Feedback destroyers?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Leonc, Jul 30, 2004.


  1. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    My band uses one of two cheap but functional, "all-in-one", 8-channel PAs, with mains and monitors. One is a Peavey, the other is a Yamaha.

    Regardless of which one we use on our gigs, we seem to be plagued by feedback issues (not to mention ultra-picky singers :rolleyes: who can't get enough of themselves even though the rest of us are going deaf from the PA/monitor levels).

    We don't use a seperate EQ unit.

    I'm thinking of looking for a feedback destroyer. Anyone have any particularly good experience with one? I know there are a variety available from Behringer, Peavey, Sabine, etc. I don't want to spend 500.00...our PAs were probably 900.00.
     
  2. riffmeister

    riffmeister Gold Supporting Member

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    Hey Leon, in one of my bands, we also use a Yamaha powered mixer (it's the 500 watt 8 input model). I know exactly the problem you are talking about. I find that I have to notch out the middle frequencies on the 7-band graphic EQ in order to minimize feedback. Even with the middle frequencies all the way down, it seems as though it's barely enough!
     
  3. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Yeah, think that's the same model...the mx88 or something like that. 400W/side. It's worse with the feedback than the Peavey. No exp with feedback destroyers though, huh?
     
  4. CGrisamore

    CGrisamore Member

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    Same problem in my band and I have the Behringer DSP1124P. I'm not convinced we've ever hooked it up right as we always seem to be rushed for time but thus far it hasn't impressed me very much, we were still getting intermittent squealing.

    Our solution for the moment has been the following.

    1. New drummer with Roland electronic drums
    2. Loaned our singer/keyboard player my Shure PSM-400 ear monitors

    End result? Stage volume is WAY down cause the drums are quiet and the keyboard player has now turned his amp down to a whisper. The ear monitors have been SO effective for this guy that now the other singers are interested....
     
  5. riffmeister

    riffmeister Gold Supporting Member

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    No..........please let me know what you find out..........THANKS! :)
     
  6. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    CGrisamore. What are you playing through to get those whisper volumes?
     
  7. Jackie Treehorn

    Jackie Treehorn Member

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    I used to use a 5 band parametric to get the PA louder by cutting the offensive frequencies. Ashly makes a great EQ that's been off people's gear radar (the early blue/grey models) which used to go for around $100/channel on Ebay. A five band graphic will likely cut way more than what's needed; you need a narrow Q.
     
  8. John Phillips

    John Phillips Member

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    My experience with feedback destroyers is this: they are usually a crutch used by people who don't know how to operate a PA properly.

    Get a good old manual 2x15 or 2x31 graphic EQ and learn how to use it... or find a soundman who can.

    Every time I've worked with a sound engineer who knows how to use a graphic EQ properly, the result has been a really good, and very consistent, sound.

    Every time I've worked with a guy who uses an automatic feedback destroyer, the result has been patchy, variable, unpredictable and artificial-sounding. The feedback destroyer needs feedback to work with. It will constantly run the system on the edge of feedback, and you'll often hear a lot of 'near feedback' and odd artifacts caused by the notch filters sweeping, which personally I find extremely annoying.

    IMO the right way to avoid feedback is to EQ the system for the room so it doesn't feed back in the first place - and leave it like that. It is likely that you won't be able to get quite the same volume like that that you can by running a feedback destroyer, but so what? You'll get a better sound.

    [/rant]


    They have their uses, it's true - you'll often see them in pro rigs dedicated to individual 'trouble' sources - but you're also likely to find that they get locked-in once the problem frequencies are identified... ie used as simple multi-band notch filters.

    Slapping one across the mains and expecting it to 'cure feedback' is not the right way to use one.

    IMO.
     
  9. CGrisamore

    CGrisamore Member

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    I'm playing through a Koch Twintone. Our keyboard player is one of those guys who can never hear no matter how loud the PA is. HE also has a Roland keyboard amp on stage that's always turned to 11. Just like acoustic drums, when you have something on stage that's really loud, everything else adjusts to that volume.

    For the last 3 gigs, I let him use my Shure PSM-400 ear monitors. Normally we run vocals only through the monitors but since the ear monitors are on a separate bus, last gig he asked our sound guy to put some keyboards in his ear monitors as well. He ended up turning his amp down so low that I could barely hear it (and I was standing directly behind him). During a break, I commented how quiet on the sound level and he said that he was worried that he was playing too loud (and this is a guy who can NEVER hear and is always cranking it up)

    BTW...this is a seven piece band and we've been fighting stage volume issues for months. it's a little early to declare this the final solution but in the course of 3 gigs, there's been an amazing transformation!
     
  10. deeval

    deeval Supporting Member

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    The best I have is a 31 band EQ and you can pretty much do a well EQ if after you are set up and do a monitor test,start boosting the frequencys one at a time till it starts to sqeal and drop that one down,do that on all the sliders and you wil see that some you have to drop way down and others will be able to boost some,
    the lower ones usally dont have to many issues,
    Good luck:)
     
  11. TieDyedDevil

    TieDyedDevil Member

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    I used one of the Behringer feddback destroyers in my PA. All its really good for is killing the feedback that can happen if your singer goes mobile and gets too close the the monitor. It really does nothing to increase the available headroom of the PA. I have to concur with the folks who recommend a narrow-band graphic EQ or simply reducing your volume.
     
  12. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    I have an old Roland feedback destroyer that I no longer need to use (my new Yamaha PA, though it lacks a dedicated feedback control circuit, just seems to not feed back in my basement). However, when I used it previously with mics into my CA Blonde with an extension speaker ("poor man's PA"), it worked great.

