Tuning the Room (and your ears)
Date: February 14, 2014
When setting up for the concert, we are often faced with trying to set up microphones and a sound system as well as the risers or stage. You flip the switch on the board, and either the high squeal or low rumble of feedback fills the room. What is wrong? Often, whether due to time constraints or sheer panic, we'll turn to a basic but crude solution: turn down the master volume until there's no feedback. This often works, but can make it hard to get the volume you need out of the sound system without inviting the return of those horrible feedback sounds. Sound Engineers train their ears to identify individual frequencies which can be reduced in order to prevent feedback without having to reduce the entire package. While it's a skill that takes great training to hone, there are some basic things that we can use to give us a couple of tools in our toolbox for the next time we set up a show.
Don't Get EQ-te
EQ is short for "equalization," and it refers to the process of balancing and shaping individual frequencies to create the sound that you desire. On a sound board, it often takes two forms: first, you may find knobs on your board for each individual channel with refer to "high," "medium," or "low." These are wide brushes to tweak the individual microphones that you have running through those channels. Second, you will often find something called a graphic equalizer, which is a series of sliders to affect a much more specific frequency for the entire board. When working with the human voice in an ensemble, many live sound engineers will often apply just a touch of boost to the higher frequencies in order to capture the particular resonance of a choir.
Feedback is, in very broad terms, when enough energy travels from the speakers back to the microphone and creates a loop which amplifies itself and creates what may be one of the worst sounds known to human ears. That's why the blanket strategy of turning down the master volume works-- it reduces the amount of energy overall. What's important to realize, though, is that like the voice or any other instrument, feedback has a frequency. Reduce that frequency individually, and you can also eliminate the feedback cycle, while leaving the volume up for your musicians.
Working the Room
Unfortunately, if you take your board to different settings, you can't just dial in a "feedback busting" setting into your EQ and leave it. Each space has a unique design which will amplify certain frequencies, supress others, and create a unique sonic palette which requires your attention. Some rooms are really "bright"-- they amplify the higher frequencies, while some sound "muffled" or "flat"-- these don't reflect a lot of energy in the higher ranges, or require you to really turn up a sound system in order to fill the space with sound. In addition, the amount of reverb in a room plays into the possibility of feedback as well. Each room is different, which is why sound engineers refer to "tuning the room"-- listening to the frequency response of each room in order to shape their graphic equalizer in a way which presents their desired sound.
This is a high art, and the ability to identify individual frequencies by ear alone takes lots of practice. There are a variety of apps for ear training which can help you identify frequencies, and even a little experience of listening to frequency spikes and deficits pays dividends in tuning a board in a new setting. Quiztones (iOS or Android, $4.99) does just what you'd think-- it gives you quizzes about audio which challenge you to identify individual frequencies.
Without having to go that level of detail, there's always the trial-by-fire method: next time you get feedback on your board, don't reach for the master volume. Reach instead for your equalizer. If the feedback sounds particularly high, start turning down high frequency channels. If it is more of a low rumble, turn down low frequencies. Remember that both speakers and the human psyche are particuarly vulnerable to the sounds produced by feedback, though, so don't plan on spending a lot of time experimenting right before your concert!