Calling all sound engineers, needing an answer A.S.A.P.

J.P. Masiongale · Post by **J.P. Masiongale** » 26 Sep 2009 11:21 pm

Hey Folks,

For all the sound engineers, or anyone in the audience who's worked with large scale pa systems, say large concert hall size or so, I have a burning question that has always confused me and I'm desperate for an answer. Here goes...

I've noticed in large pa systems they generally have flying columns over the stage, double boards, one for monitors and one for F.O.H., and also run multiple power amps to each. My question is, how in the ^&(*%$!*&(#!!!!!!! do they hook all those amps together to get the final sound through the speakers? I've contemplated trying that for a couple outdoor festivals we have coming up, where I never seem to be able to get enough power to make everything loud enough for everyone to hear in the back without major feedback problems. I've even tried cutting almost every frequency on my EQ's to compensate and still get that annoying squeal when I crank up the volume. So I'm thinking maybe more power would mean less volume and I could drive the speakers a little more.

Any help would be appreciated.

Jonathan Cullifer · Post by **Jonathan Cullifer** » 26 Sep 2009 11:39 pm

I think I understand your question, and I've never run sound at a venue that large, but I've played at many, so here goes...

If there is a feedback problem, it's most likely coming from the monitors. I've never played in a large venue where the mains were very loud onstage. The basketball arena at Belmont seats 3500 or so for a concert, and the only time we have issues with feedback is when there is a thrust at the front of the stage that extends in front of the mains. Otherwise, the low volume level and directional mikes keep that at bay. We also use in-ear monitors so we don't have problems with monitor feedback.

Most of the feedback problems I've run into come from monitors. If the stage volume is too high, it's hard to give everyone a good monitor mix without running into feedback issues somewhere along the way, especially with vocalists and acoustic guitarists. If you can somehow lower the stage volume (turn down amps, shield drums, turn down monitors), that will probably eliminate most of the feedback issues.

With the right setup, you should be able to drive your existing equipment pretty hard without having to worry about feedback.

J.P. Masiongale · Post by **J.P. Masiongale** » 26 Sep 2009 11:46 pm

Totally understandable, however, this feedback comes when I have the monitors totally off though, so that rules out that it couldn't be the monitors, and also there is no outboard gear onstage initially because we're still doing the setup and first dry run with the system before fine tuning it. Plus I always make sure to leave the monitors and mics well back behind the mains to cancel out any possible cross feedback problems that would result from that, but of course that's basic sound engineering 101. Thanks for the input though.

Dave Hopping · Post by **Dave Hopping** » 27 Sep 2009 12:00 am

+1 on holding down the stage volume.The fact that many bluegrass groups perform outside for thousands of people with ONE mic for everything should be a good lesson in the wisdom of letting the mains do the heavy lifting.

Quite awhile back I saw the Desert Rose Band at the Grizzly Rose here,with Tom Brumley subbing for Jay Dee.It was loud onstage( you could see pained looks on the players' faces) and louder out front.Not a good show.

EDIT:JP-didn't see your second post until after mine was submitted,so I didn't know about the monitors not being used.Here's a thought....While I was familiarizing myself with my little system(2 SP2's,2 Subcompact 18's,Carvin DCM-1000,Peavey CS-100,run dual mono),I decided to see what would happen if I bypassed the limiters(an Alesis 3630).Result-instant piercing feedback.I'm the most un-knowledgeable guy there is about sound reinforcement,but that little experiment convinced me that limiting is extremely useful in feedback management.

J.P. Masiongale · Post by **J.P. Masiongale** » 27 Sep 2009 12:08 am

Hey Dave,

Yeah, I can fully understand that. I always try to keep the stage volume at a happy medium, loud enough to hear what you're doing but also low enough that you could stand next to someone and carry on a conversation without having to scream, and let the mains to the punching. I usually keep the volume low when playing indoors too so that nobody goes home with a big headache. However, when playing outdoors, you don't have anything to bounce off of and the sound sort of dies out early on, also considering I have no way of putting my speakers on stands to get them higher up and no way to fly them either, so they have to sit on the main stage platform. I'm running a pair of double 15's with a 1x15 horn on top. Running these things indoors is no problem and I almost never have a feedback problem, however when I set up outside, we've always got people coming up asking to turn stuff up because they can't hear in the back at their booths or whatever, and when I crank it up, that's when the problem starts, and even cutting the master eq's almost down to nothing does not fix the problem. So that's where the whole question started. Thanks for your input.

Dave Boothroyd · Post by **Dave Boothroyd** » 27 Sep 2009 12:54 am

The hanging rigs used in big venues are very directional, and they are always, these days, controlled through a digital speaker processors that react instantly to correct problems of speaker alignment, phasing etc. They can take care of feedback from the main speaker banks before it happens too.
In addition, one of the simple reasons for using at least two desks, one for FOH and the other (or others) for Monitoring, is to ensure that monitor signals are phase reversed with respect to the mains, which also reduces feedback.
Live PA is a very high-tech business these days, and a live sound engineer does more programming on a laptop than heavy lifting and wire plugging.
Cheers
Dave

J.P. Masiongale · Post by **J.P. Masiongale** » 27 Sep 2009 1:39 am

Thanks for the input Dave,

I think I just answered my own question though with a little help from the Crown Audio website. All those power amps I was seeing are not hooked together like I thought, instead, they are only powering a couple speakers each, usually split out from the main signal by a signal processor like the DBX drive rack or something. Totally makes sense to me now, although I have gotten some great ideas from everyone here on the forum. Feel free to keep throwing tips my way, I'm always willing to learn.

