Unlike your studio or rehearsal space, where you have complete control of how your band sounds, when you play at a club (especially a small financially challenged club), there's no telling what you'll end up sounding like. The room might have poor acoustics, and the club's sound system may be in need of a major tune-up. Even setting up your own P.A. will not automatically compensate for a poorly tuned room; frequencies that sound louder than others (called resonant frequencies) or a general lack of clarity will still be part of the environment. Fortunately, with a good EQ unit and some knowledge about how to apply EQ to enhance your live sound, you'll have a much higher degree of control of the sound quality of your show, regardless of your environment.
EQ comes in four basic categories: fixed, sweepable, parametric and graphic. And within these categories are two basic types of EQ curves: shelving and peaking (also called a bell curve). Shelving allows all of the frequencies above (high shelving) or below (low shelving) a selected frequency point to be cut or boosted. Peaking has a center frequency point around which frequencies can be cut or boosted, and the width of the frequency range around the peak is called the Q (the open end of the bell).
Fixed EQ is the simplest because the frequency is fixed, but the gain (cut or boost) can be adjusted. Sweepable is sometimes called semiparametric because, even though its frequency can be adjusted within a set range (for example, 400 Hz to 6 kHz), the Q is fixed. Sweepable and fixed EQ bands are often paired together, with the high and low bands being the fixed shelving type and the midrange of the sweepable peaking type. This setup is commonly found on both P.A. and DJ mixers. Although fixed and sweepable EQ can be used to improve the overall sound of a system, much more precise control can be achieved with parametric and graphic EQ.
Parametric EQ has three controls per band: frequency, gain and Q. With the ability to adjust the Q comes exact control of specific frequencies. For example, if the club has an unnatural bump between 80 and 120 Hz, you can dial up the midway point, 100 Hz, and then adjust the width of the Q to catch exactly those frequencies you want to attenuate (to reduce but not cut completely). Comprehensive parametric EQ is rarely available on a standard DJ mixer (an exception being the Tascam X-9) or a budget P.A. system. Consequently, parametric EQ generally takes the form of a one- or two-space rack unit. These units (like the PreSonus EQ3B) are not only popular in recording studios but also effective for live applications.
Graphic EQ is a series of fixed bands spread out across the audible frequency range (20 Hz to 20 kHz). Common spacing for the bands is every octave, half-octave or one-third octave. For each band, a fader controls the frequency's cut or boost. The Q for each band is fixed (a downside to graphic EQ), and some units have bands at either end of the frequency range that are of the fixed shelving type. To really fine-tune a system's sound, you need a stand-alone unit with at least two dozen bands (such as the dbx iEQ-31 Dual 31-Band Graphic EQ/Limiter). Graphic-EQ units are extremely popular for live sound because their controls are a quick study: no fiddling with variable Q and frequency knobs. Plus, once the faders have been adjusted, the positions of the faders themselves paint a good picture of your EQ curve.
If the EQ is built into your mixer, there's nothing to hook up. But if your EQ device is a stand-alone unit, then it needs to be integrated into your system. An external EQ device should be connected between your mixer and the amps or, when necessary, the club's house mixer. Using balanced XLR connections, the main stereo outputs of your mixer should run directly into the EQ. Furthermore, the outputs of the EQ unit should be balanced XLR (or, in a pinch, balanced ¼-inch). The balanced connections will help to ensure that the signal is not degraded by the extra stage in your output chain.
It's a good idea to hook up your EQ unit ahead of time. Mount it in the same rack as your mixer, and connect the two devices using short XLR cables (about 12 inches). Have a pair of long XLR cables (such as 50 feet) connected to the EQ unit's outputs. This will make it a breeze to set up. Simply take the XLR cables from the EQ's outputs and plug them straight into the club's main power amp (make sure the amp is off first). If you often find yourself wanting to improve the sound of your stage or booth monitors, a similar system can be assembled by running the stereo output of your monitor mix through an external EQ device.
EARBALL YOUR ENVIRONMENT
Tuning a room for world-class sound is performed with complicated test equipment, from acoustics-modeling programs to multiband noise and frequency generators. Because it's impossible to lug around this type of equipment to all of your gigs, you'll need to learn how to listen to a room and “earball” its basic acoustic properties. The best way to do this is to play some simple tones (such as bass and piano) across the frequency range, as well as snippets of your music at performance levels. Stand where the audience will be and carefully listen for resonant frequencies and tones that are disappearing, or being absorbed. Identify the general frequency ranges in which these problems are occurring: low (bass drum, bass-guitar low notes), low-mid (toms, bass-guitar high notes), mid (male voice, guitar low notes), high-mid (female voice, guitar high notes), high (drum cymbals, hi-hats).
Once you've pinpointed the general frequency ranges that are a problem, you can turn to your EQ and dial in exactly those frequencies that need help. A trick for finding the frequency that you're hearing is to turn the gain on a peaking EQ band all the way up. Then, sweep the frequencies until the tone you're looking for pops out. Once you've identified the frequency, cut or boost accordingly.