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Author Topic: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496  (Read 1186 times)

Steve Hanis

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #10 on: November 29, 2019, 12:11:48 pm »


Behringer warns the user not to use them on pianos because of the length of sound decay, and the strong overtones, I suspect.  Sure enough, the first (and only) time I used one, a piano was involved.  It was a real pity to what it did to the sound.  The unit did not quite make it through soundcheck, and has not seen the light of day since (or night lights, for that matter).


Now, I have used the "bouncing ball" of the A&H QU series graph and PAFL meters, but they are guidance only, not actually setting filters.

Thanks for the reply, none of the instrument run through the filters. But with nine open wireless mics around the stage the instruments seem to be tripping the filters. Maybe I should disable the "speech" button, the speech button is supposed to increase the sensitivity.
« Last Edit: November 29, 2019, 12:14:17 pm by Steve Hanis »
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duane massey

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #11 on: November 29, 2019, 03:37:58 pm »

my basic rule with FBX: NO live or roaming filters, use only as many as you need and lock them down.
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Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

Tim McCulloch

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #12 on: November 29, 2019, 04:20:37 pm »

To add a bit:  once you've wrung 4 or 5 feedback frequencies, chances are you've got all your going to get out of it.  You'll find that deeper and wider filters are needed (or many, many more narrow filters).  At that point you are doing "gain reduction via equalizer."  I'll talk about gain reduction in a minute.

There is a limit to what can be achieved with this device and essentially it's being used to make up for small voices (needing lots of gain) with big parental expectations and what is likely some shortsightedness in the original system design (the kid's holiday programs are easily forgotten when the system design is based on making the senior pastor happy with his/her own voice).  I'd opt for an overall lower program SPL and as few open mics as possible, script permitting.

Part of my suggestion about reduced SPL is based on the basic physics of feedback - it's an actual physical sonic loop.  If you change the distance between loudspeaker and mic, the feedback frequency will change.  You can chase this for hours (literally) or you can turn down the master -4dB and then actually mix the show.  Talent that needs more gain... well, you've got a little more to give them (on the channel fader) when it's needed.

I will leave you with this, Steve.  Singing (and speaking) is 90% physiology and the 3 physiological aspects of singing are:  Breathing, Phonation, and Diction.  If a singer's shoulders move up when inhaling, the singer is wasting 60%-80% of lung capacity.  Phonation is the creation and control of vowel sounds and it works with diction - the application of consonance via the lips, tongue and teeth.  Breath control is probably the most significant issue for singers, followed by improper phonation.  When I worked with a youth musical theatre company I'd give "Uncle Tim's 5 Minute Voice Lessons", mostly about better breathing.  I can lean against a grand piano, inhale, and move the piano... and then show the "shoulders up" method which moves.. nothing.  The kids figure it out pretty quick.  I also give them a little exercise - counting 1, 2, 3,.... on pitch - with the goal of going "10 more" every couple of days until they plateau.  I'm not the music director, I'm the long suffering sound guy that needs some acoustic output from the mouths before the mics have a chance.  If I can help the kids build confidence in what they do, if I can help them understand their "instrument" better, I'm hopeful that I'll get more at the mic.  Like chicken soup, it might not help but it can't hurt.  Unless you're the chicken.... ;)
« Last Edit: November 29, 2019, 04:23:24 pm by Tim McCulloch »
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Steve Hanis

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #13 on: November 30, 2019, 10:20:10 pm »

Thanks for all the good advice, in retrospect I would have spent the money on getting matching head worn mics for all the little voices for about $18 a piece. Be that as it may, we scrounged everything we could find for  wireless mics with a mixture Shure and Sennheiser VHF and UHF old and new. No doubt the FBD is a bandaid, but a bandaid with some experimentation is hopefully better than nothing.
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Luke Geis

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #14 on: December 03, 2019, 03:12:50 pm »

Don't get us wrong, it does work. The big thing is recognizing when its function starts going the wrong way. A good engineer can acquire about 10db more in output than would be possible without any EQ in use. If you use too much EQ, you can start to reduce SPL as a result. If you cut more than you can acquire in GBF, you are going backwards. This is why we say 4-5 filters may be the practical maximum # of filters to use. The cold hard truth is that as long as you keep turning the microphone up, you will continue to acquire feedback. So the trick is to only cut the major problem frequencies to the point where the system is both loud and stable at an SPL that is LOUDER than it was without the use of EQ.

You can never make a microphone so stable that it will no longer feedback in the PA if you keep turning it up. This means the only true objective of EQ for feedback abatement, is to cut the first 2-3 frequencies that feedback. If you color the mic to make it sound good, you can end up reducing your overall SPL. There is a balancing point. This is what good engineers can find and come to; that point where overall level and quality of sound meets. 

A general rule of thumb for EQ and feedback abatement is this: Turn the mic up until you get the first feedback frequency and reduce only enough to make the ringing stop. Turn the mic up a little more until it feeds back again. If it is a different frequency, cut it until feedback stops. If the same frequency feeds back, reduce it some more until stability is reached. Continue this approach until you get multiple feedback frequencies at one time. As soon as you get multiple feedback frequencies at once, you have about as much GBF as you're going to get. This marks your practical limit of GBF. If you have to cut more than 5-6 different frequencies, STOP, you again have reached a practical limit. As you start cutting more, you just don't acquire any more actual SPL.

With 5-6 filters you should be able to get a good balance between quality of sound and GBF. So if your first few filters are only for feedback, then the last couple can be to help with sound quality. If you use all 6 filters just for feedback, you have another problem to fix.
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Tim McCulloch

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #15 on: December 03, 2019, 03:32:08 pm »

Thanks for all the good advice, in retrospect I would have spent the money on getting matching head worn mics for all the little voices for about $18 a piece. Be that as it may, we scrounged everything we could find for  wireless mics with a mixture Shure and Sennheiser VHF and UHF old and new. No doubt the FBD is a bandaid, but a bandaid with some experimentation is hopefully better than nothing.

The band aid does two things: it can make you look like a hero because you were able to cobble together all that was owned, begged or borrowed and nothing catastrophic happened, and it also sets a difficult precedent - that doing stuff in this manner worked once, therefore it will work every time.  That institutional memory of non-catastrophy means future difficulty in getting budget money to do these shows better, with less heroic EQ efforts on your part, etc.  What happens when the next person does the kid's show and doesn't have your chops or persistence?

Don't get me wrong, I'm happy for you that this can be a 'mission accomplished' moment and that no animals were harmed.  Knowing what you know now, what actions can you take between now and next time?
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

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Re: Question for those familiar with Behringer Feedback Destroyer Pro FBQ2496
« Reply #15 on: December 03, 2019, 03:32:08 pm »


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