Rick Campbell · Post by **Rick Campbell** » 27 Sep 2009 8:05 am

I'd recommend that you talk to a proaudio guy at sweetwater.com.

My opinion is that monitor mixes are a stupid thing to do. I've always believed that the monitors should be nothing more than a direct sampling of what is in the house speakers. Of course, this is assuming the band members know when to play and when to be quite.

Darvin Willhoite · Post by **Darvin Willhoite** » 27 Sep 2009 12:38 pm

You got it J.P. All of the front of house amp inputs are daisy chained, and the amps are grouped with speakers that allow the most efficient use of the amps power. Total impedance is critical, if the impedance is too low, the amps can shut down, if it's too high, the output of the amp is reduced.

Our church runs a separate monitor board on the stage, but the musicians use Aviom personal mixers and either powered hotspots, or in-ears. This allows each musician to set up their own monitor mix. The monitor board is used only for wedges for the singers. We have a total of around 6000 watts available, for an auditorium that will seat around 800. We use speaker processors for the mains as well as the monitors. This allows you to set the overall EQ to tune the speakers to the room, as well as time alignment or delay to improve the sound in a large room.

Jonathan Cullifer · Post by **Jonathan Cullifer** » 27 Sep 2009 2:48 pm

My church in Atlanta runs Stewart 2.1 amps on the line arrays (3 amps for 6 speakers) and Crown Macro Tech amps for the subs (1 amp per sub). The mains are so directional that when I have my steel amps up to a normal level, I can't hear the mains output over my amps.

Never thought about reversing the phase on the monitors. That's a good idea.

Marc Jenkins · Post by **Marc Jenkins** » 27 Sep 2009 5:13 pm

Rick Campbell wrote:My opinion is that monitor mixes are a stupid thing to do. I've always believed that the monitors should be nothing more than a direct sampling of what is in the house speakers. Of course, this is assuming the band members know when to play and when to be quite.

Hmmm. When the stage is big enough to not be able to hear the amps on the opposite side, what then? What about when it's a quite stage volume, and all you need in the monitors are vocals?

Dave Hopping · Post by **Dave Hopping** » 27 Sep 2009 6:01 pm

Marc,I was thinking about that too.Seems to me a stage that big would be in a venue that also has a big enough monitor system with its own sound guy,who could "pipe in" signal from faraway amps.

Rick Campbell · Post by **Rick Campbell** » 27 Sep 2009 7:02 pm

Marc Jenkins wrote:
Rick Campbell wrote:My opinion is that monitor mixes are a stupid thing to do. I've always believed that the monitors should be nothing more than a direct sampling of what is in the house speakers. Of course, this is assuming the band members know when to play and when to be quite.
Hmmm. When the stage is big enough to not be able to hear the amps on the opposite side, what then? What about when it's a quite stage volume, and all you need in the monitors are vocals?

It's simple. If you're hearing the same thing the audience is hearing, and it sounds good to you, then it sounds good to them. Too many different mixes going on at the same time complicates things. Having to play hard because you don't have much of your instrument in the monitor mix, (but you're blasting in the mains) causes your tone to suffer, and other nasty things. My opinion anyway.

Marc Jenkins · Post by **Marc Jenkins** » 27 Sep 2009 9:28 pm

I never want to hear the mains. I don't need to hear what the mic'd snare sounds like.

David Doggett · Post by **David Doggett** » 28 Sep 2009 7:02 am

There are two different philosophies. One is for the musicians to relinquish all control of the mix to the sound guy, and he rides the controls constantly to get the mix he likes. The monitor mixes are nothing like the mains, and are whatever each musician wants to play his part. You don't necessarily hear everything, but just whatever you need to play your part right. You might hear yourself through the monitor, or just hear other stuff there and hear yourself from your own amp pointed at your head.

The other philosophy is Rick's, where everybody hears the same main mix through the monitors. The musicians use that to play at the level they feel is right. That puts them in charge of the mix, and the sound guy doesn't fight them by constantly adjusting things. This will work if the stage volume is very low, or, even better, everyone is going direct in, with no amps on stage. It doesn't matter if the stage is big, because the stuff on the far side will be heard in the monitor mix. But if the stage volume is loud and over-rides the monitors, then you only hear yourself and what's close by, and can't hear the rest.

Richard Durrer · Post by **Richard Durrer** » 28 Sep 2009 4:28 pm

I was very intrigued by the comments re: reversing the phase on the monitors. All the speakers in our church system are individual powered boxes, including the monitors. They all use XLR ends into a snake. I run a Peavey 32FX board with 4 mains and 4 monitors. The board handles feedback killing on the mains but not the monitors. How can I reverse the phase on powered speakers?

Alvin Blaine · Post by **Alvin Blaine** » 28 Sep 2009 9:12 pm

Richard Durrer wrote:I was very intrigued by the comments re: reversing the phase on the monitors. All the speakers in our church system are individual powered boxes, including the monitors. They all use XLR ends into a snake. I run a Peavey 32FX board with 4 mains and 4 monitors. The board handles feedback killing on the mains but not the monitors. How can I reverse the phase on powered speakers?

Most lower line boards don't have any way to change phasing. However you can use an In-Line Phase Reversal adapter.