Unless you are trying to ring out a live room, EQ is highly subjective. If it's your home system, do what you like. A good way to start is to play something you are intimately familiar with that you've already heard on a great system, and tweak to that. The "smile" works for many people because it boosts the higher and lower frequencies that most people can't hear as well. However, many, but not all, albums compensate for this in the first place.

Graphic EQ's in cars largely take up dashboard space without providing much improvement over bass & treble knobs, because the subtlties of EQ will vary with road surface, weather, etc. etc.

If you are trying to EQ a room for live performances... well that's a lot more complicated. You SHOULD:

- Rent a pink noise generator.
- Rent a spectrum analyzer.
- Have an EQ channel for each set of speakers.
- Make a lot of pink noise through each set of speakers individually, and using the spectrum analyzer, flatten the room.
- After doing each set, do them all together and tweak them.
- Put away the pink noise generator
- Ring out the mics by turning up the gain past where it would normally be and walk around talking into them. The spectrum analyzer will help if you aren't good at picking the frequency that's ringing.
- A perfect flat EQ is safe, but boring. Insert very familiar CD. Play loud. Tweak as needed to create the audio characteristics of the room you desire.

However, this can all take several hours and is a lot of work for a one night gig even if the place will let you do it, which is unlikely. If you can do it once for your PA in a typical room that you would perform in, you have a baseline of what will probably sound good with your system, to help compensate for inherent weaknesses, etc. If possible, hire or beg help from someone who has done this before: it's not just science, it's art. Pay attention and ask questions though -- you will learn more about your PA setup than a spec sheet will ever tell you. Write ALL the settings down when you are happy. (Legibly!)

Then, for your typical bar performance, set up your baseline, skip to ringing out the mics and tweaking to your chosen CD (and I suggest using the same song over and over when you have picked out one that works well for you), then go on to sound check. Keep a log of your EQ settings and note how well they worked out -- eventually you will probably start modifying your baseline starting point for what usually works.

By keeping a log, when you return to the same venue, you have a better place to start from, and you also learn the stuff to avoid in general. Even if you don't ever get the chance to really pink your system, a log will go a long way toward helping you make improvements to your setup.