Cacophony Forums
Unofficial Mackie User Forums => DL1608/DL806/DL32R/ProDX Mixers => Topic started by: yigba on July 26, 2015, 01:51:28 AM
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I'm getting feedback from my vocal mics with my new QSC KW122's/K181's and wanted to utilize some sort of automatic feedback rack unit to help - I mix from stage and don't have time to experiment when I'm singing and playing guitar. I utilize the DSP from the DL1608 and the internal crossovers on the QSC's. So I thought of the following:
I have a Driverack PA basically gathering dust. So I figured I'd use only the AFS (Automatic Feedback System) system within it to automatically control the feedback. I want to send only the vocal mics (channels 1-3) thru the Driverack so I was trying to use Aux5 for this with with only the 3 vocal channels via Aux 5 sent to the Driverack, (taking channels 1-3 out of the mains in the LR channel) and then returning the Driverack signal (which is channels 1-3 via the Aux 5) to the mains via channel 15 on the LR Master.
I have triple checked the levels on each and they are at the right level - Aux 5 channels 1-3 are at unity, Driverack ins and outs are at unity and Channel 15 on the LR master are at unity. Also the Aux 5 Master is at unity.
This is not working as I am getting a very muddy low level sound out of the mains. When I connect everything with the Driverack AFS on the LR mains out it works fine - a nice strong level out of the mains.
What am I doing wrong?
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First determine if it's monitor feedback or main feedback. You'll want the DRPA between the mixer and the amp for the speakers that are causing trouble. Do set up the DRPA for those amps and speakers, then set the auto EQ. (There are tons of advice on doing that well.) Then set the anti-feedback. If it's monitors and you feed that amp with aux6, then place the DRPA between Aux 6 and the amp driving the monitors. Don't do anything else. Nothing else works with that unit. (I've got one. I like it and it does what I need.)
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I'm with Wynnd, whilst I see the logic in what you are trying to do, it would be much more straightforward to put the DRPA between the mixer and the speakers where you are getting the feedback, i.e. FOH or Monitors.
Are you ringing out the system before you start your set? You can get apps for your smart phone that will give you a crude but useful spectrum analyser to help EQ out any feedback.
Other things to examine are:
- your mic position in relation to the speakers,
- using pre-DSP on monitor feeds then EQing the monitors to remove the feedback,
- EQing the main PA in a similar way using high-Q notching
- a change of mics to something with a tighter pattern (Rode M2?)
Hope this helps.
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It's FOH that's feeding back.
Prior to the QSC KW122's I was using Bill Fitzmaurice OmniTop 12 speakers and never once had a problem with getting to the optimal vocal volume and FOH feeding back.
With my thought I was just trying to kill the feedback on the vocals so the entire mix isn't affected but I guess I can just leave the DRPA on the whole mix.
But just out of curiosity - why doesn't my method work? Shouldn't it? I mean sending an AUX 5 to an external processor and back to the board via channel 15 with all the gains at unity should return the same signal, no? Isn't that how to use external effects with the DL1608 - or any board?
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Could be any number of things causing it not to work. IIRC the PA+ in my case is a 2 in 6 out unit with it's main function to provide a separation of frequency ranges. So my first question would be which output are you routing back to CH 15? Have you listened to the PA results? I'm not sure if there is a bypass in this unit. The other possibility is that your running into phase issues due to the delays or stage wash pickup in the Vox mics. It's always best to treat feedback at it's earliest point ie. the channel or before. Mic position and type play a significant role in this. It's also easy to create a unintentional feedback loop in these mixers. It could also not be Vox creating the feedback.
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Be reasonable. Do it my way. Actually, your approach seems convoluted to me. You're speakers aren't likely to have a perfectly flat response. (Nearly none do.) So the auto-EQ can fix that issue and that alone will help with feedback. (Especially FOH problems.) Before using it, do some reading on the potential problems. I use my garage. Open the door, place the speakers right at the edge facing out and I place the mic about 20' on a mic stand on my down sloping driveway. There are very few places for acoustic reflections in that setting so it's nearly as good as an sound chamber. (And for my purposes, just what I'm looking for.) If you do this, you can get away without doing it anywhere else. (No one like pink noise.) Then just set the AFB system as normal. I usually set 6 filters fixed and let the other 6 filters float. That doesn't help when the singer decides to walk in front of the FOH speakers.
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Wynnd I bet your neighbors love you when you pull that test. :) Did I forget to mention that unless your gig is in the driveway it's totally useless for any other acoustic environment.
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I tried using 'smaart' with pink noise on my old passive system and it produced a hugely convoluted graphic eq plot (ok it was done in my very small home studio). When I listened to music through it in the same environment it sounded absolutely sh1t. This leads me to the realisation that wihout the requisite knowledge tools like 'smaart' are as much use as the proverbial chocolate fireguard. ;D
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First of all, it's not a 50,000 watt system. Secondly, just about all speakers have frequency response problems and a system that is truly flat will alway out perform one that isn't everywhere. Sure, if I did the pink noise thing everywhere I would get a slightly better situation everywhere. But I don't want to be chasing customers out the door before the gig. I'll take the small advantage of a flat frequency response over a system that has never been flat any day. I'm 62 and even with hearing aids couldn't possibly set up a system perfectly from just my hearing. (Hell, I'd be betting that most 20 year olds couldn't do it from just hearing either. Not saying they couldn't get something that works OK.)
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I don't disagree Wyn, your method is as good as any, just that I tried similar and it didn't work for me.
With a powered system the manufacturer has done the speaker optimisation (some better than others of course) and it should sound pretty good straight off. I'm happy that my new rig does. When I get to the venue I play some music (Dixie Chicks, "Ready To Run" and Skeleton Crew, "Rock And Roll Dreams" usually) over the system and use Dave Rat's method of comparing the sound over my cans with the sound coming from the FOH (that negates most 'tired ears' effects), this just to iron out any room effects. I don't usually 'ring out the room' but I rarely work with mega loud bands these days (like you I'm 62 and my ears are not what they were).
The best example of clever speaker DSP I've heard is the Bose L1 Compact. The eq plot must be all over the place with that stack of tiny speakers but the audio output is more natural sounding than anything else I've ever heard by a good margin too :mrgreen:
When it all comes down to it there are a million and one 'correct' ways to set up a system if it works for you then it's right.
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Very true. And what works for you always ought to be a good starting point. My ZXA1s are pretty flat. (Except for the matching subs.) But like most people, I now have multiple PA systems. Some bi-amped, some tri-amped, some powered. In larger outdoor situations, I combine systems for extra power. Still not covering groups larger than 5000 people. There are others better prepared for that and they are welcome to that work.
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Very true. And what works for you always ought to be a good starting point. My ZXA1s are pretty flat. (Except for the matching subs.) But like most people, I now have multiple PA systems. Some bi-amped, some tri-amped, some powered. In larger outdoor situations, I combine systems for extra power. Still not covering groups larger than 5000 people. There are others better prepared for that and they are welcome to that work.
5000??? Yikes
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Being the obsessive maniac I am I went out and bought a Driverack PA2 (anyone want my Driverack PA?) and traded my SM58's for Audix OM-6's.
I AutoEQ'd the KW122's/K181's to a flat setting - no more pink noise thankfully with the PA2 - and the speakers sounded great. No more feedback either with the different mics, which have much better feedback rejection. Didn't even have to use the AFS function on the Driverack because the mics weren't feeding back at all.
This DL1608 works great for me. I have now gotten my recordings nearly perfect using a little Tascam DR-03 recorder coming out of Aux 6. This mixer is something else.
All's well that ends well.
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What do you mean no more pink noise? How does it auto-eq without the pink noise?
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It uses a very quick sine wave. Sort of sounds like something out of Star Wars but goes by very quickly. It also has you place the RTA-M mic in 2 to 4 (you choose how many) different positions to get you the best AutoEQ. The 4 positions are the most accurate and that's what I used. It is very similar to the way my Onkyo home stereo receiver set its EQ settings.
Where the pink noise took what seemed like an eternity this new way of doing the AutoEQ is over in seconds.
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Hmm. Which I didn't know that existed.
I love what my DriveRackPX does for the sound. So far we've always had access to the venue when nobody is around so launching the rocket hasn't been an issue. I've been wondering what people do when they show up to a venue with a PX around 4pm and there are already 20 people in the room...
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With the original DriverackPA I never RTA'd a room with people in it because of that pink noise. I always had simply set the system flat in an outdoors environment and went with that in the rooms I play, with minor adjustments.
The PA2 lets you RTA the room without the jet sound - but background noise may be an issue because when I RTA'd with PA2 outdoors sometimes it had to redo one of the mic settings due to "background noise". The original PA simply had you turn up the pink noise volume until the mic got the signal level it needed.
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Haven't noticed anyone else mention this, but if you're using compression on your vocal mic, kill it.
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I have a Springsteenesque voice - I absolutely have to compress my vocals.
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I use a lot of compression on Preachers. Those guys will go from a whisper to a real loud shout in the same sentence. With compression I'm able to bring the whisper up to listening level and prevent the shouting from hurting the audience or my equipment.
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All I know is, as soon as I got rid of the compression on my vocal channels, I've never had a problem with feedback. Zero. And I can belt out the vocals too. Like Eric Burdon - it's all a matter of mic technique.
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You can really only use significant compression on vocals without monitors unless you love feedback. I do generally set the compression thresholds at -17dB on the vocal channels and use them just to shave off the occasional extreme peaks.
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You've got to get a preacher on your system to understand my usage. And no, I rarely use any compression of musicians and singers.
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Just did another gig this past Saturday and could not get the system to feedback at all even trying to invoke the AFS module in the Driverack PA2.
The Audix OM-6's seem to have worked magic for my rig.
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Glad you found the problem and as I stated before it's best to stop problems at the source than to band-aid them down the road. The OM-6 are hyper-cardioid the SM-58 are cardioid. For tight performance spaces the narrower pickup pattern of the OM-6 will be much better to avoid stage wash. The next step would be noise cancellation mics. I personally like the OM-2 over a SM-58 for cardioids.
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How close does a vocalist need to get to the OM-6?
And I would assume you need to be pretty much directly in front of it then...
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As close as is reasonably possible and your setup should take that into consideration (at sound check). A lot of vocalists don't know how to use mics and that is sad.
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A lot of vocalists don't know how to use mics and that is sad.
I completely agree. My bass player who sings backup is still getting used to the OM-6. I love it.
And yes, you have to be right on top of it. But no low mid feedback anymore!!