This is an article I posted on my website, www.funkytower.com You can read it there, as well, at http://www.funkytower.com/2009/02/03/setting-up-your-pa-system/
When you're in a band, and you're first starting out, you really want to stand out. There are many things lacking in new bands today - and one of them is the knowlege and understanding of using a basic P.A system. The result of this is playing crappy live shows. A bad P.A setup can ruin any good band's sound. In this article, I will tell you the BASICS: basic equipment for live shows, basics of EQ, etc., and make it easy enough for a child to understand.
Firstly, let's start off with equipment. You will need 1 mixer with enough channels to accomodate all your band members, 2 main speakers, 1 or 2 nice subwoofers, and some monitors - however many is up to you, but will be limited to the ammount of available AUX lines are on your board (typically 4-6), all your cables, microphones, 32-band EQ for each of your speakers and monitors D/I boxes for keyboards/guitars/instruments that will be plugged directly into your sound boardm and some nice poweramps to power your speakers, subs, and monitors. Make sure that you buy nonpowered speakers/subs.
You may wonder "Why not buy powered speakers and subs instead of paying for nonpowered speakers and subs and power amps?" The reason is this - because I assume you are new to the live sound business, you'll save yourself a lot of money should you blow a speaker's horn or woofer. If you did this with a nice powered speaker, you couldn't just replace the speaker - you have to replace the speaker and the amp inside it - not good. Where as if you blow a horn or woofer of a NON powered speaker, you don't need to replace your poweramp - and that'll save you some serious cash.
Now, it is time to set up. Here is an easy-to-understand diagram of a BASIC set up:
Let's break this down a little bit. We'll start with Monitors:
Your mixer should have Auxiliary (Aux) outputs. Each Auxiliary can be used as a monitor mix. Above each channel on your mixer, you should see knobs that say "Aux 1" or "Aux 2" etc. These knobs adjust the volume of that channel into that particular Aux or monitor's mix.
Firstly, go out an Auxiliary channel (in this case, we'll say Aux 1) into a 32 Band Equalizer (EQ.) From there, go out into 1 channel on 1 power amp, then out on the corresponding channel into 1 monitor. Plug a microphone into channel 1 of your mixer, turn the channel on, turn it up, and turn the Aux 1 knob up. You should hear some volume coming out of it. If you don't, there may be an Aux 1 send knob that needs to be turned up - if there is, then do so. (The Aux send knobs dictate how much overall volume is pushed into the monitor.) Repeat this step for Aux 2, 3, and however many monitors you want to use on your mixing board.
You may use 2 monitors per power amp should the power amp have 2 channels.
Now it is time to add mains and subs. This is a very similar setup. Basically you go out your main left and right outputs, out to two 32 band EQs, or one dual 32 band EQ, then into a crossover. What the crossover will do, basically, is separate your low frequencies from your middle and high frequencies; your low frequencies will run into your subwoofer, and the rest will run into your main speakers. Your crossover should have 2 inputs, 1 left and 1 right. Go into those appropriately from your EQ. You will have 2 corresponding outputs PLUS 1 subwoofer output; your subwoofer output will feed into it's own power amp, while the left and right outputs will go to their own poweramp. From the poweramp receiving the left and right sends, plug in your main speakers. From the poweramp receiving the 'subwoofer' send, plug in your subwoofer(s).
Now we should talk about EQ. If you've followed this setup, you should have one 32 band EQ on each speaker. Plug CD player into your mixer and play it; the reason we use a CD player is because the audio on professionally produced CD's is mixed properly. Adjust the EQ on each speaker and monitor to your liking. Be careful when doing this though; each slider on your EQ represents a frequencey, and if you over drive the frequencies, you can get an ugly sound, and even mess up your equalizer. If you want to emphasize a certain frequency - instead of turning it up, turn the rest down. I hope that makes sense ;) There's so much to adjusting to EQ, it could take a million articles to fully explain, but this should be enough to get you started.
Now we must talk about plugging in your microphones and instruments into the mixer. The way these things sound is completely up to you, but you must be careful not to blow your channels on your mixer. You should have a fader on the bottom of each channel, and a "Gain" or "Trim" knob above each channel.
To avoid peaking, use direct boxes for things you are plugging in directly to the mixer - from CD players, to mp3 players, to keyboards, and guitars/guitar amps. Set all your channel faders at "Unity" or at "0" (zero.) Let's say you have a guitar plugged into the channel you want to set first; have your guitarist play as he normally would, then slowly turn up the gain on his channel. If it starts to peak, turn the gain down until it stops, and with room to spare. You should have substantial volume coming from his channel, and you should be able to adjust the volume of his channel using the fader without peaking.
Typically, I would reccomend NOT exceeding unity on your channel's fader, unless it is temporary (i.e, emphasizing a guitar solo.)
You may wonder why I reccomend adjusting your channel's volume in this way. Well, the "Gain" or "Trim" adjusts the ammount of volume/signal that goes into the channel
, where the fader adjusts how much volume goes to your speakers. Should your trim be too high, though your faders are down, you could still blow a channel.
I should also reccomend looking into buying compressors for your vocal channels. To put it simply, a compressor, though this is excessive, will can a whisper and a scream at near the same volume. Use the compressor for vocals so that should you be too loud, you won't peak, but should you be too quiet, you will still be heard clearly - and this will help keep you from peaking your channel. This is often overlooked, but is extremely important.
There you have it. A very basic, but decent set up for live sound. Now, get out there and start jamming!