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Author Topic: Where to patch feedback eliminator?  (Read 6824 times)

Dave Rigter

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Where to patch feedback eliminator?
« on: December 14, 2011, 10:40:03 pm »

Hi all,

Need a bit of help.
I've acquired a not so expensive feedback eliminator to go into our Chapel.
Only thing is I'm sure where to patch it.
The manual says patch it into either a group and assign all mics there, or into an insert point.

Currently it's patched like this:

Main outs of SoundCraft EPM to FBQ.
FBQ outs, direct to inputs of L & R Bose L1 Portable Line Array.
Line out of L1's go to Line inputs of 2nd pair of L1's (halfway down chapel)

My concern was also that the FBQ may not receive enough level to analyze the feedback properly.
Thus I turned down the powered L1's to 25% (previously set @ 50%), so I could turn up the gain at the mixer to get a proper level @ the FBQ and incidentally at the meters.

My aim is to allow the mixer to be operated by Nuns and retirees (not ideal I know, but its what I got).

I want the FBQ to safeguard against ppl turning everything up full.
But I also need enough level so when ppl with brains put the levels @ 0 instead of +10 you can still hear.

Do I patch the FBQ at the insert points over the main mix?
If so, am I inserting the output of the FBQ there, or do the inserts "break the chain" before the mix outputs and send the "mix" to the FBQ?

I can see I actually have 2 problems.
*Unsure of where how to patch the FBQ
*Incorrect gain structure - unsure of how high to have amp settings in correlation with HA Gain....

Sorry, I'm sure it's obvious, but I have really confused myself here and would appreciate some help!

TIA!
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Marcus Wilson

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Re: Where to patch feedback eliminator?
« Reply #1 on: December 14, 2011, 11:14:47 pm »

Hi all,

Need a bit of help.
I've acquired a not so expensive feedback eliminator to go into our Chapel.
Only thing is I'm sure where to patch it.
The manual says patch it into either a group and assign all mics there, or into an insert point.

Currently it's patched like this:

Main outs of SoundCraft EPM to FBQ.
FBQ outs, direct to inputs of L & R Bose L1 Portable Line Array.
Line out of L1's go to Line inputs of 2nd pair of L1's (halfway down chapel)

My concern was also that the FBQ may not receive enough level to analyze the feedback properly.
Thus I turned down the powered L1's to 25% (previously set @ 50%), so I could turn up the gain at the mixer to get a proper level @ the FBQ and incidentally at the meters.

My aim is to allow the mixer to be operated by Nuns and retirees (not ideal I know, but its what I got).

I want the FBQ to safeguard against ppl turning everything up full.
But I also need enough level so when ppl with brains put the levels @ 0 instead of +10 you can still hear.

Do I patch the FBQ at the insert points over the main mix?
If so, am I inserting the output of the FBQ there, or do the inserts "break the chain" before the mix outputs and send the "mix" to the FBQ?

I can see I actually have 2 problems.
*Unsure of where how to patch the FBQ
*Incorrect gain structure - unsure of how high to have amp settings in correlation with HA Gain....

Sorry, I'm sure it's obvious, but I have really confused myself here and would appreciate some help!

TIA!

Hi Dave,

A lot of stuff there.

You have the FBQ in a suitable place.

I feel you may be confused about how it operates.  The unit looks for continuous, single frequency events and pops in an equaliser section to cut at that frequency.

It's not sensing level as such.  It may require the level to be over a particular level to be able to operate properly, but would be quite low, say -30dBu.  Your system should probably be well over that, without altering the power amp inputs.  In other words, if the output meter on your EPM is indicating any level at all, you should have enough for the FBQ to do it's job.  The main thing is that you don't overload it by turning the amps down too far and drive heaps of level from the desk to compensate.

The FBQ is not a limiter, so it will not stop the system going too loud, it will only catch feedback events as they occur.  If someone turns everything up full and there's lots of feedback issues, then the FBQ will run out of filters and you will still get feedback (and horrible sound)!

Basically it will do 50% of what an engineer can do with a decent equaliser, but it doesn't have a real brain, so if there's an idiot on the desk it will be powerless to fix it!!!

The mix insert points are a good place to put it.  They 'break the chain' just before the master faders. I'm not sure whether the inserts or where you have it would be best, try and see, but they are both valid.

The instructions about the group insert is so you get the FBQ only affecting the microphones and not playback or other sources.  Sometimes the eq changes can be quite severe and badly affect music or recorded material playback.

By the way, one of the best things you could do is delay the signal to the second set of Bose.   It will drastically increase the intelligibility in the rear of the room.

rgds, M.
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rgds, M.

