PA Basics: Speakers and Amps
Speakers and Amps are intrinsically linked, sometimes in the same piece of kit. The main thing to avoid is blowing the speakers by turning up the amp too far.
Speakers
Measured in watts, you need roughly 2 watts for every person you are amplifying and you don't need huge speakers to fill a room. Eg. two 400w speakers will easily provide for 200 people. Speaker quality is also not a factor of size.
Speakers have a few normal connections:
- 1/4 inch jack (normal instrument lead), which you tend to find on smaller speakers, especially the kind that have their own in-built amps (like a guitar amp or foldback)
- XLR which works well for medium sizes speakers due to being relatively well shielded
- 'Speakon' connectors look quite odd (like two round circles) and connect by a twist-and-click approach. They are well shielded and professional cables.
- Wires which you can directly connect two screws or banana clips
It doesn't matter hugely which system of cables is used, oxygen-free cables aren't particularly vital in a live PA setup, it does matter that they are securely attached.
They come in a number of sizes, the main types are:
- Bass Speakers (sometimes called Bass Cans or Bins), you need a speaker of roughly 12 inches/ 30 centimetres across to properly reproduce bass sounds. They are sometimes also called 'Woofers' or 'Sub Woofers', though this is mainly in a home system.
- Midrange tend to produce the main audible sound and are sometimes set on their own as a centre speaker. Most dialogue and singing goes through these.
- Tweeters (high frequency speakers) deal with the sharpest sounds and they are often paired with Midrange speakers in the same box.
You may also come across the name 'Foldback' or 'Monitors'. In a PA System these are usually a large midrange and a tweeter which are used on stage for musicians to hear themselves. In a studio scenario 'Monitors' are very high quality speakers used to check the quality of recordings.
Amps
They're pretty boring and heavy, sometimes very heavy. Often you'll actually find there are two amps within, one for the left and another for the right channel; and in some cases the opportunity to pair them up.
The main thing is to keep the two amps set at the same level, only in extreme cases do you need to make them different. You also want to avoid them being at the top end of their range as they lose fidelity/quality and 'spiking' could cause it to blow.
It is most important to make sure the connectors are solid, both the power cable and the communication cables (ideally one cable direct to each speaker) should be tightly screwed in or the banana clips firmly secured.
If you see a 'bridge' function it basically means that you can take a single signal and split it across the two channels inside the amp.
Parallel versus Series and 4/8 Ohms
There are several different ways you can wire up speakers and amps. Wiring in Parallel (like with lights) you can run more power-wise than in series.
Ohms are a measure of resistance and important to check. Ideally you have a 4 Ohm or 8 Ohm amp mixed with the same-rating of speaker, however you can add together the power of channels or halve them to get more out of your speakers by wiring in series or parallel. Ie. you can run 8 Ohm speakers on a 4 Ohm amp.
