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Feedback suppression for a High School Theater

akagarwal

Hi,
I am new to live sound and have tried to learn a bunch of stuff in the last few days since I have started helping out the theater department in my kid's high school. I have a questions regarding feedback suppression. They perform plays in a closed room with a fairly small stage - 20' x 20' with stadium style seating on three sides (about 12 rows) for a total of 165 seats - just to give you an idea about the size. The sound booth is located behind the last row in a small closed room (soundproof) with a clear sight to the stage through a glass windows and this is where all the sound equipment and monitors are located. They have 16 lavalier mics connected to an Allen & Heath MixWizard 3 (16:2) mixer using a Sennheiser Evolution wireless G2 Series 100 system. The mixer also has a stereo feed from an iPad for adding music to the mix. The output is feeding 2 QSC 1450 amplifiers running in parallel mode that feed 4 Peavey SP 2G speakers one in each corner of the stage. There are no stage monitors. The only monitors are in the sound booth allowing sound and light techs to hear the sounds.
So basically, there can potentially be 16 actors running around the stage with lavalier mics either acting or singing for musicals mixing with music from the iPad and we have a feedback problem from time to time that spoils the experience for the audience. Based on a recommendation from a Pro sound shop, I bought a DBX 1200 Series equalizer to notch the feedback frequencies and while I can try to ring out the system using an RTA, unfortunately there is no sound engineer available and the sound systems is operated by tech theater students who are pretty low tech and deal primarily with the mixer in order to adjust the volumes of various actors.
So, I am reconsidering my decision because I am afraid it would be too much for the theater tech students to deal with the equalizer when feedback frequencies change due to the audience makeup and temperature changes etc. I just saw another product called DBX AFS-224 which is supposed to do this automatically. I have not purchased it yet and wanted to get an expert opinion on the best product to use for our type of need.
Thanks in advance for your help.
AK
March 21, 2013 @02:06am
TimmyP1955

I've not used the Shure, but my experience with other "Feedback Eliminators" is that they are very slow to "latch on to" feedback - so that by the time the feedback is gone, everyone in the room is already shaken or perturbed. Feedback needs to be taken care of during rehearsals.
If you use an "FE", the way to go is to set it so the filters lock once they have set themselves.
March 26, 2013 @01:34am
akagarwal

I've not used the Shure, but my experience with other "Feedback Eliminators" is that they are very slow to "latch on to" feedback - so that by the time the feedback is gone, everyone in the room is already shaken or perturbed. Feedback needs to be taken care of during rehearsals.
If you use an "FE", the way to go is to set it so the filters lock once they have set themselves.

Thanks Timmy. The DBX AFS 224 has 24 filters and they can be split between fixed and live filters. The instructions recommend using 12 of them as fixed filters for permanently notching feedback frequencies and ringing them out during rehearsals and leaving the remaining 12 as live filters where they can be set to notch feedback frequencies for a specified time limit. It seems like a reasonable setup and I will give it a shot to see how well it works.
March 26, 2013 @05:32am
yeahforbes

I would also recommend setting all of them to Fixed. Having some in Live mode seems good in theory, but in practice you may experience many false positives. In other words, they may mistake non-feedback for feedback, and set the filter. I've had it happen with sine-like synthesizer patches, guitar solos, and even a straight tone (non-vibrato) singer. It's not the worst thing in the world though -- you just end up with the "missing fundamental" effect.
But like you say, the seats are not filled during rehearsal. Regardless, I would do all Fixed during rehearsal.
April 11, 2013 @05:58pm