PA Help Needed

monquixote

Had yet another gig plagued by feedback problems last night. 

We're currently using a really nice Allen and Heath desk and we use in ear monitoring so there is no monitor spill causing problems so I think the culprit is either something about the way we've got things set up, or the PA which is an HK Lucas that looks something like this:

http://im2.woodbrass.com/images/woodbrass/HK+AUDIO+LUCAS+PERFORMER.JPG

We tried using a feedback destroyer we borrowed last night, but it made no difference. 

In big open rooms it's a bit of a problem, but in a pub we can't get the vocals over the drums without it screaming and howling. 

We're at the point where we're considering buying a whole new PA, but I don't know that it's going to fix the problem.

So what I'd really like is someone who knows a bit about PA who is local to Suffolk to come to a gig and give us a hand trying to track down the problem. If we could borrow a pair of powered speakers so we can see if it's our PA that's the problem it would be even better. I'd be happy to pay a share of our gig fee (about £40-50) to anyone who would lend a hand. 

viz

The speakers are in front of the mics?

monquixote

Yep .

We always get them as far forward as we can

viz

I knew given your background but just thought I'd better rule that one out early on

Btw you're welcome to borrow my powered speakers any time if it doesn't conflict with my musical performance week - week commencing 1 May. I'd be no good at locating the fault though, but never had a feedback problem with it. 

viz

^ Carlsbro 400w gamma 15 actives. 

monquixote

viz said:

^ Carlsbro 400w gamma 15 actives. 

Thanks viz you are a prince

robinbowes

That PA should be more than adequate. HK gear is generally very good. What sort of feedback are you getting? R.

monquixote

It's fairly high pitched and is just happens continuously rather than when you do something specific. 

Having had a bit of a gig post mortem we think there might be something wrong in the configuration of the desk so it's hitting the vocal compressor really hard and over compressing everything. 

The problem we have is the only time we get to use it is at a gig when we don't have time to play about and we have a room full of punters who don't want to listen to us incessently soundchecking.

John_P

^ HK gear is very good but that rig is more designed for solo performers with backing tracks.   I suspect if hasn't got enough headroom to get clear vocals over a loud drummer,  especially if you are putting the band through it.     Underpowered PA's are easy to drive into feedback in my experience.     

benmurray85

John_P said:

Underpowered PA's are easy to drive into feedback in my experience.     

This is most likely to be the case I'm afraid, in my experience anyway. You don't say whether or not you're putting the whole band through the PA but I assume you aren't? In which case if you're getting feedback purely from vocals you're either doing something massively wrong (Im assuming thats not the case as you're clearly a clever dude!) or the PA just isn't up to the task.

At the risk of teaching granny to suck eggs before you consider making any purchases just strip everything back. Get rid of any rack stuff (BIN the feedback destroyer they're useless!) and go straight into the desk. keep an eye on your gain levels and make sure you EQ the room - thats a great habit to get into. if you can get the pa pumping with a bare minimum setup start adding stuff back in and go from there

again you've probably tried all this but as mentioned above it really does help to reiterate the basics

ICBM

monquixote said:

vocal compressor

There's your problem, I think.

Danny1969

The Lucas system is fine, I suspect you have the threshold of your compressor on the vocal channel set to low so it's biting all the time. Raise the threshold so it only bites on the louder parts.

If your using a QU16 or similar try this

Se your pre fade gain so it's well under clipping on the loudest vocal

Set your high pass filter around 100hz

Make sure the Gates off

Set your compressor so the ratio is around 3:1 and the threshold is high enough that the compressor only gives gain reduction on the loudest portions of the vocal .... no more than 5dB or so of gain reduction on the loudest bits

Set the EQ so there's a little cut between 300 and 500hz, big cut after 10K

robinbowes

monquixote said:

It's fairly high pitched and is just happens continuously rather than when you do something specific. 

Having had a bit of a gig post mortem we think there might be something wrong in the configuration of the desk so it's hitting the vocal compressor really hard and over compressing everything. 

The problem we have is the only time we get to use it is at a gig when we don't have time to play about and we have a room full of punters who don't want to listen to us incessently soundchecking.

That PA is more than enough to deliver vocals over an unamplified backline (unless you're competing with John Bonham and your guitarist has a pair of Marshall stacks!)

I'd strongly recommend turning off all unnecessary processing on the desk and try a mic straight through. It's almost certainly something set up wrong on the desk that's causing the problem.

I'd come and sort it out for you, but I'm a little too far away (York).

If you can't manage it, it would be worth getting (paying?) a local engineer to sort it out and show you how to use the desk, maybe?

R.

Danny1969

What desk is it, if it's a QU series I could send you a show file ?

EricTheWeary

Quick Google whilst hanging around for something suggested the limiter . The only reviews I found seemed to be for dj or solo performer use, nothing that would comment on it's capacity for keeping up with a drummer. Might be worth doing a PA rehearsal - seeing how cheaply you can borrow the function room in a pub on a wet Monday night and setting up as per a gig, just sorting out any issues.

ESBlonde

Lose the compressor if you don't understand it. Live vocals are best compressed individually or with lead and backing separated, avoid strapping it across the sub group. Are all your mics the same make and style? I'm local and could spend 20 min setting that rig up. It should punch above a kit.

Sporky

Do you EQ the system to the room you're in? Rule of thumb for installed audio at least is that correct EQ nets you 6dB more gain before feedback.

monquixote

Sporky;1017393" said:

Do you EQ the system to the room you're in? Rule of thumb for installed audio at least is that correct EQ nets you 6dB more gain before feedback.

We have done that when possible, but usually in a pub the landlord runs out and tells you off for making feedback noises.

Danny1969

monquixote said:

Sporky;1017393" said:

Do you EQ the system to the room you're in? Rule of thumb for installed audio at least is that correct EQ nets you 6dB more gain before feedback.

We have done that when possible, but usually in a pub the landlord runs out and tells you off for making feedback noises.

Adjusting the EQ to suit a room can help with certain things, like uneven bass response but it's not necessary to get a decent modern PA like you have  loud and clear above a drummer with no feedback issues ...... to be honest any feedback issues with a Lucas and a decent desk would be down to wedge monitors, not FOH. And your not using any wedges!

You haven't said what desk it is ... if it's a QU or similar and your not very familiar with it to work out what's wrong you can just pop your show file onto a USB pen drive and email it to me or any other engineer on here that's familiar with the product and we can see exactly where your going wrong .... no need to drive anywhere

If it's an analog desk then the above point is mute but the fact you mentioned built in dynamics makes me think it's digital 

Cabicular

Those PA s can be a bit Ringy in my experience
As others have said vocal compressor needs looked at
Notching out the offending frequency on a master EQ also works
One thing to watch is bounce from the back wall again that has caused me some issues in the past
I have to say the best thing about the line 6 desk is that the realtime EQ shows exactly where the feedback spike is and makes it a doddle to notch out

monquixote

Latest update is that indeed we had the compressor set up wrongly.

We're going to hire an old theatre in a couple of weeks and do a fake gig where we can tit around to our heart's content.