Reply To: Ringing Out The Room – Channel or Overall PEQ?

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DoctorG
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This is a complex issue because so many factors must be considered and so many variables are involved. It requires a basic knowledge of the sound characteristics of the mics, instruments, and speakers involved as well as room acoustics and a feel for sound frequencies. One also needs to know the capabilities of the mixer and its associated outboard units in order to know how best to attack the problem. For example, do you have a measurement mic, and can you view an RTA graph for the main, monitors, and channels? What GEQs are available – only outputs or also for channels? With an RTA, it is generally easy to see at what frequency the feedback is occurring, and a GEQ can be used to reduce the offending frequencies. Here are some suggestions (I’m assuming you know the factors that you need to consider with each of these.): Use directional mics as much as possible. For vocal mics, roll off (shelf) lows and highs as much as possible. Condenser mics particularly need such EQ. Don’t ignore proximity effect. Some roll-off of mid bass may be needed to correct for this. For live bands, the biggest feedback problem is the monitors. Be sure the monitors are positioned as far as possible from the mics in use and that the directional characteristics of mics and speakers have been given due consideration. Also roll out as much highs and lows as the musicians will tolerate. Keep monitor volume as low as the musicians will tolerate. Ideally, use In-ear monitors. After the levels have been established for main and monitor speakers, use an RTA and GEQ to smooth the frequency response of the room. Do this for monitors and mains separately, if possible. Be sure to pull down any frequencies that tend to project above the center line of the RTA curve. Use as narrow a Q as possible when setting the GEQ. Next, open each mic and use the RTA to remove as many feedback frequencies as possible, using a GEQ if available, or the PEQ for that channel. Start with as narrow a Q as possible, but widen the Q if several frequencies close together are involved. Don’t remove more signal than is necessary so as not to discolor the sound. Try to avoid any boosting of particular frequencies. Try to get the slider or trim as high as possible with the nomal setting of group and main sliders, but do not set the trim so high that clipping occurs. Leave some headroom there. Do this for each mic, in the places where they will be used. Next, open each combination of mics that will be used at the same time and determine if additional cuts need to be made to either EQ or level. Different vocalists tend to trigger different feedback frequencies, so you may need to re-EQ mics for different vocalists. This obviously is somewhat simplistic, but it should give you the idea of what needs to be done to minimize feedback.