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4 Posts
Discussion Starter · #1 ·
Hey, I need some info. about PA and such and how to help stop feedback.
Basically the setup is as follow

~a 20X30ft room (pretty small but wtv)
3 vocal mics (2 Behringer XM8500's and a shit apex that will soon be replaced w/ a behringer/ Sm57 type mic)into a
berhinger UB 1622 FX mixer then into a
squier 4 power amp

all in all the system is working well, but the problem is I either have to turn the volume way down (so you can no longer hear it w/ drums), or cut all the highs and most of the mids to avoid feedback. I was wondering if anyone knows a way to reduce the amount of feedback (and I've played with the positioning of the speakers).

Thx, I appreciate the help


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815 Posts
Are you using an EQ? You have to figure out what frequency is feeding back and pull it back. Also figure out which of the three mikes is causing the most problem. Add one mike at a time to the mix. It's also a good idea to start from a flat (0) position (bass, mid ,treble) and then tweak it from there. Also check the position of the mikes in relation to the speakers. Try to avoid speakers behind the mikes.

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75 Posts

Hi. Firstly, you should reconsider your choice of equipment. Those Berringer mic's are pretty poor, as are the apex. I suggest you replace them all with:

Sure SM-58's for vocals
Sure SM-57's for miking instruments/cabs/percussion (if necessary)

Why? These are time tested work horses that do the job well. You can pick them up used for less than $100.00 each. It is useful to have all of your vocal mics be the same brand/model as it makes EQ much simpler.

I would also shit-can the Berringer effects device and mixer. Simply put, they are pretty noisey, unforgiving pieces of equipment. Consider buying a used Mackie 8 or 16 channel mixer. They can be had for a song and you can't do much better than a Mackie.

I'm not so concerned about the brand of your power amp, but its power. 100 watts sounds like a lot until you put it in the context of P.A. My band routinely runs 500 watts to the house and 250 watts to the monitors, and we're an all acoustic band with no drums. The wattage isn't for the sake of volume. It's for headroom, which brings us to the subject of feedback.

Your first step is setting up the room correctly. Make sure that all microphones are on a plane that is behind the main speakers. If the mics in line with or in front of the speakers, you will have no chance of controlling feedback. This is an absolute. The mics must be well behind the main speakers.

Before each gig, you need to "ring out" the room. With all of the mics turned on, your mixer's channel an main faders all the way down, set your mixer's EQ or outboard EQ (great, if you have one) so that each fader or knob (for each band) is fully ON (faders fully UP, knobs fully to the right).

Now, set each of the channel faders to unity (0 db). Slowly turn up the main faders until you start to hear a ringing sound through the main speakers. Starting with the fader or knob on your EQ that represents the highest frequency band, turn the fader down or turn the knob to the left, slowly. At the point where the ringing sound changes for the better, stop adjusting that EQ fader and do the same for each of the others.

The goal here is to find the EQ curve that eliminates the natural ringing in the room when the PA is turned up to nearly full power. At each frequency point on your EQ, when you find the point where the audible ringing stops, take it down one notch farther, then leave it. When you can turn your mains up about half way past unity and not get any feedback, that is how you will leave your EQ settings for the night.

The Next step is to bring up the musicians and do a sound check. If any feedback occurs, isolate that musician, then try to ring-out just his mic or instrument input by finding the frequency range where the feedback is occuring, then train back the EQ fader for that range. There will be some trial and error here.

Once your sound check comes up clean, don't touch the eq again for the rest of the night. During the performance, your sound guy shoudl rely mostly on his ears to set the right levels and may need to make slight adjustments.

If you ring out the room correctly, you will get the most headroom possible without getting feedback.

The importance of having goodly amounts of mains power is that the more power you have, the more headroom you have before feedback occurs.

That's the theory, anyway.

· Registered
75 Posts
rinio said:
Hey man, Thx
That ringing out trick worked really well. Ive been thinking of replacing the mics for a while now, I just need to wai tand get some cash.
Thx again every1
I'm glad that it helped. Its hard to know if one's instructions are decipherable.

Hey, I listened to the stuff at your web site. Pretty cool. What I really find interesting is that you and I play a radically different style of music, yet the rules of good sound reinforcement practices apply to all. If you want to hear what I mean, have a listen to:



· Registered
122 Posts
cohenjs tips were good.
As others suggested, the best thing to do is upgrade some of your gear. I had the same PA I have now, but with cheap no name mics and cheap no name speakers. In other words, the two "ends" of the system were junk; it didn't matter what was in between.
Now, with an sm58 and a decent floor wedge, I can get the system plently loud for our rehersal space without feedback.

My modest system is
sm58 --> Mackie 1402 --> Aphex 108 comp --> Ashly MOSFET 2000M power amp --> Yamaha 15" floor wedge.

Adding a second wedge will make this system very usable for my very loud band.

Good luck with your PA'age :D
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