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-   -   Live show wireless lavs problem. (https://www.dvinfo.net/forum/all-things-audio/76020-live-show-wireless-lavs-problem.html)

Bruce S. Yarock September 22nd, 2006 08:53 AM

Live show wireless lavs problem.
Last night I mixed sound for what was supposed to be a 4 camera variety local talk show.I used 2 wireless lavs and a handheld wire less for the talent.I also boomed a guitar player and singer for a short set.I did two recorded mixes,one to one of the cameras and one to my Edirol.
The event was in a restaurant and I also had to run an output from my board to the house sound system (a scary tangle of rigged gear, cables etc.). In addition, they had about 10 bose speakers hanging from different parts of the ceiling.
The problem was that two of the wireless lavs (one worse than the other) fed back horrendously unless I kept the levels real low.The wireles hand held and the boomed cardiod were much better. I assume that the problem was that the house speakers created a feedback loop back through the omni lavs.
Any ideas on what caused the feedback? Also, what would I need in the future to mix both for video and for a live room mix? Would it be more controlable to run my mixer through it's own power and speakers,thereby avoiding the house rig completely? Maybe an additional room eq?
Bruce S. Yarock

Jay Massengill September 22nd, 2006 09:55 AM

The situation you are describing is a very typical problem. Omni lavs used within the speaker field almost always creates difficulty with providing enough gain before feedback.
There are a number of things you can do to help. First, the answer is yes you should use your own sound system in place of the distributed ceiling speakers of the house system. You will have much greater control of the direction of sound reinforcement in relation to where the lavs are. This is the single most important factor in controlling feedback in a simple manner.
Other factors: Use cardioid lavs, although that's not a huge improvement typically and can be prone to placement problems making the situation worse. Better yet, use headworn mics to improve gain before feedback. (Headworn mics have their own set of issues though, so maybe they aren't appropriate here.)
Use proper mic positioning and tell the talent they must speak with energy, as if they were addressing 20 or so people without using a mic.
Roll off the lows and the highs substantially. You can typically accomplish this with even the simplest of mixers.
Use more advanced EQ, preferrably a computer controlled feedback filter. (That sounds alot more sophisticated than it really is) While feedback filters aren't a miracle cure, and must be employed with some pre-work and some knowledge, they can make the final difference in success or failure.
If you only have a regular multi-band graphic or sophisticated parametric EQ, you can usually find the offending frequencies that are being overly reinforced and reduce them. This takes a fair amount of time to accomplish but is less costly than a more sophisticated feedback filter, unless you have one of the very low cost units Behringer makes. I've never used one of those, so I don't know how effective they are. The key is that you must do this work ahead of time, they really aren't good enough to handle a problem "live".

Seth Bloombaum September 22nd, 2006 09:06 PM

The layout of the restaurant might also be an issue (small and intimate is not good for lavs & pa). I've used lavs in sound reinforcement for meetings in large rooms with good pa systems. A soft talker is always an issue. Multiple mics open are always an issue. IMHO it really can't be done without someone dedicated to audio and mixing as needed - you say you mixed it, did you shoot too?

It helps if you use a mixer which offers subgroups with insert points, use all matched lavs, send all lavs to a group, insert an eq in the group, and do a ringout on that eq using a single lav.

(ringout - place the mic on the set, boost gain until you hear feedback, find that freq. on the eq and reduce it. Then boost the gain and find a new freq. Repeat... it helps to have a steep compressor or limiter on the outputs to the pa so that feedback doesn't get so loud in this process that it blows a speaker or someone's ears. Nobody will like you during ringout... Ringout is usually done after room eq.)

The sound for live meetings got a lot easier when our clients accepted use of Countryman Earset E6i microphones, which are these teeny booms that hang off the ear. They sound great and support much more gain before feedback. They'd be pretty visible on most tv-style interview shoots, which may or may not be acceptable. The mics are about $350 to $500, and are available set up for just about any wireless beltpack.

More speakers at various areas of the venue is generally a good idea, as long as they are part of a high-quality system and none near the performers. If they generally sound like crap anyways, or, there are speakers in the "stage" area that can't be turned off or disconnected then a separate system is indeed your only choice.

I've done lots of mixing for simultaneous recording and live reinforcement, it does keep you busy as the needs can be pretty different. Monitoring, for one thing - you quickly find that what you're hearing in the room is not what's going on tape, and vice-versa.

I've never worked one, but I'd guess that the big network talk shows split all mics and have one engineer mix for the house and another mix for broadcast.

Sharyn Ferrick September 22nd, 2006 09:13 PM

Most recording of events like this use a mic splitter, where you have one feed going to the pa and a independant feed going to your mixer. With todays modern mixer input stages, snakes that have a simple y wired in work very well. This way you have one mix for the pa and another mix for the recording, and you might have mics that are only for recording and not fed into the pa.


Bruce S. Yarock September 23rd, 2006 03:12 AM

Thanks, guys for the feedback (pun intended). The horrendous Bose house system along with the lavs, was recipe for disaster. If I do it again, I'll try
1- to use a couple of handheld wireless cardiods ( I used one at this show and there was no feed back).
2-Bring a couple of decent pa speakers.
3- Do a 'ringout" before the show.
4-Use a sub group for the mics.
I wish I could affored a couple of e6's...
I also have some mic splitters which I used for a small concert. maybe I'll try that route also.
If all that wasn't enough, I wa also running a 4th camera on sticks right next to my board. Talk about insane multi tasking.....
Bruce S. Yarock

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