Dealing with feedback
Question:
Jeff, I have been having trouble with achieving a good quality sound from our lavaliere systems, both ear set and chest clipped. I am not new to ringing out problem frequencies, but the problems are coming from across the entire band and there are many of them. We are using four downstage EAW micro wedge (the older versions) as our monitoring and I don’t get a loud enough volume through them before they feedback. We had a special guest speaker last week and his volume just wasn’t loud enough, but there was no way to achieve a louder volume without feedback. I would try placing the monitors in a different location, but the microphones are Omni so this wont help much. I’ve tried using a graphic EQ inserted on the channel and I am still having to use the parametric to do more surgical work instead of being able to use it to shape the butchered sound musically. Every time I complain about the volume level, I am told by my boss that the volume is fine, and it’s not. I get complaints from the lead and worship pastor about this nearly every week and I am running out of ideas. What do you think about this? Also, I heard that it is not good to use compression on lavaliere type of mics because they contribute to these specified problems. Is there any truth to this? I am using a compressor, but I am only compressing 3:1 at an average of 2-5db(max) gain reduction. Oh, and of course I’ve tried flipping the phase. Right now i have gone with using just the onboard parametric EQ and bypassing the graphic. I get a decent sound, but i need about 5db more headroom onstage and out front. Do you have any ideas?
Answer:
Tough job~
– loud environments (like having to provide foldback through stage wedges) almost always will require a direction mic. The Omni-direction sound better and are much less sensitive to exact placement and aiming, so I prefer to use them, but when you add wedges, when you add instruments or other sounds around the speaker / singer – then you are going to have much better results with direction mics.
– Remember the science – the closer to the source the less gain required. Also, the less of the sound from the mic returning to the mic, the more gain before feedback available. Use the pickup pattern of the mics, the polar patern of the speakers and watch for reflections (off the pulpit or other large surfaces–stage??). You can get 3db more gain by decreasing by half the distance between the mic and the mouth (6db with a directional mic).
– Once you get to the point where multiple frequencies are ringing at the same point (broadband), there is not much more you can do electronically. I usally call it quits at 6-8 specific notch filters (for any one mic / system).
– Compressors can cause problems if not used carefully. You have to be careful the input is stable at the gain setpoint with the compressor wide open – then you can use the compressor on top of that to pull down or “level” loud voices / yelling / etc. The problem often occurs in dialing in the compressor and gain while the input is under compression, then when it get quiet, the compressor opens up, adding an additional 3-9db gain to the channel, and it starts to ring.
– Gates (downward expander really) can help also, by dropping the gain of the channel 3 or 6 db when it is quiet, keeping a system that is on the edge from building up the ring.
– Quality equipment – obviously the higher quality of components, the better results you will get with all of this. One of the things you get with better equipment is smoother frequency responses and better / cleaner off axis rejection / pattern control / noise immunity. These properties can all help improve your gain to feedback ratios.
Hopefully that is helpful. No real magic bullet, just applying science and art carefully. Let me know if you need help brainstorming any other ideas for solutions or answering questions.
