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Feedback with mics on a thrust

Discussion in 'Sound, Music, and Intercom' started by solution95, Feb 28, 2007.

  1. solution95

    solution95 Member

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    Hello all, my name is Garth and I am a new member and a sound beginner. I am a volunteer at 2 high schools in MD and do well with lighting, but on sound I know just enough to be dangerous.

    The school is doing My Fair Lady with a 14' thrust beyond the normal stage position. There is a pod of 3 center speakers and 8 small side speakers along the walls (4 per side).

    Whenever the students walk out onto the thrust with in 20' of the speakers on the audience side, we get a lot of feedback. We are using Shure lavalier mics.

    Any suggestions to make the feedback stop?

    Thank you.
     
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    Don't use the center cluster. Front fills make a huge difference when using a thrust as well as moving speakers to the extremes of the space. A good rule of thumb is if you have your mains behind your microphones, your going to have issues.
     
    wolfman005 likes this.
  3. jkowtko

    jkowtko Active Member

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    My theater is currently running with the center cluster 6-7 feet behind the front edge of the stage area (bowed stage front), and currently I'm right on the edge of feedback, walking on eggshells every show. There are mounting issues that prevent me from moving them forward right now. So some things I did that allowed me to control the feedback reasonably well:

    1) keep the center cluster on its own volume control. I run my soundboard using the sub outs so I can keep the fronts, rears, and center cluster all on separate controls. If I sense feedback coming and/or the actors step forward, I can pull down the centers 5-10db, enough to squash the problem momentarily.

    2) I don't have an EQ set up yet, but when I do I'm sure I will be able to get some more volume out relative to what I can do now. I am also considering a feedback suppressor. Although they appear to be 'giving in' in the general sound community, a good one like the DBX AFS 224 might provide good notch filtering when needed to deal with these issues. I will try EQ first, then AFS if the EQ doesn't do it.

    3) The speakers themselves can make a huge difference. Our first attempt at a center cluster was a pair of Kustom 100s. They were pathetic ... sound bled everywhere, you pretty much got feedback when you turned them up at all, no matter where the actors were. Replacing them with the Mackie SRM450s made a huge, huge difference. The Mackies control the sound projection pretty well -- so you get lots of sound out towards the audience, and little back into the mics. I'm sure there are plenty of other speakers out there that will do well in this area, so speaker choice may be as critical as placement.

    4) The mics and mike settings can make a difference. Turn your wireless transmitter gain down as much as you can ... I found that with my cheaper lavs when the gain was turned up to high the volume got "spikey" which made it more prone to feedback. Of course, Good mics will be better at this than cheap mikes. But they may have to be really good. Our AKG C417s are not cheap mikes, but they don't do nearly as good a job as our Countryman B3s.

    5) The actors themselves will make a difference. Actors with loud voices require less gain on the equipment, and in turn less feedback. For actors with soft voices, my only suggestion is have them mount the mics closer to the mouse. I use over-the-ear-with-tape mounting which sets up the mic head like a bluetooth headset, and the mic head can be placed anywhere from sideburn position to almost at the corner of the mouth. I would worry less about how it looks then how it sounds.

    Those are my suggestions based on first year doing sound. Let me know if you find any of this to be helpful.

    Thanks. John
     

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