Q about Acoustically treating a stage

[Kris]

I frequently play a club where there is always strange feedback problems at varying frequencies in the mains, and monitors, usually an interaction between the two.

 

Some of the problem is that the sound engineer is still learning the ropes. Not much can be done there.

 

Another thing is that the stage is positioned in a corner of the bar. How does this effect the sound... It seems to me that it might be part of the problem, but I don't really know.

 

Would some Lynrd Bass traps in the rear corner and maybe some acoustical foam on the walls possibly help remedy this situation? Any other ideas?

[suremann]

Hello,

Your question covers an awful lot of area and there are many different variables at work here. I don't know if this will be much help, but maybe if we go through a few basics we can come up with some kind of solution.

 

The first thing I would look at is the position of the monitors in relation to whatever mics are live on stage. Any mic not being sung/strummed/blown/talked into should not be on until the very moment it gets sung/strummed/blown/talked into.

 

Are the mics onstage directional, and aimed so that the off-axis rejection works into the monitors?

 

Are you using any omni wireless lav's? (if you are, take them out of the wedges -- anything you hear, the mic will hear too, hence feedback)

 

Have the monitors been gained-up and rung- out? Are they EQ'd for the types of mics you use?

 

Are any mics used in front of the mains?

 

Corner-loading could be a problem in at least two ways: the first is a pronounced dispersion of low-mid. They used to field-record blues musicians playing into corners to enhance the boominess of their voices. This is variable depending on everything from the height of the ceiling to what's under the stage floor, to the angle of the walls, to the temperature of the room, and will muddy-up the mix unless the FOH is compensated for it. Second, if the monitors are close enough to the walls and the angles just right, you might get some reflection into the mics. I would hazard to guess though, that most reflection would be absorbed by the body of the performer using the mic, and therefore is not the culprit.

 

You could try putting up some material behind you, a thick banner or stage drop.

 

Some people swear by delaying the monitor signal by an imperceptible amount, or, if you have separate FOH and Monitor gain structures try reversing the polarity (at the monitor) of whatever mic is causing the problem.

 

There are some boxes that look for feedback swells, identify the frequency and automatically cut it. I know Sabine makes one, but I haven't had any luck with these.

 

But I think I would spend my time and energy working patiently and methodically with your engineer to identify exactly what's going on. If he's the club operator, and getting this every night, his ass is on the line. He's probably more concerned about it than you are.

 

It could be so much more, and I hope I didn't waste your time. If anything works let me know. If I'm wrong, please correct me.

 

Thanks

Chris

[THE MIX FIX]

Yea, you can try all that stuff. http://www.musicplayer.com/ubb/rolleyes.gif

 

My bet is, get a different engineer, and the feedback will be gone by the end of the first set, first night. http://www.musicplayer.com/ubb/tongue.gif

 

------------------

Bob.