Equalizing a Church with The Feedback Method

Written by Joseph De Buglio

Warning, this method of EQ'ing is not meant to be a substitute to having it done professionally. This method will not tell you if the speakers are out of phase, misaligned, damaged or out of the sweetspot. This is meant for central clusters, but does have limited success with L/R system too. If your speaker system meets the HIS System Standard or exceed it, then this method will get you within 5 to 10% of what it would be like had it been done with a computer. In my books, that's very good.
So, when do you need to use this method? There are times when changes are needed. Churches without climate controls may need a seasonal change or changes during a worship service.
If you have a new church, the main house EQ will need to be changed 2 to 4 times in the first year and one major change up to 5 years as the building dries out from the construction phase.
If you don't have air conditioning, you might need house EQ changes because of temperature and humidity changes during congregational singing. The room can change so much that the system can go into feedback without the soundman doing anything. Therefore, you will have to make house EQ changes on the fly as many mixer EQ may make too much of a change if you change the inputs.
Sometimes a person breaks into the system and takes the security cover off and puts on the smile curve for a special concert(thinking that it will sound better!!). For whatever the reason, this is a good method of eq'ing a system when you don't have any tools, but you need to make changes.

Getting Started

The purpose of EQing a church is to the match the performance of the speaker system, microphones and room into a a balanced compromise of gain before feedback, sonic performance and overall SPL..

It is a device used to compensate to some degree the errors in the sound system design, errors in the speakers and microphones being used and the interaction of both elements on each other. (Since there is no such thing as a perfect speaker, all speakers have some kind of error or another. This doesn't mean the speaker doesn't sound good, it is the fact that any error in a speaker, once interacting with a room, can show up as a problem.)

Feedback is the re-generated noise that is inherited in all pieces of electronics. It s the noise from the Microphone, mixer, EQ, and amplifier in the audio chain. Usually feedback starts off as being electronic noise. Then as you filter out the electronics, then it become the reaction of the room imposing itself onto the sound system.

A very good method for EQ'ing a room is by using the FEEDBACK Method. When you don't have an FFT analyzer to separate the frequency response of the room and the speaker system as a separate measurements and then seeing the combined measurement, the feedback method is the next best thing.

In a HIS Systems, it is assumed that you are using a central cluster or a Left/Center/Right Cluster system. It also accounts that you have accounted for acoustical errors in the room and already have proper speaker/speaker system alignment. Under these conditions, this method works great. For other systems types, you will have to modify this method with trial and error. However, it is most often, an excellent way to start EQ'ing a room.

Many suggest a method by which you go around the seating area, take measurement and adjust the EQ to a flat setting. I have tried this method. I have also ran pink noise and set the graph with the EQ for a flat setting. Then, when you stand at the pulpit and talk, the sound can be muddy or just awful. Part of the difficulty with either method is the room. It is a fact that most churches have acoustical problems. Some problems are on the stage, other problems are in the seating area as well. When placing the test mic in the audience area, the room can change the response greatly when you move the mic only a few feet away.

The 11 Steps

  • 1: First, start by simply placing a mic at center stage or at a center pulpit. Point the microphone straight back to where a person would be standing to give a sermon or back wall. Pointing the mic the other way doesn't work very well.
  • 2: Next use a Dynamic mic with a Cardioid pattern. - The old Shure SM58 is ideal for this. (From many tests, a Dynamic mic works better than a Condenser mic with the feedback method. If you EQ with a condenser mic, it is less forgiving(Sorry, but I don't have a better word to describe this) and switching to another brand of condenser mics for speaking later can actually sound worse. With a Dynamic mic, it is more forgiving when EQ'ing such as the old Shure SM58. The results tend to be usually better, even when using other brands of microphones afterwards.)
  • 3: On the mixer, set all of the channel EQ settings to flat for the mic on the pulpit or center stage on a stand. It is best to use a tripod base mic stand. If you use a solid bass stand, sound energy from the platform can travel up the base and shaft of the mic stand.
  • 4: Set you main house EQ to Center position. (Hopefully you have already set your gain controls for the EQ, comp/limiter and amplifiers.) (Also, bybass your comp/limiters, feedback destroyers and any other processors. You want a clean signal)
  • 5: Set the input mixer gain to off. Set the channel fader to 0dB or -10dB (This depends on the markings of the mixer.) On the main out - set the fader to -10 or 0dB (This again depends on the markings of the mixer.)
  • 6: Raise the input gain until the sound system begins to ring. Turn the gain down until the ringing stops. Now start using the channel fader to make the system ring again. It should start to ring slowly. You should be able to get an almost steady signal of a tone at a low level.
  • 7: If you have a RTA, you will see which frequency is ringing. You can also use a Multimeter with Frequency. You can get one for about $200.00 or less. I like to plug the meter into the headset out and use the PFL output for a signal. The meter will give you a digital reading, which is more accurate than an RTA.
  • 8: Start by ducking the ringing frequency down -3dB. That should cut the ringing out. If you don't have an analyzer, use the trial and error method to seek the ringing frequency. 9: Once the system is stable again, raise the fader again.
  • 10: Repeat this routine until you either hear several frequencies rise up at once or when a frequency hit -12 or 15dB. (In theory, you shouldn't need to EQ more than -6dB, but since most churches have acoustical problems, you will often find that you need to EQ at least one filter this much.)
  • 11: If you are hitting the bottom of the EQ before you hear a chorus of ringing, this is a sure indication of a room problem, a system design problem or you have only a 1/2 octave or Octave EQ.

While this is not a perfect system, it can provide excellent results if your system is designed right and the room behaves well when you don't have a tool like a TEF, MLSSA or Smartt Pro. EQ'ing is always cut only. If you have one of these tools, only then can you confidently considering boosting a frequency signal if there are serious room problems like excessive bass absorption or if speakers are misaligned and you don't have the chance to rearrange the speaker system today.

Some may suggest using Pink Noise generated through the system and EQ'ing base on that alone. Some people use this method as though it does not consider the room and it only corrects speaker flaws. This is not the case. Unless the mic is within 3 feet of the speakers, you are actually measuring the room and the speaker combined - most likely more room when greater that 30 feet from the speaker. EQ'ing for a flat response of a speaker in room can sound great. However, The same speaker in room "B" set to flat may sound terrible. When using the feedback method in room "B", it should sound as good as in room "A" - less the difference of the room or system design.

Some have suggested to Pink noise first with the test mic as close to the speaker system as possible, then use the feedback method. Tests have shown that you are more like to have so much EQ'ing that you give up a lot of system gain and overall tone is not much better. In some cases it was worse - - especially when several different mics were active.

I am sure that others can explain this better, but since many are asking, this is what I do for church sound. In a Typical HIS System, the feedback method works remarkably well when you don't have proper measurement testing tools.

By Joseph De Buglio.

Here now is simple RTA program than any PC with a soundcard can use. There are many settings to try. It is a great tool for using the feedback method. Downlad this freeware - - RTA program.

We hope you will visit us often as this site grows. This web site is for you - people wanting guidance and real help with their church sound problems. All recommendation presented here have been tested in churches. We will be posting general audio and acoustical information that is "common knowledge" but hard to find - especially for people in small towns and communities.

Thank you. Joe The Soundman.

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Copyright (c) 1996 - 2002 JdB Sound, Acoustic
Last updated, Sunday, June 09, 2002, April 2008

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