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Re: Where to patch feedback eliminator?
« Reply #2 on: December 14, 2011, 11:22:39 pm »

Never mind........
« Last Edit: December 14, 2011, 11:24:52 pm by dick rees »
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Dave Rigter

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Re: Where to patch feedback eliminator?
« Reply #3 on: December 15, 2011, 12:34:10 am »

Hi Dave,

A lot of stuff there.

You have the FBQ in a suitable place.

I feel you may be confused about how it operates.  The unit looks for continuous, single frequency events and pops in an equaliser section to cut at that frequency.

It's not sensing level as such.  It may require the level to be over a particular level to be able to operate properly, but would be quite low, say -30dBu.  Your system should probably be well over that, without altering the power amp inputs.  In other words, if the output meter on your EPM is indicating any level at all, you should have enough for the FBQ to do it's job.  The main thing is that you don't overload it by turning the amps down too far and drive heaps of level from the desk to compensate.

The FBQ is not a limiter, so it will not stop the system going too loud, it will only catch feedback events as they occur.  If someone turns everything up full and there's lots of feedback issues, then the FBQ will run out of filters and you will still get feedback (and horrible sound)!

Basically it will do 50% of what an engineer can do with a decent equaliser, but it doesn't have a real brain, so if there's an idiot on the desk it will be powerless to fix it!!!

The mix insert points are a good place to put it.  They 'break the chain' just before the master faders. I'm not sure whether the inserts or where you have it would be best, try and see, but they are both valid.

The instructions about the group insert is so you get the FBQ only affecting the microphones and not playback or other sources.  Sometimes the eq changes can be quite severe and badly affect music or recorded material playback.

By the way, one of the best things you could do is delay the signal to the second set of Bose.   It will drastically increase the intelligibility in the rear of the room.

rgds, M.

Thanks Marcus.
Yes I was concerned that a lack of level would not allow the FBQ to do what it should.
I will try placing it at the mix inserts points and see what I get from there.

Cheers for the advice!
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Jay Barracato

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Re: Where to patch feedback eliminator?
« Reply #4 on: December 15, 2011, 02:00:25 pm »

Never mind........

I would patch it in between the 15 band graphic and the sonic maximizer.


And then I would make sure nothing is hooked up to any of it.
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Jay Barracato

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Re: Where to patch feedback eliminator?
« Reply #5 on: December 15, 2011, 02:04:02 pm »

I would patch it in between the 15 band graphic and the sonic maximizer.


And then I would make sure nothing is hooked up to any of it.

I was going to post a picture of a train wreck, but I've been getting cited for excessive sarcasm lately.

I do not consider the FBX unit to be of much use in this or any such situation no matter how you patch it.  Proper system setup and control should take care of things.  I'd be more concerned about using another set of ultra-wide dispersion speakers as un-delayed reinforcement. 

Now where can I find a picture of mud????
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Re: Where to patch feedback eliminator?
« Reply #6 on: December 15, 2011, 03:17:09 pm »

I would patch it in between the 15 band graphic and the sonic maximizer.


And then I would make sure nothing is hooked up to any of it.

Jay is 100% correct if this situation affords real sound engineer support... which is sort of the point of this forum... perhaps this thread is more for the HOW area?

But Dave I think you should be up in arms about under qualified people being at the helm... If you can't get someone who can find a feedback frequency and address the issue... good luck. Whenever that system is running the public image of your venue, and probably your reputation is going to come into question. And if feedback is a common problem, groups will look for other places to meet.

I also think that Dave is in a realistic world where inexperienced persons may be left in charge of equipment. And if this is going to happen - for audience health concerns isn't it better that they do deploy a feedback device? 

If you do have to use the FBX then you want a different mixer. Get one with an insert on a bus that you only assign microphones through. Put the FBX there, and a 31 band equalizer while you're at it - and train those nuns how to use it. Then as Jay said, unplug the FBX.
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Jonathan Johnson

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Re: Where to patch feedback eliminator?
« Reply #7 on: December 15, 2011, 04:36:11 pm »

So... how does a feedback destroyer know the difference between feedback (a "continuous, single frequency event" that may be produced by interaction between loudspeakers and microphones) and an extended musical note (a "continuous, single frequency event" that may be produced by some instruments)?
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Dave Rigter

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Re: Where to patch feedback eliminator?
« Reply #8 on: December 15, 2011, 05:20:40 pm »


Thanks Nils,
Good call on moving the post to the HOW forum. Fair call.
and yes, I'm not the best FOH engineer but I'm doing the best with what I've got.
This is a school chapel setup, used at all sorts of weird times so independence from me is really what I'm aiming for.

