Rehearsal studio monitors feeding back.

[catphish]

I just got a new Mackie mixer that we've been using in the rehearsal studio, which is going into a Crown XLS602 power amp. It just powering two 115 monitors that sit directly in front of us facing the backs of the mics. I set up each channels signal exactly as directed by the manual, but I'm still getting tons of feedback though the monitors. Any ideas? Is an EQ the solution, and if so what is the process for dialing in the EQ to eliminate the frequency?

 

Another thing that I don't get is that prior to this set up, we have a Peavey Powered Mixer that we had going much louder than this new set up, but it never fed back. What gives?

Thanks for the help

[tlbonehead]

Originally posted by catphish I just got a new Mackie mixer that we've been using in the rehearsal studio, which is going into a Crown XLS602 power amp. It just powering two 115 monitors that sit directly in front of us facing the backs of the mics. I set up each channels signal exactly as directed by the manual, but I'm still getting tons of feedback though the monitors. Any ideas? Is an EQ the solution, and if so what is the process for dialing in the EQ to eliminate the frequency? Another thing that I don't get is that prior to this set up, we have a Peavey Powered Mixer that we had going much louder than this new set up, but it never fed back. What gives? Thanks for the help

How many bands of EQ are you using currently? I'm sure its just a case of having some hot frequencies that need taming. You basically find out which ones they are and tame them a bit. Have you tried sweeping your channel strip's mid control to get rid of them and find out about where they are? I assume the Mackie has a semi-parametric mid on the channels. Beyond that,mic and speaker placement,and getting rid of highly reflective walls,ceilings,and floors,is something else to look at. But mess with your EQ and find the hot frequencies.

[Brad Harris]

I set up each channels signal exactly as directed by the manual

 

 

So how is that set up then?

 

A 31band graphic eq unit (either a 1 dual channel, or 2 single channel) would be benificial in almost any situation for monitors.

 

As for how to set the eq up, there are a few different approaches, but this is the approach that I use:

 

1. Raise the gain on the eq unit around +6db

2. Raise the aux send (if run off an aux) of the microphone until it starts to feed back + back it down slightly until it doesn't want to continue to feed back

3. Raise the appropriate eq slider slightly until it feeds back. The less you need to boost the slider, the more you'll need to cut it out.

4. Repeat 2+3 a few times (3-4)

5. Back the aux send down, and go up to the mic and listen to how it sounds, and adjust the level if necessary (ie lower or more, usually it is roughly where you want it to be).

6. At the mic, cup your hand around the mic (and yes there is a trick to it ...). Generally start a few inches away from the mic head with a straight palm, move it closer to the head of the mic slowly until you are touching it, and then slowly curl/cup your hand around the mic head. At anytime it starts to ring, back your hand off, and cut that freq a little more.

7. Once I have that pretty much tamed down, the open mouth cavity check is next, which is similar to the palm check, but with your mouth (unless your show is done by hand pupets exclusively )

8. If I know the mic is moving alot (ie: talent show, high end kareoke, wireless, etc), I'll go around the whole stage listening to the monitor(s), and when I'm happy with the results I'll take a few swipes with the mic pointed towards the wedge(s) getting closer everytime. If its at a reasonable level (ie waist height right in front of the monitor), Generally there won't be a problem all night (unless your changing monitor sends, different mics, passed out singers who put the mic in the wedge, etc)

 

The reason for #1, is that on some eq units when the unit is bypassed depending on how it is done, the actual eq circutry can suck out some of the signal (even with everything at 0db). Unless I know that the particular unit that I'm using doesn't do that, I'll bump the gain up so that if the unit fails (or accidently put into bypass), the level will stay roughly the same (although no eq will be going on), so that the muso's head isn't ripped off by a louder send, and feedback. While feedback may occur even when done this way, it is significantly less.

 

An easy way to check for this is to play some tunes through the monitor, set the gain to 0db, and press the bypass continuously and raise/lower the gain until it is consistant when it is in or out. Then I usually go with a little more gain with the eq in for greater security.

[catphish]

 

Originally posted by Brad Harris I set up each channels signal exactly as directed by the manual So how is that set up then?

 

 

I set the sensitivity to 0, pan the channel hard left, solo the channel and select solo to main. I approximate the EQ settings I'll need (which is all set to 0, for lack of anything better) Then I boost the sensitivity until the output reads about 0db, then unsolo the channel and solo to main and un pan the channel.

 

I've been suspecting the EQ was the problem. The mixer doesn't have an overall eq, so I should find the hotspots on each channel? Or is a good EQ for the overall signal before the Power amp my best bet?

 

And why do you figure my peavey powered mixer ever do it?

[tlbonehead]

Originally posted by catphish I set the sensitivity to 0, pan the channel hard left, solo the channel and select solo to main. I approximate the EQ settings I'll need (which is all set to 0, for lack of anything better) Then I boost the sensitivity until the output reads about 0db, then unsolo the channel and solo to main and un pan the channel. I've been suspecting the EQ was the problem. The mixer doesn't have an overall eq, so I should find the hotspots on each channel? Or is a good EQ for the overall signal before the Power amp my best bet? And why do you figure my peavey powered mixer ever do it?

Does your mixer have sweepable mids on the channel strip? If so,and until you get a decent outboard EQ,you can use that,along with the high frequency control. Listen to the feedback and try to get an idea how high the pich is? If it is real high,use the high frequency control on the channel. If it is lower than those frequencies,start sweeping. Realize sweeping won't do anything unless you set the other pot either for cutting or boosting.(cutting to get rid of it and try boosting first to try to find the offending frequency,then cut in that area) Also,check out the Peavey EQ's with the FLS(feedback locating system)

[catphish]

No it doesn't have a sweep on it. I'll look into an EQ. Any other possibilities if that doesn't work. I downloaded some program for practicing locating the offending frequency.

[tlbonehead]

Originally posted by catphish No it doesn't have a sweep on it. I'll look into an EQ. Any other possibilities if that doesn't work. I downloaded some program for practicing locating the offending frequency.

What Mackie mixer doesn't have sweepable mids? And don't worry,an EQ will help a lot.

[catphish]

 

Originally posted by tlbonehead What Mackie mixer doesn't have sweepable mids?

 

 

The CR1604 (non vlz)

 

I'm gonna grab a Peavey 215FX with FLS....hope that helps.

 

So, anybody know why we never had a prob with the peavey power mixer?