Building and Setting Up a PA System - Part 1

Well, our forums have seen some chatter recently about live sound reinforcement. While this subject doesn't exactly fall into our typical discussion, it still affects the recording musician. So let's get on with it...

Power Up

The first thing you need to know in the venue(s) you will play in is what kind of power they have, how easy it is to get at and how good their system is. The wise travelling sound system doesn't rely on these lame, cheapo "surge protecting power strips". While they can work fine at home, on the road, you have no idea what kinds of places you are going in to, you really should invest in some "power conditioners". The difference is that the surge protectors keep an eye on spikes in current and trip or limit at a certain level of a spike. Power conditioners, on the other hand watch for peaks and valleys in the current and react accordingly to keep a nice, clean, even level of power going to your gear. The difference between them is very much like the difference between a limiter and a compressor.

Power fluctuates with every bit of activity going on within that power grid, from your neighbors air compressor turning on to the corporate headquarters of some company in the middle of town having their air conditioner turn on. If it's on your power grid, it affects, even if minimally, the flow of electricity into your outlets. Heck, even a large truck bouncing over the road in front of your house can cause a momentary spike or drop in your current. Most electical gear is built to be able to absorb the most common fluctuation ranges, but whether on the road or in your home studio, power conditioners are a good thing to have.

Mono or Stereo

I am not going to dive too far into this subject, as it is too subject to opinion and argument. Whatever you choose is fine, but typically, for smaller clubs and small outcoor events, mono is the way to go, as live shows generally are not enhanced by strong stereo fields as people are scattered on all sides of the stage and signal control is much more difficult.

'nuf said...

Speaker and Sound Board Location

In a perfect situation you will have a speaker stack for each side of the stage (more for large rooms) and your sound board and rack of gear will be dead center on the stage back a few feet, exact distance depending on the size of the venue and the size of the speakers and amps used. Best situation, just put your sound board right where the best listening spot in the room is.

Speaker setup for a typical average sized venue is often a 15" ot 18" woofer (often called the "bins")to handle the lows, and the rest of the sound handled by a "hipack" consisting of a horn and a 12" to 15" woofer.

In the rack on the stage you should have a crossover to split the signal at your determined crossover point, then send the highs out of the crossover to their amplifier and the lows out to their amplifier, then, obviously, from the amps to the speakers. With this setup we handled some pretty good sized venues holding several hundred people.

Amp size required is relative to room size. But the amplifier dedicated to the woofers should be roughly double the size of the high frequency amplifer.

Be sure, when setting up the speakers, that the horns are over the top of the crowd. High frequencies are the easiest to stop and the shortest distance before they die out. Therefore, having those as unobstructed as possible is to your advantage to help it carry as far as possible.

The last band I was in that carried around our own PA, which was mostly owned by myself, we had two amps that were 425 watts per channel, 850 "bridged" (which is both channels working as one). What we did was bridged both amps so we had two 850 watt amps, ran the signal coming to the stage into the crossover, the highs went to one amp (which was set to half-volume) and then to the hipacks, and the lows came out of the crossover, into the other amp, which had it's volume set to full, and then into the bins.

Ringing Out a Room

This is probably the most often overlooked, misunderstood, or simply not-known step of setting up a PA system for a newbie. Unfortunately, it's probably also one of the most important.

This requires a graphic EQ, the more bands the better, and more accurate the ringing out will be.

With all your levels at bottom, take a microphone, any microphone, and put on a stand out in front of the stage (typically by the sound booth which should be in the best listening position of thevenue) and raise it as close to the height of the horns on you speaker system as possible. Raise your mains to optimial level with all channels bottomed. SLOWLY raise the volume of the channel which has the mic on it that you just set up. When you start hearing feedback, go to your EQ, find the frequency that is feeding back and turn it down until the feedback stops. Then raise the volume again until feedback, find that frequency, turn it back until it stops. Repeat this process a few times, or until you start hearing multiple frequencies feeding back at the same time.

Doing this eliminates the problem frequencies from the room you are in allowing your system to increase it's headroom. Every room has different problem frequencies, so if this is a system that travels, you will do it in every new location, if it's a permanent installtion, you will do it once, then screw a peice of plexiglass or something over the EQ so nobody can mess with it for the rest of it's time in service.

A good sound engineer can, at time, get the volume level to ride the feedback, so, tho feeding back, it doesn't increase out of control while trying to find it's frequency. After a few time you will learn to identify and control the feedback bands quite quickly and the process will be quick. The feedback ranges will generally bounce between high and low frequencies so expect to bounce from one end of the EQ to the other.

Other Necessary or Desirable Gear

You may notice I have said virtual nothing about how to wire your gear together. Well, that is by design. Due to the fact there are so many different configurations available it's impossible to cover in the context of this simple little article, plus, if you have hung around HRC long enough, or have a home studio, you probably already have at least a sense of how to do this, the concepts of signal routing, gain staging and the like. That knowledge applies to live sound just as it does in the studio.

What I can do, however, is give some simple advice when looking for gear for your new PA system.

• When looking to purchase effects units, one good thing to look for is stereo units that have two inputs, as well as outputs. Some gear has only a single input, but outputs stereo signals. The dual inputs come in handy for live sound, if running a mono PA system, like most do, duals ins and outs can afford you the ability to use that unit is two mono processors.
• With mixers it's good to have at least two sub outs is handy for monitor systems. Use the mains for the FOH (front of house) signal, and use the sub outs for two different monitor signals, such as one mix for the drummer and the other for the front of stage mix.
• A limiter is nice to have as the last unit the mix goes thru before entering the crossovers or amps. PA systems often get pushed to their max and usually trigger the clip light the amp on every beat, a limiter will help protect the speakers and amps.
• Get speakers that have fused horns. It's a lot less expensive and a lot less difficult to change a fuse every show rather than the horn.
• It's helpful to get speakers that stack solidly together. When runing at the level PA speakers do, they will vibrate and bounce around a lot. It really sucks when you hipck vibrates right off the bin and lands on somebody. (I've seen it happen). And have the stack on a solid surface.

Final Thoughts

This is far from everything to know about setting up a PA, but I am hoping it's enough to get you started in the right direction, so you can get going on building your PA. Hopefully also save you from making some of the same mistakes I made through the years.