Photo courtesy of Shure
Not everyone has access to expensive (or even inexpensive) spectrum analyzers. Sometimes, all we have available is our ears...just like in the old days. As long as you have a sweepable parametric equalizer on the pastor's channel, or an outboard parametric if you don't, you can accomplish a lot just by knowing what to do. Oh yes, you'll need a victim, sorry, I mean a volunteer, to help out. Choose someone who is roughly the size and shape of the pastor, and have him wear clothing that is similar to that which the pastor wears when preaching. This will keep the acoustic anomalies to a minimum.
Make sure this volunteer has a good set of earplugs, the kind used in machine shops. Next, make sure they have been installed in his ears properly. Finally, warn him/her that there will be much squealing, howling feedback, and that you might need the volunteer's help for about an hour. He'll mostly be standing, not speaking.
“Dress” the volunteer with the pastor's mic, as close to the way the pastor wears it as possible. Then have the volunteer stand on stage where the pastor spends the bulk of his time. The process becomes more difficult if the pastor moves a lot, but not insurmountable.
Start with a flat EQ on the pastor's channel. Next, dial-in a 100 Hz high-pass filter. This could be moved as high as 125 Hz, but it will start to thin his/her voice, the higher it is set. The purpose is to reduce VLF (Very Low Frequency) feedback from the sound system (especially if there are subwoofers that receive the overall console output), but it also helps in keeping stage rumble down to a minimum. If the high-pass has an adjustable slope, use 12 dB/octave or higher. 24 dB/octave would be ideal.
Now comes the ‘fun' part. Raise the channel gain until you start to hear a slight bit of feedback. If you have a compressor/limiter on the channel, or in an outboard device, it will help greatly to keep feedback from running away and howling like a Halloween banshee. Spend a few minutes getting the ratio, input level, and output level adjusted so that the feedback sounds like a continual organ note. Don't worry too much about attack and decay settings; at this point you want the limiter to perform an “off-sheet” function, which is clamping the feedback so you can still hear it, but not letting it burst into a squeal.
Important: if the pastor uses in–ear monitors, make sure to defeat them entirely, as well as all other stage monitors.
What next?
This is where the rubber meets the road (or in this case, the output transducers meet the microphone). Make sure the entire PA system is on and set to its normal operating levels. Now, you'll need to turn up the channel level until you hear a squeal. If the tones you're hearing are what is called multi-tone, that is many tones across the spectrum, you may not be able to do much. It may be that the house system has already been EQ'd to be flat in relation to the pastor's mic. Or it might be good luck. Still, there must be at least one frequency that stands out.
Stay as far away from graphic equalizers as you can. They do not perform as they look.
The easiest way to find this frequency is to set the “Q” on the parametric quite narrow; about 1/3rd to 1/6th octave is a good starting point. Now you want to boost that parametric band by about 3 to 6 dB, and sweep it up and down, very slowly, until you find the point where it exaggerates the feedback. Then, (of course!) change the boost to a cut at the same frequency. Try narrowing the ‘Q' to the minimal point that will diminish the feedback.
Ask the volunteer to move around a bit. If a very narrow Q solves the problem, widen it slightly because temperature and humidity changes, as well as the presence or absence of the congregants will also change the room's resonant properties. And that's precisely what you are correcting for: room resonance and system anomalies.
A good rule of thumb is to set the Q to about 1/3rd octave. This is important though, you cannot duplicate the same results by using a third-octave equalizer. While the Q on the parametric may be about 1/3rd octave, which is a pretty common outcome, the band center will most likely be well off the standard ISO 1/3-octave band centers. This is the one thing that most 1/3rd-octave product designers and practitioners just don't understand. A few Hz to one side of the band center or the other makes all the difference, especially n the lower frequencies.
Upward Mobility
After you've solved that first (and usually most offensive) feedback point, work your way upward and ‘chase out' the remaining feedback points. It's always easiest to work from low to high, but that's not written in stone. If the higher frequencies are those that are giving you the most trouble, you may want to address them first. In all likelihood, you'll run out of parametric bands before you chase out all the offending feedback points.
You might consider an outboard EQ, or looping the pastor's mic back into another channel to pick up another four bands...or whatever the console offers. Or, you may have to live with the incremental improvement that you've made and as for more gear at an appropriate time.
Monitors
After you've dialed-out the most offensive feedback points from the house system (the “mains” as some like to call them), it's time to look at the monitors. Bring the pastor's monitor level up to where it normally lives, then carefully test to see if some of the monitor feedback issues have been solved by what you've corrected in the house system. It may be that you have, or it may not; it depends on the nature of the cause.
If you're fighting stage monitor feedback, it is often unrelated to house feedback. In such a case, one great trick is to parallel the pastor's mic into an open channel and use that channel to feed the monitors. By repeating the process described above, you can chase out the major feedback points from the monitors, just as you did with the house system. If there are simply not enough EQ points available, then it's time to look at an outboard parametric.
Graphics
Stay as far away from graphic equalizers as you can. They do not perform as they look. This subject will be addressed in another article in the near future.
Results
In addition to eliminating feedback points, the by-product is a greatly improved and far more natural tonality on the pastor's mic. This process can be repeated for all the mics on stage, whether instrumental or vocal, if you have the time and inclination. If you don't, try to find the time. That is your commission to help the word be spread as far and wide as possible.
Last Words
If it seems that you need a 12 dB or even a 15 dB cut at a given frequency to solve feedback and improve tonality, do not hesitate. Far too many sound engineers feel that only a touch of EQ is acceptable; they don't want to “chop up” the spectrum, especially if their latest ‘mentor' (usually from a studio) told them to avoid this. Categorically, this viewpoint is not true. Most studio engineers are working in a very flat room that probably has been expertly EQ'd when the room was commissioned. Not necessarily so with a worship center. Using enough EQ to actually make an improvement is the purpose of the exercise, and indeed the point of this article. Hey! You can always go back to flat, when you wish to see if the changes you made are improvements, or just changes. With perseverance, you can improve the sound and learn a lot in the process of doing so.
