great in an empty room!

Next time I'll ask the pres to get there earlier so we can get the mic setup well. By placing the speakers forward, he should be able to cover the stage without any problems. He's anything but a fool, but I want the system fool proof.

And, yes, the B6 is the earpiece model. It was recommended to me as a good feedback free solution in lieu of a feedback destroyer. We had both and I could hardly believe that feedback was still such a huge problem!

I've got to spend some time with the Feedback Destroyer manual. I'm sure that I could have manually dialed in some notches to really nail it. I wasn't about to push any buttons live though, without really knowing what I was doing.

And Glenn, cool idea about rear speakers. I don't think we'll have the budget for that this year though...

As it turns out, on the day following the big gig, I did a presentation myself with the same system in a one man show (roadie, tech, mixer, performer...). We had about 45 people in classroom seating in our Assembly Room, which is carpeted and has good acoustic tiles. My talk included video, so I set the speakers up on either side of the screen. I stood off to the side and was able to walk into the audience along the side aisle when the video played to check levels. I wore the B6 properly. Also the audience didn't have a noticeable effect on the room, so the feedback destroyer auto settings held up fine. There wasn't a hint of feedback. I was able to run the video with some grunt and still be able to speak easily during the dramatic/acoustic lulls. Aside from a couple of tweaks in the first few minutes, it was set and forget.

My job title isn't "audio engineer." But I spec'd the system and have been "the consultant" for our IT department. (They had the budget and have the responsibility for the system.) So first, I need to get the system to work well as a matter of pride, and second, I'll need to train the IT guys so they can set it up and run it consistently.

Oh well, by showing how difficult it is to do this right the first time, if I can nail it the next time, it will be all the more appreciated!

Thanks again for your suggestions!
Jon Fairhurst
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Old January 28th, 2008, 08:14 AM   #8
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Hello Jon,

I think it's all been covered pretty well by everyone.

1. Speaker placement is absolutely critical. You're not alone in underestimating this. I work with intelligent people all the time who have a blind or deaf spot to this fact. Now you know. Mic in front of speaker - Bad. Get them out in front of you. The further the better.

I've been doing sound long enough that I can "see" sound in a space. In the future, try visualizing the beam of sound that emanates from your speakers. Think about it as a beam of light. Any time the mic enters the beam, you may have real problems. Sometimes just angling the speakers to get the mic out of the beam works, but if the sound then bounces off of a nearby hard surface, angling may not help.

2. Your guy has low volume. That and #1 are a recipe for disaster. Turn up the mic, get feedback. Rock - hard place. Your choice of an E6 (not a B6) is the best choice you could have made. The E6i is more flexible, btw.

3. More people in the room is a good thing. They absorb sound and prevent it from being as much of a feedback problem.

I don't think the position of the mixer has much to do with it.

"Dampening" is incorrect, unless you are in water. The correct term is damping.


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Old January 28th, 2008, 11:51 AM   #9
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Hi Ty,

Thanks for your feedback. On the speaker placement, when I got into the room, everything was setup and the cables taped to the floor when I arrived. Looking back, I should have been a b@stard and forced a do-over. I knew it was wrong in theory, but the good initial sound check fooled me into submission.

And, yes, it's an E6. (I've been reading too many B6 postings lately...)

The "more people" thing is good for damping (thanks!), but it led to two problems: 1) when they were talking it was like a white noise generator that excited the room frequencies - even with system gain at zero, and 2) the frequencies shifted, making the feedback destroyer moot.

The main problem with the mixer positioning was that I was driving the system half blind (deaf?). I might have been getting more volume than I thought, and couldn't really tell how hard I could go with my panning "fix".

The worst part of the whole show was when the crowd was loud, and the pres couldn't be heard. It got things off on the wrong foot. By the end it was acceptable, but tainted by the poor start.

With better speaker positioning, more time to get the E6 properly positioned, and with a deeper working knowledge of the feedback destroyer, things should go MUCH better next time...
Jon Fairhurst
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Old January 28th, 2008, 03:44 PM   #10
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How high did you have the stands? Getting them up so they fire OVER the crowd (7-8 feet) helps enormously in most rooms - if they are too low, they can have someone stand in front of them (FB), and the front rows get blasted while the rear goesn't get sound.

You can drop volume a lot if you get the speakers up high and aim them right (watch reflected sound) - rear of the room takes care of itself that way so you don't end up with time delay issues, which don't take a very big room before you get some odd things happening. Add a live room, and echo to time delay and FB is a big enemy.

Don'cha wish all rooms were properly acoustically designed!?
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Old January 28th, 2008, 06:32 PM   #11
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Hi Dave,

I think we had the speakers at about 6 feet at the bottom, so that would make 8 feet at the top. They were placed only a couple of feet from the back wall though, so the talent was right in the beam.

