Automatic Feedback Suppresors - do they really work?

[Rockin Mike]

You ring out the pa before sound check.Mostly for the benefit of vocal monitors. For the monitors I rolled of everything below 100hz,a cut at 250 ,and another at around 2500. No feedback in the monitors ever.The mains I set by playing music and tweaked the eq until it sounded good. That simple. Once I got the eq set for mains and monitors,I rarely had to readjust it.

As I understand it with AFS there's still a process of ringing out the PA before the sound check, it's just that when you raise levels to find the ring, the AFS is supposed to detect it and notch it out automatically. Then the added benefit is if something starts ringing during the show, for example when you change somebody's monitor mix, the AFS can catch new rings. That's the theory. I've never tried it at a show (hence the thread title) though I've done it the classic way for decades.

If they don't work out they won't stay long in the rack.

 

[ThirstyMonkey]

Do you think they(the Behringers) would work if you just walked in, set up, pushed AUTO, and started the show?
I get fdbk issues sometimes on a vocal mic via the BOSE when we're in a tight area and MANY times there is no time for a "real" soundcheck.

Yes. The "Learn" button works two ways. A quick press and it automatically searches for and applies the filters. This would be your set it and forget it mode. Hold the button a little longer, and it generates quick tones that get progressively louder to cause feedback and sets the filters that way (essentially ringing out the PA). You can also manually set filters. I've had problems with auto mode notching out frequencies and making the monitor mixes sound bad. While that certainly isn't as critical as how the mains sound, I still find that manually applying EQ to the monitors helps everyone better hear themselves and helps keep stage volume under control (I apply the same EQ mentality to monitor mixes as I do the the mains). That said, it does work in Auto mode and there is a "panic" button that allows you to quickly stop feedback if it happens during a gig.

In short, I'm lucky that I have a Presonus StudioLive mixer. It has so much flexibility that we can gig without the feedback suppressors and not worry. If i had to use a board with out the EQ options, particularly on the Aux sends used for our monitors, I'd always have the suppressors on.

 

[DavC]

short answer ... YES .... the work on small bands of EQ ... most have Fixed freqs , .. with a few that search/float for newer feedback issues ... it's a good thing , ... as things change in the room , people move on stage , temp changes , humidity changes , mics move , etc .... it's good to have a robot EQ keeping watch ... !!

 

[FretNoMore]

I have a Behringer feedback suppressor for the floor monitors and it definitely works. I can hear it eliminating a squeel sometimes at soundcheck.

 

[s0c9]

Do they work.. yes! but, should you use them???
I, like most sound guys (I know) don't like to use them because they are [essentially] EQ notch filters and can make FOH sound REALLY CRAPPY when set on "auto". This is caused by most units having a limit of 12 active filters (or less) and it will drop one and set another when it detects a potentially bad frequency. Besides, if your FOH system is set up correctly you should NOT need an FBE. Much like folks who love to put BBE's into the FOH mix, they correct a symptom, but not the underlying root cause. Understanding the root of the issue and fixing that, is a far better solution the treating the symptoms.

Unless you are in a tiny little room with bounce-back, main FOH speakers seldom cause feedback loops unless you are standing right in front of the speakers with a mic. It mostly comes from monitors being too loud, not rung out before a gig, or drum mic reflections feeding back thru the vocal or guitar mics. Stage floor, wall and roof structure can also impact feedback. So playing on a tiled floor, with glass windows on either side of the venue and a "tin" roof is [obviously] going to cause more feedback than carpeted wood floor, standard walls and a coated ceiling.

Feedback basically boils down to too much volume on stage. Get that under control and no need for FBE's.

 

[FretNoMore]

So use it for the monitors, not for FOH. It's where the feedback happens, and it won't mess with the FOH sound.

 

[Rockin Mike]

I will be using them on the monitors. There is a small AFS on the DriveRack PX for the mains but I think that's there as a failsafe more than anything else.

It's best to be an experienced sound person. I'm not one. Even if I was, I wouldn't want to split my attention between the PA and the bass during a gig. So I'm trying to get the PA as simple and automated as possible.

Set it up, ring it out, soundcheck it, save it as a preset for next time, and keep the volume down.

 

[jsolberg]

That's what I have, the AFS-224s. What is the advantage of setting them up as channel inserts versus putting them inline between the board and the (powered) monitors?

If on a channel insert, they'll catch feedback from either monitors or main. More importantly it only effects that channel. If the acoustic guitar is feeding back, no sense in cutting that frequency from the vocal mics. If I had the opportunity, I would rather ring out the PA and monitors using an EQ as others have suggested. Problem is, I have very seldom had that opportunity. We play clubs mostly and none would tolerate ringing out a PA with customers in the place.

 

[TimmyP]

Whether using an auto unit or EQing manually, in order for the unit to be effective, you must duplicate the performance situation. Ringing out with an open stage (turning the level up until it rings, then EQing the ring away) may or may not apply to the performance situation. In a multi-mic situation, where the noise-makers (mouths and instruments) are using the mic at near 0 distance, ringing an open stage gets few if any of the frequencies that will feed back when a hand, face, open mouth, or reflective instrument top (or even a hat brim) are in front of the mic. In the case of the one mic bluegrass performance, the open stage is pretty close to the performance situation. But don't forget to add the missing bits: the reflective guitar top that will bounce sound from the room or monitor into the mic, the hat brim, or - ? Even once you seem to be done, when soundcheck starts you may get additional "hot" or "loose" (not feeding back, but trying to) frequencies that need attention. (Always end the soundcheck a little loud, to hunt for such spots.)