    John Phillips, I don't understand this comment at all:

    >> The feedback destroyer needs feedback to work with. It will constantly run the system on the edge of feedback, and you'll often hear a lot of 'near feedback' and odd artifacts caused by the notch filters sweeping, which personally I find extremely annoying.

    With my Yamaha unit, you didn't wait for feedback to happen, you preset the unit by raising the volume level on the PA until feedback occurred naturally at the first problem frequency, that set the first filter, X8 to set all 8 with a remaining 2 extra filters remaining free to sweep automatically to catch anything getting past the first 8.

    BUT BY THEN, you were way, way, louder than you'd ever want the PA to be, so afterwards you lowered the volume back down again. This left you with an incredible amount of extra feedback-free headroom even if 1-4 of the filters happened to stay engaged at where you ended up.

    This is no different than how a human would do it prior to a gig by "presetting" a graphic feedback unit for feedback control except that the levels were set automatically.

    I acknowledge this kind of preset system doesn't work well if you are using wireless mics that you're moving around but for stationary mics, it's simple, easy, and fool-proof.

    P.S. Maybe with an acoustic guitar I'd notice the thin notches in the sound afterwards. With vocals, I never could. And this on what is today would be an outdated unit with much "thicker" notch widths than today's units.
     
  13. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    There are a couple more pieces of info that are relevant:

    - We don't do this as a profession. We do it for fun.

    - We work in crappy little dives in LA. They don't pay worth a damn (maybe 300.00 for 6 of us).

    - We're NOT getting a soundman because we can't afford one and don't need yet another personality to contend with. Believe me, six is plenty ;).

    - The places we play often have low cielings relative to the stage and stages are NEVER deep enough to properly locate the monitors so that they're 4 or 5 feet in front of the mics.

    - The cables used with the mics and PA speakers are decent, but nothing special. Both lead singers have wireless mics though we often force them to use '58s like the rest of us when their wireless mics create problems (which is to say...almost every gig).

    - Lately, we've been using the Peavey at gigs. It's plenty loud (at least 400W per side). We're NOT going to get another PA any time soon.

    - We're not going to change band members.

    These are givens. They're not going to change. Granted, it would be nice if our bass player could devote more time/energy to really getting good with the PA. And it would be great if we had a professional soundman to handl all this rot...but...it ain't gonna happen.

    And more to the point, if there's a device that we can acquire that will enable our bassist to focus on his bass playing and having fun, rather than @#$ing around with the PA, better yet. It'll be cheaper than a soundman and money well spent.

    I'm simply asking people to describe their experience with a utilitarian device that will us analyze what the feedback problem is quickly so we can eliminate it. If the device helps eliminate it too, fine.

    If it turns out that the various units that people have experience with won't really work and our expectations are unrealistic, then that's the kind of useful info I'm trying to collect in this thread.

    Jon, what Yamaha unit are you talking about? I'm not clear on whether it was the PA head (mixer?) or a separate unit...?
     
  14. John Phillips

    John Phillips Member

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    I agree... if you follow the bit I left in bold! But that's not how 99% of soundmen who use a feedback destroyer use it... they just turn it up until they can't get it any louder, and let the unit cope with the feedback as best it can. The reason I said that the unit 'needs' feedback to work is that in order to sense problem frequencies, they have to feed back. So what you hear given the average setup is constant ringing and suddenly-suppressed near feedback, plus violent sweeping of the notch filters. Awful. Yes, this is a fault of the operator not the equipment per se, but there's no need for an automatic unit... unless you can't set up the system correctly the old-fashioned way.

    If you're going to do it the way you do, you might as well use a normal graphic EQ. In a sense, the operator becomes the 'feedback destroyer' - by simply listening for feedback, and adjusting the system EQ accordingly. Once set at the soundcheck, the overall EQ shouldn't need adjusting further anyway... normally. Wandering radio-mic users (and in my past experience, double-bass players :)) excepted... which is why they still can be useful on single sources.

    But for a whole mix, they cause at least as many problems as they solve, IMO.
     
  15. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    My Yamaha PA is an EMX 66M powered mixer.

    By the way, here's what I own but I think it may be discontinued: http://www.rolandus.com/news/archivedetails.asp?PressID=132

    P.S. John P., thanks for the clarification!
     
  16. drbob1

    drbob1 Silver Supporting Member

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    My experience with these is mostly in churches, but the sound problems are the same-low ceilings, lots of open mics, people standing too close to monitors and so on. Here's what seems to work the best in that environment:

    You NEED the 31 band EQ. It allows you to get maybe an extra 6 dB depending how bad the room is, but more important, it allows you to get the basic sound shaping to make the room sound natural. Most of these little rooms need the bass rolled off big time, otherwise it booms and swamps the vocals and lead guitar. Basically you set up the PA, turn up the volume till you start to hear some ringing, then turn each slider up till it feeds back, then back down 6 dB. Then play some canned music thru it and see how it sounds, if it's OK leave it. If there's some frequencies accentuated, adjust those. You need at least 2 31 band EQs, one for mains and one for monitors (better yet, run two monitor mixes with one of those light power amps like the ART 250 $285 new and you'll need 3 channels of EQ). Once you've "wrung out the room", patch in the feedback eliminators. You can set some or all of the filters before hand by cranking things up again (you need to have something playing or a pink noise CD), or just leave the PA down where youv've got it and let them do their job.

    I've used:
    Shure
    Roland
    Behringer
    maybe a few others.

    The Behringer Shark is 1/3 rackspace, $89.99 new and works like a champ, also has a limiter built in. Start with the EQ, though, and if money's a problem, don't go on to the FBE till you've tried just the EQ...
     

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