Live Sound Equipment - Speakers

When using speakers in the live environment, it is often best to use passive PA speakers as opposed to active ones. The difference between active and passive speakers is that active speakers have an amplifier built into them, whereas passive speakers require an external amplifier and speaker cables to work. The reason why it is best to use a passive speaker system for live sound is because from the external amplifier, you can get much more output from them due to having a larger wattage. The amplifier used to power them can also vary in size (watts), so you would need an amplifier that can take the power from the speakers, so the larger the speakers, the larger the amp would need to be. The routing of passive PA speakers to a mixing desk is very simple too, as this diagram below will explain:

As you can see from the diagram, the speakers go into the amplifier and the amplifier goes into the main outputs of the mixing desk. The speakers connect to the corresponding left and right inputs on the amplifier via speaker cables (blue wire), and then returned to the mixing desks left and right outputs via XLR cables (red wire). This is very simple set up, and the only thing to consider is getting the left and right speakers the correct way round, and by this, I mean connecting the left speaker to the left input, then taking that input to the left output of the desk, and doing the same with the right speaker. If there is a mix up in the routing then you could potentially have them the wrong way round which would make panning any audio go to the wrong speaker. It is very simple to reverse though, just swap the cables around.

Wattage and resistance

The next thing to consider when using speakers in a live sound environment is the wattage of the speakers and amps, as well as the resistance. The wattage of things is measured in watts (w for short) and wattage is basically the amount of electrical potential that something has. Using guitar amplifiers as an example, a 15 watt amp has less potential energy than say a 50 watt amp, meaning that a 50 watt amp can go much louder. In regards to speakers and amps, it works in very much the same way that the higher the wattage they both have, the more potential volume you can get out of the speaker. You have to be careful with speakers and amps though, because say you have an 800 watt amp and two 500 watt speakers, you would not be able to power the speakers because the amp wouldn’t have enough power. Two 500 watt speakers equals a kilowatt, and the amp doesn’t have a kilowatt of power, so you either need to get a bigger amp with at least 1000 watt of power, just use one 500 watt speaker or get two speakers that equal less than 1000 watt of power. It is best to balance the signal, although leaving about 100-200 watt headroom between the amp and speakers would be beneficial. Having an amp too small for the speakers wouldn’t be enough to power the speakers as I have just mentioned, but having an amp too big for speakers also wouldn’t be good either, simply because running too much power into small speakers leaves the risk of blowing the speakers and ruining them, hence why it is best to balance the signal.

Resistance plays a key part in everything because it determines how loud you can actually get your speakers. The resistance of an amplifier can vary, although they are usually around 8 ohms, ohms being the measurement of impedance (resistance). The impedance of an amplifier is relevant to the wattage and impedance of the speakers, because say for example you have two speakers at 200 watts, 8 ohms, you will be demanding 4 ohm and 400 watt out of your amplifier, whilst still feeding 200 watt in each speaker. This may sound confusing; however it is very simple once you know the formula. This diagram below will show you exactly how it works: