# Controlling feedback???



## hollowbody (Jan 15, 2008)

We played a show this weekend where we were fighting feedback all night long. This despite having a good soundcheck where everything was balanced and sounding good with no feedback. We had no sound tech, so I was trying to play with faders while playing leads, which wasn't very successful, but after the first set, we had things mostly reigned back in, but still had the occasional squeal. The first set was pretty bad though.

We were running a bunch of 58's and a Beta 58 into a Mackie CR1604. I had the mics all turned down fairly low (below unity, actually), and had the mains up to compensate. As far as I know, none of the mics were pointed at the mains or any of the monitors on stage. We were also running some acoustic instruments through the PA (couple acoustic guitars, a mando and a uke) and we had the electrics running through the board, but only into a dedicated monitor feed for the drummer, not mixed into the mains.

I'm not a sound guy, but I honestly thought we had everything dialed in pretty good on the PA side. Is there anything I'd done wrong? What do you guys do when setting up and soundchecking to make sure stuff doesn't feedback? 

We're a bar band, and we usually play smaller bars and clubs, so often we're bringing the PA and running sound ourselves (or getting a friend to do it), so I'd like to learn the general do's and don't of setting up a PA.


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## jimihendrix (Jun 27, 2009)

MXR M 195 NOISE CLAMP...???...

[video=youtube;C16zkacL4lQ]http://www.youtube.com/watch?v=C16zkacL4lQ[/video]


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## mhammer (Nov 30, 2007)

Remember that feedback occurs when the input to the mic and the ambient sound from the PA speakers or monitors are summing.

One of the oldest tricks in the book is to simply reverse the polarity of the speakers such that the speaker cones are moving forward when the mic diaphragm is moving backward. Alternatively, insertion of a very short delay (on the order of a couple of milliseconds), can prevent summing.

Finally, there is nothing like a decent parametric EQ to dial in precisely the frequency band that resonates most, and dial it back a hitch without affecting too much else.

I would NOT recommend any sort of noise gate to address PA feedback.


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## hollowbody (Jan 15, 2008)

mhammer said:


> Remember that feedback occurs when the input to the mic and the ambient sound from the PA speakers or monitors are summing.
> 
> One of the oldest tricks in the book is to simply reverse the polarity of the speakers such that the speaker cones are moving forward when the mic diaphragm is moving backward. Alternatively, insertion of a very short delay (on the order of a couple of milliseconds), can prevent summing.


Ok, couple quick questions then. If the monitors on stage are too loud, reproducing the same frequencies going into the mics, this will cause feedback as well? I just thought as long as the mics weren't pointed at the monitors or main, bob's your uncle! That could be the issue, since we did have the monitors quite loud as it was a fairly small stage and we were all very close to the drummer and wanted to hear our vocals.

Second, I have a pair of XLRs that I've wired Pin 3 hot to use with my Mackie's stereo outs because the stereo outs are wired that way on the Mackie. If I were to use one of those cables on the Mono out (which is wired the more traditional Pin 2 hot), would that achieve the polarity reversal that you mentioned? Any risks in doing so?


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## R.S.Fraser Sr. (Aug 15, 2009)

*Another thought - mic patterns*

This could be a help to you? 
It is important to note that the Beta 58s have a much different patter than the 58.
The 58 is a plain jane cardioid - with great rejection at the back.
The BETA 58s have a tail at the back and they offer far less rejection than the plain 58.
If the tail of a Beta is facing a monitor (or mains for that matter),
you can bet the rent that you will feedback.
The Beta 58s caused such a ruckus during their introduction that Shure Bros included a small cardbard template with that fit over the windscreen to show where monitors ought to be placed.

It seems like an odd way to think for some, but when you are micing on stage, try to think about what to reject, not what to pick up.

bob


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## hollowbody (Jan 15, 2008)

R.S.Fraser Sr. said:


> This could be a help to you?
> It is important to note that the Beta 58s have a much different patter than the 58.
> The 58 is a plain jane cardioid - with great rejection at the back.
> The BETA 58s have a tail at the back and they offer far less rejection than the plain 58.
> ...


Wow, I didn't know that! I just checked the user guide and you're 100% right. We did, in fact, have a monitor right behind the Beta58. I will try a different placement next time and see what happens.


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## mhammer (Nov 30, 2007)

hollowbody said:


> Ok, couple quick questions then. If the monitors on stage are too loud, reproducing the same frequencies going into the mics, this will cause feedback as well? I just thought as long as the mics weren't pointed at the monitors or main, bob's your uncle! That could be the issue, since we did have the monitors quite loud as it was a fairly small stage and we were all very close to the drummer and wanted to hear our vocals.


Pointing at the mics is simply the most efficient way to get the voice and speaker signals summing to the point of oscillating. You can point the monitors somewhere else, but if you are in an indoor space, rather than outside, there *will* eventually be a point where the reflected sound is loud enough to sum and oscillate. R. Fraser's suggestion about mic sensitivity patterns is also in keeping with this principle: if the mic's most sensitive pickup is from a different direction than where the monitor is pointed...no summing. The general principle is to think about all possible mic, speaker, volume arrangements that might produce a risk of summing and oscillation.


> Second, I have a pair of XLRs that I've wired Pin 3 hot to use with my Mackie's stereo outs because the stereo outs are wired that way on the Mackie. If I were to use one of those cables on the Mono out (which is wired the more traditional Pin 2 hot), would that achieve the polarity reversal that you mentioned? Any risks in doing so?


Quite frankly, the simpler arrangement is probably just to flip the leads to the speaker bins around.


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## hollowbody (Jan 15, 2008)

mhammer said:


> Quite frankly, the simpler arrangement is probably just to flip the leads to the speaker bins around.


We use powered speakers, so I'm running line-level between the mixer and the powered bins. Given that, it seems like the Pin 3 hot cable works out to the same thing. 

Thanks guys, this gives me a couple things to try out!


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## Rick31797 (Apr 20, 2007)

I know that some of the new power mixer have feedback control built in, i guess it works good..


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