So the height was fine. The location was not.

Good idea about the reflections. I'll take that into consideration next time, so I don't have to blast out the front row to get the sound to the back.
Jon Fairhurst
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Old January 29th, 2008, 01:24 PM   #12
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Originally Posted by Jon Fairhurst View Post
...Any tips that you can share would be appreciated!
Well, I'll throw in my two cents...

1) Speaker placement. Ideally, the mics should never be beyond the placement of the house speakers. The distance from the back wall should be a different measurement than distance from the side wall (don't create room mode problems).

Also listen for slap back echo off the back wall. Sometimes you need to rotate the speakers inwardly toward the corners for a natural diffusion.

A central cluster configuration often gives a better's just not practical in most places for a temporary install.

Run the system in MONO.

2) EQ the system for the room. Adjust for the natural curve of the room using a pink noise generator w/ calibrated mic, a 32 band graphic EQ and ring out the system.

Don't over EQ (never more than 3db adjustments from the frequency next to it)...just remove the problem frequencies and flatten out the response using a realtime analyzer.

If you don't have an RTA, find the EQ curve the old fashioned way...Flatten out the Graphic EQ and crank up the sound system (open mic) to the edge of feedback. Locate the offending frequencies through trial and error dipping them out on the Graphic EQ. Notch out each frequency one at a time till you generate and kinder gentler EQ curve with better gain and less feedback.

Don't over do it. It's just the beginning of the process.

3) Make the Mic sound good. Do a sound check with whoever will be speaking and adjust the mixer channel EQ to dial in the mic so that it sounds natural....not too bright and not too muddy...and not barking your face off. Again, don't over adjust. Mic proximity will have a huge effect.

4) Find problem frequencies. Have someone stand in the position wearing the mic and remaining quiet. Slowly crank up the volume to the edge of FEEDBACK. Locate any problem frequencies on the Realtime Analyzer so that you know right where the problems are with this voice and mic combination. You may want to tweek the graphic eq a little.

5) Lastly, Run the process with the Feedback destroyer/terminator thingy. It is able to yank a narrow frequency problem without effecting the overall tone too heavy handidly. Don't over do it. Your just trying to get a little more gain out of the mic without changing the quality of the sound.
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Old January 30th, 2008, 06:07 AM   #13
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Jim has pretty much summed up what I was going to say, but I'll repeat some of his key points...

Personally, I would scrap the Behringer Feedback Destroyer for an audio operator. I've worked on countless live productions over many, many years and I've never ever seen a "feedback destroyer" in the racks. Run the system in Mono as Jim suggested. Use a 32-band EQ for FOH (something nice and simple like a dbx 1231 or similar will do the job nicely), and maybe a parametric EQ over the wireless unit. A compressor/limiter over both mics wouldn't go astray either (which I gather you've already got covered), but as you've only got two inputs you can easily just ride the faders instead.

As long as you've got a microphone and your favourite music CD, you can "ring out" the system and make the PA sound great! No need for any high-tech gadgets!

Speaker placement is obviously very important, and you really have to just bite the bullet and "speak up" when you arrive at a gig and every thing's been set up just plain wrong! I know it's a constant battle - most clients want the PA and all the "technology" that goes with it to be invisible, but if you want good sound you need to put your foot down in the nicest and most accommodating way.

The most important thing I think you're missing is a 32-band EQ for the PA. This will solve a lot of your problems.

As I said, Jim has already summed up everything I had to say very well, but I hope this post is of some additional help...

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Old January 30th, 2008, 11:52 AM   #14
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Thanks Chris and Jim!

You've both stated what I really wanted during "the show." A 31-band EQ would have let me manually squelch some of the offending frequencies - even in real time. (In my experience, any bumps or boosts should be nice and smooth, but notching a narrow frequency is no problem.)

I was riding the 3-band EQ at the show, striving for a balance between good sound and lack of feedback, but as we all know, this is really inadequate. You use what you have though...

So... how necessary is an RTA? I've used one for my home system, using a PC a pro soundcard and an ECM8000 omni reference mic. The results were... mixed. There was a lot of noise in the measurement, and it was sensitive to mic placement. In the end I learned some things from the data, but ended up using my ears.

Also, do you recommend the impulse, pink noise, white noise or sweep method for the RTA? Or are the ears good enough?

Thanks all!
Jon Fairhurst

Last edited by Jon Fairhurst; January 30th, 2008 at 05:17 PM.
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Old January 30th, 2008, 04:58 PM   #15
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Using an RTA for a show with only two 12" boxes, and two inputs seems like REAL overkill to me! Go back to basics! Make sure next time you have a proper EQ with you, your favourite vocal microphone and CD and tune the system yourself. You're going to be mixing the show so you HAVE to trust your ears! If you don't, well then there's really no point having you behind the desk!
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