I'll see what I can do about installing a graphic.  Makes a lot of sense.

As far as gain structure goes, I'm still a little confused.
Should I be adjusting the system so that level at the desk is healthy (around -5 or 0 at the meters), then set the amps to an appropriate level?
Or, set the amps to 80% and adjust levels at the mixer accordingly?


Jay is 100% correct if this situation affords real sound engineer support... which is sort of the point of this forum... perhaps this thread is more for the HOW area?

But Dave I think you should be up in arms about under qualified people being at the helm... If you can't get someone who can find a feedback frequency and address the issue... good luck. Whenever that system is running the public image of your venue, and probably your reputation is going to come into question. And if feedback is a common problem, groups will look for other places to meet.

I also think that Dave is in a realistic world where inexperienced persons may be left in charge of equipment. And if this is going to happen - for audience health concerns isn't it better that they do deploy a feedback device? 

If you do have to use the FBX then you want a different mixer. Get one with an insert on a bus that you only assign microphones through. Put the FBX there, and a 31 band equalizer while you're at it - and train those nuns how to use it. Then as Jay said, unplug the FBX.
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Jean-Pierre Coetzee

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Re: Where to patch feedback eliminator?
« Reply #9 on: December 15, 2011, 06:02:07 pm »


Should I be adjusting the system so that level at the desk is healthy (around -5 or 0 at the meters), then set the amps to an appropriate level?
^
This has been discussed in depth before.

Leave the anti-feedback unit somewhere where some non God-fearing person can find a new home for it. I understand the need but rather just teach the nuns how not to destroy the system(churches all over have achieved bad, not destructive sound; so can you).
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Re: Where to patch feedback eliminator?
« Reply #10 on: December 15, 2011, 06:05:20 pm »

So... how does a feedback destroyer know the difference between feedback (a "continuous, single frequency event" that may be produced by interaction between loudspeakers and microphones) and an extended musical note (a "continuous, single frequency event" that may be produced by some instruments)?

It does not know the difference. It just depends on how much thought they built into the algorithms. And how lucky you are that day. Your average musical note has a harmonic structure that may or may not differ from it's internal definition of feedback, there are no guarantees.
 
The only way I've seen these devices work "well" (very loosely) is to nab the first couple of troublesome frequencies and then lock the unit down. Not completely terrible for a quick setup in a bad room, and possibly less destructive than a several bands of graphic eq. But if there is a live mode active you can be sure that in the middle of a solo it will start grabbing unintended frequencies.
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Marcus Wilson

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Re: Where to patch feedback eliminator?
« Reply #11 on: December 15, 2011, 09:31:32 pm »

It does not know the difference. It just depends on how much thought they built into the algorithms. And how lucky you are that day. Your average musical note has a harmonic structure that may or may not differ from it's internal definition of feedback, there are no guarantees.
 
The only way I've seen these devices work "well" (very loosely) is to nab the first couple of troublesome frequencies and then lock the unit down. Not completely terrible for a quick setup in a bad room, and possibly less destructive than a several bands of graphic eq. But if there is a live mode active you can be sure that in the middle of a solo it will start grabbing unintended frequencies.

I agree with Nils about the usefulness or otherwise of FBQ units, but wasn't going to go there because Dave already has one.   The last thing I ever want in a sound system is a unit with almost no intelligence tweaking around with the EQ!  If a human started doing that, it could incite me to violence!

Dave, your questions about mixer and amplifier levels are a common issue of gain structure in a sound system.  I suggest you look for a book on sound system implimentation, or suitable internet information, or look at other parts of this forum, to find information on gain structure.

From your posts, you seem to be keen on getting good results and want to learn.  Perhaps you may want to get training from Syn Aud Con or some other training organisation which is well regarded in the industry.   I can't really recommend anything near you because I live in New Zealand.

I don't mean any offence, I have been in the pro-audio industry for 30 years and still actively engage in learning.   My books on audio alone take up about 6 feet of shelf space.

rgds, M
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rgds, M.

Owned a regional sound company for 30 years.
Now work for Harman importers in New Zealand.
www.jands.co.nz
Do a bit of mastering and hire out some microphones.
Am a highly skilled electronic technician.

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Re: Where to patch feedback eliminator?
« Reply #12 on: December 15, 2011, 10:04:13 pm »


I'll see what I can do about installing a graphic.  Makes a lot of sense.


I have several church systems I've set up where the operators are either all volunteers with very little actual knowledge/experience or it's a "turn on one switch and go" system.  Both have multi-function processors which include the basic control functions of graphic EQ, parametric EQ and limiting.  I can set access levels for all the functions so that the total noobs can't adjust anything at all, those with some experience and the need to adjust the GEQ can access it with a personal password and so on.

