PA Sound Systems.
Here we are entering a very difficult subject that everyone thinks they are an expert at. there are people that think they know it all, and there are people who listen and learn, I am not going to go into great detail about the Ohms Law (but you will need to know about it if you are seriouse about sound), what I am going to do is to skim over the basics that everyone should be aware of before buying or hiring a PA.
Fist of all lets get this clear, a PA or Public Address system was originallly devised for things such as racecoarces, football stadiums etc, these are whats known as line systems. These produce a very tinny sound, as if you were listening to a transistor radio, because the amplifiers are multiple speaker amplifiers, that run on 100 volt. Have you ever stood at a football field, looked up and seen what looks like a horn, well thats what they are, they are designed for speech use only.
Some people think if they advertise that they have a PA they will get more work, well in essence thats true, because people now think that a PA is a large system, again that is true, but there a certain differences between a professional PA and a wanabee PA.
A WANABEE PA
This system is usually a single or multiple speakers that are made by one of thousands of company's that usually run through a single 15" woofer, 12" woofer or similar, the units can be linked together using as many amplifiers as needs be but will only give the same sound as your home hi fi, because the speaker enclosure itself has a built in crossover point that is fixed, and most units will not exceed 200 watts.
A PROFESSIONAL PA.
This is a system that should be split 3 or four ways, by splitting I mean through an active crossover, you should have bass units, mid range units, and top units minimum, so in reality you have to have a six speaker enclosures as an absolute minimum.
Each of these units should have a sepperate amplifier that is dedicated to that frequency only, when you start moving up the scale each amp rack should have a 32 way eq, and noise gates, these are an entity to themselves, and in order not to bore you senceless I am going to avoid these for the moment.
Basically when people advertise PA, if what they are advertising is a set of speakers that is knee height, with what looks like a single speaker in it and looks as if it's more at home with a pub DJ, you are being conned. However if what you are looking at is a little more that six sepperate enclosures, you know that you have a reasonable chance of knowing that you are dealing with the right people.
Lastly dont be fooled by peoples estimate of wattage output, as a general rule of thumb, the maximum a 12" speaker will give out is around 250 - 300 watts, a 15" around 125 - 450 watts, an 18" around 150 - 800 watts, so please bear in mind that if you are looking at a system that is stating it gives out 5000 watts and its tiny and looks to good to be true, IT IS.