Most sins committed by front of house engineers in church are not even noticed by the congregation. Overbake the electric guitar a bit? Pretty unlikely you’ll hear any complaints. Acoustic guitar a little low in the mix? There will probably be no gripes. You might not even get a second glance for failing to unmute the pastor’s mic for the first few syllables. But if there’s even the tiniest bit of feedback, buckle up, buttercup! Not only does every head in the congregation whip around to glare at you, but it feels like a half dozen white-hot spotlights immediately illuminate you for all the world to see. Okay — I may be exaggerating a little bit, but it kinda feels like that, doesn’t it? I won’t say that it’s appropriate for the congregation to exhibit such lack of grace, but on the other hand, feedback is almost always avoidable. Of course, accidents will happen, but if we’re careful about it we can curtail most of them. Let’s look into how to minimize this indignation-inducing phenomenon.
Some Basics
The cause of feedback is pretty simple… so simple that I’m betting you already have a strong handle on it. But by way of getting us all on the same page and in the same mindset, let’s deconstruct it. A sound emerges from its source — for example the mouth of a vocalist. Then a transducer (a microphone, to be exact) “hears” that sound, and converts its acoustical energy into electrical energy. That electrical signal is amplified to a usable level and passed along through our mixer and other processing, enroute to a power amplifier, which provides enough energy to enable yet another transducer (a loudspeaker) to convert the electrical signal back into acoustical energy (only louder now!). In a perfect world, that’s where it ends, singer sings, system amplifies, congregation hears and everybody’s happy. Unfortunately, however, the aforementioned microphone can also “hear” the output of the loudspeaker. If it can hear it loudly and clearly enough, it will then pass the signal along through the same chain, where it will end up emanating from the loudspeaker once again, which initiates a repeating cycle, and a nasty piercing high frequency shriek (or a low-frequency rumble or a middle frequency howl) may commence.
Thus far, our scenario describes one microphone and one loudspeaker. As you might imagine, the potential for feedback increases substantially if we have many microphones and many loudspeakers (and that is indeed the case for most of us). “But wait,” you say, “I’ve had feedback develop while there’s no sound being produced near any of my microphones!” Indeed, feedback can be instigated without a perceivable source — key word here — “perceivable.” There must be some initial energy in the system that starts the train a-rollin… to “excite the system” is how I believe most physicists would describe this. It could indeed be a sound in our acoustical space, or it could be some weird little snap, crackle, or pop in our electronics, or it could just be gremlins demonstrating chaos theory. We may not be able to perceive that little spark, but it can quickly grow into a mighty flame. Once it starts, it will indeed tend to keep on going. Bottom line — it makes sense to consider feedback for what it really is — a loop. The best way to prevent feedback outright is to reduce the possibility for the loop to start. Note that I used the term “reduce.” In order to ply our trade, we must indeed have microphones and speakers in proximity to one another, so there will always be at least a small possibility for feedback to commence.
Reducing the possibility for the loop to form is the first thing we need to do. Let’s start at the source — the microphone(s). Hopefully it’s pretty self-evident that feedback is more likely to start if microphones are pointed toward speakers. So let’s make sure our mics are NOT pointed toward speakers. This is not difficult with mics that exhibit directional polar pickup patterns — cardioid, supercardioid, hypercardioid, and so on. For this reason, most of the mics on most church platforms will be some variety of cardioid, and with good reason. But what if we need to use an omnidirectional mic on some occasion? If we can’t “point” the mic away from our speakers, distance is our friend. The closer the mic is to the speaker, the more likely feedback will start, so let’s try to keep these two elements physically separated as far apart as possible (and this principle applies even if we’re using directional mics).
In One’s Cups
One other important consideration pertains to the polar patterns our mics exhibit — a proper grip. Handheld vocal mics frequently use a physical phase-cancellation mechanism to achieve directionality, and an improper hand grip on the mic can cover the slots that accomplish this directional focus. In some cases, a cardioid mic can become nearly omnidirectional if it’s “cupped” by the vocalist. Cupping can also substantially alter the frequency response of the mic. We need to train our singers and speakers to hold the mic the right way. Related to that, we need to train vocalists and orators to keep the mic as close as possible to their mouths in order to capture sufficient signal without cranking up mic gain. The higher the gain, the more likely we get feedback. I think of it this way — as we increase input gain, the pickup pattern of a microphone expands in size, causing the mic to “reach out” and hear loudspeakers more “efficiently.” Proper mic technique can enable us to keep input gain low, thus helping reduce feedback potential.
Locating all the mics behind (upstage from) our speakers can also be very helpful — and with the usual exception of low-frequency energy, most of the speakers’ output is somewhat directional and it is preferable to point it away from our mics. We should always try to avoid getting mics in front of speakers. In the case of monitor speakers, this approach becomes a bit more challenging, since monitors are typically in closer proximity to our mics. The typical modern solution to this challenge has been to eliminate monitor speakers altogether and replace them with in-ear monitors. If, however, this solution is not possible, we’ll certainly want to engage in best practices by way of mic and speaker directionality. We also need to consider the output levels of our speakers — the louder they are, the more likely feedback will occur. Hopefully, our musicians and vocalists will be reasonable by way of their requests for monitor SPL. Equalization of monitor speakers can reduce the gain in specific frequency ranges that cause us trouble. This so-called “ringing out” can do wonders.
The Next Step
We’ve addressed ways to reduce the likelihood for feedback by decreasing gain — physically or electrically. We can go one step further, to literally interrupt the feedback loop altogether. The best way is to use the mute button. This is the best anti-feedback measure we’ve got. Think of it this way — our worship musicians finish up and walk off the platform, leaving the pastor to deliver the message. If we don’t mute the no-longer-necessary worship vocal mics, they will continue “listening” to our loudspeakers, potentially initiating feedback. If we mute them, that possibility is completely eliminated. Combine that with the optimum location of speakers and carefully chosen mics, proper mic technique, equalization as necessary, and we can almost completely eradicate the scourge of feedback.
John McJunkin is an adjunct professor at Grand Canyon University
