We get many phonecalls from our customers at Sound-Services, unsure as to how a PA system works, what sized sound system they need and how to set the equipment up, so we thought we would provide you with an on line tutorial to help you grasp the basics. We often are asked what PA stands for, just for reference it stands for Public Address.

Although public address systems operate on the same principles as your home stereo, they require a higher level of understanding

As you are probably aware, your PA system can make or break your event, whether it be your band playing down the local, and no-one being able to hear your new backing singer, or your company conference, where only the front two rows can barely hear you talking about next weeks big project.

In every way, the PA system is essential in addressing the public audience to understand what you are playing/teaching/showing/selling to them. If the system is underpowered, then no one will be able to hear you, if the system is overpowered, then you will deafen people, causing them to leave, and not return again.

I have always had a passion for music and sound, and it was when I was playing with my first band, that I realised the importance of producing a good overall sound, together, as a unit.

 

Basics

In a PA system, it is a good idea to think of the equipment split into stages, this will make it more simple for you to ascertain a problem in the right area should it arise.

There are four main stages. These are as follows

 

1: Source

The sound source is the initial piece of equipment that produces an electrical signal, this could be a microphone, a laptop, a mp3 player, a turntable, a cd player, or a tape deck. Note that microphones and vinyl turntables need a special pre-amp to boost the signal up to line level. The equipment needs to have a line level of +4db (decibels) to be correctly passed on to the next stage. This is why you can plug a cd player straight into an amplifier, and it will work, but you can't plug a microphone straight into a power amp. (We strongly advise that you do not do the above, as you will have a heavily over distorted sound, and could possibly damage your equipment/and or hearing!)

 

2: Signal Chain

The most important unit in the signal chain is the mixer. This is where volume and equalisation is applied to the sound, and then passed on to the next stage. The mixer could be a 2 channel Pioneer DJ mixer, or a 40 channel midas venue desk. They both work on the same princilpes though. It is very important to check a units operational level. This is a small two way switch that can be found on the back of the unit. The operational levels are -10db which should be used in studios and at home, and +4db which should be used in a live environment. Selecting the wrong level will cause you problems

 

3: Amplifier

Amps, or power amplifiers take a line level signal from the mixer (signal chain) and amplify this level, so that the amplifier can be plugged into the speaker, thus amplifing the sound. It is very important to ensure that you correctly match your speakers and amplifiers not with just the right power, but with the right impedance as well. If an amplifier is not paired correctly with the right loud speaker, then you will more than likely blow one or the other, or both. The power that the amplifier produces is expressed in Watts. PA amps start at around 300 Watts, and go anywhere up to about 6000 Watts.

 

4: Speakers

HF Horn
			8'' Mid Driver
			HF Horn
12'' Speaker			15'' Woofer

 

The speaker is the last source in the chain. The above cabinets are full range integrated systems incorporating a woofer and a tweeter (please see below for a description)

In any full range speaker cabinet it is possible to have (a) a woofer (b) a mid range speaker and (c) a tweeter

(a) a woofer

Woofer loudspeakers are specifically designed to reproduce low frequencies (below 500Hz) Cone type drivers are used to make the 'sound producing part' of the woofer, with a metal chasis.

(b) a mid range speaker

Generally, mid range drivers produce frequencies from 500Hz up to not higher than 1.5Khz.

(c) a tweeter

Tweeters are designed to reproduce the highest frequencies, and are mostly crossed over above 6Khz, but are crossed over lower in some speaker cabinets.

Cabling

Many people will spend hundreds, maybe thousands on their PA equipment, stereo, or instrument and amplifier, and then buy the cheapest, thin, noisy cables to connect their new equipment together.

If you are going to spend a thousand pounds on a new PA system, then budget about a hundred pounds for the leads. You want to use professional signal cables for connecting everything up to the amplifier stage, and then professional speaker cables for the cabinets. You will spend £25.00 for a xlr microphone cable, but it will last you years, instead of buying one for £10.00, and lasting for a couple of months. The last thing you want to be worrying about at a gig is if the cables are working or not!