Properly Using an Equalizer for Live Sound Application
Upper bass frequencies are usually between 175 -500 Hz. Low-mid frequencies become apparent after 500 Hz, then upper-mid frequencies are around 900 Hz. After 1000Hz, mid-range takes over from there. In order to distinguish these frequencies between each other can, and always be a learning experience. These frequencies make up most of the body of all reproduced musical sounds, not including the very lows and the very highs. These aformentioned frequencies must be managed through equalization meticulously and accurately in order to achieve a mid-band frequency balance. Each adjoining filter directly affects the one next to it. The type of E.Q. used for this application is called a 31-band graphic with +/- filters adjustable between 20Hz and 20khz.
To adjust the graphic at the front-of-house, play a favorite CD through the stereo bus output making sure that the graphic is set at 0dB/flat or unity gain. If you’re playing the CD through a couple of input channel strips, make sure the faders are at 0dB and the E.Q buttons are not engaged and the input pre-amps L.E.D’s measure +/- 3dB so as not to overload the signal path.
First, slowly turn up the CD. You will start to hear the characteristics of the room, also known as resonances. The louder you turn it up, the more of the room’s acoustic tone will cloud around the sound of the played-back music. When you get to the volume equivalent of a typical “live” performance, it should sound real boomy, harsh and unintelligible.
Second, always start attenuating or, cutting the higher frequencies first, working slowly to the lower ones. After you’ve completed your “tweak” to eliminate the harshness and the boominess, you’ll notice that the mids are the least cut and the upper-bass and low-mids are the most cut. This is due to compensating for an ill acoustic environment the soundsystem is operating in. Low-mids and mids are cut less because their wavelengths are faster and shorter. Lower and upper-bass waves are longer and can create a boomy or resonant quality, depending on the size and shape of the room and usually be attenuated the most… That is basically one way to tune a room. There are many other ways that are more technically oriented.
For instance, using your own voice at the front-of-house; using a pink-noise generator/real-time-analyzer; or using a software/computer program designed to measure acoustics and soundsystem anomalies like SMAART, CORREQT,MLSSA and several others.
For now, practice “tweaking” your system with a 31-band with a CD. Later on down the line you can try the vocal-room-tune method. As you get better and better, try the more technically comprehensive methods. You’ll be glad you did!