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Author Topic: Help! Countryman B3 lav causing insane feedback  (Read 2508 times)

Ryan Noyes

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Help! Countryman B3 lav causing insane feedback
« on: March 19, 2014, 08:53:32 PM »

First post and live-sound newbie here.  Just finished building a new PA system for a non-profit organization I belong to.  Setup as follows:

Soundcraft EPM8 analog mixer >
Behringer FBQ2469 automatic feedback destroyer/parametric EQ >
pair of QSC K12 self-powered loudspeakers, one of which I daisy-chain to a QSC KSUB subwoofer just below

On the rack, the wireless receivers are a pair of Shure SLX2, which RF-out to a Shure antenna distributor (that's sort of irrelevant -- I'm adding more receivers soon)

Mics are:
2 standard SM58
1 wireless SM58
1 Countryman B3 lav (to Shure SLX1 bodyback transmitter)

My issue is: B3 feedback.


Everything is working exactly as anticipated, except the B3 lav, which is absolutely IMPOSSIBLE to ring-out with the feedback destroyer.  The feedback is uncontrollable to the point where all twenty EQ filters on the Behringer feedback destroyer would be applied to the B3 alone (I've tried this).  Conclusion: the B3 has to go.  Use for this is spoken-word, for lectures/presentations in a room that already is an A/V guys worst nightmare (very reflective).  The B3 is omni, and it's positioning would be IN FRONT OF the mains, which is obviously a problem.  I don't think head-worn is an option.  I want a durable lav for presenters that want to walk around a room.  Is this do-able?  The room is a big rectangle with a drop ceiling at 20' above a hardwood floor.  About 60' by 20'.  I have the speakers at the end of the rectangle, and corners of a 20' wall.  No stage.  I should note: the dang SLX2 bodyback transmitter does NOT have a lowcut switch, and my mixer does not mic feedback EQ knobs for the more common feedback freqs.  The Behringer is kind-of a piece of crap, I'm discovering, but seems to do the job for the SM58's, so my gut feeling is to keep it.

Lav mic help would really be great though.  Thanks a ton in advance!

Ryan in Philadelphia
« Last Edit: March 19, 2014, 08:59:57 PM by AlphaDelta »
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Mac Kerr

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« Reply #1 on: March 19, 2014, 09:06:30 PM »

First post and live-sound newbie here.

Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section, and on the registration page when you registered.

Mac
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Luke Robinson

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Re: Help! Countryman B3 lav causing insane feedback
« Reply #2 on: March 20, 2014, 05:56:39 AM »

Sounds like there are a few issues going on here, witch can all factor into your problem. The first and largest would be having the lav in front of your main speakers. Though not impossible to correct given experience and the right tools, it is generally a big no no.

The mixer you are using does not have an eq that can really let you dial into the frequencies that are feeding back and let you adjust them. I would suggest inserting a graphic eq on the lav channel so that you can dail back the frequencies that are giving you a problem. A free RTA app for your smartphone can help you see what frequencies are a problem.

Third would be the mic element, an omni lav is not the best in a live situation In my opinion. They are great for broadcast since they pick up more sound, but for the same reason they tend to feedback more easily. Look at cardioid lavs for live situations, I think you will have much better luck with them. In particular the shure wl185 seems to have much better gain before feedback than any other lav that I have used. It also happens to be one of their more affordable options.

If you are still stuck I am also located in philly and can either myself or have one of my guys come out and consult with you. PM me if you are interested.

Luke
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Jerome Malsack

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Re: Help! Countryman B3 lav causing insane feedback
« Reply #3 on: March 20, 2014, 08:18:04 AM »

Another thing to help is the antenna distribution should have the receiving antenna and distribution should be to the receivers.
 
  On the rack, the wireless receivers are a pair of Shure SLX2, which RF-out to a Shure antenna distributor (that's sort of irrelevant -- I'm adding more receivers soon)

So what I am saying is the receivers are RF-In and not out to a Shure Antenna distributor.   

The behringer FBQ should have the ability to run some EQ also in the settings.   You should be able to cut several of the lower bass ranges to remove the Vocal cuts.  Are you planning to run some music also because this bass cuts would apply and remove the bass from the music as well.   

 
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James A. Griffin

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Re: Help! Countryman B3 lav causing insane feedback
« Reply #4 on: March 20, 2014, 11:32:36 AM »

pair of QSC K12 self-powered loudspeakers, one of which I daisy-chain to a QSC KSUB subwoofer just below

Why do you need a sub for spoken-word amplification?    Adding a KSUB, esp in the corner, brings in a lot of low frequencies that one would normally CUT for a voice mic.   

Have you ever tried it without the sub?  I'm not sure it will solve the feedback issue, but it will give you a cleaner voice sound.


The feedback is uncontrollable to the point where all twenty EQ filters on the Behringer feedback destroyer would be applied to the B3 alone (I've tried this). 

As Harry Nilsson said, "A point in every direction is the same as no point at all".    If 20 filters are engaged, something is terribly wrong.   How are you determining which 20 frequencies to cut?  RTA?   Auto-EQ from the Berhinger?
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Re: Help! Countryman B3 lav causing insane feedback
« Reply #4 on: March 20, 2014, 11:32:36 AM »


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