Everyone who uses the system should understand the on/off sequence, how to properly adjust input gain and how to coil cables so they'll last.  I use a sequenced power supply wherever possible for the on/off.  Having a board which has PFL (or "cue") per channel will make it easier to set the proper input levels.

Happy studying.   
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duane massey

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Re: Where to patch feedback eliminator?
« Reply #13 on: December 15, 2011, 11:32:08 pm »

I have found fbq's to be quite useful is certain situations IF installed and setup properly. A large portion of my clients are non-sound people with no hope of training beyond "ON/OFF", and I still get phone calls about that. My absolutes in dealing with FBQ's are simple. Don NOT use the "live" functions. Run the unit, let it do it's job, and lock it down. Using a graphic EQ to eliminate feedback certainly does more harm to the overall sound than either a parametric or an FBQ, so I don't see the advantage of going to a graphic IF it is for the purpose of eliminating feedback.
If the system is always the same (same mics, same room, etc), then "set and lock" should be very practical.
I don't think FBQ's are a great idea if you have a decent sound person, but they can be useful. I must admit my first response was "don't you mean 'pitch' rather than 'patch', but I don't want anyone to think I am sarcastic....
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Duane Massey
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Re: Where to patch feedback eliminator?
« Reply #14 on: December 16, 2011, 09:43:08 am »

I have found fbq's to be quite useful is certain situations IF installed and setup properly. A large portion of my clients are non-sound people with no hope of training beyond "ON/OFF", and I still get phone calls about that. My absolutes in dealing with FBQ's are simple. Don NOT use the "live" functions. Run the unit, let it do it's job, and lock it down. Using a graphic EQ to eliminate feedback certainly does more harm to the overall sound than either a parametric or an FBQ, so I don't see the advantage of going to a graphic IF it is for the purpose of eliminating feedback.
If the system is always the same (same mics, same room, etc), then "set and lock" should be very practical.
I don't think FBQ's are a great idea if you have a decent sound person, but they can be useful. I must admit my first response was "don't you mean 'pitch' rather than 'patch', but I don't want anyone to think I am sarcastic....

Duane....

I agree that FBX units have some application if, as you say, they are used properly.  I do as you do, letting them set the filters automatically, then locking them down.  As such, the unit has become a parametric equalizer, albeit an "automatic" PEQ.  Even the humble Behringer FBX 1100 can be implemented in such a fashion with satisfactory results.
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John Roberts {JR}

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Re: Where to patch feedback eliminator?
« Reply #15 on: December 16, 2011, 10:58:14 am »

So... how does a feedback destroyer know the difference between feedback (a "continuous, single frequency event" that may be produced by interaction between loudspeakers and microphones) and an extended musical note (a "continuous, single frequency event" that may be produced by some instruments)?
While different devices use different approaches (I ASSume), acoustic feedback has some specific unique characteristics that normal musical notes do not. For example, feedback is generally a simple single frequency, while most musical tones are complex with harmonic overtones. (AFAIK only a flute played pianissimo approaches a pure tone, and perhaps some old synths).

Another characteristic of feedback that differentiates it from music is it's envelope signature. Feed back will generally express as a slowly increasing amplitude, while most musical notes will generally start as loud as it ever gets and decay from there.

Another test to prove if a sound is feedback or music is to hit it with a few dB of cut EQ and see how it acts. Simple music with a 3dB cut will track it's original envelope trajectory, but dropped the nominal 3dB. A building feedback with stop dead in it's tracks or build much more slowly when cut a few dB.

All of these methods to definitively discriminate between feedback and music take time to perform that analysis especially for envelope signatures. So best results should come from time spent letting the device learn the room or system, by cranking up the gain and letting it find the first few worst case modes.

Expecting these to work effectively on the fly will always involve tradeoffs since you can be quick or accurate in your detection, typically not both. 
 
JR

PS: FWIW My FLS blinky lights over the GEQ sliders was not a smart system. it just compared the level in all the different filter bandpasses and indicated which one was loudest. The Peavey MENTOR (now long obsolete) was DSP based and smarter, while it only provided a light show with no actual correction applied. it probably could have in connection with PV's old digital controlled GEQ, but that would have been a pretty expensive solution and real men didn't use feedback killers back then, and PV customers surely didn't pay for expensive solutions, when a cheap one worked adequately.
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Re: Where to patch feedback eliminator?
« Reply #15 on: December 16, 2011, 10:58:14 am »


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