Setting Up A PA System
PA Systems come in many different shapes and sizes, ranging from the very elaborate systems used in large stadiums all the way down to a simple microphone patched into your home stereo. Listed below are several of the most common setups.
The Bare Bones
The above example is about as basic a system as you can get. Hooking it together is relatively simple. The most important thing to remember when hooking up any size PA is the direction of the signal. This is indicated above by the red arrows. The signal starts with your mouth (or drum, or horn, or whatever), then goes through the microphone into the system, then routes its way through the amp, and finally into the speaker where it leaves the system as a much louder sound. A good rule of thumb is to remember that when plugging something in (like an amp), whatever you plug into the input should be coming from the direction of your mouth while whatever you plug into the output should be heading toward the speaker.
An easier way to think of it might be to think of it as a river, the microphone being upstream, the speaker being downstream, and the amp being a reservoir in between. As the water (the signal) flows from upstream (the Microphone), it must enter the reservoir (the amp) through an input, and then exit the reservoir through an output until finally, it reaches the downstream side (the speaker).
So, that's the theory (complete with a picturesque metaphor). Now here is the reality. In the example above, you would plug things up in this order.
Plug the mic cord into microphone (There is only one place to plug it in. Technically it's an "output").
Plug the other end of the mic cord into the "input" of the amplifier (remember, input is coming from the microphone).
Plug the speaker cord into the speaker "output" of the amplifier (the signal is flowing out of the amp toward the speaker).
Plug the other end of the speaker cord into the "input" on the speaker (the signal is coming from the microphone through the amp to the speaker).
And there you have it. You have successfully hooked up your first basic PA system. Of course, although it will amplify the sound, this particular system won't be of much practical use to you in any real life playing situation. It still lacks three essential ingredients.
With the addition of a mixer (soundboard), an equalizer (EQ), and a set of full range speaker cabinets, we have created a small PA system that can be used both for rehearsal and for some gigs. The principle of signal direction stays consistent. As the arrows indicate, the signal again starts at the microphone passing through each component in turn until it reaches the speakers where it exits the system as an audible, much louder sound. It is important to note the order in which the components are hooked up. No matter how many more components (such as effects or compressors) are added, these basic building blocks should always line up in this order relative to each other. The EQ should always be connected somewhere between the output of the mixer and the input of the power amp, the microphone should always be on the input side of the mixer, and the speakers should always follow the amplifier.
Keeping in mind signal direction, the system shown in example 2 should be hooked up like this:
Plug the mic cord into the microphone (only one end of the cord will fit).
Plug the other end of the mic cord into any "input" channel of the mixer (input comes from the microphone).
Plug a high Z cable (patch cable) into the "main out" of the mixer (the signal is flowing out of the board toward the speakers).
Plug the other end of this cord into the "input" of the equalizer (the signal is flowing from the microphone).
Plug one end of a high Z cord into the "output" of the equalizer (the signal is flowing out of the EQ toward the speakers).
Plug the other end of this cord into the "input" of the power amp (the signal is flowing from the microphone).
Plug two speaker cords into two speaker "outputs" on the power amp (the signal is flowing through the amp toward the speakers).
Plug the other ends of these cords into the "inputs" of the speakers (the signal is coming from the microphone to the speaker).
plug anything other than a speaker into the output of a power amp. A "speaker
out" connection carries a very strong signal that can and probably will cause
damage to the other components.
The Powered Mixer
The powered mixer (pictured in the center of Example 2a) is very handy in that it combines the amplifier, the equalizer, the mixing board, and some limited effects into one relatively compact unit. These can be very convenient in some situations. They are especially useful for smaller acts (like acoustic bands), and great for rehearsal. In general, they are smaller and easier to transport, and easier and faster to hook up. Also, in many cases, buying one combined unit like a powered mixer can be considerably less expensive than buying the pieces separately. On the down side, they generally have less power than you can get using separate amps, and they often lack some controls on the EQ and Mixer, so if you are in a big loud band in a big loud room, you probably don't want to use one of these.
Stereo to Mono
You may have noticed that you have more than one channel in some (or all) of the components of your system. These are usually labeled in one of three ways; A and B, 1 and 2, or left and right. Each or the two channels will have its own inputs and outputs. What this means is that the component is stereo. Basically that means that it contains two completely separate pathways for two completely separate signals to flow through.
The system examples so far, for simplicity's sake, have been mono systems, but the principles are the same for stereo. A stereo PA can easily be used as a mono PA by simply running through only one channel in each component. For instance, If you wanted to use only channel "B" in your EQ, you would use the input and the output for channel "B", and leave the channel "A" inputs and outputs open. Of course, when you actually use the EQ, you have to remember which channel you hooked up so you can know which one you will need to adjust to change the sound of the PA. Moving the channel "A" knobs won't do anything if only channel "B" is hooked up.
The sound board is a little different in that you need only be concerned with the outputs. There are many inputs in a soundboard coming in from the many microphones on the stage, but a stereo board will have two separate "main" output channels. You need only choose one of these to use it in mono. Just remember which one you choose and adjust the knobs on the board accordingly.
The real draw back to running your stereo PA system mono is that you end up using only half of that expensive piece of equipment you bought. That isn't that big of a deal with an EQ or a crossover, but with a power amp, only using one channel means you only use half of its power. Only using half of a 500 watt amp results in only getting 250 watts of power, and that just plain stinks. This problem can be fixed by the use of "bridging", but it's a confusing and complicated setup that can be
hazardous to the health of your equipment. If done right, it's great. If done
wrong, it's disaster. In all honesty, I'm not confident enough in my own
understanding of bridging to explain it properly, so I've decided to (for the
moment) leave it out of this tutorial. However, I did find a complicated
technical description of it on the Peavey homepage.