Feedback and Monitors

Stevens R. Miller

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Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
Now, I tried to look this up by searching on "feedback" in thread titles, so I wouldn't reanimate dead threads, but there were so many that I am going to ask forgiveness ahead of time, as I start a new one.

I'm helping with lights and sound in our middle school production of "Aladdin Jr." We're getting some feedback during performances. Our set up includes the following:

  • Soundcraft GB2 audio mixer, into which all sources run.
  • Eight Audio Technica 2000 series wireless mikes with ATW-T210 body-packs.
  • Seven Audio Technica 3000 series wireless mikes with ATW-T310 body-packs.
  • Three "choir" microphones hung above stage right, center stage, and stage left.
  • Four floor microphones set on the first row of audience seating (roped off).
  • Two floor-standing house speakers set far apart just off the lip of the stage.
  • One center cluster of house speakers, hung at the ceiling, just in front of the proscenium.
  • Two on-stage monitors, facing up stage, on the lip, at stage left and stage right.

We tend to get feedback when someone with a wireless mike gets close to one of the monitors, or when that person stands directly under the center cluster.

The GB2 has a Group 1-2 bus, a Group 3-4 bus, and a Mix bus, all with their own outputs. We have the stage left house speaker on the Group 4 output, the stage right house speaker on the Group 3 output, and the center cluster on the Group 1 output. The monitors are on the Mix output, daisy chained together.

Does it make any sense to assign the microphones to Groups 1-2, and 3-4, but not the Mix bus, so they don't play out of the monitors (leaving them playing only the musical tracks)? Would this defeat their purpose? Any other ideas?

We're pretty sure the feedback is through the monitors, though we haven't had an opportunity to run controlled tests. A big source of frustration in this production is due to the fact that my tech crew and I get very limited amounts of time to use the equipment on our own. It's either off-limits (because the school day is in progress, and we can't be disturbing nearby classes), or rehearsal is in progress.

Any help would be gratefully accepted.

(Also, can anyone tell me what the "Matrix" bus in the GB2 is for? It doesn't have a master slider, just some knobs in inconvenient locations.)
 

jkowtko

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Joined
Jan 9, 2007
Location
Redwood City, CA
Matrix is generally just one additional layer of mixing, that uses the groups and main mix as the "input channels". This is often used when you are doing very different things with the main mix and/or groups, and you need a final output that encompasses all of them. It can also be used jsut to provide additional outputs. I have seen control room, lobby, sub, and center speakers use matrix outputs.

Center clusters that are hung in existing auditoriums tend to be terrible on feedback. The speakers are hung sideways so that the dispersion pattern is incorrect, and mostly are useful as lecture speakers. I tend to turn the center cluster down to fill level only, or off completely.

Two things that will affect feedback in general signficantly are:
* mic element placement -- forehead mount will generally be less prone to feedback than cheek/ear mount.
* EQ of input channels. Pulling down the mids and lows for each actor tends to help me.

Unforunately you are running an analog board ... if you had a digital board you could use the PEQ on the monitor output channels to tweak them for feedback. The monitor's don't have to sound great so it doesn't matter if you butcher the sound, only that the actors can hear them. If you have GEQ that you can devote to the monitor channels, that should help.

Regarding your use of groups -- I've generally used aux for center cluster, sub, and monitors. Aux gives you volume control of each channel feeding into the aux. This might help you as well.

-- John
 

Footer

Senior Team
Senior Team
Premium Member
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Nov 24, 2005
Location
Saratoga Springs, NY
Take the mics out of the monitors. Only run tracks to the monitors. If you must put the mics through the wedges put a graphic EQ in line and notch out the feedback frequencies as close as you can.

Second, move your monitors over to an Aux Send so you have some control over what goes there and at what level. If you have to put the mics in the wedges, keep it as low as you can. Omnidirectional mics+monitors=bad day.
 

Stevens R. Miller

Well-Known Member
Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
Matrix is generally just one additional layer of mixing, that uses the groups and main mix as the "input channels". This is often used when you are doing very different things with the main mix and/or groups, and you need a final output that encompasses all of them. It can also be used jsut to provide additional outputs. I have seen control room, lobby, sub, and center speakers use matrix outputs.
Thanks! The Group/Mix concept seemed fairly self-explanatory, but the GB2's (rather abbreviated, imho) user's guide doesn't address Matrix.

Two things that will affect feedback in general signficantly are:
* mic element placement -- forehead mount will generally be less prone to feedback than cheek/ear mount.
* EQ of input channels. Pulling down the mids and lows for each actor tends to help me.
I can trim down the voices as you suggest, particularly since most of my actors still have their children voices (that is, they are all still pretty much tenors and sopranos, rather than basses and altos). so cutting out the lows won't make much difference.

Now I have to ask this: what's a "forehead mount" look like? I am guessing we are using cheek/ear mount (since that matches where we've attached and taped the boom). Is there another option?

Regarding your use of groups -- I've generally used aux for center cluster, sub, and monitors. Aux gives you volume control of each channel feeding into the aux. This might help you as well.
I'd like to try that. I'm the new guy in this particular community. A long-time predecessor has become this school's regular sound consultant and he set up the whole rig the way it is. He hasn't been able to do the shows or rehearsals, so that's where I come in. In all humility, I will say I know a pretty fair amount about electronics, but I have no prior experience with mixers, theater, or the equipment we're using. I'm learning as fast as I can, and, even though my colleague clearly means well, I do see signs that he's not quite the expert I had originally hoped he'd be. However, he was there first and has done a lot of truly helpful work, so I think I'd be out of line to suddenly step in and start changing everything. If I can find a diplomatic way to suggest we re-route from the auxiliary senders, I'll do it. I very much like the idea of being able to mix the tracks differently into the monitors from how we mix them into the house speakers.
 

Stevens R. Miller

Well-Known Member
Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
...move your monitors over to an Aux Send so you have some control over what goes there and at what level. If you have to put the mics in the wedges, keep it as low as you can. Omnidirectional mics+monitors=bad day.
Yes, I see the appeal of this arrangement. See above for my comments on the social issue that complicates things for me, a bit.

Thanks for the good advice!
 

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