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Wedge Feedback


stingrayfan
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Been having a bit of a problem with our two powered wedges at the last couple of gigs. They're feeding back the minute you turn them up. Taken all the usual precautions like making sure we're behind the main speaker cabs but I can't figure why they feedback so early. We're a three piece who all have mics, and the two powered wedges run off an Aux feed on our mixer. We only run vocals through the mixer.

Is there anything else I should be doing? EQ'ing? Positioning? We've tried doing a monitor mix first and it doesn't help. It's mainly the lead singer's wedge that causes the feedback. Tried changing his mic too.

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Which mic are you using? Is the pickup pattern cardioid, supercardioid or something else?

It's quite possible that if you place the wedge directly in front of the microphone stand that the mic will pick up some of the monitor feed. I know this has been the case for me in the past when using supercardioids, as the pickup pattern was as below:



Is this of any help? Apart from that I can only really suggest a problem with a cable somewhere along the line, or perhaps the monitors themselves are to blame?

Danny

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Are they powered wedges ? If so check the EQ settings to make sure that the controls haven't been nudged in transit. Set the EQ flat to begin with. Try to avoid boosting any EQ if possible. If you have a graphic EQ try cutting the EQ on each slider in turn (set them all flat then put one slider down - try that then put it back to 0 then try the next slider and so on).

For most mics the best feedback rejection position is directly behind the mic "on-axis" - i.e. not off to the left or right but directly behind the mic.

If you are playing with a solid wall immediately behind you, try moving the mic forward, away from the wall. You'll get sound reflections off the back wall that will go straight into the mic and can cause feedback. Moving the mic away from the wall - even only a foot or two, can help here.

If all else fails you can get "feedback destroyers" and attach that between the AUX send and the monitor. This will look for "ringing" frequencies in the monitor path and automatically reduce the level of that frequency to cut the feedback. A feedback destroyer shouldn't be necessary if you follow the above steps but is there as a last resort.

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[quote name='BOD2' post='57738' date='Sep 9 2007, 09:39 AM']A feedback destroyer shouldn't be necessary if you follow the above steps but is there as a last resort.[/quote]
Even if you have a 31 band graphic EQ it does you little good taming feedback if you don't know which frequencies are the offenders. Also, 31 band EQs have wide bandwidth 1/3 octave filters, so they remove too much information. Feedback destroyers use narrow bandwidth filters that kill the feedback without destroying intelligibility, and they find the offending frequencies on their own.
[quote]Is there anything else I should be doing? EQ'ing?[/quote]Absolutely, you can't run monitors without their own dedicated EQ. If you don't have one you should purchase an EQ that has a feedback destroyer built in.

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[quote name='stingrayfan' post='57656' date='Sep 9 2007, 10:44 AM']Been having a bit of a problem with our two powered wedges at the last couple of gigs. They're feeding back the minute you turn them up. Taken all the usual precautions like making sure we're behind the main speaker cabs but I can't figure why they feedback so early. We're a three piece who all have mics, and the two powered wedges run off an Aux feed on our mixer. We only run vocals through the mixer.

Is there anything else I should be doing? EQ'ing? Positioning? We've tried doing a monitor mix first and it doesn't help. It's mainly the lead singer's wedge that causes the feedback. Tried changing his mic too.[/quote]
Hi, You need to position them so the centre of the speaker is pointing straight at your eyes. If they are pointing at your knees, you will never near em, so you'll try to turn them up way too high!
I usually put my monitors on a flightcase so they are aimed correctly if there isn't 3 or 4 feet of stage available in front of me to get them aimed correctly.
To cure any more problems, the new Behringer FBQ2496 feedback destroyer is excellent. It was £100 from Digital Village. I use one on my main PA and I'm getting another one for the monitor system. You have to learn how to use them, but they work very well indeed.
Mr Gig

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The other "basic" rule about monitors that is easily overlooked is to keep the level as low as you can manage with - lower levels mean less chance of feedback.

To that end, as mr gig suggests, try to get the monitors as close to the ears of those using them as is practical as this means you can turn them down more.

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[quote name='BOD2' post='57775' date='Sep 9 2007, 10:52 AM']To that end, as mr gig suggests, try to get the monitors as close to the ears of those using them as is practical as this means you can turn them down more.[/quote]Which brings up another point: each player needs their own monitor. One can't place them adequately close when they must be shared.

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A good 31band graphic (pref. Klark Teknik) is what you need for monitors.
The feedback eliminators can cause a bit of trouble if you leave them on search. You can hear the parametrics shooting around, trying to cut notes that are actually music not feedback!
Some engineers method is to insert a graphic on each monitor, leave an open mike (no desk eq) onstage, turn up the poweramp/channel till they feed, then find the offending frequency and reduce it in the graphic then turn up the power amps/mic channel more till the next frequency feeds etc.
This is effective but extremely unpleasent to listen to. It is also not possible if the punters are already in the venue unless you want them all to leave!

You can find the frequencys and reduce them by the note they relate to on you instrument (440hz is A etc) if you find a chart of the notes this can be really useful as you can identify it quickly and turn it down in the graphic when feedback starts, after a while you'll start to recognise the frequencies.
The best basic setup is to get the singer to sing through the monitors on their own (no eq on the desk channel) and eq the graphic till they sounds balanced and as natural as possible (this may not be possible with some singers!)

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[quote name='dub' post='59856' date='Sep 13 2007, 01:22 PM']A good 31band graphic (pref. Klark Teknik) is what you need for monitors.
The feedback eliminators can cause a bit of trouble if you leave them on search. You can hear the parametrics shooting around, trying to cut notes that are actually music not feedback!
Some engineers method is to insert a graphic on each monitor, leave an open mike (no desk eq) onstage, turn up the poweramp/channel till they feed, then find the offending frequency and reduce it in the graphic then turn up the power amps/mic channel more till the next frequency feeds etc.
This is effective but extremely unpleasent to listen to. It is also not possible if the punters are already in the venue unless you want them all to leave!

You can find the frequencys and reduce them by the note they relate to on you instrument (440hz is A etc) if you find a chart of the notes this can be really useful as you can identify it quickly and turn it down in the graphic when feedback starts, after a while you'll start to recognise the frequencies.
The best basic setup is to get the singer to sing through the monitors on their own (no eq on the desk channel) and eq the graphic till they sounds balanced and as natural as possible (this may not be possible with some singers!)[/quote]
I don't know if the other feedback destroyers have this facility, but the new Behringer one I'm using has a freeze facilty. During soundcheck, it notches out all the feedback as you (puposely) wind up the mic levels to very high levels to induce feedback. You then freeze those settings for the gig. It's basically the same as spending ages doing the same thing with a graphic, but it's all done for you - and very quickly! There will probably be some automatic filters left on, but unless someone points a mic into the PA speakers or monitors, you're unlikely to trigger them. You can set the time those auto filters will stay on too, so they will just handle those weird things that vocalists do with mics and then reset themselves. I use a 3.2 kilowatt PA rig and 800 watts of monitors (in fairly small venues sometimes), and those feedback destroyers are great!
Mr Gig

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