Public Address Systems - Basics

If you are entering the world of public address systems for the first time and you don't have any idea what to look for in a sound system then there is quite a lot to learn. Don't be put off by this, though, as there are a few things that we can look at to get you started on buying your first pa system. Let's start by asking some simple questions. This will make the difference between buying something more powerful or not powerful enough for your needs.

What do I need it for?


If you just want a sound system to sing Karaoke through in the comfort of your own home then you will only need a small public address system. However, if you are a musician and play mostly pubs then you will be needing something at least medium power, but preferably larger. If it is for outdoor events then you will be needing something much larger and much more powerful again.


What is Watts?


In terms of speakers the Watts are the amount of power it takes to power them. If you are looking at pa speakers you will usually find the Watt rating on the back of the speakers. Be careful when looking at the rating as some speakers will rate themselves by maximum Watts e.g. 200W(MAX). This doesn't mean the speaker can handle 200 Watts all the time, rather that it can only handle 200 Watts for short sporadic durations. Using a speaker at it's maximum rating for any length of time will probably damage the speaker. A better way for speakers to be rated is RMS (root mean squared). If a speaker is rated at 200W (RMS) then this is a more accurate way of identifying how much power you can feed into a speaker from an amp without the speaker distorting or being damaged. Usually you can double the RMS rating to get the Watts MAX e.g. 200W RMS = 400W Max.


In other words if you have a pa speaker that is rated at 100 Watts RMS then it will require 100 Watts of power to get them working at their best. The thing you have to watch out for, though, is that if you buy really cheap p.a. Speakers then they may be ineficient at using power and this is why they have a big Watt rating.


Probably the best way to figure out just how loud speakers will be the SPL rating (sound pressure level) measured in decibels. If you are lucky enough to get information on the back of the speaker casing with regards to this then you are on to a winner at figuring out just how loud the speaker is. Generally speaking a speaker that is 95 db or above is going to be very loud indeed.


If you are being put off with the complexity of speaker ratings then there is a general rule of thumb when it comes to how powerful your speakers and amplifier need to be. It is a very general rule of thumb and should only be used a crude indicator of the potential 'loudness' of the public address system. The rule of thumb is 1 Watt per person. In other words if you have to be heard in a pub with 100 people then you will need a system that has an amplifier and speakers that deliver 100 Watts of power.

Your choice of amplifier will depend on your choice of speakers too. It is generally advised to have a more powerful amplifier than the rating of the speakers as this will mean that the amplifier wont have to be driven to its limits all the time to get the speakers pumping. So if you have chosen an amplifier that outputs 600 Watts per channel then you might be looking to have speakers that are rated at 300W RMS.

What kind of mixer do I need?

Their are two kinds of mixers - powered and unpowered. A powered mixer has a built in amplifier so you don't have to carry around two pieces of equipment, but should you ever feel the need for a more powerful amp you are going to have to buy a seperate amp and mixer or a much more powerful powered mixer. An unpowered mixer will need to be hooked up to a seperate amp to be of any use, but has the advantage of being more versatile as you can plug it into a more powerful amp should the need arise. Some mixers have on board effects such as delay which reduce the need for external effects. If your mixer is to be used for your band then you will need something that has enough inputs for vocals, guitar, bass, drums etc. Be wary of cheap public address systems that have a lot of channels, but not much power as the quality of the sound being produced may be pretty bad.

Will I be using it much?


If you are in a band or are starting a career as a solo artist then you will need something that is robust and can survive being knocked around the back of a van on occasion or dropped on the pub floor. Most pa speakers come with plastic corner protectors that provide some protection from the inevitable bumps and scrapes, but another option would be to buy plastic ABS speakers. These are much more robust and can stand the test of time with a well travelled musician. If you are going to be using your pa system on regular occasions you will probably want to have a more powerful system as you may sometimes be playing to much larger audiences. There is nothing more frustrating than reaching number ten on the amp and you still can't be heard over the crowd.


These are just a few of the fundamental questions that you should ask yourself before buying a pa system. There are many more complexities that you may also want to research. These include buying the right cables, surge protectors, speaker stands, mics etc, but as you become more certain about what you need you will begin to build up an arsenal of information in these other areas. You can buy a basic system fairly cheap, but depending on your needs you can be paying thousands for something decent so it is important to know what you need rather than what you want.


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